Cells Revision - IBBIONINJA

8/19/2019 Cells Revision - IBBIONINJA

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CELL


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Cells

2.1 Cell Theory2.1.1 Outline the cell theory

The cell theory states that:

1. All living things are composed of cells (or cell products)

2. The cell is the smallest unit of life

3. Cells only arise from pre-eisting cells

2.1.2 Discuss the evidence for the cell theory

Microscopes:

!icroscopes have increased man"s a#ility to visualise tiny o#$ects

All living things %hen vie%ed under a microscope have #een found to #e made of

cells and cell products (e.g. hair) Note: Certain types of cells do not conform to the standard notion of %hat

constitutes a cell

!uscle cells contain multiple nuclei

&ungal hyphae consist of multiple cells that share a continuous cytoplasm

'ight vs lectron !icroscopes

Experimental Evidence:

Cells removed from tissues can survive independently for short periods of time

othing smaller than a cell has #een found to #e a#le to live independently

periments #y &rancesco *edi and 'ouis +asteur have demonstrated that cells

cannot gro% in sealed and sterile conditions

,istory of the Cell Theory

2.1.3 State that unicellular organisms carry out all the functions of life

nicellular organisms (such as amoe#a paramecium euglena and #acterium) are the

smallest organisms capa#le of independent life.

All living things share / #asic characteristics:

ovement: 'iving things sho% movement either eternally or internally

R

eproduction: 'iving things produce offspring either seually or aseually Sensitivity: 'iving things can respond to and interact %ith the environment

Growth: 'iving things can gro% or change si0e shape

Respiration: 'iving things use su#stances from the environment to mae

energy

Excretion: 'iving things ehi#it the removal of %astes


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Nutrition: 'iving things echange materials and gases %ith the environment

2.1.4 Compare the relative sizes of molecules, cell memrane thic!ness, viruses,

acteria, organelles and cells, using appropriate S" units

Relative sizes: Unit Conversion Table:

A molecule 1 nm

Cell mem#rane thicness /.4 nm 5irus 166 nm (range: 26 - 266 nm)

7acteria 1 - 4 um

8rganelles 916 um

uaryotic cells 9166 um

iagram of the *elative ;i0es and ;cale of 7iological !aterials

Cell ;i0e and ;cale ('earn


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Magnification = Size of image (with ruler) ÷ Actual size of object (according to

scale bar)

To calculate the actual size of a magnified specimen the equation is simply re-arranged:

Actual size = Size of image (with ruler)> !agnification 2.1.% &'plain the importance of the surface area to volume ratio as a factor limiting cell

size

The rate of meta#olism of a cell is a function of its mass volume

The rate of material echange in and out of a cell is a function of its surface area

As the cell gro%s volume increases faster than surface area (leading to a

decreased ;A:5ol ratio)

?f the meta#olic rate is greater than the rate of echange of vital materials and

%astes the cell %ill eventually die

,ence the cell must conse=uently divide in order to restore a via#le ;A:5ol ratio

and survive Cells and tissues specialised for gas or material echange (e.g. alveoli) %ill

increase their surface area to optimise the transfer of materials

!icrovilli increase surface area allo%ing for a more efficient echange of materials

heat

2.1.( State that multicellular organisms sho$ emergent properties

mergent properties arise from the interaction of component parts: the %hole is greater

than the sum of its parts

!ulticellular organisms are capa#le of completing functions that individual cells could

not undertae - this is due to the interaction #et%een cells producing ne% functions


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?n multicellular organisms:

Cells may group together to form tissues

8rgans are then formed from the functional grouping of multiple tissues

8rgans that interact may form organ systems capa#le of carrying out specific

#ody functions

8rgan systems carry out the life functions re=uired #y an organism

'evels of Anatomical 8rganisation

2.1.) &'plain

that cells in

multicellular organisms

differentiate to carry out specialised functions y e'pressing

some of their genes and not others

All cells of an individual organisms share an identical genome - each cell

contains the entire set of genetic instructions for that organism

The activation of different instructions (genes) %ithin a given cell #y chemical

signals %ill cause it to differentiate from other cells lie it

ifferentiation is the process during development %here#y ne%ly formed cells

#ecome more specialised and distinct from one another as they mature

Active genes are usually pacaged in an epanded and accessi#le form

(euchromatin) %hile inactive genes are mainly pacaged in a condensed form

(heterochromatin)

ifferentiated cells %ill have different regions of A pacaged as

heterochromatin and euchromatin depending on their function


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ifferential


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. #lood cells: 7one marro% transplants for cancer patients %ho are immuno-

compromised as a result of chemotherapy

2.2 Prokaryotic Cells

2.2.1 Dra$ and lael a diagram of the ultrastructure of &scherichia coli &. coli- as ane'ample of a pro!aryote

Representation

$% &%

2.2.2

n notate the

diagram $ith the function of each of the named structures

Cell 'all: A rigid outer layer made of peptidoglycan that maintains shape and protects

the cell from damage or #ursting if internal pressure is high

Cell Membrane: ;emi-permea#le #arrier that controls the entry and eit of su#stances

