Revision - Biology

8/8/2019 Revision - Biology

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Cell theoryAll organisms are composed of one or more cells

Cells are the smallest units of life

All cells come from pre-existing cells

Functions of Life

Metabolism ² includes all the chemical reactions that occur within an organism

Growth ² it may be limited but it is always evident in one way or another

Response ² Response to the environment is important to the survival of the

organism

Reproduction ² it involves the hereditary molecules that can be passed onto the

offspring

Homeostasis ² it refers to maintaining a constant internal environment. Examples

of constant internal environments may involve temperature and acid-base levels.

Nutrition ² it is all about providing a source of compounds with many chemical

bonds, which can be broken to provide the organism with the energy and the

nutrients necessary to maintain life.

Cells and sizes

Cells are made up of different subunits

Cells are relatively large and in decreasing size order are:

y Organelles

y Bacteria

y Viruses

y Membranes

y Molecules

1 millimetre (1mm) = 1000 micrometers (1000m)

1 micrometre (1) = 1000 nanometres (1000 nm)

Limiting Cell Size

Surface area to volume ratio effectively limits the size of cells

y In the cell, the rate of heat and waste production and rate of resource

consumption are functions that depend of the volume

y Most chemical reactions occur in the interior of the cell and its size affects

the rate of these reactions

y The surface area controls what materials go in and out of the cell.

y Cells with more SA per unit volume are able to move more materials in and

out of the cell for each unit of volume of the cell.

y Large cells has relatively less surface area to bring in its needed materials

and to rid the cell of waste have modifications to allow them to functionproperly

y Accomplished by shape changes such as spherical long and thin

y Cells are limited to the size they can attain so they can carry out all the

functions of life

Cell Reproduction and Differentiation

Cells can reproduce themselves



y In multicellular organisms, this allows the possibility of growth, it also allows

for the replacement of damaged or dead cells.

y The single cell has the ability to reproduce at a very rapid rate and the

resulting cells then go through a differentiation process to produce all the

required cell types that are necessary for the well-being of the organism.

Cellular Differentiation

It is the development of cells in specific ways.Hormones, cell to cell signals, and chemicals determine how a cell develops.

y Cells in multicellular organisms differentiate to become specialized.

y Each cell is specialized for one particular function.

Ex. nerve cells transmit messages

y Group of differentiated cells form a tissue

y Cells contain nucleus, chromosomes, DNA, divide into genes

y All cells have all genes and could develop in any way but not all are turned on

² some are switched on.

Ex. cells in your toes have information on how to make pigment for your eye color

but this gene is turned off.

Stem Cells

Stem cells Cells within organisms that can retain their ability to divide and

differentiate into various cell types.

y They are found in most, if not all, multi-cellular organisms.

y They are characterized by the ability to renew themselves through mitoticcell

division and differentiating into a diverse range of specialized cell types.

y Stem cells divide to form a specific type of tissue, they also produce some

cells that remain as stem cells. This allows for the continual production of a

particular type of tissue.

Example of a use of stem cells

1. The placenta and umbilical cord of a baby is used as a source of stem

cells. At the end of childbirth, the placenta is taken and placed on a stand,

with the umblical cord hanging down from it. Blood drains out of the

umbilical cord and is collected ² about 100cm 3. The cord blood contains

many hematopoietic stem cells. These cells can divide and differentiate

into any type of blood cell.



2. Red blood cells are removed from the cord blood and the remaining fluid is

then tested to find its tissue type, checked for disease-causing organisms and

stored in liquid nitrogen , in a special bank of cord blood.

3. Cord blood can be used to treat patients, especially children, who have

developed certain forms of leukemia. This is a cancer in wchich the cells in

bone marrow divde uncontrollably, producing far too many white bloodcells. The patient·s tissue type is matched with cord blood in the bank. If

suitable cord blood is available, the patient is given chemotherapy drugs that

kill bone marrow cells, including the cells causing leukemia.

4. The selected cord blood is taken from the bank, thawed and introduced

inot the patient·s blood system, usually via a ven in the chest or arm. The

hematopoietic stem cells establish themselves in the patient·s bone

marrow, where they divide repeatedly to build up a population of bone

marrow cells to replace those killed by the chemotherapy drugs.



Prokaryotic Cellsy Prokaryotic cells are much smaller and

simpler than eukaryotic cells.

y Size: 1 to 10 micrometres

y Bacteria are prokaryotic cells

y Their DNA is not enclosed within a

membrane and is one circular chromosome

y Their DNA is free; it is not attached to

proteins

y They lack membrane-bound organelles such

as the ribosome

y Their cell wall is made up of a unique

compound called peptidoglycan

Cell Wall - Maintains cell shape, provides physical protection, and prevents cell

from bursting in a hypotonic environment. In contrast from Eukaryotic cell walls,

usually made of cellulose or chitin, cell walls in prokaryotes [bacterial cells] contain

peptidoglycan; a network of modified-sugar polymers cross-linked by short

polypeptides.

