Bioenergetics in the Cytosol

Question 1

high free energy of hydrolysis are sometimes depicted as

Answer 1

a squiggle (~).The chemical group attached to the squiggle is readily transferred to an acceptor molecule. ATP is a good example

Question 2

bonds that have a standard free energy of hydrolysis at pH of 7 equal to greater than -29KJ/mol

Answer 2

high energy bonds

Question 3

H2O + ATP  ADP Pi

Answer 3

G’= -35 KJ/mol

Question 4

Glucose + Pi  Glucose-6-phosphate + H2O

Answer 4

G’ = +14 KJ/mol

Question 5

ATP + Glucose  Glucose-6-phosphate + ADP

Answer 5

G’ = -21 KJ/mol

Question 6

ATP has a standard free energy of hydrolysis of

Answer 6

(G’)= -35 KJ/mol

Question 7

The Phosphate groups are ionized at pH 7, this produces …

Answer 7

electrostatic propulsion between phosphate groups

Question 8

Reactions during which phosphate is removed will be favored because the electrostatic repulsion is decreased as the result of the

Answer 8

hydrolysis

Question 9

ATP can phosphorylate many different compounds because

Answer 9

an electronegative group (such as hydroxyl ) can attack the electropositive phosphorus

Question 10

enzymes that catalyze phosphoryl group transfers-

Answer 10

kinases

Question 11

PEP

Answer 11

phosphoenolpyruvic acid

Question 12

PEP is a better donor than

Answer 12

ATP. G’= -62 KJ/mol

Question 13

The removal of the phosphate allows for

Answer 13

an enol-keto tautomerization, with the keto form being more stable than the enol form.

Question 14

What is the reason for the high free energy of hydrolysis of Acyl Derivatives of Phosphate and Coenzyme A?

Answer 14

Acyl Derivatives of Phosphate and Coenzyme A resonate poorly.
In a normal ester, electrons shift from oxygen but phosphorus hinders resonance as does the sulfur.
Sulfur does not form double bonds easily and the positive charge in phosphorus does not allow the electrons from oxygen to shift.

Question 15

Acyl derivatives of Phosphate are used to make

Answer 15

ATP

Question 16

Acyl derivatives of CoA are used to make ATP as well as

Answer 16

as the transfer of acyl groups

Question 17

Group transfer reactions are important to the biosynthesis

Answer 17

of proteins, lipids, carbohydrates and nucleic acids. The transfers occur by means of high energy donors of ATP (or other nucleotide derivative), acyl-coenzyme A and acyl-phosphates.

Question 18

ATP as a donor

Answer 18

ATP can donate phosphate
ATP can donate (pyrophosphate (PPi)
ATP can donate AMP

Question 19

A series of group transfer reactions are necessary for

Answer 19

peptide bond formation

Question 20

step A of peptide bond formation

Answer 20

The AMP from ATP is transferred to the carboxyl group of the amino acid. This is driven by the hydrolysis of pyrophosphate

Question 21

What type of bond is it that connects the amino acid to the AMP?

Answer 21

?

Question 22

Step B.

Answer 22

The AMP of the acyl-AMP is replaced by tRNA. This is reversible

Question 23

Step C.

Answer 23

The tRNA is replaced by the amino group of the amino acid docked in the ribosome. This has a large free energy change and is not reversible. The amino acid-tRNA bond is an acyl-phosphate bond

Question 24

What supplies the energy to form the peptide bond?

Answer 24

breaking of the acyl phophate bond

Question 25

The amino acid (alanine) is attached to the tRNA by the

Answer 25

3’ end of the “A” nucleotide.

Question 26

The amino acid (alanine) is attached to the 5’ end of the “A” nucleotide and

Answer 26

the 3’ end links to the tRNA.

