3.2 Cells Flashcards

Question

Describe the behaviour of chromosomes & role of spindle fibres during **prophase**.

Answer 1

● 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

Answer 2

● Spindle fibres attach to chromosomes by their centromeres ● Chromosomes align along equator

Answer 3

● Spindle fibres shorten / contract ● Centromere divides ● Pulling chromatids (from each pair) to opposite poles of cell

Answer 4

● Chromosomes uncoil, becoming longer / thinner ● Nuclear envelopes reform = 2 nuclei ● Spindle fibres / centrioles break down

Answer 5

● Within multicellular organisms, not all cells retain the ability to divide (eg. neurons) ● Only cells that do retain this ability go through a cell cycle

Answer 6

Parent cell divides to produce 2 genetically identical daughter cells for: ● Growth of multicellular organisms by increasing cell number ● Replacing cells to repair damaged tissues ● Asexual reproduction

Answer 7

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

Answer 8

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

Answer 9

Binary fission: 1. Replication of circular DNA 2. Replication of plasmids 3. Division of cytoplasm to produce 2 daughter cells ● Single copy of circular DNA ● Variable number of copies of plasmids

Answer 10

Being non-living, viruses do not undergo cell division. 1. Attachment proteins attach to complementary receptors on host cell 2. Inject viral nucleic acid (DNA/RNA) into host cell 3. Infected host cell replicates virus particles: - Nucleic acid replicated - Cell produces viral protein / capsid / enzymes - Virus assembled then released *(different viruses have different attachment proteins so require different receptor proteins on host cell = some viruses can only affect certain cells)

Answer 11

● Molecules free to move laterally in phospholipid bilayer ● Many components - phospholipids, proteins, glycoproteins and glycolipids

Answer 12

● 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

Answer 13

● 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

Answer 14

● Restricts movement of other molecules making up membrane ● So decreases fluidity (and permeability) / increases rigidity

Answer 15

● 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

Answer 16

● High or low pH increases permeability - Transport proteins denature as H / ionic bonds break, changing tertiary structure

Answer 17

● As concentration increases, permeability increases ● Ethanol (a lipid-soluble solvent) may dissolve phospholipid bilayer (gaps form)

Answer 18

● Phospholipid bilayer is fluid → membrane can bend for vesicle formation / phagocytosis ● Glycoproteins / glycolipids act as receptors / antigens → involved in cell signalling / recognition

Answer 19

● 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)

Answer 20

● Increasing surface area of membrane increases rate of movement ● Increasing concentration gradient increases rate of simple diffusion

Answer 21

● Restricts movement of water soluble (polar) & larger substances eg. Na+ / glucose ● Due to hydrophobic fatty acid tails in interior of bilayer

Answer 22

● 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)

Answer 23

● 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

Answer 24

● 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

Answer 25

● 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)

Answer 26

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.

Answer 27

● Increasing surface area of membrane increases rate of movement ● Increasing water potential gradient increases rate of osmosis

Answer 28

● Substances move from area of lower to higher concentration / against a concentration gradient ● Requiring hydrolysis of ATP and specific carrier proteins

Answer 29

● Increasing surface area of membrane increases rate of movement ● Increasing number of carrier proteins increases rate of active transport

Answer 30

1. Complementary substance binds to specific carrier protein 2. ATP binds, hydrolysed into ADP + Pi, releasing energy 3. Carrier protein changes shape, releasing substance on side with higher concentration 4. Pi released → protein returns to original shape

Answer 31

● 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

Answer 32

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.)

Answer 33

● 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

Answer 34

● Foreign molecule / protein / glycoprotein / glycolipid ● That stimulates an immune response leading to production of antibody

Answer 35

● 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)

Answer 36

1. Pathogens (disease causing microorganisms) eg. viruses, fungi, bacteria 2. Cells from other organisms of the same species (eg. organ transplants) 3. Abnormal body cells eg. tumour cells or virus-infected cells 4. Toxins (poisons) released by some bacteria

Answer 37

1. Phagocyte attracted by chemicals / recognises (foreign) antigens on pathogen 2. Phagocyte engulfs pathogen by surrounding it with its cell membrane 3. Pathogen contained in vesicle / phagosome in cytoplasm of phagocyte 4. Lysosome fuses with phagosome and releases lysozymes (hydrolytic enzymes) 5. 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).

Answer 38

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

Answer 39

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

Answer 40

● 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

Answer 41

● 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

Answer 42

● 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

Answer 43

● Injection of antigens from attenuated (dead or weakened) pathogens ● Stimulating formation of memory cells

Answer 44

1. Specific B lymphocyte with complementary receptor binds to antigen 2. Specific T helper cell binds to antigen-presenting cell and stimulates B cell 3. B lymphocyte divides by mitosis to form clones 4. Some differentiate into B plasma cells which release antibodies 5. Some differentiate into B memory cells 6. On secondary exposure to antigen, B memory cells rapidly divide by mitosis to produce B plasma cells 7. These release antibodies faster and at a higher concentration

Answer 45

● 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

Answer 46

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)

Answer 47

● 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

Answer 48

- RNA & Reverse transcriptase - Capsid - Lipid envelope - Attachment protein

Answer 49

1. HIV attachment proteins attach to receptors on helper T cell 2. Lipid envelope fuses with cell-surface membrane, releasing capsid into cell 3. Capsid uncoats, releasing RNA and reverse transcriptase 4. Reverse transcriptase converts viral RNA to DNA 5. Viral DNA inserted / incorporated into helper T cell DNA (may remain latent) 6. Viral protein / capsid / enzymes are produced - DNA transcribed into HIV mRNA - HIV mRNA translated into new HIV proteins 7. Virus particles assembled and released from cell (via budding)

Answer 50

● 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

Answer 51

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

Answer 52

● Antibody produced from genetically identical / cloned B lymphocytes / plasma cells ● So have same tertiary structure

Answer 53

● 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.

Answer 54

● 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.

Answer 55

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)

Answer 56

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)

Answer 57

● Compare to test to show only enzyme causes colour change ● Compare to test to show all unbound antibodies have been washed away

Answer 58

● 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

Answer 59

● 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?

3.2 Cells Flashcards

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