CH4006 Biosciences I – Exam Revision Flashcards

These QUESTION_AND_ANSWER flashcards cover key concepts from the CH4006 Biosciences I examination topics, spanning microbiology, physiology, biochemistry, genetics, and pharmacology.

What is the main difference between aerobic and anaerobic respiration in bacteria?

Aerobic respiration uses oxygen as the terminal electron acceptor; anaerobic respiration uses alternative acceptors (e.g., nitrate, sulfate) and occurs in the absence of oxygen.

Which two key enzymes allow aerobic or facultative bacteria to detoxify reactive oxygen species?

Catalase and superoxide dismutase (often with peroxidase) convert hydrogen peroxide and superoxide radicals into harmless products.

How are microaerophilic bacteria defined?

They require oxygen for growth but at concentrations lower than that of the atmosphere (~2–10% O₂).

What is meant by a facultative anaerobe?

A bacterium that can grow with or without oxygen, switching between aerobic respiration and fermentation/anaerobic respiration as needed.

Define alveolar ventilation.

The volume of fresh air reaching the alveoli per minute for gas exchange.

Give the formula for calculating alveolar ventilation (VA).

VA = (Tidal Volume − Physiologic Dead Space) × Respiratory Rate.

What characterizes a metacentric chromosome?

The centromere is positioned in the middle, producing arms of equal length.

What characterizes an acrocentric chromosome?

The centromere is near one end, producing a very short p-arm and a long q-arm.

Distinguish heterochromatin from euchromatin.

Heterochromatin is tightly packed, transcriptionally inactive DNA; euchromatin is loosely packed, transcriptionally active DNA.

Define gluconeogenesis.

The metabolic pathway that synthesises glucose from non-carbohydrate precursors such as lactate, glycerol, and amino acids.

Define glycogenesis.

The synthesis of glycogen from glucose for energy storage.

Define glycogenolysis.

The breakdown of glycogen to release glucose-1-phosphate (and subsequently glucose-6-phosphate).

List four possible targets in the viral replication cycle for antiviral drugs.

Attachment/entry, uncoating, nucleic-acid synthesis, protein processing/maturation, assembly and release.

Why should patients avoid grapefruit juice when taking cyclosporine?

Grapefruit compounds inhibit intestinal CYP3A4 and P-glycoprotein, reducing cyclosporine metabolism and efflux, thereby raising blood levels and toxicity risk.

Which cytochrome P450 isoenzyme is most strongly inhibited by grapefruit furanocoumarins?

CYP3A4.

Briefly describe the double-helix structure of DNA.

Two antiparallel polynucleotide strands twist into a right-handed helix; sugar-phosphate backbones on the outside; complementary base pairs (A-T, G-C) held by hydrogen bonds inside.

How is DNA compacted to fit inside the nucleus?

DNA wraps around histone octamers forming nucleosomes → chromatin fibre → looped domains → heterochromatin/scaffold → chromosomes during mitosis.

How can agar plating be used to enumerate bacteria?

By spreading a diluted sample on agar, counting colony-forming units (CFUs) and multiplying by the dilution factor to estimate viable cell numbers.

How do selective and differential media help differentiate bacteria on agar plates?

Selective agents inhibit unwanted microbes, while differential indicators (e.g., pH dyes) reveal characteristic metabolic reactions, producing distinctive colony colours or zones.

Outline the three cytoplasmic steps of peptidoglycan synthesis during bacterial division.

(1) UDP-NAM formation, (2) sequential addition of amino acids to build a pentapeptide, (3) linkage to undecaprenyl phosphate (lipid carrier) before translocation across the membrane.

What is the mechanism by which penicillin inhibits bacterial cell-wall synthesis?

Penicillin binds to penicillin-binding proteins (transpeptidases), blocking cross-linking of peptidoglycan strands, leading to weakened walls and osmotic lysis.

Identify components 1–7 of the urea cycle (starting with ammonium).

1 = Carbamoyl phosphate, 2 = Ornithine, 3 = Citrulline, 4 = Aspartate, 5 = Argininosuccinate, 6 = Arginine, 7 = Urea.

Which gene is mutated in ornithine transcarbamylase (OTC) deficiency, and which enzyme is deficient?

Mutation in the OTC gene → deficiency of ornithine transcarbamylase.

Which gene is mutated in carbamoyl-phosphate synthetase I (CPS1) deficiency?

Mutation in the CPS1 gene → deficiency of carbamoyl-phosphate synthetase I.

Which gene and enzyme are affected in citrullinemia type I?

ASS1 gene mutation → deficiency of argininosuccinate synthetase.

Which gene and enzyme are affected in argininosuccinic aciduria?

ASL gene mutation → deficiency of argininosuccinate lyase.

Which gene and enzyme are affected in argininemia?

ARG1 gene mutation → deficiency of arginase 1.

Name three conditions that increase expression of carbamoyl-phosphate synthetase-1 (CPS-1).

High-protein diet, prolonged fasting (increased amino-acid catabolism), and chronic metabolic acidosis.

Define solution tonicity.

A measure of a solution’s ability to cause water movement across a semi-permeable membrane due to non-penetrating solute concentration.

What happens to red blood cells placed in a hypertonic solution?

Water exits the cells; they shrink (crenate).

What happens to cells placed in a hypotonic solution?

Water enters the cells; they swell and may lyse.

Describe an isotonic solution with respect to cells.

Solute concentration equals that inside the cells; no net water movement, cells maintain normal shape.

State La Place’s law as applied to alveoli.

Pressure (P) inside an alveolus is directly proportional to surface tension (T) and inversely proportional to radius (r): P = 2T ⁄ r.

How does pulmonary surfactant reduce the work of breathing according to La Place’s law?

Surfactant lowers surface tension more in smaller alveoli, equalising pressures, preventing collapse (atelectasis), and reducing the pressure needed to inflate alveoli.