Citric Acid Cycle

Question 1

Reactive site on pyridine nucleotides

Answer 1

. Nicotinamide ring that accepts 1 H+ and 2 e- to form a hydride

Question 2

Similarities btw NAD/H and NADP/H

Answer 2

. Similar structure 
. Identical reactive sites 
. Carry 1 proton and 2 electrons 
. Free in solution 
. Bind to enzymes temporarily during reactions

Question 3

Differences btw NAD/H and NADP/H

Answer 3

. Enzymes bind to one or the other
. NAD accepts reducing equivalents in catabolic rxns to generate NADH using dehydrogenase
. NADPH donates reducing equivalents in anabolic rxns to generate NADP using reductases

Question 4

Flavins reducing equivalents

Answer 4

FAD/FADH/FADH2 (flavin adenine denucleotide)

FMN/FMNH/FMNH2 (flavin mononucleotide)

Question 5

Pyridine reducing equivalents

Answer 5

. NAD/H (nicotinamide adenine dinucleotide)

. NADP/H (nicotinamide adenine dinucleotide phosphate)

Question 6

Reactive site in flavins

Answer 6

. Isoalloxazine ring

. Accepts 2 protons and 2 electron in 2 steps

Question 7

Properties of flavins

Answer 7

. Bound very tightly embedded in in active site of flavoproteins
. Not molecules in solution but found inside of cell
. Found in cellular respiration rxns

Question 8

CoA structure

Answer 8

. Carries acetyl group and fatty acid group

. Sulfhydryl group (SH) reactive site

Question 9

CoA properties

Answer 9

. Acetyl groups carried as acetyl CoA
. Fatty acyl groups carried as acyl CoA
. Hydrolysis of acetyl CoA and acyl CoA by water is thermodynamically favored

Question 10

T/F Good nutrition is essential to metabolism

Answer 10

T

Question 11

TCA is the final common pathway for _____

Answer 11

Oxidation of biological molecules including glucose, fatty acids, and amino acids

Question 12

T/F O2 is needed to accept electrons from NADH and FADH2 regenerating NAD and NAD for another round of cycle

Answer 12

T

Question 13

Location of TCA

Answer 13

Mitochondria

Question 14

Pyruvate dehydrogenase complex

Answer 14

. Rxn that connects glycolysis and TCA
. Large complex w/ multiple polypeptides, several vitamin cofactors (thiamine, pyrophosphate, lipoid acid, FAD, NAD, and CoA
. Key irreversible step in humans bc they can’t make pyruvate from acetyl CoA

Question 15

Positive effectors of pyruvate dehydrogenase

Answer 15

. Pyruvate

. NAD

Question 16

Neg. effectors of pyruvate dehydrogenase

Answer 16

. Acteyl CoA

. NADH

Question 17

Pyruvate dehydrogenase feedback inhibition

Answer 17

. Acetyl CoA and NADH are products of reaction

. Accumulation indicates cell is making too much

Question 18

Covalent modification of pyruvate dehydrogenase

Answer 18

. Liver pyruvate dehydrogenase is regulated by phosphorylation
.Kinase is activated by inc. in ratio of acetyl CoA/CoA or NADH/NAD or ATP/ADP and Phosphorylation of PD causes dec. activity
. Dephosphorylation inc. activity

Question 19

T/F Most fatty acids can be converted into sugar

Answer 19

F, most CANNOT be converted to sugar

Question 20

Role of TCA

Answer 20

. Important for aerobic generation of energy (catabolism)

. Provides intermediates for cellular biosynthesis (anabolism)

Question 21

Catabolic roles for TCA

Answer 21

. Glucose 
. Fatty acids
. Ketone bodies
. Amino acids 
. Ethanol 
. All make acetyl CoA for TCA

Question 22

Yield of ATP from each NADH and FADH2 in TCA cycle

Answer 22

. NADH: 2.5 ATP

. FADH2: 1.5 ATP

Question 23

Important enzymes in TCA

Answer 23

. Citrate synthase
. Isocitrate dehydrogenase
. Alpha-ketoglutarate dehydrogenase

Question 24

Allosteric regulation of citrate synthase

Answer 24

. Neg. by citrate

Question 25

Allosteric regulation of Isocitrate dehydrogenase

Answer 25

. Pos. By ADP and Ca2+ | . Neg. by ATP and NADH

Question 26

Allosteric regulation of alpha-ketoglutarate dehydrogenase

Answer 26

. Pos. By Ca2+ | . Neg. by NADH and Succinylcholine CoA

Question 27

Enzymes are often inhibited by accumulation of ____

Answer 27

Immediate products and/or products of the cycle

Question 28

Coupling of TCA

Answer 28

. NADH produced is converted back to NAD via ETC and oxidative phosphorylation . if ETC is halted then TCA can’t continue either

Question 29

Use of citrate in biosynthesis

Answer 29

. Fatty acids | . Cholesterol

Question 30

Alpha-ketoglutarate use in biosynthesis

Answer 30

. Glutamate, purines, DNA and RNA | . Other amino acids

Question 31

Succinylcholine CoA use in biosynthesis

Answer 31

. Heme

Question 32

Oxaloacetate use in biosynthesis

Answer 32

. Glucose | . Aspartate, asparagine, other amino acids

Question 33

Anaplerotic reactions

Answer 33

. Replenish the cellular supply of metabolic intermediates

Question 34

Pyruvate carboxylase

Answer 34

. Important in liver for replenishment of TCA intermediates . Pyruvate+CO2+ATP+H2O -> oxaloacetate+ADP+Pi+2H . Requires biotin (carries O2)

Question 35

Allosteric activator of pyruvate carboxylase

Answer 35

Acetyl CoA (present when intermediates are drawn off for something else and oxaloacetate can’t combine w/ CoA)

Question 36

Glutamate dehydrogenase

Answer 36

. Glutamate+NAD/NADP -> alpha-ketoglutarate+NH4+NADH/NADPH . Gln can be converted to Glu then to alpha ketoglutarate . 3 carbon amino acids Ala and Ser converted to pyruvate then is acted upon by pyruvate carboxylase

Question 37

Vitamin required for NAD/NADH/NADP/NADPH

Answer 37

Niacin (nicotinic acid vitamin)

Question 38

vitamin required for flavin synthesis?

Answer 38

Riboflavin

Question 39

Vitamin required for CoA synthesis

Answer 39

. Pantothenic acid

Question 40

What cells don’t have mitochondria?

Answer 40

RBCs

Question 41

Net reaction of TCA

Answer 41

Acetyl CoA + 3NAD +FAD +GDP +P+2H2O -> 2CO2+3NADH+FADH2+GTP+CoA