1

Cell Structure and Function

All living things are made of ________. Some, like us, contain many millions of

cells. Such organisms are referred to as being _________________. Other

organisms are composed of only one cell and are said to be

________________. Diagrams of some common unicellular organisms are

drawn below.

Most cells are so small that they can only be seen using a microscope. All cells

contain _______________ surrounded by a flexible membrane called the

_________ membrane. Using a very powerful electron microscope, it is

possible to see many of the structures inside a cell. These structures are called

cell ______________ and they are responsible for carrying out the chemical

processes which maintains the cell. These chemical processes contribute to the

cell’s metabolism. Many metabolic reactions are catalysed by ____________.

A series of such reactions is called a _____________ pathway.

The diagrams on handouts 1 and 2 show the organelles that are present in a

typical plant and animal cell, and the table on page 2 summarises the functions

of the various organelles within these cells.

2

ORGANELLE

FUNCTION

NUCLEUS contains chromosomes (DNA) which provide the

recipe for making cell _____________.

MITOCHONDRION site of aerobic ______________ (which in

turn produces ATP).

ENDOPLASMIC

RETICULUM

(rough or smooth)

involved in the ____________ of proteins for

export from the cell.

RIBOSOMES site of ____________ synthesis – found on

the surface of RER or free in the cytoplasm.

GOLGI APPARATUS

(or golgi body)

involved in the packaging and processing of

____________ ready for secretion from the

cell.

SECRETORY

(GOLGI) VESICLE

a sac derived from the ________

__________ containing the finished

___________ which it then secretes from cell

by fusing with the cell ____________.

LYSOSOMES a sac which contains powerful digestive

___________ which are used to destroy

bacteria.

PLASMA CELL

MEMBRANE

controls what enters or leaves a cell.

CHLOROPLAST only found in _________ cells; contain

_____________ used to trap light energy

needed for _________________.

VACUOLE found in many plant cells; contains water with

salts and sugars. Contributes to cell turgor.

CELL WALL only found in ___________ cells. Made of

cellulose it gives cells strength and rigidity. It

is freely (or totally) permeable.

= only found in animal cells

*

*

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Organelles Working Together

The organelles inside a cell do not work in isolation. Instead they work together

in order to synthesise, transport, package and eventually secrete

____________ from the cell. Handout 3 gives some examples of such

proteins.

The nucleus contains the _____________ information (or recipe) needed to

make ______________. Proteins are then synthesised in the

_____________. They are then _______________ by either the rough or

smooth _________________ ________________. Then, they are packaged

and processed ready for secretion in the ________ _____________. Parts

of the golgi apparatus nip off to form secretory _____________ which

contain the finished _____________ (e.g. an ___________ like amylase or a

_____________ like ADH). The secretory vesicle fuses with the cell

_____________ and the ____________ is secreted from the cell.

The diagram below shows how all of these organelles work together. Note how

sacs which detach from the ER join up to form the _________

____________.

Processing and Secretion of a Protein.

The sequence in which these organelles become involved in the production of a

protein for secretion is:

nucleus → ____________ → ______________ _______________

→ _________ _____________ → vesicles

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What can organelles tell us?

We can work out what the function of a cell is by simply looking at the

organelles (and the number of them) in a cell. For example:

1. __________ cells and sperm cells contain many _______________

compared to other cells e.g. skin. This is because both of these types of

cells require a lot of energy.

2. Palisade mesophyll cells in the leaves of plants contain many, many

______________. This is because this is the part of the leaf where

most __________________ occurs.

3. Cells is our salivary glands, pancreas, liver and pituitary gland, are

abundant in ________ ______________. This is because all of these

types of cells are involved in secreting proteins.

4. White blood cells contain a lot of _____________. The powerful

digestive enzymes in these organelles help these cells to destroy

bacteria or other foreign bodies (e.g. viruses).

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Cell Structure Related to Function

It is important in Biology to remember that the structure (i.e. how a cell is

built) of a cell is closely related to it’s function. Here are some examples.

CELL TYPE FUNCTION HOW STRUCTURE IS

RELATED TO

FUNCTION

WHITE BLOOD CELL

To surround and then

destroy bacteria and other

foreign bodies (e.g. viruses).

Able to change their

_________ which then allows

them to surround bacteria.

Contain many

_____________ which then

destroy bacteria.

ROOT HAIR CELL

To absorbs __________

and minerals from the soil.

Present a __________

_____________ _______ in

contact with the soil and so

increases the amount of water

it is able to absorb.

SPERM CELL

To fertilise an egg cell. Has a ________ that it uses

to swim towards the egg. It’s

tail is packed full of

_______________ which

supply it with loads of energy

needed for it’s journey.

EPITHELIAL CELL

These cells (found in our

windpipe) are used to sweep

mucus away from the lungs

and into the nose or mouth.

Covered in tiny hairs called

________. The cilia beat

upwards, wafting the mucus

towards the mouth or nose and

away from the lungs.

RED BLOOD CELL

To transport oxygen around

the body.

These cells are bi-concave

(like a refresher). This gives

them a large ____________

_______. They also contain

_______________ which

has an affinity (loves) oxygen.

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ABSORPTION AND SECRETION

There are three main ways in which substances can be absorbed into or

secreted from a cell. These are:

1. ______________

2. ______________

3. ___________ _______________

DIFFUSION

Diffusion is the _________________ of molecules from a region of

_______ concentration to a region of _____ concentration. The difference

that exists between the two regions is called the concentration

_______________.

Diffusion is important to cells because it is the process by which molecules

either ________ or _______ a cell. Substances which enter a cell by

diffusion include __________ and dissolved food like ___________.

