3.2 Cells Flashcards
What is the structure and function of the cell-surface membrane and in which cells can it be found?
Structure:
- Phospholipid bilayer.
Function:
● Selectively permeable → enables control of movement of substances in / out of cell
● Molecules / receptors / antigens on surface → allow cell recognition / signalling
Found in: animal, plant, algal and fungal cells
What is the structure and function of the nucleus and in which cells can it be found?
Structure:
- Double membrane (nuclear envelope) encloses and protects DNA. Outer membrane of envelope is continuous with rer for easy transportation of substances.
- Nuclear pores allow entry & exit of substances.
- Nucleoplasm contains chromatin (during cell division condenses to form chromosomes) and nucleolus (makes RNA & ribosomes).
Function:
Controls all activities within the cell. Contains DNA required for protein synthesis.
Found in: animal, plant, algal and fungal cells
What is the structure and function of mitochondria and in which cells can they be found?
Structure:
- Double membrane isolates respiratory reactions from general cytoplasm (so high conc of enzymes + substrates can be maintained). Inner membrane folds to form cristae (increase SA for attachment of enzymes).
- Matrix.
- Inner membrane spanned with proteins (allows entry of pyrovic acid + oxygen & exit of ATP + carbon dioxide).
- Contains DNA + ribosomes involved in protein synthesis.
Function:
Site of aerobic respiration whereby ATP is produced for energy release.
Found in: animal, plant, algal and fungal cells
What is the structure and function of chloroplasts and in which cells can they be found?
Structure:
- Double membrane isolates photosynthetic reactions from general cytoplasm.
- Stroma contains series of flattened sacs (thylakoid membranes) which can be stacked into grana (increased SA for assembly of chlorophyll + attachment of enzymes) - also contains starch granules & lipid droplets.
- Lamella - thylakoid linking grana.
- Contains DNA + ribosomes involved in nucleic acid & protein synthesis.
Function:
Site of photosynthesis. Absorbs light energy.
Found in: plant and algal cells
What is the structure and function of the Golgi apparatus & Golgi vesicles and in which cells can they be found?
Structure:
- Stack of membrane bound fluid filled flattened sacs (cisternae).
- Vesicles often seen on the edges of the sacs (small membrane sacs).
- Receives proteins & lipids from the ER & modifies them.
- Proteins/lipids then packaged into vesicles to be transported.
Golgi body function:
Processes & packages new lipids & proteins. Makes lysosomes.
Golgi vesicles function:
Transports lipids & proteins processed by Golgi body.
Found in: animal, plant, algal and fungal cells
What is the structure and function of lysosomes and in which cells can they be found?
Structure:
- Type of Golgi vesicle.
- Spherical sacs surrounded by single membrane.
- Contain powerful enzymes which digest and break down materials.
Function:
Releases lysozymes used to digest/break down pathogens or worn out cell components.
Found in: animal, plant, algal and fungal cells
What is the structure and function of ribosomes and in which cells can they be found?
Structure:
- Very small organelle that floats freely in cytoplasm or bound to RER.
- Not membrane bound.
- Large & small subunit (ribosomal RNA and protein).
Function:
Site of protein synthesis.
Found in: animal, plant, algal and fungal cells
What is the structure and function of the rough endoplasmic reticulum (rer) and in which cells can it be found?
Structure:
- Series of flattened membrane bound sacs (cisternae) continuous with the nucleur membrane.
- Covered in ribosomes (protein synthesis).
Function:
Folds & processes proteins.
Found in: animal, plant, algal and fungal cells
What is the structure and function of the smooth endoplasmic reticulum (ser) and in which cells can it be found?
Structure:
- Series of flattened membrane bound sacs (cisternae) continuous with the nucleur membrane.
- No ribosomes (involved in making lipids).
Function:
Synthesises & processes lipids.
Found in: animal, plant, algal and fungal cells
What is the structure and function of the cell wall and in which cells can it be found?
Structure:
- Rigid structure.
- Made of cellulose (in plants).
- Made of chitin (in fungi).
