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A LEVEL BIOLOGY > T2: Cells > Flashcards

T2: Cells Flashcards

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1
Q

Define the term eukaryotic and prokaryotic cell.

A

eukaryotic: DNA is contained in a nucleus; membrane bound specialised organelles
prokaryotic: DNA is ‘ free ‘ in cytoplasm, no organelles e.g. bacteria & archaea

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2
Q

Describe the structure and function of the cell membrane.

A

structure: phospholipid bilayer with extrinsic and intrinsic proteins embedded function:
- isolates cytoplasm from extracellular environment
- selectively permeable to reguglate transport of substances
- involved in cell recognition

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3
Q

Explain the role of cholesterol, glycoproteins & glycolipids in the cell surface membrane

A

cholesterol: steroid molecule connects phospholipids & reduces fluidity
glycoproteins: cell signalling, cell recognition ( antigens) & binding cell together
glycolipids: cell signalling & cell recognition

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4
Q

Describe the structure of the nucleus

A
  • surrounded by nuclear envelope , a semi-permeable double membrane with pores
  • nuclear pores allow substances to enter/exit
  • dense nucleolus made of RNA & proteins assembles ribosomes
  • the nucleoplasm ( equivalent of cytoplasm that exists in the nucleus.)
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5
Q

Describe the function of the nucleus.

draw it

A
  • contains DNA coiled around chromatin into chromosomes
  • controls cellular processes
  • site of ttranscription producing mrna
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6
Q

Describe the structure of a mitochondrion.

A
  • surrounded by double membrane
  • folded inner membrane forms cristae which is the site of electron transport chain
  • fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, proteins
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7
Q

Describe the structure of a chloroplast and how its structure relates to its function. (4)

draw it

A
  • Starch grains / lipid droplets store products of
    photosynthesis;
  • double membrane - provides large surface for light absorption.
  • Thylakoids: flattened discs stack to form grana; contain photosystems with chlorophyll.
  • Intergranal lamellae: tubes attach thylakoids in adjacent grana.
  • Stroma: fluid-filled matrix.- vesicular plastid
  • Permeable membrane allows diffusion of gases /carbon dioxide;
  • Stacking / arrangement of grana/thylakoids maximises
    light catchment
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8
Q

State the function of mitochondria and chloroplasts.

A

mitochondria : site of aerobic respiration to produce ATP
chloroplasts: site of photosynthesis to convert solar energy to chemical energy

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9
Q

Describe the structure and function of the Golgi apparatus

A
  • series of flat membrane-bound sacs
    function:
  • proteins transported from RER to golgi apparatus via vesicles and fuse with cis face
  • modifies & packages proteins for export
  • at transface, , small vesicles bud of and move towards the cell membrane, where they fuse, releasing their contents by
    exocytosis.
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10
Q

describe the structure and function of a lysosome

A
  • membrane bound
  • contains hydrolytic enzymes
  • acidic environment
  • involved in cell death and digestion
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11
Q

describe the structure and function of a ribosome

A
  • formed of rRNA+ protein
  • site of protein synthesis via translation
    large subunit: joins amino acids
    small subunit: contains mRNA binding site
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12
Q

describe the structure and function of the endoplasmic reticulum (ER)

A

structure : network of cisternae and flattened sacs .
rough ER: ribosomes on suface synthesise proteins. Proteins transported inside RER. Proteins packaged into vesicles for transport
smooth ER: Involved in the production, processing and storage of lipids, E.g steroids + cholesterol

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13
Q

Describe the structure of the cell wall in plants and bacteria

A
  • bacteria: made of the polysaccharide murein
  • plants: made of cellulose
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14
Q

state three functions of the cell walls

A
  • mechanical strength and support
  • physical barrier against pathogens
  • part of apoplast pathway (plants) to enable easy diffusion of water
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15
Q

Describe the structure and function of the cell vacuole in plants.