Substances that leave a cell by diffusion include ____________

______________. Water can either enter or leave a

cell.

OSMOSIS

Osmosis is described as a “special case of diffusion”. Osmosis is defined as:

It is the plasma cell membrane of a cell that acts as a ______________

permeable membrane.

THE MOVEMENT OF WATER MOLECULES FROM A REGION OF HIGH

CONCETRATION TO A REGION OF LOW CONCENTRATION THROUGH A

SELECTIVELY PERMEABLE MEMBRANE.

OXYGEN

CARBON DIOXIDE

DISSOLVED FOOD

(e.g. glucose)

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THE EFFECT OF OSMOSIS ON CELLS

In order to understand how osmosis affects plant or animal cells, we must be

familiar with the following terms which describe the concentration of water

molecules in a solution surrounding cells compared to the concentration of

water molecules inside the cells.

TYPE OF SOLUTION CONCENTRATION OF WATER

MOLECULES

has a higher concentration of water

molecules than the cells

has the same concentration of

water molecules than the cells

has a lower concentration of water

molecules than the cells

So:

if cells are placed in a hypotonic solution, water will _________ them

by __________ , and the cells will therefore _______ weight.

if cells are placed in a hypertonic solution, water will _________ them

by __________ , and the cells will therefore _______ weight.

if cells are placed in an isotonic solution, the same number of water

molecules will enter as leave the cells, therefore their weight will stay

the same i.e. they will neither _______ nor ________ weight.

In the experiment drawn below, the bag would ______ weight as water would

________ the bag by __________.

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THE EFFECT OF OSMOSIS ON ANIMAL CELLS

The diagram below shows the effect of osmosis on an animal cell when it is

placed in a hypotonic, isotonic or hypertonic solution.

THE EFFECT OF OSMOSIS ON PLANT CELLS

The diagram below shows the effect of osmosis on a plant cell when it is placed

in a hypotonic, isotonic or hypertonic solution.

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Animal cells will _________ when they are placed in a hypotonic solution, but

plant cells will not. This is because plant cells have a ______ _______ which

prevents this from happening.

Summary

Effect of solution on cells

CELL TYPE

HYPOTONIC

ISOTONIC

HYPERTONIC

ANIMAL

burst

no change

shrink

PLANT

become

TURGID

no change

become

PLASMOLYSED

(or FLACCID)

N.B. Neither diffusion or osmosis require ___________ (ATP) therefore

they are not dependent on the process of ____________

_________________. In other words they are not active but

____________ processes.

ACTIVE TRANSPORT

Apart from diffusion and osmosis, another way in which molecules can

enter or leave a cell is by __________ transport.

During active transport, molecules move from a region of ______

concentration to a region of _______ concentration. Molecules

therefore move against a __________________ ________________.

Since molecules are moving against a concentration gradient, active

transport requires ____________ (ATP).

Since active transport requires energy (ATP), this means that it is

dependent on the process of __________ _______________ which of

course produces energy (ATP).

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Active transport differs from diffusion in two ways:

1. During diffusion, molecules move from a high concentration to a low

concentration; during active transport, it is the opposite (low to high).

2. Diffusion is not an energy-requiring process; active transport is in other

words, diffusion is a _____________ process, active transport is an

__________ process.

The diagram below shows how substances can either be actively transported

into or out of a cell across the plasma cell membrane. Note that it is a

_____________ molecule present in the membrane structure that is

responsible for actively transporting molecules into or out of a cell.

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Selective uptake of ions by active transport

The table below shows that an aquatic plant is able to select and accumulate

certain ions via active transport. The data confirms that:

the ions are being absorbed by active transport because there is a

__________ concentration of potassium (K) outside than inside

it is selective because more ______________ than ______________

ions are being absorbed.

Conditions required for active transport

Since active transport requires ______________ (supplied by ATP), this

means that it is dependent on the process of aerobic respiration (which of

course produces ATP). If respiration ceases, so will active transport. Factors

that affect aerobic respiration, will therefore affect respiration. Such factors

include:

temperature (affects the ____________ that control respiration)

_____________ concentration (as the O2 concentration decreases, so

will the rate of respiration – less ATP = less active transport)

_____________ availability (since it is the main respiratory substrate)

All of the above factors indirectly affect active transport because they

directly affect ____________ _______________. The graph at the top of

the next page shows how temperature can affect the rate at which nitrate ions

are active absorbed.

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The graph below shows how oxygen concentration can affect the rate at

which nitrate ions are active absorbed.

Remember, temperature affect the ______________ that control aerobic respiration.

Description: As temperature increases to 30oC, the rate of active

transport _____________. Above 30oC, the rate of active transport

________________.

Explanation: As the temperature increases up to 30oC , the enzyme

controlling respiration will be becoming more active. More respiration = more ATP for

active transport. As the temperature goes above 30oC, the rate of active transport

decreases, because the enzymes are being ________________.

Remember, oxygen concentration affects rate of aerobic respiration.

Description: As oxygen concentration increases to 30%, the rate of active

transport _____________. Above 30%, the rate of active transport remains

________________.

Explanation: More oxygen = more aerobic respiration

more respiration = more ATP/energy.

active transport requires ATP/energy

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Cell membranes

Cells are enclosed by a membrane called the _________ cell membrane. In

addition, many organelles such as mitochondria, endoplasmic reticulum, golgi

apparatus, chloroplasts and the nucleus itself are bound by one or two plasma

membranes.