Function:
Strengthens & supports cell, prevents them from changing shape or bursting under pressure due to osmosis.
Found in: plant, algal and fungal cells
What is the structure and function of the cell vacuole and in which cells can it be found?
Structure:
- Surrounding membrane called the tonoplast.
Function:
Contains cell sap to keep cell turgid (maintains pressure inside cell).
Found in: plant cells
How do prokaryotic cells differ from eukaryotic cells?
- They are much smaller
- They have no membrane-bound organelles
- They have smaller ribosomes
- They have no nucleus - instead they have a single circular DNA molecule that is free in the cytoplasm
- They have a cell wall that contains murein (a glycoprotein)
- Some may have one or more plasmids (small loops of DNA)
- Some may have a capsule surrounding the cell (secreted layer to protect against attacking immune cells)
- Some may have one or more flagella (for mobility)
What is the structure of viruses?
- They are are acellular & non-living - invade & reproduce inside host
- They contain genetic material (DNA or RNA)
- They are surrounded by a capsid (protein coat which encloses genome (nucleic acids))
- They have attachment proteins (allow virus to attach to host cell)
What is magnification?
What is resolution?
● Magnification = number of times greater image is than size of the real (actual) object.
- Magnification = size of image / size of real object
● Resolution = minimum distance apart 2 objects can be to be distinguished as separate objects
What are the differences between optical microscopes & electron microscopes?
Optical:
- Uses light to form image.
- Low resolution (wavelength of light is long).
- Max magnification of x1500.
Electron:
- Uses electrons to form image.
- High resolution.
- Max magnification of x1000000.
What is a condenser (found in an optical microscope)?
Gather light from the microscopes light source & concentrate it onto the specimen being viewed.
What are the 2 types of electron microscope?
- Transmission electron microscope (TEM)
- Scanning electron microscope (SEM)
What are the features of TEMs & SEMs?
TEMs:
Work by: Using electromagnets to focus a beam of electrons which is transmitted through the specimen. (Denser parts of the specimen absorb more electrons, making them look darker in the image).
+ Give high resolution images.
+ Can see internal structures of organelles & ribosomes.
- Image viewed is 2D.
- Have to view specimen in vacuum (only non-living specimens can be viewed).
- Can only view very thin specimens.
- Does not show colour.
- Complex preparation so artefacts often present.
SEMs
Work by: Using electromagnets to deflect/bounce electrons off the specimens surface. These can then be detected in cathode ray tube to form image.
- Produces lower resolution images than TEMs.
+ Image viewed is 3D.
- Have to view specimen in vacuum (only non-living specimens can be viewed).
+ Can view thicker specimens.
- Complex preparation so artefacts often present.
- Does not show colour.
What are microscope artefacts and how did the first scientists distinguish between artefacts & organelles?
Things you can see down the microscope that aren’t part of the cell/ specimen you’re looking at. Usually made during the preparation of the specimen and shouldn’t be there.
(Common in electron micrographs as specimens need lots of preparation before viewing).
The first scientists could only distinguish by repeatedly preparing specimens in different ways. If an object could be seen with 1 prep technique & not another it was likely to be an artefact.
What is cell fractionation and what are the steps?
- Homogenisation (breaking up the cells)
- vibrating the cells or grinding them up in a blender
- breaks open plasma membrane & releases organelles into solution
- must be ice-cold (to reduce lytic enzyme activity (produced by bacteria/ viruses - enzymes that would break down cell wall/membrane)), isotonic (same concentration to prevent damage to organelles by osmosis (lysis/bursting)), buffer (maintain pH to reduce denature of enzymes) - Filtration (getting rid of the big bits)
- Homogenised cell solution is filtered through a gauze to separate any large cell debris/tissue debris from the organelles - Ultracentrifugation (separating the organelles)
- cell fragments poured into tube
- put in centrifuge & is spun at low speed
- heaviest organelles (like nuclei) get flung to bottom of tube & form thick sediment at bottom (the pellet)
- the rest stay suspended in fluid above (the supernatant)
- supernatant drained off, poured into another tube & spun at higher speed
- process repeats at higher & higher speeds until all organelles are separated in order of mass (nuclei, mitochondria, lysosomes, E.R, ribosomes) (plant cells: chloroplasts in between nuclei & mitochondria)
How do you calculate total magnification of a microscope?