A

structure:
- surrounded by a single membrane: tonoplast
- contains cell sap : mineral ions, water, enzymes , soluble pigments
function:
- controls turgor pressure
- absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm

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16
Q

Explain some common cell adaptations

A
  • folded membrane or microvilli increase surface area e.g. for diffusion
  • many mitochondria = large amounts of ATP for active transport
  • walls one cell thick to reduce distance of diffusion pathway
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17
Q

State the role of plasmids in prokaryotes

A
  • small ring of DNA that carries non-essential genes
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18
Q

State the role of flagella in prokaryotes

A
  • rotating tail propels ( usually unicellular) organism
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19
Q

state the role of the capsule in prokaryotes

give 3

A
  • a polysaccharide layer:
  • prevents desiccation
  • provides mechanical protection against phagocytosis & external chemicals
  • attaches the cell to surfaces
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20
Q

Give three structural properties shared by eukaryotic and prokaryotic cells

similar structures

A
  • cell membrane
  • cytoplasm
  • ribosomes
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21
Q

Contrast eukaryotic and prokaryotic cells

A
  • PC are smaller and always unicellular, whereas eukaryotic cells are larger and often multicellular.
  • PC lack membrane-bound organelles and a nucleus, while eukaryotic cells always have membrane-bound organelles and a distinct nucleus.
  • PC have circular DNA that is not associated with proteins, whereas eukaryotic cells have linear chromosomes associated with histone proteins.
  • PC have smaller ribosomes (70S), whereas eukaryotic cells have larger ribosomes (80S).
  • Prokaryotic cells reproduce by binary fission, which is asexual, whereas eukaryotic cells reproduce by mitosis and meiosis.
  • Prokaryotic cells have cell walls made of murein (peptidoglycan), while eukaryotic plant cells have cell walls made of cellulose and fungi have cell walls made of chitin.
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22
Q

Give4 reasons why are viruses referred to as ‘ particles’ instead of cells?

A
  • acellular & non-living
  • no cytoplasm
  • can’t self-reproduce
  • no metabolism
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23
Q

Describe the structure of a viral particle

A
  • linear genetic material (DNA or RNA ) & viral enzymes e.g. reverse transcriptase
  • genetic material surrounded by capsid ( protein coat made of capsomeres)
  • contains attachment proteins and lipid envelope
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24
Q

Describe the structure of an enveloped virus.

A
  • simple virus surrounded by matrix protein
  • matrix protein surrounded by envelope derived from cell membrane of host cell
  • attachment proteins on surface
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25
Q

state the role of the capsid on viral particles.

A
  • protect nucleic acid from degradation by restriction endonucleases
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26
Q

state the role of attachment proteins on viral particles.

A
  • enable viral particle to bind to complementary sites on host cell
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27
Q

Describe how optical microscopes work

A
  1. lenses focus rays of light and magnify the view of a thin slice of specimen
  2. different structures absorb different amount and wavelengths of light
  3. reflected light is transmitted to the observer via the objective lens and eyepiece
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28
Q

outline how a student could prepare a temporary mount of tissue for an optical microscope

A
  1. Obtain thin section of tissue e.g. using ultra tome or by maceration.
  2. Place plant tissue in a drop of water.
  3. Stain tissue on a slide to make structures visible.
  4. Add coverslip using mounted needle at 45° to avoid trapping air bubbles.
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29
Q

Suggest the advantages and limitations of using an optical microscope.

3/2

A

+ colour image
+ can show living structure
+ affordable
limit:
- 2D image
- lower resolution than electron microscopes = cannot see ultrastructure

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30
Q

Describe how a transmission electron microscope (TEM) works.

A
  1. Pass a high energy beam of electrons through a thin slice of specimen
  2. more dense structures appear darker since they absorb more electrons
  3. Focus image onto fluorescent screen or photographic plate using magnetic lenses
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31
Q

Suggest the advantages and limitations of using a TEM.

2/4

A

+ electrons have shorter wavelength than light = high resolution , so ultrastructure visible
+ high magnification ( x 500,000)
limitations:
- 2D image
- requires a vacuum so cannot show living structures
- extensive preparation may introduce artefacts
- no colour image

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32
Q

Describe how a scanning electron microscope (SEM) works.

