EOM: BIOCHEMISTRY

Question 1

What is a high energy bond?

Answer 1

A chemical bond that releases as much or more energy when broken than that released by ATP hydrolysis.

Question 2

Which enzyme catalyses the rate-limiting step of the Kreb’s cycle?

Answer 2

Isocitrate synthase
Note: pyruvate hydrogenase is also important as it is a convergence point (pyruvate –> acetyl coA) and therefore increases the influx of acetyl-coA from glycolysis into TCA cycle.

Question 3

Which molecule is the end product of fatty acid beta oxidation?

Answer 3

Acetyl coA

Question 4

Name the features of ketoacidosis.

Answer 4

• High glucose due to a lack of insulin
• Low pH - ketones are acidic so H+ concentration is high
• Low pCO2 as body responds to acidosis by increasing breathing to get rid of CO2 (hence increase pH)

Question 5

Which of the following is not an endocrine organ?

• Adrenal gland
• Hypothalamus
• Spleen
• Pancreas
• Thyroid

Answer 5

Spleen

Question 6

State 2 features of steroid hormones.

Answer 6

• Made up of cholesterol

- Secreted by 3 steroid glands: adrenal cortex, testes and ovaries

Question 7

Describe the difference between anabolic and catabolic reactions.

Answer 7

• Anabolic steroids build small molecules into bigger ones e.g. glycogen synthesis
• Catabolic steroids break down large molecules into smaller ones e.g. beta-oxidation

Question 8

The average amount of protein we require each day is:

Answer 8

0.8 g/kg of body mass

Question 9

What is the body’s normal response to an increase in ECF osmolality?

Answer 9

Release of ADH from the posterior pituitary gland (produced in the hypothalamus), which stimulates the thirst centre as well as increasing water retention.

Question 10

What is renin released in response to?

Answer 10

A decrease in renal perfusion.

Question 11

Describe the RAAS.

Answer 11

1. Renin (=angiotensinogenase) is an enzyme secreted by juxtaglomerular cells in the kidney.
2. It acts on angiotensinogen –> angiotensin I
3. Angiotensin I is coverted to angiotensin II by ACE (angiotensin-converting enzyme).
4. Angiotensin II stimulates aldosterone secretion by the zona glomerulosa in the outer cortex of the adrenal glands.
5. Aldosterone stimulates Na+ reabsorption (and so water retention) in the kidneys –> increases preload, as well as causing vasoconstriction –> increases afterload

Question 12

Name 5 features of membrane channels.

Answer 12

• Can be voltage/ligand-gated
• Have a narrow pore
• Are selective for size and charge
• Do not use active transport
• Usually transport ions e.g. K+, Na+

Question 13

Give examples of primary and secondary active transport.

Answer 13

• Primary: Na+/K+ ATPase

- Secondary: Na+/glucose co-transport proteins (energy is generated by active transport of an ions i.e. Na+)