CHEM 331 M1 Study Questions (Answers)

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1. Stage I: ATP invested to phosphorylate glucose and cleave 6C glucose molecule to 3C moleucles

Stage II: Two 3C molecules are converted to compounds with high Pi transfer potential that participate in thermodynamically favorable reactions that convert ADP to ATP.

2. Investment: 1 ATP from glucose à G6P; 1ATP from F6P à FBP

Production: 2 ATP from 1,3-BPG à 3PG; 2 ATP from PEP à pyruvate (Recall: there are 2x 3C molecules)

3. Glucose is oxidized in the glycolysis process and reduces NAD+ to make NADH. But not sure about the oxidation state count exactly? (Please elaborate, someone...)

4. Condensed version (no structure):

Note: Ions aren’t really essential, but provided to help you think of the mechanism & their involvement J

Glucose à G6P, uses 1 ATP, catalyze by hexokinase + Mg2+

G6P à F6P, catalyzed by phosphoglucose isomerse (PGI)

F6P à FBP, uses 1 ATP catalyzed by phosphofructokinase (PFK) + Mg2+

FBP à GAP + DHAP, catalyzed by aldolase

DHAP à GAP, catalyzed by triose phosphate isomerase (TPI)

2x GAPà 2x 1,3-BPG, catalyzed by GAP dehydrogenase (GAPDPH), consumes 2 NAD+ and 2 Pi

2x 1,3BPG à 2x 3PG, catalyzed by phosphoglycerate kinase (PGK), produces 2ATP

2x 3PG à 2x 2PG, catalyzed by phosphoglycerate mutase (PGM)

2x 2PG à 2x PEP, catalyzed by enolase & Mg2+

2x PEP à 2x pyruvate, catalyzed by pyruvate kinase (PK) & Mg2+, K+

5.

Phosphorylation, cofactor Mg2+

Isomerization (more specifically aldose to ketose isomerization)

Phosphorylation, cofactor Mg2+

Aldol cleavage or retro aldol condensation

Isomerization

Phosphorylation (via acyl thioester intermediate and high E acyl phosphate formation)

Phosphorylation of ADP

Functional group transfer

Dehydration

Phosphorylation

6. Aldol cleavage occurs between C3 and C4 for FBP, which needs a carbonyl and a hydroxyl at C2 and C4. If glucose wasn’t converted to fructose, cleavage gives products of unequal carbon chain length. Cleavage of FBP results in interconvertible C3 intermediate that can enter the same catabolic pathway (ie. glycolysis).

7. TPI interconverts GAP and DHAP to maintain the equilibrium ratio because the reaction between enzyme and substrate is diffusion controlled. As a result, more DHAP is efficiently converted to GAP as more GAP is used for the second stage of glycolysis.

8. Kinase reactions = direct phosphate transfer from ATP or to ADP via nucleophilic attack

GAPDH reaction = uses electrophilicity of thioesters (formed with the catalytic residue Cys in enzyme) to promote nucleophilic attack of inorganic phosphate to form acyl phosphate compound

9. 1,3-BPG (2) and PEP (2).

10.? Dehydrating 2PG allows it to form enol pyruvate when ADP nucleophillically attack the phosphate group. The tautomerization from the enol pyruvate to its keto form is highly exergonic, which ultimately drives the formation of ATP.

11. Phosphate hydrolysis from BPG is highly exergonic and thermodynamically favourable. Free energy released from this reaction is sufficient to drive the originally endergonic and thermodynamically unfavourable reaction of ADP phosphorylation to ATP.

12. Pyruvate – can be further oxidized to CO2 to release more energy.

NADH – Under aerobic conditions, electrons from NADH drive oxidative phosphorylation. Under anaerobic conditions, they must be reduced to regenerate NAD+ to keep glycolysis running.

13. 1. Oxidative metabolism

2. Anaerobic homolactatic fermentation

3. Anaerobic alcohol fermentation

14.

Homolactic fermentation: pyruvate + NADH à lactate + NAD+,

Alcoholic fermentation: pyruvate + NADHà alcohol + NAD+ , TPP cofactor, ADH

15. TPP is a cofactor that binds to pyruvate decarboxylase that stabilizes the carbanion formed during decarboxylation.

16. Enzymes with very negative ∆G values (i.e. catalyze highly exergonic reactions).

Includes hexokinase, PFK, PK.

17. PFK is regulated by ATP, a co-substrate and inhibitor. It has 2 binding sites for ATP, with the substrate site binding ATP at T/R state, the inhibitor binding ATP at only T state. At high [ATP], binding of inhibitor site shifts the enzyme to T state and prevents the substrate F6P, which only binds R state, from binding.

Inhibition can also be overcome with AMP and ADP that signal ATP depletion in the cell and increase glycolytic flux.

18. [ATP] in vivo around only 10% between rest and vigorous activity while metabolic flux through glycolysis may be 100-folds. Therefore another mechanism is needed to regulate enzyme activity (via AMP and ADP).

19.

Mannose metabolism:

Mannose à Mannose-6-P (hexokinase) à F6P (phosphomannose isomerase) à glycolysis

Galactose metabolism:

Galactose à Galactose-1-P (galactokinase) + UDP-glucose à glucose-1-phosphate + UDP-galactose (galactose-1-P uridylyl transferase)

G1P à G6P (by phosphoglucomutase)

UDP-galactose à UDP-glucose (by UDP-galactose-4-epimerase) with NAD+ as cofactor

Fructose metabolism:

Muscle: fructose converted to F6P by hexokinase à glycolysis

Liver (1): Fructose converted to F1P by fructokinase à glyceraldehyde and DHAP by F1P aldolase

Glyceraldehyde converted to GAP by glyceraldehyde kinase; DHAP converted to GAP by TPI à glycolysis

Liver (2): From glyceraldehyde , ADH can convert to glycerolà glycerol-3-P by glycerol kinase à DHAP by glycerol phosphate dehydrogenase à DHAP à GAP à glycolysis

20. Hexokinase – can phosphorylate mannose to M6P; can also phosphorylate fructose in muscle to F6P

TPI – used in liver metabolism of glucose converting DHAP to GAP