Chapter 31 Amino Acid Synthesis

Front 1

What do microorganisms use to reduce N2 to NH3?

Back 1

ATP and reduced ferredoxin, a powerful reductant

Front 2

What catalyzes the fixation of N2?

Back 2

molybdenum-iron cluster in nitrogenase

Front 3

Higher organisms consume fixed nitrogen to synthesize what? (3)

Back 3

amino acids

nucleotides

other nitrogen-containing biomolecules

Front 4

What does ammonia exist as in aqueous solutions?

Back 4

(NH4)+

Front 5

What are the major points of entry of (NH4)+ into metabolism?

Back 5

glutamine or glutamate

Front 6

How many amino acids can human begins synthesize?

Back 6

11/20

Front 7

True or false: the pathways for the synthesis of nonessential amino acids are quite simple.

Back 7

true

Front 8

What catalyzes the reductive amination of alpha-ketoglutarate to glutamate?

Back 8

glutamate dehydrogenase

Front 9

What takes place in the synthesis of most amino acids?

Back 9

transamination reaction

Front 10

What is synthesized by the transamination of pyruvate?

Back 10

alanine

Front 11

What is synthesized by the transamination of oxaloacetate?

Back 11

aspartate

Front 12

What is tetrahydrofolate?

Back 12

carrier of activated one-carbon units

Front 13

carries one-carbon units at three oxidation states, which are interconvertible

Back 13

tetrahydrofolate

Front 14

What is the major donor of activated methyl groups?

Back 14

SAM

Front 15

How is SAM synthesized?

Back 15

by the transfer of an adenosyl group from ATP to the sulfur atom of methionine

Front 16

What is formed when an activated methyl group from SAM is transferred to an acceptor?

Back 16

S-adenosylhomocysteine

Front 17

What happens to S-adenosylhomocysteine?

Back 17

hydrolyzed to adenosine and homocysteine

Front 18

What happens to homocysteine?

Back 18

methylated to methionine to complete the activated methyl cycle

Front 19

What are most of the pathways of amino acid biosynthesis regulated by?

Back 19

feedback inhibition

Front 20

What is feedback inhibition?

Back 20

Committed step is allosterically inhibited by the final product.

Front 21

requires extensive interaction and includes both negative and positive regulation

Back 21

regulation of branched pathways

Front 22

series of reactions in which groups from methionine are converted into a biochemically reactive form through the formation of SAM

Back 22

activated methyl cycle

Front 23

What is SAM?

Back 23

S-adenosylmethionine

Front 24

What can an active methyl group be transferred from SAM to?

Back 24

acceptor molecules such as norepinephrine

Front 25

What can methionine be regenerated from in the activated methyl cycle?

Back 25

homocysteine and N5-methyltetrahydrofolate

Front 26

What is the committed step?

Back 26

first irreversible step in a metabolic pathway under physiological conditions

Front 27

What is the committed step catalyzed by?

Back 27

allosteric enzyme

Front 28

regulatory strategy in which the enzyme catalyzing the committed step common to several pathways is incrementally inhibited by the products of each of the pathways

Back 28

cumulative feedback inhibition

Front 29

regulatory strategy in which the committed step common to several pathways is catalyzed by different enzymes with the same catalytic properties but different regulatory properties

Back 29

enzyme multiplicity

Front 30

each enzyme responds to the final product of one of the pathways having the committed step in common

Back 30

enzyme multiplicity

Front 31

What is nitrogen fixation?

Back 31

conversion of nitrogen gas (N2) into ammonia

Front 32

What is the first step in the flow of nitrogen into amino acids, nucleotides, and other nitrogen-containing compounds in organisms?

Back 32

nitrogen fixation

Front 33

catalyzes the reduction of diatomic nitrogen to ammonia

Back 33

nitrogenase complex

Front 34

What is nitrogenase complex found in?

Back 34

bacteria and the blue-green algae

Front 35

prosthetic group that plays a key role in transamination reactions

Back 35

pyridoxal phosphate (PLP)

Front 36

What is PLP?

