rEVISION

Question 1

Which forces predominantly keep the structure of an alpha-helix protein stable

Answer 1

Hydrogen bonds between the C=O of one residue and the N-H of another residue, 4 amino acids along the helix, stabilise the entire structure.

Question 2

What is the optimum pH for the enzyme lysozyme?

Answer 2

at pH 5.0, Asp52 is ionised and Glu35 is unionised, allowing for lysis between the NAG and NAM units of polymers in bacterial cell walls.

Question 3

is glucose always converted to glucose-6-phosphate by hexokinase

Answer 3

No

This reaction can also be catalysed by a slightly different enzyme, glucokinase, in the liver

Question 4

Why is regeneration of NAD + essential?

Answer 4

Because otherwise the dehydrogenation of glyceraldehyde-3-phosphate cannot occur

Question 5

Why is regeneration of NAD + essential?

Answer 5

Because otherwise the dehydrogenation of glyceraldehyde-3-phosphate cannot occur

Question 6

A deficiency in which option affects the Link reaction from pyruvate to acetyl coenzyme A?

Answer 6

Thiamine, or B1, is needed to form Thiamine pyrophosphate, which is a prosthetic group in the Pyruvate Dehydrogenase complex. A deficiency in B1 leads to Beri-Beri

Question 7

Where in the cell does the TCA cycle occur?

Answer 7

The mitochondrial matrix

Question 8

Which TCA participant is linked with malate on an antiporter in the malate-aspartate shuttle?

Answer 8

The malate-aspartate shuttle system uses two membrane carriers and four enzymes. Hydrogen is transferred from cytoplasmic NADH to oxaloacetate to give malate, a reaction catalysed by cytosolic malate dehydrogenase (MDH). Malate is transported into the mitochondria where it is rapidly re-oxidised by NAD+ to give oxaloacetate and NADH (catalysed by mitochondrial MDH). Oxaloacetate and glutmate then undergo transamination to give the pair alpha-ketoglutarate and aspartate, which can exit the mitochondrial matrix via specific transporters in exchange for malate and glutamate respectively

Question 9

: Which option best applies to ATP synthase?

Answer 9

the active site of the beta subunit has 3 states
As the discs of the c subunits rotate, the attached gamma subunit also rotates, but it is asymmetrical. This forces structural changes in the beta subunit between 3 states: open, loose binding and tight binding. ADP could be produced if ATP synthase rotates in the opposite direction.

Question 10

In the first step of fatty acid biosynthesis, the production of malonyl CoA is catalysed by which enzyme and coenzyme combination?

Answer 10

Acetyl CoA carboxylase with biotin

Question 11

At which Carbon is cholesterol acylated in its storage form?

Answer 11

3

Question 12

At which Carbon is cholesterol acylated in its storage form?

Answer 12

3

Question 13

In the first step of fatty acid biosynthesis, the production of malonyl CoA is catalysed by which enzyme and coenzyme combination?

Answer 13

Acetyl CoA carboxylase with biotin/vitamin b7

Question 14

Which of the following is a function of cholesterol?

Answer 14

Cholesterol is a precursor of steroid hormones, not peptide hormones. High concentration of cholesterol cause low membrane fluidity. It cannot be metabolised to palmitate.

Question 15

Cholesterol becomes the steroid hormone precursor pregnenolone via which enzyme?

Answer 15

cholesterol desmolase

Question 16

Which of the following components would be found in the core of a lipoprotein?

Answer 16

triacylglycerol

Apart from triglycerols, cholesterol esters could also be found at the core of a lipoprotein.
About the other options: Free cholesterols, phospholipids and proteins are in the surface layer.
Haem group is found at the core of erythrocytes.

Question 17

Which of the following components would be found in the core of a lipoprotein?

Answer 17

triacylglycerol

Apart from triglycerols, cholesterol esters could also be found at the core of a lipoprotein.
About the other options: Free cholesterols, phospholipids and proteins are in the surface layer.
Haem group is found at the core of erythrocytes.

Question 18

Which enzyme catalyses the regulated step of cholesterol synthesis?

Answer 18

The formation of mevalonate is the regulated step and is catalysed by HMG CoA reductase- i.e the step is the slowest

Question 19

During cholesterol synthesis, how many molecules of Isopentenyl pyrophosphate are used to form one molecule of squalene?

Answer 19

6

Question 20

Which of the following is usually ABSENT from Low-Density Lipoproteins?

Answer 20

Free fatty acid

Fats are transported as triacylglycerol and not as free fatty acid.

Question 21

Where are lipoprotein lipase found?

Answer 21

Lipoprotein lipase is found on CAPILLARY endothelial cells.

Question 22

Chylomicrons travel from the lacteals to enter the blood stream at the left subclavian vein

Answer 22

Lacteals are part of the lymphatic system. The lymphatic system drains into the thoracic duct which deposits into the blood stream at the LEFT subclavian vein.

Question 23

what activates lipoprotein lipase?

Answer 23

APOPROTEIN C-II pays a key role in activating lipoprotein lipase.

Question 24

how many steps are required to convert lanosterol to cholestrol

Answer 24

19

Question 25

Where in the cell does protein modification and quality control generally occur?

Answer 25

Modification of proteins occurs in the rough ER, of lipids, generally in the smooth ER. The ribosomes are the site of translation and the Golgi apparati of packaging

Question 26

Which statement most accurately describes to constitutive secretion?

Answer 26

Secretion in this case is continuous regardless of environmental factors

Question 27

give an example of golgi apparatus function

Answer 27

• Protein transport occurs in both directions between ER/ribosomes and the apparati.
• Folding of protein chains generally occurs in the rough ER
• An example of Golgi apparatus function is the phosphorylation of mannose on lysosomal proteins

Question 28

what does gluconeogenesis use at its starting point

Answer 28

-oxaloacetate

Question 29

Which reacts in the presence of malate dehydrogenase to form malate in the malate-aspartate shuttle?

Answer 29

Oxaloacetate

Question 30

Which donates an electron to another of the options to produce cytosolic glycerol-3-phosphate?

Answer 30

NADH

Question 31

Which is linked to malate on an antiporter?

Answer 31

In the malate-aspartate shuttle, malate is pumped into the matrix and alpha-ketogluterate out

Question 32

Which reacts to form aspartate inside the mitochondrial matrix?

Answer 32

Oxaloacetate

Question 33

Which produces glucocorticoids?

Answer 33

the adrenals

Question 34

what body parts do gluconeogenesis?

Answer 34

the liver and the kidneys

Question 35

Which is the main glycogen store for maintenance of blood glucose?

Answer 35

The liver

Though skeletal muscle normally stores in total more glycogen, this is predominantly for its own metabolism