Biochem 2 Quiz 2

1st phase of the PPP

oxidative generation of NADPH (2 NADP+ yields 2 NAPDH)

2nd phase of the PPP

nonoxidative interconversion of a variety of phosphorylated 3-, 4-, 5-, 6-, and 7-C sugars

PPP reactions take place in the


nonoxidative PPP phase has three reactions. The net result of these reactions is

the conversion of three pentoses into two hexoses and one triose ( 3 C5 <--> 2 C6 + C3 )

Transaldolase (in PPP) converts a 3-C and 7-C sugar into

a 6-C and 4-C sugar

Transketolase (in PPP) converts a 4-C and a 5-C sugar into

a 6-C sugar and a 3-C sugar

the PPP and Glycolysis are linked by

transketolase and transaldolase

the rate of the oxidative phase of the PPP is controlled by the level of


Which reaction is the rate-limiting step of the PPP

the first reaction (the dehydrogenation of glucose 6-phosphate by glucose 6-phosphate dehydrogenase)

4 modes of PPP

1. ribose 5-phosphate needs exceed the needs for NADPH
2. the NADPH and ribose 5-phosphate needs are balanced
3. more NADPH is needed than ribose 5-phosphate
4. NADPH and ATP are both required

PPP is required for

rapid cell growth

the Calvin cycle and the PPP are

mirror images

Glycogen is in the ___ of all tissues


the largest stores of glycogen are in the

liver and skeletal muscle

3 steps of glycogen degradation

1. release of glucose 1-phosphate from glycogen
2. remodeling of glycogen to allow continued degradation
3. conversion of glucose 1-phosphate into glucose

3 possible fates of glucose 6-phosphate

1. processing by the glycolytic pathway
2. conversion into free glucose for release into the blood
3. processing by the PPP

glycogen synthesis requires

an activated form of glucose, UDP-glucose

glycogen breakdown: ___ degrades glycogen from the non-reducing ends of the molecule; ___ is converted to glucose 6-phosphate by ___ - no ATP is expended

glycogen phosphorylase; glucose 1-phosphate, phosphoglucomutase

PLP (Pyridoxal Phosphate Cofactor) forms a ___ base with a ___ residue at the ___ site of the ___; the ___ substrate promotes cleavage of an a-___-linkage in glycogen by ___ a proton to the ___ glucose; a ___ intermediate forms; the ___ and ___ substrate

Schiff, lysine, active, phosphorylase; phosphate, 1,4, donating, departing; carbocation; carbocation, phosphate, glucose 1-phosphate

glycogen phosphorylase cannot cleave near branch points and can only cleave

a-1,4-glycosidic bonds

a transferase shifts a small oligosaccharide near the branch point to a nearby chain, thereby making the glucose moieties accessible to the


what does a debranching enzyme like a-1,6-glucosidase do?

cleaves the a-1,6 bond at the branch point, releasing a free glucose

a ___ at the active site of phosphoglucomutase is ____; phosphoglucomutase forms a ___ intermediate by ___ its bound phosphoryl group to ___; the phosphoryl group is restored to the enzyme with the formation of ___

serine, phosphorylated; 1,6-biphosphate, donating, glucose 1-phosphate; glucose 6-phosphate

glucose 6-phosphatase generates free glucose from

glucose 6-phosphate in liver

phosphorylase regulation:
the key regulatory enzyme for glycogen degradation is

glycogen phosphorylase

phosphorylase regulation:
phosphorylase exists in 2 forms

a less active b form where a serine residue is phosphorylated and a more active a form
(both the a form and the b form display an equilibrium between R and T states; in the b form, the T state is favored, whereas in the a form, the R state is favored)

a ___ at the active site of phosphoglucomutase is ____


glycogen breakdown: glycogen phosphorylase ___ glycogen from the ___ ends of the molecule

degrades, non-reducing

what does the liver maintain

adequate blood glucose levels

the default state of liver phosphorylase is

the a form in the R state

liver phosphorylase is prepared to

generate blood glucose unless signaled otherwise

liver phosphorylase and muscle phosphorylase are


what is a negative regulator of liver phosphorylase?

(facilitating the transition from the R state to the T state)

the monomer that is used to extend the glycogen chain in synthesis


UDP-glucose (uridine diphosphate glucose)

the glucose donor in glycogen synthesis

how is UDP-glucose synthesized?

UDP-glucose pyrophosphorylase
(in a reaction that produces a pyrophosphate (PPi))

glycogen synthase

transfers a glucose moiety from UDP-glucose to the C-4 terminal residue of a glycogen chain to form an a-1,4-glycosidic bond


a polysaccharide of glucose residues


a dimer of two identical subunits

a branching enzyme generates branches by

cleaving an a-1,4-linkage, moving a block of approximately 7 glucoses, or synthesizing an a-1,6 linkage

glycogen synthase is the key regulatory enzyme in

glycogen synthesis

oxidation of glucose 6-phosphate derived from glycogen yields

about 31 molecules of ATP

Glycogen is an efficient storage form of