Energy production (Carbs 2)

Question 1

What enzyme hydrolyses lactose?

Answer 1

lactase into glucose and galactose

Question 2

Where is galactose metabolised?

Answer 2

liver - and kidney and GI tract

Question 3

What is the overall reaction for galactose + ATP?

Answer 3

galactose + AMP –> glucose-6-phosphate + ADP

Question 4

How can galactose be converted into glucose?

Answer 4

-epimerase reversible reaction
-galactose can be made from glucose via UDP-glucose

Question 5

When is the epimerase reaction important?

Answer 5

during lactation when breast tissue is synthesising large amounts of lactose for milk production

Question 6

Name two conditions that affect galactose metabolism

Answer 6

lactose intolerance and galactosaemia

Question 7

Why can’t those with galactosaemia utilise galactose?

Answer 7

they lack the kinase or transferase enzyme

Question 8

How can you tell the difference between lacking a kinase or transferase enzyme in galactosaemia?

Answer 8

-kinase - rarer, accumlation of galactose in tissues
-transferase - more common, more serious as both galactose and galactose-1-phosphate accumulate in tissues

Question 9

What does the accumulation of galactose in tissues lead to?

Answer 9

-galactose gets reduced to galactitol due to aldose reductase
-this depletes some tissues of NADPH

Question 10

How can cataracts be formed due to accumulation of galactose?

Answer 10

-loss of NADPH, structure of lens is damaged
-high conc of galactose can cause non-enzymatic glycolysation of lens protein

Question 11

How does glaucoma form?

Answer 11

accumulation of galactose and galactitol in the eye may lead to raised intraocular pressure (glaucoma)

Question 12

Describe the metabolism of fructose

Answer 12

-liver
-soluble enzymes that catalyse the conversion to glyceraldehyde-3-phosphate

Question 13

What happens to some of the glucose-6-phosphate if not entered into glycolysis?

Answer 13

metabolised by the pentose phosphate pathway

Question 14

What are the major functions of the pentose phosphate pathway?

Answer 14

-produce NADPH in cytoplasm
-produce ribose for synthesis of nucleotides

Question 15

What happens in phase 1 of the pentose phosphate pathway?

Answer 15

glucose-6-phosphate is oxidised and decarboxylated by the enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in reactions that require NADP+

Question 16

What happens in phase 2 of the pentose phosphate pathway?

Answer 16

a complex series of reactions converts any unused 5C sugar phosphates into intermediates of glycolysis
-fructose-6-phosphate
-glyceraldehyde-3-phosphate

Question 17

What is the overall equation for the pentose phosphate pathway?

Answer 17

3 glucose-6-phosphate + 6NADP+ –> 3CO2 + 6NADPH + 6H+ + 2 fructose-6-phosphate + glyceraldehyde-3-phosphate

Question 18

How do you regulate the pentose phosphate pathway?

Answer 18

by controlling the activity of glucose-6-phosphate dehydrogenase - by the NADP+/NADPH ratio in the cell

Question 19

How does the NADP+/NADPH ratio control glucose-6-phosphate dehydrogenase?

Answer 19

NADPH inhibits, NADP+ activates

Question 20

Describe the G6PD deficiency defect

Answer 20

• x-linked gene defect found in those originating from the mediterranean region and black USA males
  -point mutations in the gene coding for glucose-6-phosphate, reduced activity of enzyme, low levels of NADPH

Question 21

Why is NADPH required for the structural integrity and function of key proteins?

Answer 21

-this is dependent on glutathione which is made by the body
-GSH protects the cell against oxidative damage
-in order to do this NADPH is required to recycle GSH back to its active reduced form

Question 22

Which cells are most impacted by G6PD deficiency and why?

Answer 22

RBC because the pentose phosphate pathway is their only source of NADPH and they are at increased risk of oxidative damage

Question 23

How is haemolysis caused?

Answer 23

haemoglobin and other proteins become cross-linked by disulphide bonds due to oxidative damage and form insoluble aggregates (Heinz bodies) - leading to premature destruction of RBC and haemolysis

Question 24

What chemicals can cause acute haemolysis?

Answer 24

chemicals that reduce the levels of NADPH like antimalarials, sulphonamides, glycosides