Long Answer Questions

Question 1

Describe the action of the sodium potassium pump

Answer 1

1 the sodium potassium pump transports ions against the steep concentration gradient
2the sodium pump requires energy from hydrolysis of ATP
3the maintenance of iron gradient by the pump accounts for a significant part of basil metabolic rate for the protein has a higher affinity for sodium ions inside the cell from inside the cell bind five the protein becomes phosphorated by ATP, which changes the confirmation of the pump
7the affinity of sodium ions decreases resulting in sodium being released outside of the cell eight potassium ions from outside of the cell bind to the sodium potassium pump and de phosphorylation occurs which changes the confirmation
11 potassium ions are taken into the cell
12 the affinity returns to the start
13 three sodium miles are transported out of the cell and two potassium ions are transported into the cell

Question 2

Give an account of meiosis

Answer 2

1. Meiosis produces four haploid gametes…
2. ..from one diploid gamete mother cell.
3. Interphase is where DNA replications occurs.
4. During meiosis I, homologous chromosomes line up at the equator of the cell.
5. Homologous chromosomes are the same size and shape.
6. They carry the same genes at same gene loci…
   7….but may carry different alleles / one from each parent.
7. They have their centromere at the same place.
8. During meiosis I, crossing over may occur…
9. …at points called chiasmata.
10. This process shuffles sections of DNA between the homologous pairs, allowing the recombination of alleles to occur thus increasing variation.
11. Genes on the same chromosome are said to be linked.
12. There is a correlation between the distance between linked genes and their frequency of recombination / description or definition of chromosome mapping.
13. Independent assortment occurs as a result of meiosis I, with homologous chromosomes being separated irrespective of their maternal and paternal origin.
14. Homologous chromosomes are separated by spindle fibres.
15. This increases variation in the gametes.
16. During meiosis Il, chromatids are pulled apart (and four haploid gametes are produced).

Question 3

Discuss the syntheses and post- translational modification of membrane proteins

Answer 3

1. Synthesis/translation begins on cytosolic ribosomes
2. Signal sequence is a short stretch of amino acids
   OR
   Signal sequence is at one end
3. Signal sequence halts translation
4. (Signal sequence directs)
   ribosome to dock with ER/to form
   RER
5. Translation continues after docking
6. Protein inserted into membrane of ER
7. Vesicle (containing protein) buds off
8. Vesicles move to Golgi apparatus
9. Proteins move through the Golgi
10. (Movement through Golgi) by vesicles budding off one disc and fusing to the next (in the stack)
11. Post-translational modification occurs in the Golgi
12. Major modification is the addition of the carbohydrate.
13. Various sugars added in steps
14. Vesicles leave the Golgi and transfer to the membrane.
15. Vesicles move along microtubules

Question 4

Discuss the role of proteins in controlling progression through the cell cycle checkpoints

Answer 4

1. Checkpoints at G1, G2, M
2. Cyclins accumulate (during cell growth)
3. Cyclins combine with and activate cyclin-dependent
   kinases (CDKs)
4. Active CDKs phosphorylate proteins that regulate progression through the cell cycle/act at checkpoints
5. If phosphorylation reaches a threshold/sufficient
   phosphorylation progression to next stage/through a checkpoint occurs
6. Retinoblastoma protein (Rb) is a tumour suppressor
7. Rb acts at G1 checkpoint
8. Rb inhibits transcription of genes encoding proteins needed for
   DNA replication
9. Rb phosphorylated by (G1) cyclin-
   CDK/active (G1) CDK
10. Phosphorylation inhibits Rb
11. When Rb is inhibited/ phosphorylated DNA replication takes place/cell cycle progresses (from G1 to S)
12. DNA damage activates p53
13. (p53) can arrest the cell cycle/ cause cell death/apoptosis
14. Proto-oncogenes code for proteins that control/stimulate cell division
15. Proto-oncogenes can mutate to form oncogenes
16. Oncogenes encode proteins that deregulate the cell cycle/ promote the formation of tumours

Question 5

Discuss the methods of sharing, and the importance of both sharing and reviewing, scientific findings.

