Bio 31 HMP Shunt

Question 1

What three pathways are there in the HMP Shunt?

Answer 1

Oxidative and forward/reverse of the non-oxidative branches.

Question 2

Rate limiting enzyme of the oxidative branch and its regulation?

Answer 2

G6PD
increased by [G6P] and [NADP+]
decreased by [NADPH]

Question 3

What is the primary enzyme of the non-oxidative branches and it’s regulation and function?

Answer 3

Transketolase
Coenzyme is TPP
Not regulated, but affected by coenzyme concentration.

Question 4

What is the purpose of the HMP shunt?

Answer 4

To produce Ribose-5P and NADPH.
The ribose is used to make nucleotides.
Process is very active in the liver, adrenals, lactating mammary glands, adipose tissue.

Question 5

What is the purpose of NADPH?

Answer 5

1) Fatty acid synthesis in liver, adipose, and mammary glands
2) Steroid synthesis in testes, ovaries, placenta, adrenal cortex
3) Glutathione reduction in erythrocytes

Question 6

What is the purpose of the reversible non-oxidative branch?

Answer 6

Provides a way for the body to use broken down ribose sugars for energy and a way to create more ribose when the need is high. Allows the body flexibility based on the its needs.

Question 7

What is the relationship between NADPH and glutathione?

Answer 7

Glutathione (G-SH) is a natural antioxidant. It reduces H2O2 to produce water and itself becomes G-S-S-G. NADPH donates electrons to return it to its reduced form so.

Question 8

How is fructose metabolized?

Answer 8

It is first trapped by fructokinase, then cleaved Aldolase B into glyceraldehyde and DHAP which can both enter glycolysis or gluconeogenesis. It can also be consumed through lipogenesis.

Question 9

Why is metabolism of fructose faster than glucose?

Answer 9

Because it skips the rate limiting step of glycolysis.

Question 10

How does fructose get into a cell?

Answer 10

It is not insulin dependent and does not cause insulin to be released when ingested.

Question 11

What is essential fructosuria?

Answer 11

Deficiency of fructokinase

Fructose can’t be trapped in cells so it accumulates in the urine and doesn’t cause any issues.

Question 12

What is Fructose poisoning?

Answer 12

Deficiency in aldolase b which makes Fructose-1P build up in the cells and cause death.

Question 13

How is galactose metabolized?

Answer 13

It is first phosphorylated by galactokinase.
It then must be converted to UDP-galactose in order to be used in the cell.
UDP-galactose can be converted into its epimer UDP-glucose which can then be used for energy.
If there is a shortage of galactose, it can be made by converting glucose.
Galactose is used to make lactose, glycoproteins, glycolipids, and glycosaminoglycans

Question 14

What does galactose-1-phosphate uridyltransferase do?

Answer 14

Uses UDP-glucose to help convert galactose-1P into UDP-galactose.

Question 15

What does UDP-hexose 4-epimerase do?

Answer 15

Converts between UDP-glucose and UDP-galactose.

Question 16

What happens if there is a deficiency in galactokinase?

Answer 16

Galactose collects in the blood and in cells. Eventually, the concentration gets high enough for aldose reductase to use it to make galactitol which draws fluid into lens, nerves, and kidneys and cause damage. Causes cataracts.

Question 17

What are the sources in the body for NADPH?

Answer 17

In cells with mitochondria, there are two sources: HMP Shunt and malic enzyme.
In cells without mitochondria like RBC’s, HMP Shunt is the only source.