Magnification of objective lens x Magnification of eyepiece lens
How do you calculate the magnification of an image?
Image size / Actual size
Describe how the size of an object viewed with an optical microscope can be measured.
Once calibrated with the stage micrometer 1 division is:
25µm at x400
100µm at x100
- Line up (scale of) eyepiece graticule with (scale of) stage micrometre
- Calibrate eyepiece graticule - use stage micrometre to calculate size of divisions on eyepiece graticule
- Take micrometre away and use graticule to measure how many divisions make up the object
- Calculate size of object by multiplying number of divisions by size of division
- Recalibrate eyepiece graticule at different magnifications
How do eukaryotic cells divide/replicate?
The cell cycle.
- interphase
- mitosis
- cytokinesis
Describe the stages of the cell cycle in eukaryotic cells.
- Interphase
● (S phase) DNA replicates semi-conservatively
- Leading to 2 chromatids (identical copies) joined at a centromere
● (G1/G2) number of organelles & volume of cytoplasm increases, protein synthesis - Mitosis
● Nucleus divides
● To produce 2 nuclei with identical copies of DNA produced by parent cell - Cytokinesis
● Cytoplasm and cell membrane (normally) divide
● To form 2 new genetically identical daughter cells
What division stages are there in mitosis?
Prophase, Metaphase, Anaphase, Telophase
(PMAT)
What is the structure of the chromosomes of a cell at the beginning of mitosis?
Chromosomes made of 2 strands joined in the middle by a centromere. The separate strands = chromatids.
The are 2 strands because each chromosome has already made an identical copy during interphase.
When mitosis is over they are 1 strand.
> < - chromosome < - 1 chromatid
Describe the behaviour of chromosomes & role of spindle fibres during prophase.
● Chromosomes condense, becoming shorter / thicker (so visible)
- Appear as 2 sister chromatids joined by a centromere
● Nuclear envelope breaks down
● Centrioles move to opposite poles forming spindle network
Describe the behaviour of chromosomes & role of spindle fibres during metaphase.
● Spindle fibres attach to chromosomes by their centromeres
● Chromosomes align along equator
Describe the behaviour of chromosomes & role of spindle fibres during anaphase.
● Spindle fibres shorten / contract
● Centromere divides
● Pulling chromatids (from each pair) to opposite poles of cell
Describe the behaviour of chromosomes & role of spindle fibres during telophase.
● Chromosomes uncoil, becoming longer / thinner
● Nuclear envelopes reform = 2 nuclei
● Spindle fibres / centrioles break down
What causes cancer?
Mitosis is a controlled process.
● Mutations in DNA / genes controlling mitosis can lead to uncontrolled cell division
● Tumour formed if this results in mass of abnormal cells
- Malignant tumour = cancerous, can spread (metastasis)
- Benign tumour = non-cancerous
What do most cancer treatments do?
Many are directed at controlling the rate of cell division.
This kills the tumour cells but also kills normal cells.
● Some disrupt spindle fibre activity / formation
- So chromosomes can’t attach to spindle by their centromere
- So chromatids can’t be separated to opposite poles (no anaphase)
- So prevents / slows mitosis
● Some prevent DNA replication during interphase
- So can’t make 2 copies of each chromosome (chromatids)
- So prevents / slows mitosis
How to prokaryotic cells divide/replicate?
Binary fission.
What are the steps of binary fission?
- Circular DNA + plasmids replicate (DNA once & plasmids many times).
- The cell gets bigger & DNA loops move to opposite poles of cell.
- Cytoplasm begins to divide (& new cell walls begin to form).
- Cytoplasm divides & 2 daughter cells produced, each with one copy of circular DNA but many plasmid copies.
How do viruses replicate if they are acellular?
Do not undergo cell division as not alive - invade and reproduce inside host cells.
