Energy Production Carbohydrates (2)

Question 1

Explain the role of lactate dehydrogenase in glucose metabolism

Answer 1

• lactate dehydrogenase converts Pyruvate into lactate. In turn , NADH is oxidised into NAD+

Question 2

How many grams of lactate do we have in our body without doing any strenuous exercise ?

Answer 2

40-50g

Question 3

What is the destination of lactate after it has been made in red blood cells / muscle tissues ?

Answer 3

• lactate is metabolised by the liver and kidney into pyruvate via lactate dehydrogenase. In turn , NAD is reduced into NADH + H+.

Pyruvate is then converted into glucose via gluconeogenesis.?

Question 4

What is the

Fate of lactate in the heart ?

Answer 4

Lactate is converted into Pyruvate through lactate dehydrogenase. In turn , NAD is reduced into NADH + h+. Pyruvate is then oxidised which produces energy and Co2.

Question 5

What is the normal concentration of lactate ?

Answer 5

1mM

Question 6

What does it mean when the concentration of lactate is between 2-5mM

Answer 6

• must have been exercising anaerobically , shock ,
• hyperlactaceimia.
• won’t affect blood ph.

Question 7

What happens whe. The lactate concentration rises above 5mM

Answer 7

Lactic acidosis

Blood ph reduced

Question 8

How are other sugars metabolised - fructose

Answer 8

Fructose can be metabolised into fructose 1 phosphate via fructokinase. ATP is used.
I
- fructose-1-phosphate is then metabolised by aldolase into an intermediate that can then enter glycolysis.g

Question 9

What are th consequences of fructokinase being deficient ?

Answer 9

• fructose conc increases , but when fructose is detected in the urine it is not harmful.

Question 10

What are the consequences of aldolase being deficient or absent ?

Answer 10

Fructose-1-phosphate would increase , which could lead to liver cz

Question 11

How is galactose metabolised ?

Answer 11

• galactose is metabolised into galactose-1-phosphate by galactokinase. This uses ATP.
• galactose-1-phosphate is then metabolised into glucose 1-phosphate. through the enzyme uridyl-transferase. And UDP-glucose is converted into UDP galactose by UDP - galactose 4 - epidermase.

Question 12

What is galactosemia ?

Answer 12

• unable to utilise galactose.
• can occur when there is a deficiency in galactokinase which is rare.
• can occur when there is a deficiency in Uridyl transferase which is more serious and common.

Question 13

What is a consequence of galactosaemia ?

Answer 13

Galactose can enter other pathways

• for example galactose can be converted into galactitol by the enzyme aldose reductase ( NADPH is converted into NADP)

Question 14

Why is the conversion of galactose into galactitol an issue ?

Answer 14

Because I because it uses up NADPH supply.

• prevents maintenance of free sulphydryl groups on cysteine residues.
• loss of structural and functional integrity of some proteins that depend on free SH groups , for examples proteins in the lens of the eyes.

Question 15

What is the pentose phosphate pathway ?

Answer 15

Not all the glucose -6-phosphate enters glycolysis. some enters the pentode-phosphate pathway.

Question 16

What is the importance of the pentose phosphate pathway ?

Answer 16

• produces C5 sugar ribose which are used to make RNA and DNA.
  2) produces NADPH in cytoplasm which plays an important role in RBC as it needs to maintain free SH groups.
• NADP is also necessary for lipid synthesis.

Question 17

What are the characteristics of pentose - phosphate pathway ?

Answer 17

• Co2 produced which means it is irreversible.
• no ATP made.
• NADP is converted into NADPH using glucose 6-P dehydrogenase.

Question 18

What are the clinical consequences of glucose 6-phosphate dehydrogenase deficiency?

Answer 18

• 1)NADPH is required for the reduction of oxidised glutathione into its reduced form.
  2) lower levels of active reduced glutathione leaves cells such as red blood cells susceptible to oxidative damage.
  3) HB in RBC. Becomes cross linked by disulfide bridges. This results in ‘ Heinz bodies’.
  4) which leads to destruction of red blood cells , causing anaemia.

Question 19

What is the rate limiting enzyme in the pentose phosphate reaction?

Answer 19

• glucose-6-phosphate dehydrogenase.

Question 20

What is the importance of NADPH?

Answer 20

1) maintaining free -SH groups on amino acid residues. this helps to maintain the functional and structural integrity of proteins.
2) reducing power for biosynthesis. for example reducing oxidised glutathione into reduced glutathione.
3) detoxification reactions.

Question 21

How do you treat galactosaeima ?

Answer 21

• low galactose / lactose diet.