Plasma Membrane ² separates the content of the cell from its surroundings,

regulates the passage of material

Flagella ² they are hair-like growths on the outside of the cell wall and their main

function is in joining bacterial cells in preparation for the transfer of DNA from one

cell to another.

Cytoplasm ² supports the organelles, and also contains important chemicals for the

cell

Ribosomes ² contributes to the manufacture of substances important to the cellfunction e. Protein Synthesis

Naked DNA ² DNA (deoxyribonucleic acid) that is not in a nucleus

Binary Fission

Prokaryotic cells divide by a very simple process called Binary Fission

1. The DNA is copied

2. Two daughter chromosomes become attached to different regions on the

plasma membrane

3. Cell divides into two genetically identical daughter cells.



Eukaryotic Cells

y Eukaryotic Cells occur in organisms

such as algae, protozoa, fungi, plants

and animals.

y Size: 5 to 100 micrometres

Organelles of Eukaryotic Cells

Endoplasmic reticulum ² it transports

materials throughout the internal region of

the cell. Smooth ER does not have any

ribosomes on its exterior surface while the

Rough ER does have.

Ribosomes ² they do not have an exterior

membrane and they carry out protein

synthesis in the cell

lysosomes

golgi apparatus

mitochondrianucleus

chloroplasts

centrosomes

vacuoles

Comparing Eukaryotic Cells and Prokaryotic Cells

Prokaryotic cells

y Genetic material is a naked loop of DNA located in the cytoplasm, in a

region called the nucleoid.

y Mitochondria is not present: the mesosome is used instead.

y Ribosomes are small, about 70 Svedburg units.y Few or no membrane-bound organelles are present.

y Most importantly, Prokaryotes have no nucleus present whereas Eukaryotic

cells have a nucleus present.

Eukaryotic cells

y Genetic material takes the form of chromosomes (usually 4 or more) within

the nucleus.

y Mitochondria is always present.

y Ribosomes are larger than in Prokaryotic cells, about 80 Svedburg units.

y M

ost organelles are membrane-bound.



Membranes

Phospholipids

The ¶backbone· of the membrane is a bilayer produced from huge number of

molecules called phospholipids.

Each phospholipid is made out of a 3-carbon compound called glycerol.

Two of the glycerol carbons have fatty acids attached

y Fatty acids not water soluble non-polar hydrophobic

y They do not strongly attract one another allows membrane to become

fluid or flexible allows the endocytosis

Thethird carbon is attached to a highly polar organic alcohol that includes a bond to

a phosphate group.

y Phosphorylated alcohol water soluble polar hydrophilic

The two regions allow the phospholipids to always align as a bilayer if there is water

present

The membrane is stable as the hydrophobic and hydrophilic properties of the

different regions of the phospholipid molecules cause them to form a stable bilayerin an aqueous environment

What maintains the overall structure is the tendency water has to form hydrogen

bonds.

Cholesterol

y Located in the hydrophobic region (fatty acids) in animal cells

y They determine the membrane·s fluidity, which changes with temperature.

y Allow effective membrane function at a wider range of temperatures than if

they were not present

Plant cells have NO cholesterol depend on saturated or unsaturated fatty

acidsto main proper membrane fluidity

Proteins

y Creates extreme diversity in membrane function

y Embedded in the fluid matrix of the phospholipid bilayer

2 major types of proteins

Integral Protein has both hydrophobic and hydrophilic regions

y The hydrophobic region with non-polar amino acids is in the mid-section of

the phospholipid membrane holding the membrane in place.



y The hydrophilic region is exposed to water solutions on either side of the

membrane

Peripheral Proteindo not protude into the middle hydrophobic region and

remain on the surface of the membrane

y They are often anchored to an integral protein

Membrane Protein Functionsy Hormone binding sites have specific shapes exposed to the exterior

that fit the shape of specific hormones. This attachment between the protein

and the hormone causes a change in shape in the protein and results in a

message being relayed to the interior of the cell.

y Enzymatic action enzymes are attached to membrane and they catalyze

chemical reactions. Enzymes can be in the interior or exterior of the cell.