Cytoplasm: &luid component %hich contains the en0ymes needed for all meta#olicreactions

Nucleoid: *egion of the cytoplasm %hich contains the genophore (the proaryotic

A)

!lasmid: Additional A molecule that can eist and replicate independently of the

genophore - it can #e transmitted #et%een #acterial species

Ribosome: Complees of *A and protein that are responsi#le for polypeptide

synthesis (proaryotic ri#osomes are smaller than euaryotes - /6;)

Slime Capsule: A thic polysaccharide layer used for protection against dessication

(drying out) and phagocytosis

(la)ella *sin)ular la)ellum+: 'ong slender pro$ection containing a motor protein

%hich spins the flagella lie a propellor ena#ling movement!ili *sin)ular pilus+: ,air-lie etensions found on #acteria %hich can serve one of t%o

roles

,ttachment pili: ;horter in length they allo% #acteria to adhere to one another

or to availa#le surfaces

Sex pili: 'onger in length they allo% for the echange of genetic material

(plasmids) via a process called #acterial con$ugation


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2.2.3 "dentify structures from 2.2.1 in electron micrographs of &. coli

lectron !icrograph of &scherichia coli

2.2.4 State that acterial cells divide y inary fission

7inary fission is a form of aseual reproduction and cell division used #y proaryotic

organisms

?t is not the same as mitosis there is no condensation of genetic material and no

spindle formation

?n the process of #inary fission:

The circular A is copied in response to a replication signal The t%o A loops attach to the mem#rane

The mem#rane elongates and pinches off (cytoinesis) forming t%o separate

cells

The +rocess of 7inary &ission


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2.3 Eukaryotic Cells2.3.1 Dra$ and lael a diagram of the ultrastructure of a liver cell as an e'ample of an

animal cell

Representation $%

B


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2.3.2 nnotate the diagram from 2.3.1 $ith the functions of each named structure

Cell Membrane: ;emi-permea#le #arrier that controls the entry and eit of su#stances

Cytosol: The fluid portion of the cytoplasm (does not include the organelles or other

insolu#le materials)Nucleus: Contains hereditary material (A) and thus controls cell activities (via

transcription) and mitosis (via A replication)

Nucleolus: ;ite of the production and assem#ly of ri#osome components

Ribosome: Complees of *A and protein that are responsi#le for polypeptide

synthesis (euaryotic ri#osomes are larger than proaryotes - 6;)

Mitochondria: ;ite of aero#ic respiration %hich produces large =uantities of chemical

energy (AT+) from organic compounds

-ol)i ,pparatus: An assem#ly of vesicles and folded mem#ranes involved in the

sorting storing and modification of secretory products

.ysosome: ;ite of hydrolysis digestion #reado%n of macromolecules!eroxisome: Catalyses #read%on of toic su#stances lie hydrogen peroide and

other meta#olites

Centrioles: !icrotu#ule-organising centres involved in cell division (mitosis meiosis

and cytoinesis)

Endoplasmic Reticulum: A system of mem#ranes involved in the transport of

materials #et%een organelles


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Rou)h ER: ;tudded %ith ri#osomes and involved in the synthesis and transport

of proteins destined for secretion

Smooth ER: ?nvolved in the synthesis and transport of lipids and steroids as

%ell as meta#olism of car#ohydrates

2.3.3 "dentify the structures in 2.2.1 in electron micrographs of a liver cell lectron !icrograph of a 'iver Cell

2.3.4 Compare pro!aryote and eu!aryote cells

Similarities: 7oth have a cell mem#rane

7oth contain ri#osomes

7oth have A and cytoplasm


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%ierences:

2.3.# State three differences et$een plant and animal cells

'a#elled iagram of a


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2.3.% Outline t$o roles of e'tracellular components!lants

The cell %all in plants is made from cellulose secreted from the cell %hich serves the

follo%ing functions:

+rovides support and mechanical strength for the cell (maintains cell shape)

+revents ecessive %ater uptae #y maintaining a sta#le turgid state

;erves as a #arrier against infection #y pathogens

,nimals

The etracellular matri (C!) is made from glycoproteins secreted from the cell %hich

serve the follo%ing functions:

+rovides support and anchorage for cells

;egregates tissues from one another

*egulates intercellular communication #y se=uestering gro%th factors

2.4 Membranes2.4.1 Dra$ and lael a diagram to sho$ the structure of memranes


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2.4.2 &'plain ho$ the hydrophilic and hydrophoic properties of phospholipids help to

maintain the structure of cell memranes

Structure o !hospholipids

Consist of a polar head (hydrophilic) made from glycerol and phosphate

Consist of t%o non-polar fatty acid tails (hydropho#ic)

