Glycolysis and Gluconeogenesis

Question 1

What is glycolysis

Answer 1

A set of reactions that converts glucose into pyruvate

Question 2

Where does glycolysis take place and how many reactions?

Answer 2

Cytoplasm. 10 reactions

Question 3

1st stage of glycolysis

Answer 3

1. glucose converted into fructose 1,6-biphosphate by phosphorylation, isomerization, another phosphorylation.
2. fructose 1,6 then cleaved by aldolase into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate.
3. two molecules of atp consumed per glucose molecule

Question 4

2nd stage glycolysis

Answer 4

1. glyceraldehyde 3..oxidized and phosphorylated, forms 1,3 biphosphoglycerate.
2. This transfers a phosphoryl group to ADP to form ATP and 3-phosphoglycerate.
3. phosphoryl shift and dehydration form phosphoenolpyruvate.
4. Another ATP made as phosphoenolpyruvate converted to pyruvate.
5. 2 molecules of pyruvate made from 1 glucose, net gain 2 ATP

Question 5

What is the electron acceptor in the oxidation of glyceraldehyde 3-phosphate?

Answer 5

NAD+

Question 6

What must be regenerated for glycolysis to continue?

Answer 6

NAD+

Question 7

How do aerobic organisms regenerate NAD+?

Answer 7

The NADH formed in glycolysis transfers its electrons to O2 through ETC, regenerating NAD+

Question 8

What are the 2 ways that anaerobic organisms regenerate NAD+?

Answer 8

Fermentation. Some organism reduce pyruvate to lactate to regenerate NAD+, others reduce pyruvate to ethanol.

Question 9

2 roles of the glycolytic pathway

Answer 9

1. Degrades glucose to generate ATP.

2. Provides building blocks for the synthesis of cell components.

Question 10

Reactions of glycolysis are reversible except…

Answer 10

Reactions catalysed by hexokinase, phosphofructokinase, pyruvate kinase.

Question 11

What is the most important control element in glycolysis.?

Answer 11

Phosphofructokinase

Question 12

How is phosphofructokinase inhibited and activated?

Answer 12

Inhibited - High levels of ATP and citrate

Activated - AMP and fructose 2,6-biphosphate (This biphosphate signals that glucose is abundant in the liver)

Question 13

In which situations is phosphofructokinase active?

Answer 13

When either energy or cellular building blocks are needed

Question 14

Hexokinase

Answer 14

Inhibited by glucose 6-phosphate

Question 15

When does glucose 6-phosphate accumulate?

Answer 15

When phosphofructokinase is inactive

Question 16

What inhibits and activates pyruvate kinase?

Answer 16

Inhibits - ATP and alanine inhibit allosterically (binding not at active site)
Activates - Fructose 1,6-biphosphate

Question 17

When is pyruvate kinase maximally active?

Answer 17

When energy is low and glycolytic intermediates accumulate

Question 18

What is gluconeogenesis and where does it mainly occur?

Answer 18

Synthesis of glucose from non-carb sources, such as lactate, AA’s, glycerol, and alanine produced from pyruvate. Occurs mainly in the liver.

Question 19

What new reactions are required by gluconeogenesis to bypass the irreversibility of 3 reactions in glycolysis

Answer 19

1. Pyruvate carboxylated in mito to oxaloacetate, which is then decarboxylated and phosphorylated in cyto to phosphoenolpyruvate.
2. ATP and GTP consumed.
3. Catalyzed by pyruvate carboxylase and phosphoenolpyruvate carboxykinase
4. Other new reactions are - fructose 1,6-biphosphate and glucose 6-phosphate are hydrolysed.

Question 20

How are gluconeogenesis and glycolysis linked?

Answer 20

Reciprocally regulated. One relatively inactive while other is highly active.

Question 21

What are 2 key control points in gluconeo.. and glycolysis regulation?

Answer 21

Phosphofructokinase and fructose 1,6-biphosphatase.

Question 22

What is fructose 2,6-biphosphate?

Answer 22

An intracellular signal molecule present when glucose abundant, activates glycolysis and inhibits gluconeo..by regulating the 2 key control enzymes.