Enzymes Regulation Questions and Answers

Answer: C

Correct answer: competitive inhibition

A competitive inhibitor resembles the substrate closely enough to occupy the active site, so the two compete for it. The effect can therefore be overcome by raising the substrate concentration - which is what raises the apparent \(K_m\) while leaving \(V_{max}\) unchanged. Allosteric and non-competitive inhibitors bind elsewhere.

Answer: C

Correct answer: Decreasing colloidal osmotic pressure across the capillary wall

Plasma proteins, albumin especially, hold water in the capillary by colloid osmotic (oncotic) pressure, which opposes the hydrostatic pressure driving fluid out. If the protein concentration falls - through starvation, liver failure or protein loss in the urine - that inward pull weakens, fluid accumulates in the tissues, and oedema results.

Answer: B

Correct answer: RBCs

Red blood cells outnumber every other blood cell by a wide margin - about 5 million per microlitre, against 4,000-11,000 white cells. The reason is functional: they carry oxygen, and the body needs an enormous surface area of haemoglobin to do it.

Answer: C

Correct answer: Both

Regulation operates at two levels, and both are needed. Activity control - allosteric effects, phosphorylation - adjusts existing enzymes within seconds. Control of synthesis - induction and repression - changes how much enzyme there is at all, over a much longer period. Fast control handles moment-to-moment demand; slow control matches the cell’s enzyme complement to its circumstances.

Answer: C

Correct answer: 7.3

A red cell is about 7.2-7.5 μm across - near enough the diameter of the smallest capillaries, which it must deform to pass through. Its biconcave shape is what allows that flexibility, and also gives it a large surface area for the size of its volume.

Answer: D

Correct answer: All of the above

An allosteric enzyme has an active site where catalysis happens, a separate allosteric site where the regulator binds, and the modifiers that bind there. All three are part of the description - what defines the class is that the two sites are distinct and that binding at one changes the other.

Answer: C

Correct answer: 250

Haemoglobin binds carbon monoxide with roughly 200-250 times the affinity it has for oxygen, so even a small concentration of CO in the air captures a large fraction of the haemoglobin. Worse, the carboxyhaemoglobin formed shifts the dissociation curve leftwards, so the oxygen still carried is released less readily - which is why CO poisoning is so dangerous at concentrations that seem trivial.

Answer: A

Correct answer: RNA acting as enzymes

A ribozyme is a molecule of RNA that acts as a catalyst. Its discovery by Cech and Altman overturned the assumption that all enzymes are proteins, and it matters for another reason: the peptidyl transferase activity of the ribosome is itself a ribozyme, so protein synthesis is catalysed by RNA. That is one of the strongest arguments for an early RNA world.

Answer: A

Correct answer: Activation of proenzymes

Reversible covalent modification - phosphorylation above all - switches enzymes on and off by attaching and removing a group. Many proenzymes are activated in this way, and the modification can be undone by the opposing enzyme, a phosphatase. (Activation by cleavage, as with pepsinogen, is the irreversible kind.)

Answer: D

Correct answer: None of the above

Creatine kinase has three isoenzymes, made from two subunit types: CK-MM in skeletal muscle, CK-BB in brain, and the hybrid CK-MB in heart muscle. Since three is not among the options, the answer is none of them. The MB form’s rise in blood was long used to diagnose myocardial infarction.