The plasma membrane is composed of ___________ and

________________ (fat) molecules. The phospholipids form two layers (called

a bi-layer) which can move – making the membrane ___________ (flexible).

The protein molecules are dispersed throughout the phospholipids forming a

_________ pattern – and they too can move freely within the membrane.

For this reason, the membrane is described as ________ - _________.

Because membranes are composed of ____________ and

__________________, they are easily damaged by _______ temperatures,

acids and by fat solvents such as ___________. This can be demonstrated by

using plant cells which have a coloured sap (e.g. beetroot). When the membrane

of these cells is damaged, the coloured sap leaks out into the surrounding fluid.

The protein molecules in the membrane have many functions. These include:

___________ which speed up many reactions e.g. protein synthesis.

receptor sites for hormones which then influence the activity of the cell.

proteins which actively transport materials across the membrane using ATP

as a source of __________.

proteins which form _______ (or channels) in the membrane through which

molecules can enter or leave the cell by ______________ .

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The membrane is described as being ______________ permeable, because it

will only allow some molecules to pass through and this depends on the

_______ of the molecule.

Experiment to demonstrate the structure of the plasma

membrane.

We can do an experiment to demonstrate the structure of the plasma

membrane. To do this we would use a plant whose cells contain a coloured sap

(in their vacuoles). An example of a plant we could use is _____________,

which has red/purple sap.

If a piece of beetroot “bleeds” this means that the plasma membranes

surrounding the cells themselves and the plasma membranes surrounding their

vacuoles have been damaged. This damage is irreversible.

The investigation as shown below was set up for one hour:

Results

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TEST

TUBE

TREATMENT

DOES BLEEDING

OCCUR?

A

B

C

D

Explanation

A Bleeding __________ occur because water does not affect the

structure of the plasma membrane.

B Bleeding __________ occur because the acid denatures the

_____________ molecules in the membrane which causes it to break

down. This then allows the sap to leak out of the cell and the surrounding

liquid turns red.

C Bleeding __________ occur because the alcohol dissolves the

__________________ molecules in the membrane which causes it to

break down. This then allows the sap to leak out of the cell and the

surrounding liquid turns red.

D Bleeding __________ occur because the high _________________

denatures the _____________ molecules in the membrane which

causes it to break down. This then allows the sap to leak out of the cell

and the surrounding liquid turns red.

NOTE Neither water or a salt or sugar solution will damage the

plasma membrane - as long as they are at a ______

temperature.

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The Cell Wall

The cell wall is the non-living outer boundary of _________ cells. It is mainly

composed of a structural carbohydrate called _____________, which is laid

down in ___________ as shown in the diagram below. This is what gives a

plant cell it’s shape and keeps it fairly rigid.

Unlike the membrane, the cell wall is totally (or freely) _____________ - in

other words it does not prevent anything from leaving or entering a cell.

It is the cell wall which prevents a plant cell from bursting when it is placed in a

________________ solution.

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Aerobic Respiration

The whole point of aerobic respiration is to release the ____________

energy in the food we eat. ___________ is needed to release this energy.

The equation below summarises aerobic respiration.

Most of this energy ends up being ___________ in our cells in a compound

called ATP ( ______________ _______________), but some of this energy

ends up being lost as ________.

ATP

ATP is a compound which is made from adenosine and three phosphates (Pi). It

is made by joining a molecule of ADP (adenosine ____________) with a single

phosphate (Pi) molecule. To join these two molecules together requires energy.

This energy comes from our ________ .

So, the chemical energy in food, ends up being stored in _____. The

production of ATP from ____ and ____ is called PHOSPHORYLATION,

which can be summarised by the following equation:

ADP + Pi ATP

When cells require an _______________ source of energy, the “high energy”

bond between the last two _____________ molecules breaks and energy is

released for cellular processes that include:

muscle ________________ _________ transport

FOOD + OXYGEN → ___________ ____________ + _____________ + ENERGY

(e.g. glucose)

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mitosis/meiosis (to separate the chromosomes) DNA ________________ protein synthesis phagocytosis (to allow membrane to move and engulf bacteria).

Cells need a constant supply of ATP, so it is re-synthesised as quickly as it is

broken down. All living things respire - this is often referred to as “chemical”

or “tissue” respiration (to distinguish it from the common use of the word

“respiration” to mean “breathing”).

ATP acts as a link between aerobic respiration and other cell processes which

require ATP to drive them e.g. protein synthesis as shown in the diagram below.

OXIDATION AND REDUCTION

Oxidation is the _______ of _____________ atoms, and when this

happens, energy is _______________. (Remember “OIL” = oxidation is

loss).

Reduction is the _______ of _____________ atoms, and when this

happens, energy is _______________. (Remember “RIG” = reduction is

gain).

[Respiration is often referred to as a process involving the “oxidation of

foodstuffs”. This is because during respiration, hydrogen atoms are removed

from the respiratory substrate (e.g. glucose) and used to produce energy

(ATP)].

ADP + Pi

Food +

oxygen

CO2 +

H2O

Amino

acids

Proteins

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INTERNAL STRUCTURE OF A MITOCHONDRION

The diagram below shows the internal structure of a mitochondrion. This cell

organelle is the site of ___________ ________________.

1μm (micrometer or micron) = 1000th of a millimetre.

A typical cell contains around 1000 mitochondria, but those cells which have a

high __________ requirement, e.g. _________ and ___________ cells

have many more.

