Metabolism 2: glycolysis (Miss Dawson) Flashcards
What is glycolysis ?
Glycolysis is the first step in the breakdown of glucose. It allows the cell to produce NRG, reducing power and carbon compounds that can be used for synthesis or work.
What makes glycolysis unique ?
It is the only way to produce TAP w/o using mitochondria or oxygen. However, only about 10% of glucose’s NRG can be released in this way.
What are the sources of glucose in the fed state ?
The fasting/exercice state ?
The starvation state ?
Fed state: glucose from digestion
Exercice/fasting: glycogen
Starvation : Gluconeogenesis (lactate, AAs, glycerol)
Which enzyme breaks down a part of the glycogen chain into glucose-1 phosphate ?
Glycogen phosphorylase.
Which enzyme converts glucose-1 phosphate to glucose-6 phosphate ?
Phospho-glucomutase.
What are the final product of glycolysis ?
2 pyruvate molecules, to ATPs (net) and two NADHs.
What happens to NADH in aerobic conditions ?
In anaerobic conditions ?
With O2, NADH in can be oxidized back to NAD+ in the mitochondrion.
W/o O2, NADH is oxidized back to NAD+ as it serves as a coenzymes to lactate dehydrogenase, which converts pyruvate into lactate.
In yeast, pyruvate is directly converted into actetyldehyde and NADH is converted to NAD+ while acetaldehyde is converted into ethanol.
In humans, which tissues produce the most lactate ?
Red blood cells and exercising white muscles. The liver takes up the lactate and can use the three Cs for gluconeogenesis (which also requires NRG).
Show all the steps of glycolysis.
- Glucose phosphorylate to G6P by hexokinase. 1 ATP required
- G6P converted to F6P by phosphoglucose isomerase.
- F6P converted to F1,6bP by phosphofructokinase. 1 tap required.
- F1,6bP broken into dihydroxyacetone-phosphate and glyceraldehyde-3-phosphate by fructose biphosphate aldose.
- Dihydroxyacetone-phosphate converted to glyceraldehyde-3-phosphate by triose phosphate isomerase.
- Glyceraldehyde-3-phosphate converted to 1,3-biphosphoglycerate by glyceraldehyde-3-phosphate dehydrogenase. 1 (NADH+ + H+) produced.
- 1,3-biphosphoglycerate converted to 3-phosphoglycerate by phosphoglycerate kinase. 1 ATP produced
- 3-phosphglycerate converted to 2-phosphglycerate by phosphoglycerate mutase.
- 2-phosphoglycerate mutase converted to phosphoenolpyruvate (PEP). 1 H2O released
- PEP converted to pyruvate by pyruvate kinase. 1 ATP produced.
Steps 6 to 10 happen twice because F1,6bP is broken into two parts at step 4
Glycolysis produced two NADH molecules. How many ATP can these produced when oxidized in the mitochondrial respiratory chain ?
5 ATPs
What does glycolysis produce in anaerobic conditions ?
2 lactate molecules that can be reoxidized in the liver and converted to glucose.
What does glycolysis regulate and how can it be monitored ?
Glycolysis can be used to bring down the glucose levels in the blood. It can be inhibited in some tissues to save glucose for other that need it more. Glycolysis provided NRG to cells that have now/few mitochondria and low O2 supply. It also breaks down glucose so that it can be used for fat synthesis.
What is the most important regulatory enzyme in glycolysis ?
Phosphofructokinase-1 ! This enzyme is the major flux controller in muscle ! It is allosterically enhanced by AMP, and inhibited by ATP, citrate and low pH (acidification due to lactate formation).
How does glycolysis vary in the key organs in the fed state ?
Sk muscle: glycolysis increases, FA breakdown decreases
Adipose tissue: glucose taken up and broken down for fat synthesis
Small intestine: release glucose from direction in the blood
Liver: receives glucose first:, glycolysis increases, also gluconeogenesis and fat synthesis
How does glycolysis vary in the key organs during exercise ?
Sk muscle: glucose is taken up form the blood, glycogen stores broken down, glycolysis increases and lactate is produced
Liver: glycogen breakdown is stimulated and the glucose is released into the blood