A
  1. focus a beam of electrons onto a specimen’s surface using electromagnetic lenses
  2. reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate
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33
Q

Suggest the advantages and limitations of using an SEM

2/3

A

+ 3D image
+ electron shave a shorter wavelength than light + high resolution
- requires a vacuum = cannot show living structures
- no colour image
- only shows outer surface

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34
Q

Define magnification and resolution.

A

Magnification: factor by which the image is larger than the actual specimen.
Resolution: smallest separation distance at which 2 separate structures can be distinguished from one another.

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35
Q

Explain how to use an eyepiece graticule and stage micrometer to measure the size of a structure.

A
  1. Place micrometer on stage to calibrate eyepiece graticule.
  2. Line up the scales.
  3. Count how many graticule divisions are in 100um on the micrometer.
  4. Use calibrated values to calculate actual length of structures.
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36
Q

State an equation to calculate the actual size of a structure from microscopy.

A

actual size = image size / magnification

  • triangle : IAM
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37
Q

Outline what happens during cell fractionation and ultracentrifugation.

A
  1. Blend and homogenize tissue to break open cells & release organelles.
  2. Place cold, buffered, isotonic solution
  3. Filter homogenate to remove debris.
  4. Perform differential centrifugation:
    a) Spin homogenate in centrifuge.
    b) The most dense organelles in the mixture form a pellet.
    c) Filter off the supernatant and spin again at a higher speed.
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38
Q

state the order of sedimentation of organelles during differential centrifugation.

“Never Make Lightly Rated Popcorn, Seriously Rude”

A

most dense —-> least dense

nucleus , mitochondria , lysosomes, RER , plasma membrane , SER, ribosomes

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39
Q

Explain why fractionated cells are kept in a cold, buffered, isotonic solution.

A

cold: slow action of hydrolase enzymes.
buffered: maintain constant pH.
isotonic: prevent osmotic lysis/ shrinking
of organelles.

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40
Q

state what the cell cycle is and outline its stages

A
  • cycle of division with intermediate growth periods
    1. interphase
    2. mitosis or meiosis ( nuclear division)
    3. cytokinesis ( cytoplasmic division)
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41
Q

Explain why the cell cycle does not occur in some cells.

A
  • After differentiation, some types of cell in multicellular organisms
  • no longer have the ability to divide.
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42
Q

What is the difference between the cell cycle and mitosis?

A
  • cell cycle includes growth period between divisions ; mitosis is only 10% of the cycle & refers only to nuclear division
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43
Q

Describe the process of Interphase

A

three phases:
- G1: cell synthesises proteins for replication and cell size increases. The cell increases in mass and size
- S phase: DNA replication occurs
- G2 phase: preparation for mitosis + more growth

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44
Q

State the purpose of mitosis

A

produces 2 genetically identical daughter cells
- Growth of multicellular organisms
- tissue repair /cell replacement
- asexual reproduction

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45
Q

Give the stages of mitosis

A
  1. Prophase
  2. Metaphase
  3. Anaphase
  4. Telophase
46
Q

Outline what happens during prophase

A
  1. Chromosomes condense , becoming visible.
  2. centrioles move to opposite poles of cell ( animal cells ) & mitotic spindle fibres form
  3. Nuclear envelope & nucleolus break down = chromosomes free in cytoplasm
47
Q

Outline what happens during metaphase

A
  • sister chromatids line up at cell equator, attached to the mitotic spindle by their centromeres
48
Q

Outline what happens during anaphase

A
  • it requires energy from ATP hydrolysis
    1. Spindle fibres contract and centromeres divide
    2. Sister chromatids separate into 2 distinct chromosomes & are pulled to opposite poles of cells
    3. Spindle fibres break down
49
Q

Outline what happens during telophase

A
  1. Chromosomes decondense , becoming invisible again
  2. New nuclear envelopes form around each set of chromosomes = 2 new nuclei, each with 1 copy of each chromosome
50
Q