1. Virus attaches to host cell receptor proteins (using their attachment proteins). *
2. Genetic material is released into host cell.
3. Genetic material & proteins are replicated by host cell ‘machinery’.
4. Viral components assemble.
5. Replicated virus released from host cell.
*(different viruses have different attachment proteins so require different receptor proteins on host cell = some viruses can only affect certain cells)
What is the structure of all cell membranes?
fluid-mosaic model
What are the features of the fluid mosaic model?
● Molecules free to move laterally in phospholipid bilayer (fluid)
● Many components:
● Phospholipids form a bilayer- fatty acid tails face inwards, phosphate heads face outwards
● Proteins
- Intrinsic / integral proteins span bilayer eg. channel and carrier proteins
- Extrinsic / peripheral proteins on surface of membrane
● Glycolipids (lipids with polysaccharide chains attached) found on exterior surface
● Glycoproteins (proteins with polysaccharide chains attached) found on exterior surface
● Cholesterol (sometimes present) bonds to phospholipid hydrophobic fatty acid tails
What is the arrangement of phospholipids in membranes?
● Bilayer, with water present on either side
● Hydrophobic fatty acid tails repelled from water so point away from water / to interior
● Hydrophilic phosphate heads attracted to water so point to water
What is the function of cholesterol in membranes?
● Restricts movement of other molecules making up membrane
● So decreases fluidity (and permeability) / increases rigidity
Explain how temperature affects permeability of cell-surface membranes.
● As temperature increases, permeability increases
- Phospholipids gain kinetic energy and fluidity increases
- Transport proteins denature at high temperatures as H bonds break, changing tertiary structure
● At very low temperatures, permeability increases
- Ice crystals can form which pierce the cell membrane and increase permeability
Explain how pH affects permeability of cell-surface membranes.
● High or low pH increases permeability
- Transport proteins denature as H / ionic bonds break, changing tertiary structure
Explain how lipid-soluble solvents eg. alcohol affect permeability of cell-surface membranes.
● As concentration increases, permeability increases
● Ethanol (a lipid-soluble solvent) may dissolve phospholipid bilayer (gaps form)
Suggest how cell membranes are adapted for other functions.
● Phospholipid bilayer is fluid → membrane can bend for vesicle formation / phagocytosis
● Glycoproteins / glycolipids act as receptors / antigens → involved in cell signalling / recognition
Describe how movement across membranes occurs by simple diffusion.
● Lipid-soluble (non-polar) or very small substances eg. O2, steroid hormones
● Move from an area of higher conc. to an area of lower conc. down a conc. gradient
● Across phospholipid bilayer
● Passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances)
What factors affect rate of diffusion?
● Increasing surface area of membrane increases rate of movement
● Increasing concentration gradient increases rate of simple diffusion
Explain the limitations imposed by the nature of the phospholipid bilayer.
● Restricts movement of water soluble (polar) & larger substances eg. Na+ / glucose
● Due to hydrophobic fatty acid tails in interior of bilayer
Describe how movement across membranes occurs by facilitated diffusion.
● Water-soluble (polar) / slightly larger substances
● Move down a concentration gradient
● Through specific channel / carrier proteins
● Passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances)
Explain the role of carrier and channel proteins in facilitated diffusion.
● Shape / charge of protein determines which substances move
● Channel proteins facilitate diffusion of water-soluble substances
- Hydrophilic pore filled with water
- May be gated- can open / close
● Carrier proteins facilitate diffusion of (slightly larger) substances
- Complementary substance attaches to binding site
- Protein changes shape to transport substance
What factors affect facilitated diffusion?
● Increasing surface area of membrane increases rate of movement
● Increasing number of channel / carrier proteins increases rate of facilitated diffusion
● Increasing concentration gradient increases rate of facilitated diffusion
- Until number of channel / carrier proteins becomes a limiting factor as all in use / saturated
Describe how movement across membranes occurs by osmosis.
● Water diffuses / moves
● From an area of high to low water potential (ψ) / down a water potential gradient
● Through a partially permeable membrane
● Passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances)
What is water potential?