Answer 5

1. (scientific findings)
   published/shared so work can be repeated/verified/built upon
2. Publication in
   journals/articles/papers
3. Peer review by scientists/ experts in relevant field
4. (to) assess/evaluate scientific quality of submitted manuscript
5. (peer review) make recommendations about suitability for publication
6. Review articles summarise current knowledge/findings in a (particular) field.
7. (Findings also) shared by seminars/talks/posters at conferences/ media
8. Increasing public understanding
   OR
   Reducing misrepresentation of science

Question 6

Give an account of the experimental cycle with a brief description of the purpose of each stage.

Answer 6

1. Observation/ discussion to come up with idea
2. Testable hypothesis. A prediction of the experiment outcome
3. Experimental design. Protocol of the experiment outcome
4. Gathering and recording results. Provides new data
5. Analysis of data. Evaluate results. Assess strengths/ weaknesses
6. Conclusion. What the overall results show
7. New hypothesis. To refine the theory/ thoughts for next experiment

Question 7

The structure of amino acids and 4 levels of protein structure

Answer 7

1. Diagram/description of generalised structure of an amino acid.
2. (Amino acids only) differ in (structure of) R group.
3. TWO from:
   Types of R groups are acidic/ basic/polar/hydrophobic
4. (Different) R groups give different hydrogen-bonding capacity/chemical reactivity
   MAX 2 from Pts 1 to 4
5. Primary structure (of a protein) is the order of amino acids (in a polypeptide/protein)
6. (Amino acids) linked by peptide bonds
   OR
   Diagram showing peptide bond
7. Secondary structure from hydrogen bonding (between amino acids)
8. Along backbone
   OR
   not between R groups
9. a-helix, B (-pleated) sheet and turns are types of secondary structure
10. Tertiary structure is folding of polypeptide/3-D shape of protein
11. Tertiary structure stabilised by interactions between R groups
12. TWO from:
    • Hydrophobic interactions
    • lonic bonds
    • London dispersion forces
    • Hydrogen bonds
    • Disulphide bridges
13. Disulphide bridges are covalent bonds between R groups containing sulfur/cysteines
    MAX 6 from Pts 5 to 13
14. Quaternary structure is the (spatial) arrangement of subunits (in proteins)
    OR
    Quaternary structure (in proteins) with more than one subunit/multi-subunit
15. Prosthetic group is a non-protein component
16. (Prosthetic group) necessary for function/tightly bound
    MAX 1 from Pts 14 to 16

Question 8

Describe the generation and transmission of a nerve impulse in a neuron

Answer 8

1. Resting membrane potential is no net flow of ions across membrane
2. Neurotransmitter released into synapse/initiate response.
   OR
   vesicles containing neurotransmitter fuse with membrane
3. Neurotransmitters bind to specific/their receptors (at synapse)
4. Neurotransmitter receptors are ligand-gated (ion) channels
   OR
   Binding of neurotransmitter opens (ligand-gated) channels
5. Sodium ions enter neuron/cell
   OR
   Sodium ions move down electrochemical/concentration gradient
6. Initial depolarisation of plasma membrane
7. sufficient ion movement/ membrane depolarised beyond a/ reaches threshold
8. Opening of voltage-gated sodium channels triggered
9. More sodium ions enter cell
   OR
   further depolarisation
10. sodium channels close/ inactivated
11. (Then voltage-gated) potassium
    channels open
12. Potassium ions move out of cell
    OR
    Membrane repolarises
13. Resting membrane potential restored
    OR
    Ion gradients re-established by sodium-potassium pump
14. Depolarisation of a patch/region of membrane causes neighbouring regions (of membrane) to depolarise
    OR
    Wave of electrical excitation/ depolarisation along (neuron’s)
    membrane
15. When action potential/wave of depolarisation reaches end of neuron a response in connecting cell stimulated

Question 9

Describe the structure of viruses and explain why they are classified as parasites

Answer 9

1. Viruses contain DNA RNA nucleic acids
2. Viruses have antigens on their surface
3. Some viruses are surrounded by lipid membranes
4. Phospholipids are derived from host cell
5. Retroviruses contain reverse transcriptase
6. Virus cells can only replicate inside a host cell

Question 10

Process of gel electrophoresis

Answer 10

Proteins are separated by gel electrophoresis

This process separates proteins based on their charge and shape

Proteins move through a gel which act like a seive

An electrical current is passed across the gel

Protein travel towards the electrode with an opposite charge

Smaller proteins will travel faster through the gel than larger proteins