Important enzymes

Question 1

What is the name of the molecule that acts as as small free energy store in muscle and which enzyme catalyses the reaction (forward and backward) of energy storage/release?

Answer 1

Store: creatine phosphate
Enzyme: creatine kinase
creatine + ATP –> creatine phosphate + ADP

Question 2

What are the group of enzymes called that hydrolyse dietary polysaccharides into glucose, maltose and smaller polysaccharides (dextrins)?

Answer 2

glycosidase enzymes

Question 3

What type of glycosidase enzyme is secreted in the mouth?

Answer 3

Salivary amylase

starch&glycogen –> glucose, maltose and smaller polysaccharides (dextrins)

Question 4

What type of glycosidase enzyme is secreted into the duodenum?

Answer 4

Pancreatic amylase

starch&glycogen –> glucose, maltose and smaller polysaccharides (dextrins)

Question 5

What are the names of the gyocosidase enzymes which break down dietary disaccharides (maltose and sucrose), maltose and dextrins in the duodenum and jejunum, releasing the monosaccharides glucose, fructose and galactose?

Answer 5

Lactase
Glycoamylase
sucrase/isomaltase

Question 6

Where are the glycosidase enzymes lactase, glycoamylase and sucrase/isomaltase found in the gut?

Answer 6

They are large glycoprotein complexes that are attached to the brush border membranes of the epithelial cells of the duodenum and jejunum

Question 7

What is the function of hexokinase?

Answer 7

Converts glucose + ATP –> glucose-6-phosphate + ADP in all tissues

Question 8

What is the function of glucokinase

Answer 8

Converts glucose + ATP –> glucose-6-phosphate + ADP

in the liver

Question 9

What is the role of glycerol kinase?

Answer 9

It is an enzyme found in the liver (not in adipose) which can catalyse:
glycerol + ATP –> glycerol phoshate + ADP
Which can then be used to synthesise triacylglycerol and be stored as be stored as fat

Question 10

What is the role of myokinase in muscle?

Answer 10

It enables the high energy of hydrolysis phosphate bond in ADP to drive ATP synthesis under emergency conditions:
2ADP ATP + AMP

Question 11

What is the role of phoshofructokinase (PFK)?

Answer 11

It is the most important rate-limiting step of glycolysis and catalyses:
fructose-6-phosphate + ADP –> fructose 1,6-bisphosphate + ADP
This commits glucose to glycolysis

Question 12

What is the role of glucose 6-phosphate dehydrogenase?

Answer 12

It is the first enzyme (and key regulated enzyme) in the pentose phosphate pathway

Question 13

Deficiency in which enzymes can cause galactosaemia?

Answer 13

galactokinase, galactose-1-P uridyl transferase or UDP-galactose 4’-epimerase

Question 14

What is the name of the enzyme that is involved in the conversion of galactose to galacitol in galactosaemia?

Answer 14

Aldose reductase

Question 15

What is the role of pyruvate dehydrogenase (PDH)?

Answer 15

Enzyme complex which irreversibly converts:

pyruvate + CoA + NAD+ –> acetyl-CoA + CO2 + NADH + H+

Question 16

What is the role of isocitrate dehydrogenase?

Answer 16

It catalyses an early irreversible step of the citric acid cycle:
isocitrate + NAD+ –> alpha-ketoglutarate + NADH + CO2

Question 17

What is the role of pyruvate carboxylase?

Answer 17

It catalyses the reaction of pyruvate into oxaloacetate to:

1. Replace intermediates lost to biosynthesis from the TCA cycle
2. A means of avoiding the irreversible step 10 of glycolysis in gluconeogenesis

Question 18

What is the role of aldehyde dehydrogenase?

Answer 18

Catalyses the reaction:
acetaldehyde + NAD+ –> acetate + NADH
In alcohol metabolism

Question 19

What is the role of fatty acyl CoA synthase?

Answer 19

It activates fatty acids by linking them to coenzyme A (creates a high energy bond):
fatty acid + CoA + ATP -> fatty acyl CoA + ADP + 2Pi

Question 20

Glycerol from adipose tissue or from enterocytes (dietary TAGs) can be transported to the liver in the blood. In the liver it is activated by what enzyme into glycerol phosphate?

Answer 20

Glycerol kinase

Question 21

What is the function of the enzyme HMG-CoA synthase?

Answer 21

Synthesises HMG-CoA from acetyl coA (and acetoacetyl CoA)

Question 22

What is the function of the enzyme HMG-CoA lyase?

Answer 22

Converts HMG-CoA into acetoacetate which can then be converted into the other two ketone bodies (acetone and beta-hydroxybutyrate)

Question 23

What is the function of the enzyme HMG-CoA reducatase?

Answer 23

Converts HMG-CoA into Mevalonate (the first step in the synthesis of cholesterol and therefore also steroid hormones)

Question 24

What is the name of the enzyme that statins inhibit?

Answer 24

HMG-CoA reductase