A measure of how likely water molecules are to move out of a solution. Pure (distilled) water has the maximum possible ψ (0 kPA).
Increasing solute concentration decreases ψ.
What is an isotonic solution?
What happens if you put a cell in an isotonic solution?
What is an hypotonic solution?
What happens if you put a cell in an hypotonic solution?
What is an hypertonic solution?
What happens if you put a cell in an hypertonic solution?
What factors affect rate of osmosis?
● Increasing surface area of membrane increases rate of movement
● Increasing water potential gradient increases rate of osmosis
Why can water diffuse directly across the phospholipid bilayer?
How else can water travel through cell membranes?
Describe how movement across membranes occurs by active transport.
● Substances move from area of lower to higher concentration / against a concentration gradient
● Requiring hydrolysis of ATP and specific carrier proteins
What factors affect active transport?
● Increasing surface area of membrane increases rate of movement
● Increasing number of carrier proteins increases rate of active transport
Describe the role of carrier proteins and the importance of the hydrolysis of ATP in active transport.
- Complementary substance binds to specific carrier protein
- ATP binds, hydrolysed into ADP + Pi, releasing energy
- Carrier protein changes shape, releasing substance on side with higher concentration
- Pi released → protein returns to original shape
Describe how movement across membranes occurs by co-transport.
● Two different substances bind to and move simultaneously via a co-transporter protein (type of carrier protein)
● Movement of one substance against its concentration gradient is often coupled with the movement of another down its concentration gradient
Describe an example that illustrates co-transport.
Absorption of sodium ions and glucose (or amino acids) by cells lining the mammalian ileum:
1. ● Na+ actively transported from epithelial cells to blood (by Na+/K+ pump)
● Establishing a conc. gradient of Na+ (higher in lumen than epithelial cell)
2. ● Na+ enters epithelial cell down its concentration gradient with glucose against its concentration gradient
● Via a co-transporter protein
3. ● Glucose moves down a conc. gradient into blood via facilitated diffusion
(The movement of sodium can be considered indirect / secondary active transport, as it is reliant on a concentration gradient established by active transport.)
Explain the adaptations of some specialised cells in relation to the rate of transport across their internal and external membranes.
● Membrane folded eg. microvilli in ileum → increase in surface area.
● More protein channels / carriers → for facilitated diffusion (or active transport - carrier proteins only)
● Large number of mitochondria → make more ATP by aerobic respiration for active transport
What is an antigen?
● Foreign molecule / protein / glycoprotein / glycolipid
● That stimulates an immune response leading to production of antibody
How are cells identified by the immune system?
● Each type of cell has specific molecules on its surface (cell-surface membrane / cell wall) that identify it
● Often proteins → have a specific tertiary structure (or glycoproteins / glycolipids)
What types of cells and molecules can the immune system identify?
- Pathogens (disease causing microorganisms) eg. viruses, fungi, bacteria
- Cells from other organisms of the same species (eg. organ transplants)
- Abnormal body cells eg. tumour cells or virus-infected cells
- Toxins (poisons) released by some bacteria
Describe phagocytosis of pathogens (non-specific immune response)
- Phagocyte attracted by chemicals / recognises (foreign) antigens on pathogen
- Phagocyte engulfs pathogen by surrounding it with its cell membrane
- Pathogen contained in vesicle / phagosome in cytoplasm of phagocyte
- Lysosome fuses with phagosome and releases lysozymes (hydrolytic enzymes)
- Lysozymes hydrolyse / digest pathogen
Phagocytosis leads to presentation of antigens where antigens are displayed on the phagocyte cell-surface membrane, stimulating the specific immune response (cellular and humoral response).
Describe the response of T lymphocytes to a foreign antigen (the cellular response)
T lymphocytes recognise (antigens on surface of) antigen presenting cells eg. infected cells, phagocytes presenting antigens, transplanted cells, tumour cells etc.
