Glycolysis Flashcards
What is the first step of glycolysis? What enzymes are involved, and what type of reaction is occurring?
Glucose converted to glucose-6-phosphate using hexokinase. Phosphorylation occurs as ATP is split to Pi and ADP.
What reaction of glycolysis is irreversible- why is this?
Phosphorylation of glucose- this commits the cell to the subsequent reaction and the negative charge traps the glucose inside the cell
What is the second step of glycolysis? Why does this occur?
Glucose-6-phosphate to fructose-6-phosphate, using phosphoglucose isomerase. When cleaved, the fructose can be split into equal halves.
What is the third step of glycolysis?
Fructose-6-phosphate is converted to fructose-1,6-bisphosphate using phosphofructokinase (PFK). One ATP is hydrolysed to form Pi and ADP
Why is regulation of phosphofructokinase needed?
It is needed to control the entry of sugars into the glycolysis pathway- to control the metabolic pathway
How many ATP molecules are used in the first half of glycolysis? During what stages?
2: Phosphorylating glucose in step 1 and phosphorylation of fructose-6-phosphate in step 3 using PFK
What happens in step 4 of glycolysis?
Fructose-1,6-bisphosphate is hydrolysed, using aldolase, to form dihydroxyacetone phosphate, and glyceraldehyde-3-phosphate.
What happens to dihydroxyacetone phosphate, formed from step 4 of glycolysis?
Isomerisation: triose phosphate isomerase (TPI) converts it to glyceraldehyde-3-phosphate, so there are 2x GP
What is the only fatal glycolytic enzymopathy?
Deficiency in triose phosphate isomerase- sufferers die within the first 6 years of their lives.
What does a kinase enzyme do?
Transfers phosphate groups
What occurs in step 6 of glycolysis?
The 2 glyceraldehyde-3-phosphates are oxidised, using glyceraldehyde-3-phosphate dehydrogenase.
NAD+ becomes NADH, as Pi is added to GP, forming 1,3-bisphosphoglycerate (x2)
What is the importance of the formation of NADH? When does this occur during glycolysis?
NADH is needed to generate more ATP during oxidative phosphorylation within the mitochondria.
NADH is made when glyceraldehyde-3-phosphate is oxidised to form 1,3-bisphosphoglycerate.
What occurs during step 7 of glycolysis?
1,3-bisphosphoglycerate has 1 phosphate group removed, using phosphoglycerate kinase. This forms ATP from ADP, and 3-phosphoglycerate.
What occurs during step 8 of glycolysis?
3-phosphoglycerate undergoes isomerisation to form 2-phosphoglycerate, using phosphoglycerate mutase
What occurs during step 9 of glycolysis?
2-phosphoglycerate undergoes dehydration, to form phosphoenolpyruvate, using the enzyme enolase.
What is the last step of glycolysis?
Phosphoenolpyruvate has 1 phosphate removed, using pyruvate kinase. This forms pyruvate, and ATP from ADP.
What is the net gain of ATP from glycolysis of one glucose molecule? Explain why this occurs
2 ATP molecules:
One ATP is used to phosphorylate glucose, and another to phosphorylate fructose-6-phosphate.
When 1,3-bisphosphoglycerate becomes 3-phosphoglycerate, one Pi is removed to form ATP (x2). When phosphoenolpyruvate becomes pyruvate, one Pi is removed and added to ADP, forming ATP (x2).
What are the products from glycolysis of one glucose molecule?
2 ATP & 2 NADH (from oxidation of 2 molecules of glyceraldehyde-3-phosphate)
Where does glycolysis occur?
In the cytosol
Is glycolysis aerobic or anaerobic?
Anaerobic- it takes place even when there is no oxygen
What 2 main concepts occur during glycolysis?
First, the formation of 2 high energy compounds (G3P) using ATP.
Then, the splitting of these compounds to generate ATP
What types of reaction are occurring in all 10 steps of glycolysis (in order)?
1) Phosphorylation/group transfer
2) Isomerisation
3) Phosphorylation/group transfer
4) Hydrolysis
5) Isomerisation
6) Redox & phosphorylation/group transfer
7) Group transfer (phosphate removal)
8) Isomerisation
9) Dehydration (group removal)
10) Group transfer (phosphate removal)
What is the only part of glycolysis that requires the coenzyme NAD+?
The oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, forming NADH also
Why is glucose-6-phosphate committed to the rest of the metabolic pathway?
Glucose-6-phosphate will not bind to the glucose transporter proteins, so will not leave the cell
Why is transportation of NADH into the mitochondria needed?
So, during oxidative phosphorylation more reduced cofactors can be reoxidised, forming more ATP. Also, the NAD+ made can be used for glycolysis (anaerobic conditions in particular)
How is NADH transported into the mitochondria?
Only the electrons are moved!! The glycerol phosphate shuttle for the skeletal muscle and brain, and the malate-aspartate shuttle for the liver, kidney and heart
How do shuttles work?
Cytoplasmic and mitochondrial forms of the same enzyme, to translocate high energy electrons.
Why can NADH not move into the mitochondria?
Inner membrane is impermeable to NADH/NAD+, so the electrons alone are moved
How may defects in TCA cycle occur? What occurs due to these defects?
Mutations of TCA genes coding for certain enzymes reduces activity of the TCA cycle. So, lactate generation tends to occur even when there is abundant oxygen.
