Biochem Chap 23

Front 1

Which reaction/enzyme requires acetyl-CoA as an allosteric activator?

Back 1

pyruvate carboxylase which converts pyruvate to oxaloacetate.

Front 2

Nucleoside diphosphate kinase

Back 2

Can convert any nucleoside diphosphate to nucleoside triphosphate (reversible reaction)

Front 3

PEPCK

Back 3

PEP carboxy kinase. removes a CO2 from oxaloacetate to form pyruvate enolate. which is then phosphorylated using GDP to become phosphoenol pyruvate.

Front 4

Why is GTP energetically equivalent to ATP?

Back 4

Because the phosphoryl groups can be interchanged b/w ATP and GDP using nucleoside disphosphate kinase.

ATP + GDP <--> ADP + GTP

Front 5

Where is NADH primarily found?

Back 5

In the mitochondria.

Front 6

Sum of gluconeogenesis from pyruvate to glucose

Back 6

2 Pyruvate + 4 ATP + 2GTP + 2 NADH + 6 H2O --> glucose + 4 ADP + 2 GDP + 6Pi + 2 NADH + 2H+

Front 7

How many ATP molecules are used up during gluconeogenisis?

Back 7

12 ATP molecules

Front 8

Principle of Regulation

Back 8

1. control of flux through any pathway requires that flow through the rate-limiting step varies in response to metabolic requirements.

2. fundamentally, when the energy demands of a cell increase, glycolysis should increase, and the rate of synthesis of glucose via gluconeogenesis should decrease.

Front 9

Regulatory mechanisms of glycolysis/gluconeogenesis

Back 9

1. allosteric interactions

2. cAMP dependent covalent modification (phosphorylation/dephosphorylation)

Front 10

Why regulate glycolysis and gluconeogenesis at more than one point?

Back 10

1. many other pathways interconnect with glycolysis

2. glycolysis is not just a catabolic pathway functioning solely for ATP generation. Some of its intermediates are precursors in other biosynthetic pathways. Consequently, the regulatory needs of hte cell are too complicated to be served by a single rate limiting step.

Front 11

Why do rapidly proliferating cells have high activity of the pentose phosphate pathway?

Back 11

NADPH is the ultimate electron source for the reduction of ribnonucleotides to deoxyribonucleotides for DNA synthesis. So, rapidly proliferating cells have high activity of the pentose phosphate patway for production of NADPH and ribose-5-phosphate

Front 12

Ribose-5-phosphate

Back 12

Precursor for nucleotide biosynthesis

Front 13

Primary functions of pentose phosphate pathway

Back 13

1. **To provide ribose-5-pentoses

2. To provide the reducing power NADPH for reductive biosynthess.

3. To metabolize dietary pentoses (derived primarily from the digestion of nucleic acids).

Front 14

Physiological Role of NADPH

Back 14

1. NADPH and NADH are NOT METABOLICALLY INTERCHANGEABLE. (even though NADPH only differs from NADH only by the addition of a phosphate group at the 2'-OH group of NADH's adenosine moiety.

NADPH is used for reductive biosynthesis; NADH is for oxidation of metabolites (such as glucose)

Many endergonic reactions, notably the reductive biosynthesis of fatty acids and cholesterol, as well as photosynthesis, require NADPH as reducing power, in addition to ATP.

NADPH is the ultimate source for the reduction of ribonucleotides to deoxyribonucleotides for DNA synthesis.

Front 15

Where does the pentose phosphate pathway operate?

Back 15

Exlcusively in the cytosol.

Front 16

where does glycolysis occur?

Back 16

Exclusively in the cytosol.

Front 17

Which enzyme is found in the mitochondria?

Back 17

pyruvate carboxylase: found exclusively in the mitochondria. So pyruvate must be transported into the mitocondria to be converted to oxaloacetate. Where it can be converted to PEP by PEPCK. PEP can be directly transported from the mitochondria to the cytosol. Without PEPCK, oxaloacetate must be converted to either malata (using malate dehydrogenase) or aspartate (via aspartate aminotransferase...where NH3 is often donated by glutamate.

PEPCK.

varies with species:
in humans, more or less equally distributed b/w the cytosol and mitochondria

in mice and rats: exclusively in the cytosol

in rabbits: exclusively in the mitochondria.

Front 18

Role of PEPCK

Back 18

converts oxaloacetate to phosphoenol pyruvate using GTP.

Front 19

How is the is the delta G for the conversion of pyruvate to PEP decreased for 0.9 to -22.6?

Back 19

the PEP formed is consumed in other reactions, so its concentration remains low. Decreasing the PEP concentration decreases delta G.

Front 20

Which enzyme requires acetyl CoA as an allosteric activator?

Back 20

pyruvate carboxylase.

Front 21

Which tissues are heavily involved in fatty acid synthesis and cholesterol synthesis? Which pathway do they use?

Back 21

Liver, adipose tissue, and adrenal cortex are rich in the pentose phosphate pathway

Front 22

Overall reaction for Pentose phosphate pathway

Back 22

3 G6P + 6 NADP+ + 3 H2O ---> 6 NADPH + 6H+ + 3CO2 + 2F6P + GAP.

Front 23

Stage 1 of the Pentose Phosphate Pathway

Back 23

includes steps 1-3. Oxidative reactions.

1. G6P + NADP+ --> 6-Phosphoglucono-delta-lactone + NADPH+ H+ (via glucose-6-phosphate dehydrogenase)

2. 6-phosphoglucono-delta-lactone + H2O --> 6-phosphogluconate + H+ (via 6-phospho-glucono-lactonase)

3. 6-phosphogluconate + NADP+ --> Ribulose-5-phoshate + NADPH + CO2 (via phosphogluconate dehydrogenase.


3.