Overview of Metabolism/Fermentation

Question 1

Catabolic pathways proceed from….

Answer 1

Catabolic pathways proceed from complex precursors toward progressively simpler products.

Question 2

Anabolic pathways from…..

Answer 2

Anabolic pathways (blue) from simpler precursors toward more complex products.

Question 3

What is energy charge?

Answer 3

Energy Charge

• indicates the capactiy of cell to do work
• is an index used to measure the energy status of biological cells.
• It is related to ATP, ADP and AMP concentrations.

Question 4

When a catabolic pathway is upregulated, will the value of the cellular “energy charge” increase or decrease? Explain.

Answer 4

Energy charge

• will increase b/c catabolis pathways lead to increased [ATP]
• high [ATP] = high energy charge

Question 5

True or False: Pyruvate carboxylase is not allosterically regulated by ADP.

Answer 5

False

Question 6

Is ADP more likely to be a (+) or a (-) effector of pyruvatecarboxylase activity?

Briefly explain your reasoning.

Answer 6

• ADP is more likely to be a (-) effector.
• A product of the Pyruvatecarboxylase rxn of :
  pyruvate —-> oxoaloacetate is ADP and ATP is a reactant
• le chatelier’s principle

Question 7

Succinctly describe the biochemical logic for the following observations

a) F-1,6-BP is an allosteric activator of pyruvate kinase. Why should pyruvate kinase be responsive to increasing [F-1,6-
BP]?

Answer 7

(a) The synthesis of F-1,6-BP from glucose consumes 2 ATP. For the glycolytic pathway to yield ATP, the intermediates must make it past the pyruvate kinase (PK) step. Upregulation of PK ensures that the initial investment of 2 ATP/glucose will produce 4 ATP for a net gain of 2 ATP/glucose.

Question 8

Succinctly describe the biochemical logic for the following observations:

b) Glucagon binding to receptors on hepatocytes upregulates glycogen phosphorylase and downregulates PFK-1. Your answer should address why it is critical that both of these effects occur upon glucagon binding.

Answer 8

(b) Glucagon is secreted when blood [glucose] is low, and it stimulates increased glucose export from liver into circulation. Upregulating phosphorylase will release G-1-P from glycogen, which leads to increased glucose export. Downregulating PFK-1 inhibits glycolysis and promotes gluconeogenesis, which also increases glucose export. Both of these responses make sense in response to glucagon signaling.

Question 9

Under aerobic conditions, pyruvate is……

Answer 9

Under aerobic conditions, pyruvate is shuttled into the Citric Acid Cycle, where it is completely oxidized to CO2 and H2O, and the NADH is oxidized via electron transport.

Question 10

Under anaerobic conditions, pyruvate…..

Answer 10

Under anaerobic conditions, pyruvate undergoes fermentation to lactate, or ethanol + CO2, with concomitant conversion of NADH to NAD+.

Question 11

Draw mechanism and answer the name for the enzyme responsible for: Homolactic fermentation

Answer 11

Question 12

Describe:

Alcoholic fermentation

Answer 12

Yeast converts pyruvate to ethanol in a two-step pathway:

• Alcoholic fermentation starts with the nonoxidativedecarboxylation of pyruvate to acetaldehyde, catalyzed bypyruvate decarboxylase.
• NAD+ is regenerated via the NADH-dependent reduction ofacetaldehyde to ethanol, catalyzed by alcohol dehydrogenase.

Question 13

Draw R and P: Pyruvate decarboxylase and alcohol dehydrogenase RXNs

Answer 13

Question 14

Draw The “business end” of TPP

Answer 14

Question 15

What is TPP?

Answer 15

Thiamine Pyrophosphate (TPP)

It acts as a cofactor in the step 1 of the alcoholic fermentation with Pyruvate decarboxylase

Question 16

Draw Mechanism: Pyruvate decarboxylase

Answer 16

Question 17

The aldolase and PDC reactions set up an ________ to an ________.

Answer 17

Question 18

Draw the Mechanism: Alcohol Dehydrogenase

Answer 18