,rran)ement in Membrane

+hospholipids spontaneously arrange in a #ilayer

,ydropho#ic tail regions face in%ards and are shielded from the surrounding

polar fluid %hile the t%o hydrophilic head regions associate %ith the cytosolic and

etracellular environments respectively

Structural !roperties o !hospholipid #ilayer

+hospholipids are held together in a #ilayer #y hydropho#ic interactions (%ea

associations) ,ydrophilic hydropho#ic layers restrict entry and eit of su#stances

+hospholipids allo% for mem#rane fluidity flei#ility (important for functionality)

+hospholipids %ith short or unsaturated fatty acids are more fluid

+hospholipids can move hori0ontally or occasionally laterally to increase fluidity

&luidity allo%s for the #reaing remaing of mem#ranes (eocytosis

endocytosis)

2.4.3 /ist the functions of memrane proteins


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T

ransport: +rotein channels (facilitated) and protein pumps (active)

R

eceptors: +eptide-#ased hormones (insulin glucagon etc.)

A

nchora)e: Cytoseleton attachments and etracellular matri

C

ell reco)nition: !,C proteins and antigens

I

ntercellular /oinin)s: Tight $unctions and plasmodesmata

Enzymatic activity: !eta#olic path%ays (e.g. electron transport chain)

2.4.4 Define diffusion and osmosis

%iusion:

The net movement of particles from a region of high concentration to a region of lo%

concentration (along the gradient) until e=uili#rium

0smosis:

The net movement of %ater molecules across a semi-permea#le mem#rane from a

region of lo$ solute concentration to a region of high solute concentration untile=uili#rium is reached

8smosis


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2.4.# &'plain passive transport across memranes in terms of simple diffusion and

facilitated diffusion

The plasma mem#rane is semi-permea#le and selective in %hat can cross

;u#stances that move along the concentration gradient (high to lo%) undergo

passive transport and do not re=uire the ependiture of energy (AT+)

Simple diusion:

;mall non-polar (lipophilic) molecules can freely diffuse across the mem#rane

(acilitated diusion:

'arger polar su#stances (ions macromolecules) cannot freely diffuse andre=uire the assistance of transport proteins (carrier proteins and channel proteins) to

facilitate their movement (facilitated diffusion)

2.4.% &'plain the role of protein pumps and 0 in active transport across memranes

Active transport is the passage of materials against a concentration gradient

(from low to high)

This process requires the use of protein pumps which use the energy from ATP

to translocate the molecules against the gradient

The hydrolysis of ATP causes a conformational change in the protein pump

resulting in the forced movement of the substance

Protein pumps are specific for a given molecule, allowing for movement to be

regulated (e.g. to maintain chemical or electrical gradients)

An example of an active transport mechanism is the Na+ /K

+ pump which is

involved in the generation of nerve impulses


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Types of Membrane Transport

2.4.7 Explain how vesicles are used to transport materials within a cell between the

endoplasmic reticulum, Golgi apparatus and plasma membrane

Polypeptides destined for secretion contain an initial target sequence (a signal

recognition peptide) which directs the ribosome to the endoplasmic reticulum

The polypeptide continues to be synthesised by the ribosome into the lumen of

the ER, where the signal sequence is removed from the nascent chain

The polypeptide within the rough ER is transferred to the golgi apparatus via a

vesicle, which forms from the budding of the membrane

The polypeptide moves via vesicles from the cis face of the golgi to the trans face

and may be modified along the way (e.g. glycosylated, truncated, etc.)

The polypeptide is finally transferred via a vesicle to the plasma membrane,

whereby it is either immediately released (constitutive secretion) or stored for a delayed


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release in response to some cellular signal (regulatory secretion = for a more

concentrated and more sustained effect)

Overview of Vesicular Transport

2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and

reform during endocytosis and exocytosis

The membrane is principally held together by the relatively weak hydrophobic

associations between phospholipidsThis association allows for membrane fluidity and flexibility, as the phospholipids (and to

a lesser extent the proteins) can move about to some extent

This allows for the breaking and remaking of membranes, allowing larger substances

access into and out of the cell (this is an active process)

Endocytosis

The process by which large substances (or bulk amounts of smaller substances)

enter the cell without travelling across the plasma membrane

An invagination of the membrane forms a flask-like depression which envelopes

the material; the invagination is then sealed off forming a vesicle


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There are two main types of endocytosis:

1. Phagocytosis

The process by which solid substances (e.g. food particles, foreign pathogens)

are ingested (usually to be transported to the lysosome for break down)

2. Pinocytosis

The process by which liquids / solutions (e.g. dissolved substances) are ingested

by the cell (allows quick entry for large amounts of substance)