Question 27

ATP is made in the cytosol by the

Answer 27

phosphorylation of ADP by means of high energy phosphoryl donor (these reactions are catalyzed by kinases)

Question 28

donors for substrate level phosphorylation

Answer 28

1,3 bisphosphoglycerate (1,3 BPGA) and Phosphoenolpyruvate (PEP) are found in glycolysis Succinyl-CoA is found in the TCA cycle Acetyl phosphate is derived from acetyl CoA used frequently in fermentation With the exception of PEP all the high energy donor are produced by oxidation reactions. PEP is produced by hydrolysis

Question 29

What provides the energy to add inorganic phosphate to the carbonyl group?

Answer 29

oxidation of phosphoglyceraldehyde. the electron acceptor is NAD

Question 30

Acetyl phosphate donates phosphate to ADP to produce ATP and is an important source of ATP under

Answer 30

anaerobic conditions

Question 31

acetyl phosphate is made by

Answer 31

acetate kinase

Question 32

pyruvic acid + pyruvate ferredoxin oxidoreductase (anaerobic)

Answer 32

acetyl-CoA, CO2, H2

Question 33

pyruvic acid + pyruvate dehydrogenase (aerobic)

Answer 33

acetyl-CoA, CO2, NADH

Question 34

pyruvic acid + pyruvate formate lyase (anaerobic)

Answer 34

acetyl CoA, formic acid

Question 35

Although acetyl phosphate is made from acetyl CoA, the energy was supplied by

Answer 35

the oxidative decarboxylation of pyruvate.

Question 36

Pyruvate dehydrognease, the electron acceptor is

Answer 36

NAD (NADH is produced).This happens under aerobic conditions

Question 37

The acetyl CoA that is formed under aerobic conditions does not proceed to

Answer 37

acetyl-phosphate, instead Acetyl-CoA enter the Krebs cycle

Question 38

Pyruvate dehydrogenase

Answer 38

Aerobic pathway (intermediate step between glycolysis and TCA cycle) Pyruvate + NAD+ + CoA > Acetyl-CoA + CO2 + NADH + H+ Acetyl-CoA typically enters TCA cycle for complete oxidation

Question 39

Under anaerobic conditions, what catalyzes acetyl-coA from pyruvate?

Answer 39

pyruvate-ferredoxin oxidoreductase . H2 is produced

Question 40

Pyruvate-formate hydrogen lyase

Answer 40

Pyruvate-formate hydrogen lyase reaction Pyruvate + CoA > acetyl-CoA + formic acid (formate) In this reaction the electrons stay with the carboxyl group (formate

Question 41

Acetyl-Phosphate from Acetyl-CoA

Answer 41

Acetyl-CoA + Pi > Acetyl-PO4 + CoA The reaction is (reversibly) catalyzed by phosphotransacetylase (PTA). This reaction usually follows the acetyl-CoA formation from Pyruvate-ferredoxin oxidoreductase or pyruvate-formate hydrogen lyase

Question 42

Acetate Kinase (ACK)

Answer 42

Acetyl-Phosphate is used in a substrate level phosphorylation reaction to form ATP. The route from Acetyl-CoA to ATP is referred to as ACK-PTA because the reations often together

Question 43

Succinyl-Coenzyme A

Answer 43

Succinyl CoA is made from the oxidative decarboxylation of alpha–keto glutarate. The enzyme that catalyzes the reaction is alpha–keto glutarate dehydrogenase and involve a similar mechanism as pyruvate dehydrogenase. This is because pyruvate and –keto glutarate are structurally similar (alpha–keto acids)

Question 44

Succinate Dehydrogenase

Answer 44

This is an oxidative decarboxylation. This ultimately supplies the energy for the next step which is to make ATP

Question 45

Succinate Thiokinase (ATP in the TCA cycle)

Answer 45

this is the step that makes ATP

Question 46

Pyruvate dehydrogenase

Answer 46

PEP + ADP ----> pyruvate + ATP

Question 47

Enolase (dehydration) reaction

Answer 47

2 pga ----> PEP + H20