Explain the procedure for a root tip squash experiment

A
  1. Prepare a temporary mount of root tissue
  2. Focus an optical microscope on the slide.
  3. Count total number of the cells in the field of view and number of cells in a stage of mitosis
  4. Calculate mitotic index ( proportion of cells undergoing mitosis)
51
Q

Explain how to prepare a temporary root tip mount

A
  1. Place root in hydrochloric acid to halt cell division & hydrolyse middle lamella.
  2. Stain root tip with a dye that binds to chromosomes.
  3. Macerate tissue in water using mounted needle.
  4. Use mounted needle at 45° to press down coverslip & obtain a single layer of cells. Avoid trapping air bubbles.
52
Q

Name two dyes that bind to chromosomes

A
  • toluidine blue ( blue)
  • acetic orcein ( purple-red)
53
Q

Why is only the root tip used when calculating a mitotic index

A
  • meristematic cells at root tip are actively undergoing mitosis
  • cells further from root tip are elongating rather than dividing
54
Q

What are tumour suppressor genes?

A
  • Genes that code for proteins to trigger
    apoptosis
  • slow down cell cycle to prevent tumour formation
  • (e.g. p53 acts between G1 & S in interphase so damaged DNA cannot replicate).
55
Q

How can mutation to tumour suppressor genes & proto-oncogenes cause cancer?

A

· Tumour suppressor: no production of a protein needed to slow the cell cycle.
· Disruption to cell cycle -> uncontrolled cell division ->tumour.

56
Q

Suggest how cancer treatments control the rate of cell division.

A
  • Disrupt the cell cycle:
  • prevent DNA replication
  • disrupt spindle formation = inhibit metaphase / anaphase
57
Q

How do prokaryotic cells replicate?

A

Binary fission:
- DNA loop replicates. Plasmids replicate in cytoplasm.
- Cell elongates, separating the 2 DNA loops.
- Cell membrane contracts & septum forms.
- Cell splits into 2 identical progeny cells, each with 1 copy of the DNA loop but a variable number of plasmids.

58
Q

Why are viruses classified as non-living?

A

They are acellular: no cytoplasm, no
metabolism & cannot self-replicate.

59
Q

Outline how viruses replicate.

A
  1. Attachment proteins attach to receptors on host cell membrane.
  2. Enveloped viruses fuse with cell membrane or move in via endocytosis & release DNA/ RNA into cytoplasm OR viruses inject DNA/ RNA.
  3. Host cell uses viral genetic information to synthesise new viral proteins/ nucleic acid.
  4. Components of new viral particle assemble.
60
Q

How do new viral particles leave the host cell?

A

a) Bud off & use cell membrane to form
envelope.
b) Cause lysis of host cell.

61
Q

Why is it so difficult to develop effective treatments against viruses?

A
  • Replicate inside living cells
  • thus difficult to
    kill them without killing host cells.
62
Q

Describe the fluid mosaic model of membranes.

A

fluid: phospholipid bilayer in which individual phospholipids can move = membrane has flexible shape
mosaic: extrinsic and intrinsic proteins of different sizes and shapes are embedded.

63
Q

Explain the role of cholesterol & glycolipids in membranes

A

cholesterol: connects phospholipids & reduces fluidity for stability
glycolipids: cell signalling & cell recognition

64
Q

explain the functions of extrinsic and intrinsic proteins in membranes.

A

extrinsic:
- binding sites receptors e..g. for hormones
- antigens
- bind cells together
- involved in cell signalling
intrinsic:
- electron carriers (respiration/photosynthesis)
- channel proteins ( facilitated diffusion)
- carrier proteins ( facilitated diffusion/ active transport)

65
Q

Explain the functions of membranes within cells

A
  • provide internal transport system
  • selectively permeable to regulate passage of molecules into/out of organelles
  • provide reaction surface
  • isolate organelles from cytoplasm for specific metabolic reactions
66
Q

Explain the function of the cell membrane

A
  • isolates cytoplasm from extracellular environment
  • selectively permeable to regulate transport of substances
  • involved in cell-signalling/cell reconition
67
Q

Name and explain 3 factors that affect membrane permeability

A
  • temperature: high temperature denatures membrane proteins/ phospholipid molecules
  • pH: changes tertiary structure of membrane proteins
  • use of a solvent: may dissolve membrane
68
Q

Outline how colorimetry could be used to investigate membrane permeability.