The central matrix contains the enzymes that are involved in the _________

_________; the cristae contains the enzymes that are involved in the

_____________ system (also called the hydrogen transfer system).

THE CHEMISTRY OF RESPIRATION

Respiration can be divided into 3 separate but continuous processes:

1. ________________

2. The ________ Cycle (sometimes called the citric acid cycle).

3. The ________________ system (sometimes called the

_______________ transfer system).

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GLYCOLYSIS

Glycolysis takes place in the ___________________ of a cell. No

____________ is needed for glycolysis to occur. Glycolysis involves the

splitting of ___________ (6C) into two molecules of _____________

acid (2 X 3C). This produces ________ molecules of ATP, but since

_______ molecules of ATP are needed to split the glucose in the first

place, the NET GAIN is 2 molecules of ATP.

So, whether oxygen is available or not, the end products of glycolysis

are:

2 molecules of _____________ _______

a net gain of _______ molecules of ATP

In order for glycolysis to occur in the first place, both ______ and

____________ must be available to the cell.

If oxygen is not available to the cell - in other words if conditions are

______________, then the anaerobic phase of respiration occurs.

The pyruvic acid remains in the ________________ of the cell and is then

respired anaerobically as follows:

During anaerobic respiration, the only source of ATP comes from

_______________. Note that plant cells include fungus (like yeast) and

animal cells include bacteria.

THE KREB’S CYCLE

If oxygen is available, the pyruvic acid diffuses from the _______________

into the central matrix of the mitochondrion. It is here that the Kreb’s Cycle

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occurs. Unlike glycolysis, ____________ is needed for this stage. The

diagram below outlines the Kreb’s Cycle.

Each molecule of pyruvic acid loses a ___________ atom (as carbon dioxide).

This produces a 2-carbon compound called __________. (This joins with an

enzyme called CoA, forming a compound called Acetyl CoA).

This newly formed 2C compound then joins with a 4C compound already present

in the central matrix of the ____________________. This produces a ___-

carbon compound called _________ acid. Each molecule of citric acid then

loses a carbon atom (as __________ _____________) to produce a 5-

carbon compound which in turn loses a carbon atom to produce a _____ carbon

compound. It is this 4C compound that joins with the 2C acetyl compound and

the cycle begins

again. _____ molecules of ATP are produced as a direct result of the Kreb’s

cycle.

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THE CYTOCHROME SYSTEM

The cytochrome system is sometimes called the _______________ transfer

system - this is because it consists of a series of _____________ carriers

(called cytochromes). The cytochrome system occurs in the ___________ of

the mitochondria. Oxygen is needed. 34 molecules of ATP are produced from

one molecule of ____________ during the cytochrome system.

During glycolysis and the Kreb’s cycle, carbon and _________________

atoms are removed from the original ___________ molecule. After hydrogen

atoms have been removed, they are picked up by a single hydrogen carrier

molecule called ______ , which is reduced to NADH2.

NAD is used to transfer the hydrogen atoms from the cytoplasm or the

central matrix to the ___________ of the mitochondria. On arriving at the

cristae, they are released by NAD and then pass through the cytochrome

system.

As the hydrogen atoms pass through the cytochrome system, the most

important compound that is produced is _____. ___________ function is to

act as the final hydrogen acceptor. When oxygen combines with hydrogen at

the end of the cytochrome system, __________ is produced.

Apart from glucose (a carbohydrate) other respiratory substrates include fats,

fatty acids, glycerol and proteins. Cell proteins (like the body’s muscles e.g. the

heart) are only ever used as a respiratory substrate in times of acute

____________________.

Handout 4 on page 23 shows a more detailed outline of chemical respiration.

CARRIER 1 CARRIER 2 CARRIER 3 CARRIER 4

NAD

NADH2

OXYGEN

WATER

ATP

ATP

ATP

ADP

ADP

ADP

Pi

Pi

Pi

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ENZYME INHIBITORS

An enzyme inhibitor is a substance that can either _____________ an

enzyme or block it’s active site. This means that the enzyme can no longer join

with it’s ______________. The diagram below illustrates how an inhibitor can

stop an enzyme’s activity by blocking it’s active site. (DO NOT ATTEMPT TO

MEMORISE NAMES!)

Because the inhibitor mimics the shape of the enzyme’s substrate, the inhibitor

can block the active site by fitting into it. This results in the enzyme becoming

inactive i.e. it can no longer function. Inhibitors can therefore a affect a

metabolic pathway as shown in the diagram below.

If an enzyme inhibitor affects enzyme 2, then this would result in compound B

_______________ and compound C ________________. Although the

inhibitor affects enzyme 2, it does not affect the activity of enzyme 1.

enzyme 1 enzyme 2 compound A compound B compound C

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DNA AND PROTEIN SYNTHESIS

THE STRUCTURE OF DNA

DNA = ________________________ ________

Chromosomes are found in the _____________ of a cell. Each chromosome

consists of many _________. These genes contain the _____________

information which determines an organism’s characteristics. Genes are made

of _______.

DNA is an example of a _______________ acid. Nucleic acids like DNA are

made from millions of repeating units called _______________. The

structure of a single nucleotide is shown below.

There are _______ different bases in DNA. Their names are:

1. ______________ (A)

2. _______________ (T)

3. _______________ (G)

4. _______________ (C)

A SINGLE NUCLEOTIDE OF DNA

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It is only the ________ which makes one nucleotide different from another.