- Specific helper T cells with complementary receptors (on cell surface) bind to antigen on antigen-presenting cell → activated and divide by mitosis to form clones which stimulate:
● Cytotoxic T cells → kill infected cells / tumour cells (by producing perforin)
● Specific B cells (humoral response)
● Phagocytes → engulf pathogens by phagocytosis
Describe the response of B lymphocytes to a foreign antigen (the humoral response)
B lymphocytes can recognise free antigens eg. in blood or tissues, not just antigen presenting cells.
1. Clonal selection:
● Specific B lymphocyte with complementary receptor (antibody on cell surface) binds to antigen
● This is then stimulated by helper T cells (which releases cytokines)
● So divides (rapidly) by mitosis to form clones
2. Some differentiate into B plasma cells → secrete large amounts of (monoclonal) antibody
3. Some differentiate into B memory cells → remain in blood for secondary immune response
What are antibodies?
● Quaternary structure proteins (4 polypeptide chains)
● Secreted by B lymphocytes eg. plasma cells in response to specific antigens
● Bind specifically to antigens forming antigen-antibody complexes
Describe the structure of an antibody
Explain how antibodies lead to the destruction of pathogens
● Antibodies bind to antigens on pathogens forming an antigen-antibody complex
- Specific tertiary structure so binding site / variable region binds to complementary antigen
● Each antibody binds to 2 pathogens at a time causing agglutination (clumping) of pathogens
● Antibodies attract phagocytes
● Phagocytes bind to the antibodies and phagocytose many pathogens at once
Explain the differences between the primary & secondary immune response
● Primary- first exposure to antigen
- Antibodies produced slowly & at a lower conc.
- Takes time for specific B plasma cells to be stimulated to produce specific antibodies
- Memory cells produced
● Secondary- second exposure to antigen
- Antibodies produced faster & at a higher conc.
- B memory cells rapidly undergo mitosis to produce many plasma cells which produce specific antibodies
What is a vaccine?
● Injection of antigens from attenuated (dead or weakened) pathogens
● Stimulating formation of memory cells
Explain how vaccines provide protection to individuals against disease
- Specific B lymphocyte with complementary receptor binds to antigen
- Specific T helper cell binds to antigen-presenting cell and stimulates B cell
- B lymphocyte divides by mitosis to form clones
- Some differentiate into B plasma cells which release antibodies
- Some differentiate into B memory cells
- On secondary exposure to antigen, B memory cells rapidly divide by mitosis to produce B plasma cells
- These release antibodies faster and at a higher concentration
Explain how vaccines provide protections for populations against disease
● Herd immunity- large proportion of population vaccinated, reducing spread of pathogen
- Large proportion of population immune so do not become ill from infection
- Fewer infected people to pass pathogen on / unvaccinated people less likely to come in contact with someone with disease
Active artificial/natural
Passive artificial/natural
-
Describe the differences between active and passive immunity
Active immunity
- Initial exposure to antigen eg. vaccine or primary infection
- Memory cells involved
- Antibody produced and secreted by B plasma cells
- Slow; takes longer to develop
- Long term immunity as antibody can be produced in response to a specific antigen again
Passive immunity
- No exposure to antigen
- No memory cells involved
- Antibody introduced from another organism eg. breast milk / across placenta from mother
- Faster acting
- Short term immunity as antibody hydrolysed (endo/exo/dipeptidases)
Explain the effect of antigen variability on disease and disease prevention
● Antigens on pathogens change shape / tertiary structure due to gene mutations (creating new strains)
● So no longer immune (from vaccine or prior infection)
- B memory cell receptors cannot bind to / recognise changed antigen on secondary exposure
- Specific antibodies not complementary / cannot bind to changed antigen
Describe the structure of a HIV particle
- RNA & Reverse transcriptase
- Capsid
- Lipid envelope
- Attachment protein
Describe the replication of HIV in helper T cells
- HIV attachment proteins attach to receptors on helper T cell
- Lipid envelope fuses with cell-surface membrane, releasing capsid into cell
- Capsid uncoats, releasing RNA and reverse transcriptase
- Reverse transcriptase converts viral RNA to DNA
- Viral DNA inserted / incorporated into helper T cell DNA (may remain latent)
- Viral protein / capsid / enzymes are produced
- DNA transcribed into HIV mRNA
- HIV mRNA translated into new HIV proteins - Virus particles assembled and released from cell (via budding)
Explain how HIV causes the symptoms of acquired immune deficiency syndrome (AIDS)
● HIV infects and kills helper T cells (host cell) as it multiplies rapidly
- So T helper cells can’t stimulate cytotoxic T cells, B cells and phagocytes
- So B plasma cells can’t release as many antibodies for agglutination & destruction of pathogens
● Immune system deteriorates → more susceptible to (opportunistic) infections
● Pathogens reproduce, release toxins and damage cells
Explain why antibiotics are ineffective against viruses
Viruses do not have structures / processes that antibiotics inhibit:
● Viruses do not have metabolic processes (eg. do not make protein) / ribosomes
● Viruses do not have bacterial enzymes / murein cell wall
What is a monoclonal antibody?
