EXAM 3: Pentose Phosphate Pathway, Glycogen Synthesis, Gluconeogensis

Question 1

pentose phosphate pathway

Answer 1

utilizes glucose-6P

products: NADPH and ribose-5-phosphate

Question 2

pentose phosphate pathway NADPH

Answer 2

electron donor

reductive biosynthesis of fatty acids and steroids
repair of oxidative damage
needed in liver, adipose, erythrocytes

Question 3

ribose-5-phosphate in pentose phosphate pathway

Answer 3

biosynthetic precursor of nucleotides

DNA, RNA synth; coenzyme synth; rapidly growing cells

in cytosol

Question 4

PP path:

oxidative phase

Answer 4

generates NADPH and ribose-5-P

Question 5

oxidative phase molecules and path

Answer 5

glucose 6P (redox)

6-phosphogluconate (redox)

Ribulose 5P (+CO2)

Ribose 5P

nucleotides, coenzymes, DNA, RNA

Question 6

ribulose and xylulose

Answer 6

epimers; ketone is ribulose of ribose (aldehyde)

Question 7

nonoxidative phase

Answer 7

regeneratets glucose-6P from ribose -5P

Question 8

PP pathways

Answer 8

both produce NADPH and ribose-5P

if ribose 5P isn’t needed: nonoxidative phase to recycle it to glucose-6P

Question 9

nonoxidative phase molecules and path

Answer 9

2 Ribose-5P + 4 xylulose-5P 
=
4 Fructose-6P + 2 glyceraldehyde-3P
=
5 glucose-6P

Question 10

when is the nonoxidative phase used?

Answer 10

in tissues requiringmore NADPH than ribose-5P

liver, adipose

2 cycles of pathway convert six 5 carbon sugars to five 6 carbon sugars

Question 11

NADPH regulates..

Answer 11

partitioning into glycolysis vs pentose phosphate pathway

glycolysis: if ATP needed
PP pathway: if NADPH or nucleotides needed

Question 12

glycogen synthesis

Answer 12

when glucose6P conc is high and ATP is high

control osmotic pressure by synthesizing glycogen

Question 13

phosphoglucomutase

Answer 13

glucose-6P to glucose-1P

glycogen synthesis

Question 14

UDP-glucose pyrophosphorylase

Answer 14

glucose 1P + UTP = UDP-glucose

pyrophosphate cleaved off of UTP; UMP is attached to phosphate of glucose-1P

Question 15

inorganic pyrophosphatase

Answer 15

breakdown of pyrophosphate to 2 pi in glycogen synthesis (after UDP-glucose pyrophosphorylase)

makes reactions favorable

Question 16

glycogenin

Answer 16

starter molecule

enzyme; forms a protein core of glycogen molecule

catalyzes addition of first 8 glucose residues to itself using UDP-glucose as substrate

Question 17

glycogen synthase

Answer 17

continues synthesis of straight chains of glucose after first 8 monomers are attached to glycogenin on both branches

glycosyltransferase activity
chain-extending activity

uses UDP-glucose to attach glucose to chain with a1-4 linkage until at least 11 monomers; branch

Question 18

glucosyltransferase activity

Answer 18

transfers glucose to glycogenin; UDP is leaving group

Question 19

glycogen branching enzyme

Answer 19

makes branches

transfers 6-7 glucose monomers from growing chain to the C6 hydroxyl group of a glucose on same chain or another chain

a1-6 connection

Question 20

gluconeogenesis

Answer 20

building carbs

almost all living things

3 irreversible reactions

Question 21

glycolysis vs gluconeogenesis

Answer 21

opposing pathways both thermodynamically favorable

reversible reactions used by both pathways

irreversible reactions of glycolysis must be bypassed in gluconeogenesis

euk: mitochondria and cytosol

Question 22

first bypass reaction of gluconeogenesis

Answer 22

pyruvate to phosophoenolpyruvate

2 steps, both require energy

not favorable, so concentrations matter

Question 23

first step of first bypass reaction

Answer 23

pyruvate carboxylase catalyzes pyruvate to oxaloacetate

ATP phosphorylates bicarbonate to activate it

Euk: requires transport of pyruvate into the mitochondria

Question 24

second step of first bypass reaction

Answer 24

phosphoenolpyruvate carboxykinase

oxaloacetate to phosphoenolpyruvate; carboxyl group is removed

phosphorylation using PO4 from GTP

loss of carboxyl and hydrolysis of phosphate from GTP both needed to produce PEP

mito or cyto depending on organism

Question 25

when is NADH used in first bypass reaction?

Answer 25

oxaloacetate to malate

Question 26

when is NADH MADE in first bypass reaction?

Answer 26

malate to oxaloacetate lactate to pyruvate CYTOSOL

Question 27

why must NADH be produced in the cytosol during gluconeogenesis?

Answer 27

to maintain NADH levels so gluconeogenesis can continue to run

Question 28

second bypass reaction

Answer 28

fructose-1,6-bisphosphate to fructose-6-phosphate via fructose-1,6-bisphosphatase oppositely regulated with PFK-1

Question 29

third bypass reaction

Answer 29

glucose-6P to glucose + Pi glucose-6-phosphatase only in tissues that send glucose out to other parts of the body (liver)

Question 30

gluconeogensis reaction

Answer 30

2 pyruvate + 4ATP + 2GTP + 2NADH + 2H+ + 4H2O = glucose + 4ADP + 2GDP + 6Pi + 2NAD+

Question 31

what does gluconeogenesis cost

Answer 31

4 ATP 2 GTP 2 NADH but physiologically necessary

Question 32

brain, nervous system, and red blood cells generate ATP almost entirely from

Answer 32

glucose

Question 33

when glycogen stores are depleted,

Answer 33

glucose must come from somewhere

Question 34

plants use gluconeogenesis

Answer 34

to make carbs after carbon fixation

Question 35

animals can produce glucose from

Answer 35

sugars (lactate, pyruvate, oxaloacetate) or proteins (amino acids that can be converted to citric acid intermediates or pyruvate)

Question 36

product of fatty acid degradation

Answer 36

Acetyl-CoA

Question 37

can animals produce glucose from FA?

Answer 37

no; no net conversion of acetyl-CoA to oxaloacetate plants, yeast, bacteria can via diff pathway