So, since there are only four different bases, there can only be four different

_________________ in DNA .

DNA is a double stranded structure. It’s two strands are twisted like a spiral

staircase. This structure is called a ___________ _________. The

phosphate and _______________ sugar molecules form it’s backbone. The

bases pair off and are held together by weak ________________ bonds.

Adenine always pairs with ______________ and vice versa, and guanine always

pairs with _____________ and vice versa. For this reason they are referred

to as __________________ base pairs. The diagram below shows the DNA

double helix.

DNA REPLICATION

A huge coiled and folded strand of DNA makes up one chromosome.

Chromosomes are found in the _____________ of cells. Before cells divide,

an exact copy of the DNA must be made. This process is called DNA

________________ and it is important because it ensures that each new cell

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receives the correct amount of ____________ information for it to grow and

___________ properly. DNA replication occurs at the very end of mitosis

just before the _______________ divides the parent cell into two

genetically identical daughter cells

In order for DNA replication to occur, the following four things must be

present in the cell.

1. many of the four free _________________ in DNA

2. the original DNA molecule (which acts as a template to copy)

3. the correct ______________

4. _____ which provides the energy needed for this process.

Stages of DNA Replication

DNA replication occurs as follows:

1. the DNA double helix __________ from one end only

2. the weak _______________ bond between the complementary

bases __________.

3. the two strand of DNA ____________ exposing their bases

4. free ________________ find their complementary nucleotide on

the open DNA strands

5. weak hydrogen bond form between the _________

6. bonds then form between the phosphate of one nucleotide to the

_________________ of the next

7. each new DNA molecule coils to form a double __________.

HANDOUT 5 on page 28 shows the process of DNA replication.

One half (i.e. one of the strands) of each new DNA double helix comes from the

original DNA molecule. The other half has been made from free DNA

________________ joining together. Since 50% or half of the original DNA

molecule ends up in the new DNA molecule, DNA replication is referred to as

being semi -_____________________.

28

29

DNA Content of Cells

Not all cells in our body contain the same amount of DNA. Since

____________ (sex cells) eggs and __________ in animals; pollen grains and

__________ in plants, contain ________ the number of chromosomes as

somatic (non-sex) cells, they contain half the amount of DNA as somatic cells.

Mature red blood cells do not have a nucleus therefore they have no

chromosomes and in turn will have no DNA. The table below summarises the

DNA content of some human cells.

CELL TYPE UNITS OF DNA

liver 6.0

sperm

mature red blood cell

muscle

gamete mother cell

egg (ovum)

young red blood cell

skin cell (just before

cell completely divides)

12.0

If a DNA molecule contains 1000 bases, and 200 of these bases are adenine,

then _______ bases will be thymine. This leaves 600 bases which will be

divided equally between cytosine and ____________. So, in this particular

molecule of DNA 300 bases will cytosine and 300 will be guanine.

The Genetic Code

The sequence of _______ in our DNA contains a “code” or recipe for making

cell _____________ e.g. enzymes, hormones etc. Proteins are made from

single units called ________ ________ . There are approximately ____

different amino acids which need to be “coded” for. If only one base coded for

1 amino acid, we could only code for ____ different amino acids (1 per base)

leaving _____ amino acids that will not be “coded” for. If two bases “coded”

for 1 amino acid, _____ different amino acids could be “coded” for, leaving

____ amino acids that will not be “coded” for. If three bases “code” for 1

amino acid, _____ different amino acids could be “coded” for which is more

than enough.

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So, THREE BASES CODE FOR 1 AMINO ACID - this makes the genetic

code a triplet code. Each triplet of _________ , only codes for one specific

amino acid and no other. Each amino acid however may have more than one

triplet of bases “coding” for it. For example the triplet CAA will only code for

the amino acid called __________ and only ___________ , but the triplet

CAC also codes for valine (and only valine).

The diagram below shows the genetic code. DO NOT ATTEMPT TO LEARN

ANY OF THIS CODE .

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The Role of RNA in Protein Synthesis

RNA stands for _________________ _________ and as the name suggests,

like DNA it is also a ______________ acid. There are two types of RNA.

These are:

1. mRNA (messenger RNA)

2. tRNA (transfer RNA)

The Structure of mRNA

Like DNA, mRNA is made from many single ________________. However

the sugar in mRNA is called __________. In mRNA, the base

____________ does not exist - it is replaced by a base called

____________. mRNA is single-stranded unlike DNA which is double-

stranded. The table below summarises the structural differences between

DNA and mRNA.

DNA mRNA

SUGAR BASES STRANDS

DNA is only found in the _____________ of a cell, whereas mRNA is found in

both the ______________ and the ________________ of a cell.

TRANSCRIPTION (of DNA into mRNA)

During the process of transcription, the genetic code in our DNA is transferred

to mRNA. This needs to happen because this code is going to provide the recipe

for making a ____________ and proteins are synthesised in the

_____________. This is the only way that the genetic code (in our DNA) can

get to the ribosomes.

During transcription, a section of the DNA molecule unwinds and unzips. (This

section represents one gene) This allows mRNA complementary bases (A-U; T-

A; C-G and G-C) to bind temporarily (via the formation of weak

______________ bonds) with the exposed bases on this section of one of the

DNA strands.

32

Once a single complementary strand of mRNA has been synthesised, the weak

hydrogen bonds between the bases _________. This then allows the mRNA

strand to peels off. It then leaves the _____________ through a pore in the

______________ membrane and makes its way to a ______________ .

Ribosomes are found free in the cytoplasm or attached to the rough

________________ ________________. A diagram showing the

transcription of DNA into mRNA is shown below.

