Pentose Phosphate Pathway

Question 1

What are the substrates for pentose/hexose phosphate shunt?

Answer 1

glucose 6P

NADP+

Question 2

Where in the cell does it occur?

Answer 2

Cytoplasm

Question 3

What is the rate limiting enzyme?

Answer 3

glucose 6-phosphate dehydrogenase

Question 4

Activator of G6PD

Answer 4

NADP+

Question 5

inducer of G6PD

Answer 5

insulin

Question 6

inhibitor of G6PD

Answer 6

NADPH

Question 7

major products of pathway?

Answer 7

ribose 5P

NADPH

Question 8

in what process is ribose 5P utilized?

Answer 8

nucleotide synthesis

Question 9

in what process is NADPH utilized?

Answer 9

fatty acid synthesis, chain elongation 
cholesterol synthesis 
NT syntesis
reduction of glutathione in RBC - detox
**not used in e- transport chain

Question 10

Oxidative Phase Enzymes

Answer 10

glucose 6- phosphate
lactonase
6-phsophogluconate dehydrogenase

Question 11

Oxidative Phase Rxn

Answer 11

glucose 6-P –> —> —> ribulose 5-phosphate –> ribose 5-P

release NADPH

Question 12

Non-Oxidative Phase Enzymes

Answer 12

ribose 5P back into glycolytic intermediates- fructose 6P, glyceraldehyde 3P

Question 13

Glucose 6P dehydrogenase deficiency

Answer 13

low NADPH concentration
effect manifested in RBC
NADPH is used in glutathione defense system

Question 14

Why are RBC particularly vulnerable to oxidative damage

Answer 14

RBC have capacity to carry large amt of O2
prone to oxidative damage bc they have no ETC to reduce O2
hemolytic anemia

Question 15

Glutathione Defense system

Answer 15

Hb+ 02 –> superoxide O2-

1. superoxide dismutase turn it into hydrogen peroxide
2. glutathione peroxidase - hydrogen peroxide–> H20
3. glutathione reductase- uses GSH and NADPH

Question 16

Cellular need NADPH only

what is direction of the pathway

Answer 16

oxidative rxns to produce more NADPH from G6P

nonoxidative rxn will convert ribulose 5P to fructose 6-P and G3P to resyntesize Glucose 6P

Question 17

Cellular need NADPH + ribose 5P

what is direction of the pathway

Answer 17

oxidative rxn

isomerization of ribulose 5P to ribose 5P

Question 18

Cellular need ribose 5P only

what is direction of the pathway

Answer 18

no oxidative rxn, high NADPH inhibits g6P dehydrogenase
nonoxidative rxn in reverse
fructose 6P and G3P to ribose 5P

Question 19

Cellular need NADPH + pyruvate

what is direction of the pathway

Answer 19

both oxidative and non oxidative rxns are used

ribose 5P feed back into glycolytic pathway

Question 20

sucrose

Answer 20

glucose alpha 1,2 fructose

Question 21

lactose

Answer 21

galactose beta 1,4 glucose

Question 22

mannose

Answer 22

derived from ingested polysaccharids and glycoproteins

Question 23

Fructose metabolism enzymes to enter glycolysis

Answer 23

fructokinase
Aldolase B
Glyceraldehyde kinase

Question 24

Fructosuria

Answer 24

deficiency in fructokinase
thus can’t covert fructose to fructose1P
fructose seen in blood and urine
but 90% is eventually metbolized

Question 25

Fructose Intolerance

Answer 25

aldolase B deficiency fructose 1P can't breakdown to glyceraldehyde or DHAP fructose 1P inhibits gluconeogenesis and glycogenolysis hypoglycemia and lactic acidosis

Question 26

Mannose metabolism enzymes to enter glycolysis

Answer 26

hexokinase phosphomannose isomerase aldolase A and B

Question 27

Galactose Metabolism enzymes to enter glycolysis

Answer 27

galactokinase glactose1-P uridylytransferase epimerase results in Glucose 1-P and UDP galactose

Question 28

Classical Galactosemia

Answer 28

deficiency in galactose 1P uridylyltransferase accumulate galactose 1P neurological effects and liver damage

Question 29

Non classical Galactosemia

Answer 29

deficiency in galactokinase buildup of galactose galactose is reduced to galactitol => cataracts