7.b Carbohydrate metabolism 1: glycolysis

Question 1

Hexokinase is an important enzyme for which step of the glycolysis? And why?

Answer 1

First step.
Because there are many isoforms.

Question 2

Tell about hexokinases 1 -4 in terms of Km. What is the name of no 4?

Answer 2

Isomers 1-3 have low Km’s (high affinity)
Isomer 4 has a high Km, only active is there are very high glucose concentrations. Mainly present in liver, pancreas, hypothalamus and small intestine (very metabolically active).
Name = glucokinase

Question 3

Why is it useful to have an enzyme with such a high Km (low affinity)?

Answer 3

 At high glucose levels, hexokinases 1-3 are still working but they cannot increase their activity more.

Glucokinase can increase its enzyme activity along with the increasing glucose concentration

Question 4

What happens at step 2 of glycolysis? (use metabolic map)

Answer 4

2. Glucose-6-ph -> isomerization -> fructose 6-phosphate (no energy)

Question 5

What happens at step 3 of glycolysis? (use metabolic map)

Answer 5

3. Fructose-6-ph > phosphorylation > fructose 1,6-bisphosphate. 1 ATP needed.

Question 6

What happens at step 4 of glycolysis? (use metabolic map)

Answer 6

Cleavage -> 2x glyceraldehyde-3-p

Using aldolase, fructose-1,6-bisphosphate is cleaved into DHAP which can be easily converted into glyceraldehyde-3-ph. In the end, you mostly end up with 2x glyceraldehyde-3-p
(no energy)

Question 7

What happens at step 5 of glycolysis? (use metabolic map)

Answer 7

5. Oxidation of 2x glyceraldehyde-3-phosphate -> 2x bisphosphoglycerate. YIELDS cytoplasmic NADH: 1.5 ATP x 2 = 3 ATP

Question 8

What happens at step 6 of glycolysis? (use metabolic map)

Answer 8

6. Substrate-level phosphorylation = Direct 1 ATP generation in one single step. x2 = 2 ATP

Question 9

What happens at step 7 of glycolysis? (use metabolic map)

Answer 9

7. Isomerization step: rearranging the phosphate groups from 2x 3-phosphoglycerate to 2x 2-phosphoglycerate (no energy)

Question 10

What happens at step 8 of glycolysis? (use metabolic map)

Answer 10

8. Dehydration: H2O Is released. 2x Phospho-endolpyruvate (PEP) generated. No energy

Question 11

What happens at step 9 of glycolysis? (use metabolic map)

Answer 11

9. PEP -> pyruvate. Substrate-level phosphorylation, because in one step you generate the ATP. x2 = 2 ATP. FINAL STEP = ONE-WAY ONLY!!!

Question 12

Via what shuttle can reducing equivalents (NADH) be transported into the cytoplasm?

Answer 12

glycerophosphate shuttle. ATP yield = 1.5 ATP

Question 13

Where can you find the glycerophosphate shuttle?

Answer 13

Outer mitochondiral membrane, at the oxidative phosphorylation site by glycerol-3-phosphate dehydrogenase

Question 14

Regulatio of glycolysis: what is the most regulated enzyme? How is it regulated?

Answer 14

PFK1 = phosphofructokinase 1. 3rd step.

AMP = upregulation of glycolysis
ATP + citrate + acetyl-CoA = downregulation

Question 15

Glycolysis -> pyruvate =
TCA cycle =
Pyruvate -> acetyl-CoA =

Cytoplasmic/mito?

Answer 15

Glycolysis to pyruvate: cytoplasmic
TCA cycle uses Acetyl-CoA: mitochondrial
Pyruvate -> acetyl-CoA: mitochondria

Question 16

Pyruvate -> AcetylCoA
Mitochondial oxidation of pyruvate: happens with PDH pyruvate dehydrogenate multi-enzyme complex. what is released in this step?

Answer 16

2x CO2, 2x NADHm

Question 17

What is the ATP yield of glucose oxidation?

Answer 17

30 ATP
glucose -> 2 pyruvate = -2+4+3 = 5 ATP
2 pyruvate -> 2 acetyl-CoA = 2x2.5= 5 ATP
2 acetyl-CoA = 2 cycles = 20 ATP

= 30