A
  1. Use plant tissue with soluble pigment in vacuole. Tonoplast & cell-surface membrane disrupted = 1 permeability = pigment
    diffuses into solution.
  2. Select colorimeter filter with complementary colour.
  3. Use distilled water to set colorimeter to 0. Measure absorbance/ % transmission value of solution.
  4. high absorbance/ low transmission = more pigment in solution.
69
Q

Define osmosis

A
  • water diffuses across semi-permeable membranes from an area of high water potential to an area of lower water potential until a dynamic equilibrium is established.
70
Q

what is water potential?

A
  • pressure created by water molecules measured in kPa
  • the more solute , the more negative water potential
71
Q

How does osmosis affect plant and animal cell?

A

osmosis into cell:
plant: protoplast swells = cell turgid
animal: lysis
osmosis out of cell:
plant: protoplast shrinks= cell flaccid
animal: crenation

72
Q

Suggest how a student could produce a desired concentration of solution from a stock solution.

A
  • volume of stock solution = required concentration x final volume needed / concentration of stock solution.
  • volume of distilled water = final volume needed - volume of stock solution.
73
Q

Define simple diffusion

A
  • passive process requires no energy from ATP hydrolysis
  • net movement of small, lipid-soluble molecules directly through the bilayer from an area of high concentration to an area of lower concentration
74
Q

Define facilitated diffusion.

A
  • passive process
  • specific channel or carrier proteins with complementary binding sites transport large and/or polar molecules/ions down the concentration gradient
75
Q

explain how channel and carrier proteins work.

A

Channel:
- hydrophilic channels bind to specific ions = one side of the protein closes & the other opens
Carrier:
- binds to complementary molecule.
- conformational change releases molecule on other side of membrane;
- in facilitated diffusion, passive process;
- in active transport, requires energy from ATP hydrolysis

76
Q

Name 5 factors that affect the rate of diffusion

A
  • temperature
  • diffusion distance
  • surface area
  • size of molecule
  • difference in concentration ( how steep the concentration gradient is )
77
Q

State Fick’s law

A
  • rate of diffusion is proportional to the:
  • surface area x difference in concentration / thickeness of membrane
78
Q

How are cells adapted to maximise the rate of transport across their membranes.

A
  • many carrier / channel proteins
  • folded membrane increases surface area
79
Q

Explain the difference between the shape of a graph of concentration (x-axis) against rate (y-axis) for simple vs facilitated diffusion.

A

Simple diffusion: straight diagonal line; rate of
diffusion increases proportionally as concentration increases.
Facilitated diffusion: straight diagonal line later levels off when all channel/ carrier proteins are saturated.

80
Q

Define active transport.

A
  • Active process: ATP hydrolysis releases phosphate group that binds to carrier protein, causing it to change shape.
  • Specific carrier protein transports molecules/ ions from an area of low concentration to area of higher concentration (i.e. against concentration gradient).
81
Q

Compare and contrast active transport and facilitated diffusin.

A
  • both may involve carrier proteins
  • active transport requires energy from ATP hydrolysis ; facilitated diffusion is a passive process
  • facilitated diffusion may also involve channel proteins
82
Q

Define co transport

A
  • transport of one substance is coupled with the transport of another substance across a membrane.
83
Q

Explain how co-transport is involved in the absorption of glucose/amino acids in the small intestine.

A
  1. Na+ actively transported out of epithelial cells & into bloodstream.
  2. Na+ concentration is lower in epithelial cells than lumen of gut.
  3. Na + and glucose/ amino acids from lumen to epithelial cells occurs via a carrier protein via down electrochemical gradient.
84
Q

define antigen (2)

A
  • Foreign protein or polysaccharide
  • (that) stimulates an immune response / production of antibody;
85
Q

how does phagocytosis destroy pathogens?