The mRNA now holds the genetic code which provides the recipe to make

a ______________ e.g. amylase, ADH etc. Three bases in a row (one

after the other) on the mRNA strand “code” for one specific _________

________. A triplet of three bases on an mRNA strand is called a

_________. If there are 549 nucleotides (or bases) on a single strand

of mRNA, it will provide the recipe to synthesise a protein molecule that

consists ____ amino acids (i.e. 549 ÷ 3 = ____ ).

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The diagram below shows the 64 mRNA codons and the amino acids that

they “code” for.

Amino acids need to be carried to the ______________ where they will

be joined together to form a protein. tRNA molecules act as the amino

acid carriers.

The Structure of Transfer RNA (tRNA)

tRNA is not a strand – it is a molecule on its own. One such tRNA

molecule is drawn below.

The exposed triplet of bases on a tRNA molecule is called an

_______________ of which there are _____ different ones. Each

anticodon “codes” for one specific amino acid. It is this _____________

34

that will determine the amino acid that the tRNA molecule will carry to

the ribosome. The above tRNA molecule will carry the amino acid called

___________.

Functions of tRNA

to transfer amino acids to the _______________

to allow codon/ _____________ links to form

to bring amino acids side by side (to allow _____________ bonds to

form between them

TRANSLATION

Translation refers to the process when mRNA is translated into a protein.

Translation therefore takes place at the _______________, because

these are the organelles that are responsible for protein synthesis.

It is the sequence of the _________ in mRNA that will determine

the sequence of the _______ _______ in the protein that will be

synthesised. It is this sequence of amino acids that makes one protein

different from another. Once the protein has been synthesised, it is

then _________________ by the rough endoplasmic reticulum to the

_________ ___________ where it is packaged and processed ready

for secretion.

HANDOUT 6 which follows shows the process of translation.

MUTATIONS

If a gene mutates, this will alter the sequence of the _______ in the

DNA that the gene is made from. This in turn, will alter the sequence of

the amino acids of the _____________ that this particular gene holds

the recipe to make. As a result a different protein will be synthesised.

Depending on the circumstances this may give the organism and advantage

or a disadvantage -see unit 2.

35

Proteins

Proteins are organic* compounds composed of atoms of carbon,

______________ , oxygen and ____________. They are large, complex,

three-dimensional molecules. There are thousands of different proteins. Each

protein molecule is composed of a large number of building blocks called

_______ _______ which are linked together by __________ bonds.

Proteins have many important roles to play in both plants and animals. These

roles include:

all ___________ are proteins and they control metabolic pathways e.g.

respiration and photosynthesis

many hormones are proteins

______________ which protect our body from disease and infection,

are proteins

the plasma membrane consists of ________________ and protein

molecules – see page 13.

muscle tissue is composed mainly of protein

our red blood cells contain ________________ which is the protein

that transports oxygen around the body

Proteins can be classified as FIBROUS or GLOBULAR.

A) FIBROUS PROTEINS

These proteins are ______________ in water. They are

structural proteins that can resist being pulled or stretched and so they

are quite strong. Fibrous proteins are arranged in long parallel strands as

shown in the diagram below.

B) GLOBULAR PROTEINS

These proteins are not completely soluble in water. They are usually

involved in some type of metabolic reaction. Globular proteins are roughly

spherical in shape as shown in the diagram below.

Examples of each type of protein are given in the table below.

*organic compounds contain the element carbon

36

FIBROUS PROTEINS GLOBULAR PROTEINS

collagen (found in bone, tendons and

ligaments)

enzymes (e.g. amylase which breaks down

starch to maltose)

actin and myosin (found in muscles) hormones (e.g. ADH which controls the

level of water in the blood)

keratin (found in hair, nails and skin) antibodies (e.g. immunoglobulin which

defends the body against

infection)

elastin (another protein found in

ligaments)

plasma membrane proteins (e.g. like the

ones in the cell membrane that are

involved in active transport).

Remember, it is the sequence (order) of amino acids in a protein that makes

one protein molecule different from another (not only in function but in shape),

and it is the sequence of ______ in DNA that will determine what the

sequence of amino acids will be.

The shape of a protein molecule is very important to its function, especially

enzymes that are specific to their ___________ and antibodies that are

produced in response to specific _____________.

37

CELLULAR DEFENCE IN PLANTS AND ANIMALS

VIRUSES

Viruses are extremely small, and are capable of causing disease. Antibiotics

don’t affect them, and we therefore have to rely on our own body’s defence

systems to deal with them. Viruses also attack other animals, plants and even

bacteria.

STRUCTURE OF A VIRUS

All viruses contain either DNA or ________ that is surrounded by a

____________ coat like the one shown in the diagram below.

VIRAL REPLICATION

As the name suggests, viruses are able to make __________ copies of

themselves. In doing so, they interfere with the host cells biochemistry, and

use compounds supplied by the host cell to replicate. In doing so, they destroy

the host cell.

In order for viruses to replicate, four things must be supplied by the host cell

for replication to be possible. The four things are:

______ which supplies the energy needed for replication

free __________________ (to make copies of it’s DNA or RNA)

_______ _________ to make the protein coat that surrounds the

virus

___________ involved in replication and protein synthesis

38

STAGES OF VIRAL REPLICATION

Using ATP, free nucleotides, amino acids and enzymes supplied by the host cell,

viruses replicate. The diagram below shows the stages of viral replication.