They can be grouped to create a metabolic pathway

y Cell adhesion provided by proteins when they hook together in various

ways to provide permanent or temporary connections (junctions)

y Cell-to-cell communication these proteins include attached molecules

of carbohydrate.T

hey provide an identification representing each celly Channels for passive transport some proteins contain channels that

penetrate the membrane. This creates a pathway for substances to go

through such as the process of passive transport (high to low concentration)

y Pumps for active transport contains proteins that can change shape to

shuttle a substance from one side of the membrane to another and requires

the expenditure of energy (ATP)



Passive Transport

y Do NOT require energy

y Occurs in situations where there are areas of different concentrations

y Movement is along the concentration gradient (high to low)

Diffusion is the passive movement of particles from a region of higher

concentration to a region of lower concentration, as a result of the randommotion of particles.

Facilitated Diffusion is a particular type of diffusion that involves a membrane

with specific carrier proteins that are capable of combining with the substance to

aids its movement. This does not require energy.y Rate of facilitated diffusion will level off when total saturation of available

carrier occurs.

Osmosis is the passive movement of water molecules , across a partiallypermeable membrane, from a region of lower solute concentration to a region of

higher solute concentration.



Active Transport

Do require energy ATP is required

Movement is against the concentration gradient

Allows cell to maintain interior concentration of molecules that are different

from exterior concentrations.

Animal cells have higher concentration of potassium ions than their exterior

environmentThe cell allows the maintenance of this condition by pumping potassium ions

into the cell and by pumping sodium ions out

Sodium-potassium pump

1. A specific protein binds to 3 intracellular sodium ions

2. Binding of sodium ions causes phosphorylation by ATP

3. The phosphorylation causes the protein to change its shape, and therefore

expelling the sodium ions to the exterior

4. 2 extracellular potassium ions bind to different regions of the protein and this

causes the release of the phosphate group

5. loss of phosphate group restores the protein·s original shape and therefore

causing the release of the potassium ions into the interior



End

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Endocytosis

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s macromolec les to enter the cell y Occ rs hen a ortion o

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y The ends o$

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Extocytosis

Allo& s molecules to leave the cell

Begins in the ribosome·s o'

the rough ( ) and progresses through a series o'

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our

steps until produced a substance that is then secreted to the exterior o'

the cell

0 1

Protein produced by the ribosome·s o2

the rough 3 4

enters the 3 4

2 5 Protein exits the

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7

the golgi apparatus 8 a vesicle isinvolved

9 @ As the protein moves through the Golgi apparatus A it is modified and exits on the tr ans side inside a vesicle

B

C The vesicle D ith the modified protein inside moves to and fuses D ith the plasma membrane E this results in the secretion of the contents from the cell



Chemistry of LifeThe majority of organic molecules found in living organisms can be classified into one

of four types:

Oxygen

Carbon

Hydrogen

Oxygen

Structure of Water

The hydrogen and oxygen atoms in a single water molecule are held together by a

type of bond called a polar covalent bond.

Elements in Living Things

Sulphur ² it is found in two amino acids that are important for giving proteins their

shape

Calcium ² it is the most common mineral in the human body ² nearly all of it is

found in the bones and teeth. It·s most important role is in bodily functions, such as

muscle contraction and protein regulation.

Phosphorus ² it is found mostly in the bones but also in the molecule ATP, which

provides energy in cells for driving chemical reactions.

Iron ² it is a key element in the metabolism of almost all living organisms. It is also

found in hemoglobin, which is the oxygen carrier in red blood cells.

Sodium ² it is a electrolyte that is vital for electrical signalling in nerves. It can also

regulate the amount of water in the body.

Monosaccharide: Glucose, Fructose and ribose

Disaccharide: Maltose (Glucose + Glucose) and Sucrose (Glucose + Fructose)

Polysaccharide: Starch (made of glucose subunits) and Glycogen (made of glucose

subunits, but linked differently from starch). (Plants use mostly starch, humans use

mostly glycogen)

State one function of a monosaccharide and one function of a

polysaccharide

Glucose, a monosaccharide has many important functions. Glucose molecules are

used in respiration. Glucose is building blocks larger carbohydrates such as



starch, glycogen, and cellulose.

Starch, a storage polysaccharide for plants.

Cellulose and Chitin, are polysaccharides important for structure.

State three functions of lipids Energy storage: Fat in humans. Oil in plants.

Heat insulation: A layer of fat under the skin reduces heat loss.

Buoyancy: Lipids are less dense than water.

Discuss the use of carbohydrates and lipids in energy storage.

Lipids and carbohydrates are excellent for storing energy in living organisms.

Carbohydrates are usually used to store energy in the short-term while lipids

are used for the long-run.

Advantages of Lipids

Contain more energy per gram. Therefore lighter to store.

Lipids are insoluble in water; do not interfere with osmosis.

Advantages of Carbohydrates

More easily digested, so energy is released more easily from them.

Carbohydrates are soluble in water, so easier to transport.

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