A
  • phagocyte moves towards pathogen via chemotaxis
  • phagocyte engulfs pathogen via endocytosis to form a phagosome
  • phagosome fuses with lysosome to form a phagolysosome
  • lysosome releases hydrolytic enzymes digesting the pathogen
  • phagocyte absorbs the products from pathogen hydrolysis.
86
Q

Explain the role of antigen-presenting cells ( APCs)

A
  • macrophage displays antigen from pathogen om its surface ( after hydrolysis in phagocytosis )
  • enhances recognition by Th cells which cannot directly interface with pathogens/antigens in body fluid.
87
Q

Name the 2 types of specific immune response.

A
  • cell mediated
  • humoral
88
Q

Outline the process of the cell-mediated response.

A
  1. Complementary T lymphocytes bind to a foreign antigen on MHC molecules found on APCs.
  2. These T cells become activated T cells.
  3. T helper cells release cytokines that stimulate both:
  4. Clonal expansion of helper T cells (rapid mitosis), which either become memory cells or help trigger the humoral response by activating B cells.
  5. Clonal expansion of cytotoxic T cells (Tc cells), which secrete the enzyme perforin to destroy infected cells.
89
Q

Outline the process of the humoral response.

A
  1. Complementary T lymphocytes bind to foreign antigen on antigen-presenting T cells.
  2. Release cytokines that stimulate clonal expansion (rapid mitosis) of complementary B lymphocytes.
  3. B cells differentiate into plasma cells.
  4. Plasma cells secrete antibodies with
    complementary variable region to antigen.
  5. B memory cells are also produced.
90
Q

what is an antibody (2)

A
  • protein / immunoglobulin specific to an antigen;
  • Produced by B cells
    OR
    Secreted by plasma cells;
91
Q

Describe the structure of an antibody.

A
  • Quaternary structure: 2 ‘light chains’ held together by disulfide bridges, 2 longer ‘heavy chains’.
  • Binding sites on variable region of light chains have specific tertiary structure complementary to an antigen.
  • The rest of the molecule is known as the constant region.
92
Q

what are monoclonal antibodies

A
  • antibodies which have the same tertiary structure
  • they are complementary to specific antigens .
  • they are produced from a single clone of B cells.
93
Q

what are memory cells?

A

· Specialised T/ B cells produced from
primary immune response.
. Remain in low levels in the blood.
. Can divide very rapidly by mitosis if
organism encounters the same pathogen
again

94
Q

Contrast the primary and secondary immune response.

A
95
Q

what causes antigen variability?

A
  1. Random genetic mutation changes DNA base sequence.
  2. Results in different sequence of codons on mRNA
  3. Different primary structure of antigen = H-bonds, ionic bonds & disulfide bridges form in different places in tertiary structure.
  4. Different shape of antigen.
96
Q

Explain how antigen variability affects the incidence of disease.

A
  • memory cells no longer complementary to antigen = individual not immune = can catch the disease more than once.
  • many varieties of a pathogen = difficult to develop vaccine containing all antigen types.
97
Q

Compare passive and active immunity. Give examples.

A

· both involve antibodies
. can both be natural or artificial
- passive natural: antibodies in breast milk/ across placenta
- passive artificial: anti-venom, needle stick injections
- active natural: humoral response to infection
- active artificial: vaccination

98
Q

Contrast passive and active immunity.

A

passive:
- no memory cells & antibodies not replaced when broken down = short term
- immediate
- antibodies from external source
- direct contact with antigen not necessary.
Active:
- memory cells produced = long term
- time lag
- lymphocytes produce antibodies
- direct contact with antigen necessary.

99
Q

DESCRIBE vaccination.

A
  1. vaccine contains dead/inactive from of a pathogen or antigen
  2. triggers primary immune response
  3. memory cells are produced and remain in the bloodstream , so secondary response is rapid & produces higher concentration of antibodies
  4. Pathogen is destroyed before it causes symptoms
100
Q

what is herd immunity?

