Pentose Phosphat & ROS

Question 1

What is the main purpose of the oxidative pentose phosphate pathway?

What about the main purpose of the non-oxidative pentose phosphate pathway?

Answer 1

Oxidative: produces NADPH and ribose

Nonoxidative : converts pentoses to glycolytic intermediates

Question 2

In the oxidative arm of theh PPP, what is glucose oxidized to?

Answer 2

CO₂

Question 3

What are the 2 major products of the PPP?

Answer 3

NADPH and Ribose

Question 4

What enzyme is the regulated step of the PPP?

Answer 4

Glucose 6 Phosphate Denydrogenase (1st enzyme in PPP, also 1st committed step–> regulated step)

Question 5

How is glucose 6 phosphate dehydrogenase regulated?

Answer 5

Sensitive to NADPH: NADP+ ratio.

The cell wants to keep the levels of NADPH high. When NADPH:NADP+ ratio is high, the PPP is inhibited. When levels of NADPH drop, the PPP is activated b/c it is the major source of NADPH production in cells.

Question 6

Compare and contrast NADH and NADPH.

Answer 6

Question 7

What is NADPH used for in the cell?

Answer 7

Lipid biosynthesis

Deoxyribonucleotide synthesis

ROS

Detoxification

Question 8

Describe the non-oxidative PPP

Answer 8

The ribose that is produced through the oxidative PPP can be recycled back to make glycolytic/gluconeogenic intermediates

Question 9

In what cell is theh PPP the only means of producing NADPH and why?

Answer 9

In red blood cells because the other major source of NADPH is linked to the mitochondria and RBCs don’t have mitochondria

Question 10

Describe the reaction of lipids with hydroxyl radicals

Answer 10

Radical reacts with lipid to form lipid radical, which reacts with oxygen to form peroxyl radical which reacts with another lipid to form lipid radical and lipid peroxide –> these radicals are dangerous and need to be neutralized

Question 11

Describe the antioxidant relationship between vitamin E, vitamin C, glutathione and NADPH.

Answer 11

Vitamin E scavenges ROS and becomes oxidized, Vitamin C scavenges free radicals and also regenerates reduced vitamin E, glutathione maintains reduced vitamin C and scavenges free radicals as well. NADPH is oxidized to reduce Glutathione and reset the antioxidant system.

Question 12

• What is the polyol pathway?
• When is this pathway favored?
• What is the result on NADPH levels + oxidiative capacity?

Answer 12

• The polyol pathway converts glucose to sorbitol
• Hyperglycemia (diabetes) pushes glucose into this pathway
• Conversion to sorbitol depletes stores of NADPH and reduces cells ability to deal with ROS