Week 4 Skildum PPP and Gluconeogenesis

Question 1

What are the two major functions of the pentose phosphate pathway?

Answer 1

Generate NADPH + H

Generation of 5 carbon sugars (for synthesizing ribose components of nucleotides)

Question 2

What are the two phases of the PPP?

Answer 2

1. Oxidative phase (not reversible, produce NADPH + H)
2. Regenerative phase (reversible, transketolase & transaldolase)

Question 3

What are sources of fructose in the diet?

Answer 3

honey, fruit, and high fructose corn syrup

Question 4

What are sources of galactose in the diet?

Answer 4

milk, lactose

Question 5

What does the polyol pathway generate?

Answer 5

Synthesizes fructose (from glucose) in the seminal vesicles, to provide energy for sperm.

Question 6

What two places does the polyol pathway occur?

Answer 6

Seminal vesicles

Eye (forms cataracts when excess sugar)

Question 7

Where is fructose primarily metabolized?

Answer 7

In the liver.

Question 8

What are the basic steps in fructose metabolism?

Answer 8

• Into cell via GLUT V
• Phosphorylation (frucktokinase)
  
  • requires ATP, traps fructose in cell
• Aldolase B* cleaves into 3C and 3C
  
  • produces glyceraldehyde and dihydroxyacetone
  • both products can enter glycolysis
• Glyceraldehyde must hydrolize ATP to become Glyceraldehyde-3-P to enter glycolysis ($$$)

Question 9

As a product of fructose metabolism, where can Glyceraldehyde 3-phosphate go?

Answer 9

1. Glycolysis (bypasses PFK-1)
2. Gluconeogenesis (most common in liver)

Question 10

What enzyme can directly phosphorylate fructose in the muscle?

Answer 10

Hexokinase. Then it can enter glycolysis.

(glucose is preferred substrate in muscle)

Question 11

What causes Essential Fructosuria?

Answer 11

Dysfunctional fructokinase

• can’t make fructose-1-phosphate
• fructose in the urine
• BENIGN!

Question 12

What disease is caused by dysfunctional Aldolase B?

Answer 12

• Hereditary fructose intolerance
  
  • No metabolic fate for fructose-1-phosphate
  • trapped in cell
  • uses up available phosphate → no ATP synthesis
  • Hypoglycemia due to no ATP
  • Lactic acidosis present

Question 13

How do you treat Hereditary fructose intolerance?

Answer 13

Avoid fructose, no fruit

(patient asymptomatic until fructose ingested in early life)