A
  • vaccinating large proportion of population reduces available carriers of the pathogen.
  • protects individuals who have not been vaccinated e.g. those with a weak immune system
101
Q

Suggest some ethical issues surrounding the use of vaccines

A
  • production may involve use of animals
  • potentially dangerous side-effects
  • clinical tests may be fatal
  • compulsory vs opt-out
102
Q

Describe the structure of HIV.

A

· Genetic material + viral enzymes
(integrase & reverse transcriptase) surrounded by capsid.
. Surrounded by viral envelope derived from host cell membrane.
. GP120 attachment proteins on surface.

103
Q

How does HIV result in the symptoms of AIDS?

A
  1. Attachment proteins bind to complementary CD4 receptor on TL cells.
  2. HIV particles replicate inside T cells, killing or damaging them.
  3. AIDS develops when there are too few T cells for the immune system to function.
  4. Individuals cannot destroy other pathogens & suffer from secondary diseases/ infections.
104
Q

Describe how HIV is replicated. (4)

A
  1. Attachment proteins attach to receptors on helper T cell/lymphocyte;
  2. Nucleic acid/RNA enters cell;
  3. Reverse transcriptase converts RNA to DNA;
  4. Viral protein/capsid/enzymes produced;
  5. Virus (particles) assembled and released (from cell);
105
Q

Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells). (4)

A
  1. RNA converted into DNA using reverse transcriptase
  2. DNA /inserted into (helper T cell) genome/nucleus;
  3. DNA transcribed into (HIV m)RNA
  4. (HIV mRNA) translated into (new) HIV/viral proteins (for assembly into viral particles);
106
Q

Explain how HIV affects the production of antibodies when AIDS develops
in a person. (3)

A
  1. Less/no antibody produced;
  2. (Because HIV) destroys helper T cells;
    Accept ‘reduces number’ for ‘destroys’
  3. (So) few/no B cells activated / stimulated
    OR
    (So) few/no B cells undergo mitosis/differentiate/form plasma cells;
    3
107
Q

Why are antibiotics ineffective against viruses

A
  • antibiotics often work by damaging murein cell walls to cause osmotic lysis. Viruses have no cell wall.
  • viruses replicate inside host cell = difficult to destroy them without damaging normal body cells.
108
Q

Suggest the clinical applications of monoclonal antibodies.

A
  • pregnancy tests by detecting HCG hormones in urine
  • Diagnostic procedures e.g. ELISA test
  • targeted treatment by attaching drug to antibody so that it only binds to cells with abnormal antigen e.g. cancer cells due to specificity of tertiary structure of binding site
109
Q

Explain the principle of the direct ELISA test

A
  1. Monoclonal antibodies bind to bottom of test plate.
  2. Antigen molecules in sample bind to antibody. Rinse excess.
  3. Mobile antibody with ‘reporter enzyme’ attached binds to
    antigens that are ‘fixed’ on the monoclonal antibodies. Rinse excess.
  4. Add substrate for reporter enzyme. Positive result: colour change.
110
Q

Explain the principle of an indirect ELISA test.

A
  1. Antigens bind to bottom of test plate.
  2. Antibodies in sample bind to antigen. Wash away excess.
  3. Secondary antibody with ‘reporter enzyme’ attached binds
    to primary antibodies from the sample.
  4. Add substrate for reporter enzyme. Positive result: colour change.

detects presence of an antibody against a specific antigen

111
Q

Suggest some ethical issues surrounding the use of monoclonal antibodies.

A
  • production involves animals
  • drug trials against arthritis & leukaemia resulted in multiple organ failure.
112
Q

Describe the role of antibodies in producing a positive result in an ELISA
test. (4)

A
  1. (First) antibody binds/attaches /complementary (in shape) to antigen;
  2. (Second) antibody with enzyme attached is added;
  3. (Second) antibody attaches to antigen;
    Accept (second) antibody attaches to (first) antibody (indirect ELISA test).
  4. (Substrate/solution added) and colour changes;

A LEVEL BIOLOGY (9 decks)

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