● Antibody produced from genetically identical / cloned B lymphocytes / plasma cells
● So have same tertiary structure
Explain how monoclonal antibodies can be used in medical treatments
● Monoclonal antibody has a specific tertiary structure / binding site / variable region
● Complementary to receptor / protein / antigen found only on a specific cell type (eg. cancer cell)
● Therapeutic drug attached to antibody
● Antibody binds to specific cell, forming antigen-antibody complex, delivering drug
Some monoclonal antibodies are also designed to block antigens / receptors on cells.
Explain how monoclonal antibodies can be used in medical diagnosis
● Monoclonal antibody has a specific tertiary structure / binding site / variable region
● Complementary to specific receptor / protein / antigen associated with diagnosis
● Dye / stain / fluorescent marker attached to antibody
● Antibody binds to receptor / protein / antigen, forming antigen-antibody complex
Examples vary, eg. pregnancy tests. You’ll need to interpret information in the question on how these work.
M
Explain the use of antibodies in the ELISA (enzyme-linked immunosorbent assay) test to detect antigens
Direct ELISA
1. Attach sample with potential antigens to well
2. Add complementary monoclonal antibodies with enzymes attached → bind to antigens if present
3. Wash well → remove unbound antibodies (to prevent false positive)
4. Add substrate → enzymes create products that cause a colour change (positive result)
OR sandwich ELISA
1. Attach specific monoclonal antibodies to well
2. Add sample with potential antigens, then wash well
3. Add complementary monoclonal antibodies with enzymes attached → bind to antigens if present
4. Wash well → remove unbound antibodies (to prevent false positive)
5. Add substrate → enzymes create products that cause a colour change (positive result)
Explain the use of antibodies in the ELISA test to detect antibodies
Indirect ELISA
1. Attach specific antigens to well
2. Add sample with potential antibodies, wash well
3. Add complementary monoclonal antibodies with enzymes attached → bind to antibodies if present
4. Wash well → remove unbound antibodies
5. Add substrate → enzymes create products that
cause a colour change (positive result)
Suggest the purpose of a control well in the ELISA test
● Compare to test to show only enzyme causes colour change
● Compare to test to show all unbound antibodies have been washed away
Discuss some general ethical issues associated with the use of vaccines and monoclonal antibodies
● Pre-clinical testing on / use of animals- potential stress / harm / mistreatment
- But animals not killed & helps produce new drugs to reduce human suffering
● Clinical trials on humans- potential harm / side-effects
● Vaccines - may continue high risk activities and still develop / pass on pathogen
● Use of drug - potentially dangerous side effects
Suggest some points to consider when evaluating evidence and data relating to the use of vaccines and monoclonal antibodies
● What side effects were observed, and how frequently did they occur?
● Was a statistical test used to see if there was a significant difference between start & final results?
● Was the standard deviation of final results large, showing some people did not benefit?
● Did standard deviations of start & final results overlap, showing there may not be a significant difference?
● What dosage was optimum? Does increasing dose increase effectiveness enough to justify extra cost?
● Was the cost of production & distribution low enough?