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

39

CELLULAR DEFENCE MECHANISMS IN ANIMALS

___________ blood cells help us to defend our body against disease and

infection. There are two types of white blood cells:

1. _________________

2. _________________

PHAGOCYTES

These types of white blood cells work by ______________ foreign particles

e.g. bacteria. This is a process called ___________________ which is shown

in the diagram below. Once ingested, the bacteria are destroyed by the

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

40

powerful digestive enzymes contained in special cell organelles inside the

phagocytes called ______________.

Phagocytic white blood cells like the one drawn above, is a good example of a

cells whose structure is related to it’s function:

1. phagocytes are able to change their _________, and this allows them to

surround and engulf bacteria.

2. phagocytes contain many _____________. The powerful digestive

___________ inside these organelles destroy the bacteria and render

them harmless.

LYMPHOCYTES

These types of white blood cells produce globular proteins called

________________ in response to foreign proteins called

______________. (Viruses and bacteria have a distinctive protein coat which

is individual to them). Antibodies are said to be _____________ because

different antibodies are produced in response to different antigens. Only one

specific type of ____________ can attack a specific type of

____________, so we have thousands of different _______________ , each

one designed to produce a ___________ antibody.

41

REJECTION OF TRANSPLANTED TISSUES OR ORGANS

When a tissue or an organ (e.g. a kidney) is transplanted from one person to

another there is the possibility that it may be _______________ (unless the

donor is an identical twin). This is because the transplant patient’s immune

system regards the transplanted tissue or organ as a collection of foreign

_____________, and attempts to destroy it - this is known as tissue

rejection.

Phagocytes and lymphocytes treat the transplanted tissue or organ like any

other antigen, but rejection can be minimised in two ways:

1. By matching a donor who is ________________ as similar as possible

to the recipient. This is why family members make good donors.

2. Using special drugs called ______________________ drugs which

unfortunately weaken the body’s immune system, and these drugs must be

taken for the rest of their life. An advantage of taking these drugs is

that the transplanted tissue or organ is not “attacked” by our own

phagocytes and lymphocytes, but a disadvantage is that the transplant

patient is open to attack from other pathogens (disease-causing micro-

organisms).

CELLULAR DEFENCE MECHANISMS IN PLANTS

Plants too can be attacked by pathogens, but they don’t have an immune

system like us and so don’t produce phagocytes or lymphocytes (and

therefore do not produce _______________ ). Many plants defend

themselves against infection and disease by producing chemicals that are

either _______________ , or are enzyme ______________ . For

example:-

NICOTINE

TANNINS

RESINS

Resins are sticky chemicals. They help to prevent the spread of infections by

________________ holes in the bark of trees for example.

42

PHOTOSYNTHESIS

During photosynthesis, the energy change is from ________ to

______________. Photosynthesis can be summarised by the following

equation.

So, photosynthesis is the process by which plants with chlorophyll manufacture

carbohydrates (e.g. glucose) from carbon dioxide and __________ using

_______ energy from the Sun. Oxygen is released as a by-product.

The Fate of Light Energy

Three things can happen to the light that strikes a leaf. It can either be

absorbed, ______________ or transmitted, as shown in the diagram below.

Visible light is made from 7 different colours. Each colour is determined by it’s

wavelength. In Biology, we refer to these colours of light as the

_________________ spectrum (R O Y G B I V).

Red Orange Yellow Green Blue Indigo Violet

light energy CARBON DIOXIDE + WATER FOOD + OXYGEN

chlorophyll (e.g. glucose)

A ______________ (5%)

B _______________ (12%)

C ______________ (83%)

700 600 500 400

wavelength

43

Absorption of Light

Light energy is absorbed by “chlorophyll” which is found in the

________________. Not all plant cells have chloroplasts e.g. the cells in the

roots of plants. This is because these cells never see the light of day!

The diagram below shows the internal structure of a chloroplast.

So, chloroplasts are the organelles found in plants cells where the process of

___________________ occurs. The “chlorophyll” whose function is to absorb

light energy is found in the __________ (pleural = grana) of the chloroplasts.

The synthesis of glucose takes place in the __________ of the chloroplasts,

during the Calvin Cycle (see page )

The Role of Chlorophyll in Photosynthesis

Apart from chlorophyll (a and b), plants also contain other ________-

absorbing pigments. These are referred to as ____________ pigments. They

can be extracted from leaves and then separated using a simple technique

called ________________.

44

Chromatography

Leaves are firstly ground up using a mortar and pestle, and _______ which

helps to rupture the cells. __________ (or propanone) is the solvent that is

used to extract these pigments from the leaves.

The resulting green liquid is then spotted repeatedly onto chromatography

paper. When a _________________ green spot has been produced, the

paper is dipped in another solvent and left for a few minutes.

Chromatography works on the basis of _______________. Some of the light-

absorbing pigments are more soluble than others. The ______ soluble the

pigment, the further up the paper it travels. The pigments always appear in the

same order as shown in the diagram below.

Function of Having Different Pigments

The advantage to the plant of having more than one light-absorbing pigment is

that it EXTENDS THE ___________ OF WAVELENGTHS OF LIGHT

THAT THE PLANT CAN ___________ FOR PHOTOSYNTHESIS.

This additional ________ energy absorbed by the accessory pigments is

passed on from chlorophyll b, xanthophyll and _____________ to

chlorophyll a molecules which carry out photosynthesis.