Exocytosis

The process by which large substances exit the cell without travelling across the

plasma membrane

Vesicles (usually derived from the golgi) fuse with the plasma membrane

expelling their contents into the extracellular environment

The Process of Exocytosis


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2.5 Cell Diision2.#.1 Outline the stages in the cell cycle, including interphase 1, S, 2 -, mitosis and

cyto!inesis

The cell cycle is an ordered set of events that culminates in cell gro%th anddivision into t%o daughter cells

?t can roughly #e divided into t%o main stages:

1nterphase

The stage in the development of the cell #et%een t%o successive ! phases

This phase of the cell cycle is a continuum of 3 distinct stages (< 1 ;


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2.#.2 State that tumours cancers- are the result of uncontrolled cell division and that

these can occur in any organ or tissue

The cell cycle is controlled #y a comple chemical control system that responds

to signals #oth inside and outside of the cell

Tumor suppressor genes produce proteins %hich inhi#it cell division %hile proto-

oncogenes produce proteins that promote gro%th and division

!utations to these genes result in uncontrolled cell division resulting in the

formation of a tumour

Tumours can gro% in si0e %hich causes damage local tissue@ they may also

spread to other parts of the #ody (malignant tumours)

iseases caused #y the gro%th of tumours are collectively no%n as cancers

Cancer in Tasmanian evils

2.#.3 State that interphase is an active period in the life of a cell $hen many metaolic

reactions occur, including protein synthesis, D replication and an increase in the

numer of mitochondria and chloroplasts

?nterphase is an active period in the life of a cell - many events need to occur #efore a

cell can successfully undergo division:

Protein synthesis: The cell needs to synthesise ey proteins and en0ymes to

ena#le it to gro% copy its contents and then divide

AT! production: The cell %ill need to generate sufficient =uantities of AT+ in

order to successfully divide

Increase number o or)anelles: The cell needs to ensure #oth daughter cells

%ill have the necessary num#ers of organelles needed to survive

DN, replication: The genetic material must #e faithfully duplicated #efore

division (this occurs during the ; phase)


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As none of these processes can occur during the ! phase interphase contains gro%th

checpoints to ensure division is via#le

G1

: A checpoint stage #efore A replication during %hich the cell gro%s

duplicates organelles synthesises proteins and produces AT+

S: The stage during %hich A is replicated

G2

: A checpoint stage #efore division during %hich the copied A is checed

for fidelity (mutations) and final meta#olic reactions occur

2.#.4 Descrie the events that occur in the four phases of mitosis

!rophase

A supercoils causing chromosomes to condense and #ecome visi#le under a

light microscope As A %as replicated during interphase the chromosomes are each comprised

of t%o genetically identical sister chromatids $oined at a centromere

The centrosomes move to opposite poles of the cell and spindle fi#res #egin to

form #et%een them (in animals each centrosome contains 2 centrioles)

The nuclear mem#rane is #roen do%n and disappears

Metaphase

;pindle fi#res from the t%o centrosomes attach to the centromere of each

chromosome

Contraction of the microtu#ule spindle fi#res cause the chromosomes to line up

separately along the centre of the cell (e=uatorial plane)

,naphase

Continued contraction of the spindle fi#res cause the t%o sister chromatids to

separate and move to the opposite poles of the cell

8nce the t%o chromatids in a single chromosome separate each constitutes a

chromosome in its o%n right


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Telophase

8nce the t%o sets of identical chromosomes arrive at the poles the spindle fi#res

dissolve and a ne% nuclear mem#rane reforms around each set of chromosomes

The chromosomes decondense and are no longer visi#le under a light

microscope The division of the cell into t%o daughter cells (cyto!inesis) occurs concurrently

%ith telophase

2.#.# &'plain ho$ mitosis produces t$o genetically identical nuclei

uring interphase (the ; phase) the A %as replicated to produce t%o copies of

genetic material

These t%o identical A molecules are identified as sister chromatids and are

held together #y a single centromere

uring the events of mitosis (as descri#ed in 2.4.) the sister chromatids are

separated and dra%n to opposite poles of the cell

Dhen the cell divides (cytoinesis) the t%o resulting nuclei %ill each contain one

of each chromatid pair and thus #e genetically identical

2.#.% State that gro$th, emryonic development, tissue repair and ase'ualreproduction involve mitosis

Growth: !ulticellular organisms increase their si0e #y increasing their num#er of cells

through mitosis

A

sexual reproduction: Certain euaryotic organisms may reproduce aseually #y

mitosis (e.g. vegetative reproduction)

T

issue Repair: amaged tissue can recover #y replacing dead or damaged cells


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Embryonic development: A fertilised egg (0ygote) %ill undergo mitosis and

differentiation in order to develop into an em#ryo

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