Back 36

pyridoxal phosphate

Front 37

What is PLP derived from?

Back 37

vitamin B6

Front 38

Trace the flow of nitrogen from atmospheric N2 to glutamine.

Back 38

N2 -nitrogenase complex> NH3/(NH4)+ -glutamate dehydrogenase> glutamate -glutamine synthetase> glutamine

Front 39

What amino acids are derived from oxaloacetate?

Back 39

MTKIND

Front 40

What amino acids are derived from phosphoenolpyruvate and erythrose 4-phosphate?

Back 40

WFY

Front 41

What amino acids are derived from pyruvate?

Back 41

AVL

Front 42

What amino acids are derived from ribose 5-phosphate?

Back 42

H

Front 43

What amino acids are derived from alpha-ketoglutarate?

Back 43

QPER

Front 44

What amino acids are derived from 3-phosphoglycerate?

Back 44

GCS

Front 45

What organisms are capable of nitrogen fixation?

Back 45

diazotrophic

Front 46

What is methylated to form methionine?

Back 46

homocysteine

Front 47

What conenzyme is required by aminotransferases?

Back 47

pyridoxal phosphate

Front 48

What is responsible for nitrogen fixation?

Back 48

nitrogenase complex

Front 49

What is a common amino acid donor?

Back 49

glutamate

Front 50

True or false: the mechanistic complexity of nitrogenase is necessary because nitrogen fixation is a thermodynamically unfavorable process.

Back 50

false, favorable but the reaction is not kinetically possible without ATP (high activation energy)

Front 51

Nitrogen-fixing bacteria on the roots of some plants can consume as much as 20% of the ATP produced by the plant—consumption that does not seem very beneficial to the plant. Explain why plants tolerate this loss of valuable resources and what the bacteria are doing with the ATP.

Back 51

The bacteria provide the plant with ammonia by reducing atmospheric nitrogen.

Front 52

What are the seven precursors of the 20 amino acids?

Back 52

oxaloacetate

pyruvate

ribose-5-phosphate

phosphoenolpyruvate

erthrose-4-phosphate

alpha-ketoglutarate

3-phosphoglycerate

Front 53

If an animal is fed N15-labeled aspartate, many amino acids bearing the N15 label subsequently appear. What reactions take part in the transfer of the label?

Back 53

A reversible transamination reaction will transfer the labeled amino group from aspartate to alpha-ketoglutarate to form glutamate and oxaloacetate. Glutamate is an amino-group donor for the synthesis of many amino acids from their corresponding ketoacids.

Front 54

Differentiate between SAM and tetrahydrofolate.

Back 54

Both carry one-carbon units. SAM is a more useful methyl donor than tetrahydrofolate because it has a greater transfer potential.

Front 55

Which of the 20 amino acids can be synthesized directly from a common metabolic intermediate by a transamination reaction?

Back 55

DEA

Front 56

Propose a scheme of sequential feedback inhibition that would result in the production of equal amounts of Y and Z for the following pathway:

A -> B -> C that splits into D->E->Y and F->G->Z.

Back 56

Y could inhibit the C->D step, Z could inhibit the C->F step, and C could inhibit A->B.

Front 57

Propose a scheme of concerted feedback inhibition that would result in the production of equal amounts of Y and Z for the following pathway:

A -> B -> C that splits into D->E->Y and F->G->Z.

Back 57

Y could inhibit the C->D step, Z could inhibit the C->F step, and the A->B step could be inhibited only in the presence of both Y and Z.

Front 58

We have identified three biomolecules that carry activated one-carbon units of some sort. Name these three carriers.

Back 58

tetrahydrofolate

SAM

biotin

Front 59

A person on a diet lacking in methionine would not be able to synthesize adequate amounts of proteins. However, insufficient protein synthesis would not be the only biochemical problem such a person would face. What other biosynthesis would be affected by a lack of dietary methionine?

Back 59

Methionine is a component of SAM, which is a methyl donor for the synthesis of phosphatidylcholine from phosphatidylethanolamine.