MOST SOLUBLE

LEAST SOLUBLE

CAROTENE ( ___________ )

XANTHOPHYLL ( ____________ )

CHLOROPHYLL a ( _____________ )

CHLOROPHYLL b ( _____________ )

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Absorption Spectrum and Action Spectrum

The wavelengths of light absorbed by a pigment can be displayed as a graph

called the ______________ ___________. Because “chlorophyll” absorbs

mainly _____ and _____ wavelengths of light and ________ green

wavelengths of light, “chlorophyll” appears green to our eyes. The absorption

spectrum for chlorophyll a is shown in the graph below.

If an absorption spectrum graph peaks at the green wavelength of light, this is

not due to absorption by chlorophyll a or b (which reflects green), but will in

fact be due to light being absorbed by either ____________ or

_______________.

If a plant lacks magnesium, it will not be able to absorb as much light as a plant

that is not deficient in this element. This is because magnesium is needed by

plants to make _______________ . The less chlorophyll a plants make, the

less light they are able to absorb.

Is absorbed light actually used by the plant for photosynthesis? This can

be checked by growing plants in different _________ of light using different

coloured light bulbs and noting how well they grow. If the results of such an

experiment are plotted, a graph called an _________ _________ is

obtained. The action spectrum for a plant is drawn on the following page.

46

ACTION SPECTURM GRAPH

(measures the rate of photosynthesis at each wavelength of light)

The rate of photosynthesis can be measured as:

volume of ____ absorbed, or

volume of ____ released, or all measured over a period of time

increase in dry mass

If an absorption spectrum graph and an action spectrum graph follow a similar

pattern, then we could conclude that the light being absorbed by the pigment is

actually being used for _________________.

If the graphs do not follow a similar pattern, then it is likely that other

pigments are involved in absorbing different wavelengths of light.

}

47

THE CHEMISTRY OF PHOTOSYNTHESIS

Photosynthesis can be divided into two stages. The products of the first stage

however, are required for the second stage to occur. These two stages are:

Stage 1 the ________-dependent stage (photolysis and

photophosphorylation)

Stage 2 the __________ Cycle or the ___________ fixation stage

Stage 1

This stage (which requires light energy) takes place in the __________

of the chloroplast. The light energy which is absorbed by

______________ can either be used to:

1. split __________ molecules into ______________ atoms and oxygen

gas which is then released by the plant as a by-product. This process of

using light energy to split water molecules is called PHOTOLYSIS.

The hydrogen atoms are picked up by a “hydrogen carrier” molecule

called NADP which is reduced to NADPH2. NADP carries the hydrogen

atoms to the _________ of the chloroplast where they are needed for

the Calvin Cycle.

2. make ATP. Light energy is used to join _____ and _____ together to

make ATP. This process is called PHOTOPHOSPHORYLATION. ATP is

also needed for the Calvin Cycle to occur.

The two processes of the light-dependent stage ( ________________ and

_______________________ ) are outlined in the diagram on the next page.

48

THE LIGHT-DEPENDENT STAGE (occurs in the ___________ of a chloroplast)

When light energy splits a molecule of water into ______________ atoms

and __________ gas, the hydrogen atoms are picked up and carried by NADP

(as NADPH2) from the ___________ to the stroma of the chloroplast.

The source of the oxygen released during photosynthesis is therefore

____________.

BOTH NADPH2 AND ATP ARE NEEDED FOR STAGE 2. WITHOUT THEM,

THE CALVIN CYCLE CANNOT OCCUR.

light energy

CHLOROPHYLL

energy energy

WATER (H20)

ADP + Pi ATP

oxygen gas (released as a by-product)

hydrogen atoms

NADP NADPH2

49

Stage 2

The second stage of photosynthesis (i.e. the Calvin Cycle), does not

require light energy. In simple terms, during this stage, carbon dioxide is

______________ by the hydrogen atoms which have come from

__________ to make carbohydrates (CHO’s) e.g. ____________.

The Calvin Cycle is a series of metabolic pathways, each controlled by a

different ____________ . The Calvin Cycle takes place in the

___________ of the chloroplast.

50

Carbon dioxide is picked up by the carbon dioxide acceptor molecule called

_____________ __________________ (RuBP). When they combine,

glycerate phosphate (GP) is produced. GP is then reduced using hydrogen

atoms supplied by _________. This requires energy which comes from

______. The end product is glucose. The glucose is broken down by the plant

during respiration to produce ATP. The plant however, might join some of

these glucose molecules together to form either:

1. __________ for storage or

2. _____________ which is the structural carbohydrate that plant

_______ ________ are composed of.

Limiting Factors

Three factors can limit the rate at which a plant can photosynthesise. The

three limiting factors are:

1. _________________ (which affect enzyme activity)

2. light _______________

3. ___________ ______________ concentration

Below shows a typical limiting factors graph that often appears in higher exam.

51

IMPORATANT EXAM INFORMATION

You will often be asked to name the compounds in both RESPIRATION and the

CALVIN CYCLE. Not only do you need to know their names, you need to know

how many CARBON ATOMS these compounds contain. These tables should help

you to do this!!

RESPIRATION

Name of compound Number of carbon atoms

(in a single molecule) GLUCOSE

PYRUVIC ACID

ACETYL (Co A)

CITRIC ACID

CARBON DIOXIDE (CO2)

PHOTOSYNTHESIS

Name of compound Number of carbon atoms

(in a single molecule) GLYCERATE PHOSPHATE (GP)

RIBULOSE BIPHOSPHATE (RuBP)

GLUCOSE

CARBON DIOXIDE (CO2)

52

Handout 1

53

Handout 2