Metabolism 3 & 4 Flashcards
1
Q
What are common metabolic reactions (6)
A
- oxidation-reduction → oxidation = give H⁺ & electrons, reduction = accept H⁺ & electrons
- ligation → join molecules covalently
- isomerisation
- group transfer → transfer functional groups within the same molecule
- hydrolysis → split bond via H₂O addition
- addition or removal of functional groups → removal to create a double bond or addition of a functional group across a double bond.
2
Q
What is glycolysis (7)
A
- catabolic - Complex carbs → monosaccharides
- occurs in the cytoplasm
- glucose → ATP
- aerobic /anaerobic
- 10 steps divided into two stages each with 5 steps.
- Step 1 = glucose → x2 glyceraldehyde 3-phosphate - requires energy
- Step 2 = glyceraldehyde 3-phosphate → to pyruvate via oxidation - produces energy
3
Q
Why does stage 1 of glycolysis require energy (2)
A
- Kinase enzyme catalyses the hydrolysis of the terminal phosphate group of ATP, converting it to ADP
- This makes steps 1 & 3 irreversible
4
Q
What happens in stage 1 glycolysis (5)
A
- Phosphorylation at C6 - glucose → glucose 6-phosphate (hexokinase), ATP → ADP (kinase at terminal phosphate)
- Isomerisation - glucose 6-phosphate → fructose 6-phosphate, 6-membered ring to 5-membered ring
- Phosphorylation - Fructose 6-phosphate → fructose 1,6 diphosphate ATP → ADP (kinase at terminal phosphate)
- Cleavage - fructose 1,6-diphosphate → x2 triose phosphates
- Isomerisation - dihydroxyacetone phosphate → glyceraldehyde 3-phosphate (rapid rearrangement reaction)
5
Q
What happens during stage 2 glycolysis (5)
A
- Oxidation & phosphorylation - glyceraldehyde 3-phosphate → 1,3-diphosphoglycerate (add P on C1)
- Transfer phosphate from 1,3-disphosphoglycerate to ADP to produce ATP, leaving 3-phosphoglycerate (2 ATP produced)
- Mutation - movement of phosphate 3-phosphoglycerate → 2-phosphoglycerate
- Dehydration - 2-phosphoglycerate → phosphoenolpyruvate
- Conversion - phosphoenolpyruvate → pyruvate (2 ATP produced)
6
Q
How much ATP is generated from glycolysis (3)
A
- Net gain = 2
- 2 ATP lost - stage 1
- 4 ATP produced - stage 2
7
Q
What is done to pyruvate in anaerobic and aerobic conditions
A
Anaerobic = reduced by NADH to form lactate and NAD+.
Aerobic = further metabolised in the Krebs cycle.
This prevents a lack of NAD⁺ in both conditions
8
Q
Where are the points of control in glycolysis (2)
A
- step 3 - phosphorylation of fructose 6-phosphate through kinase enzymes
- step 10 - Conversion of phosphoenolpyruvate into pyruvate through kinase enzymes
9
Q
How is acetyl-coa formed (6)
A
- Pyruvate is transported from the cytoplasm into the mitochondria.
- Oxidative decarboxylation (lose two terminal oxygens) by pyruvate dehydrogenase - pyruvate → acetyl coenzyme A (acetyl-CoA), which produces CO2 and NADH (NAD⁺ → NADH).
- pyruvate + CoA-SH → acetyl S and CoA (acetyl-CoA)
- NAD+ gains hydrogen from SH to form NADH.
- NADH is then oxidised in the electron transport chain
- Acetyle-CoA is the fuel for the Krebs Cycle.
10
Q
What happens during the Krebs Cycle stage 1 (4)
A
- Condensation- acetyl-CoA + oxaloacetate → citrate. (Point of feedback control)
- Isomerisation - alcohol group of citrate is moved to form isocitrate. Tertiary → secondary
- Oxidatative decarboxylation - alcohol is removed = ketone, CO2 is removed from isocitrate = alpha-ketoglutarate (there is also a reduction of NAD+ to form NADH facilitated by gaining the hydrogen that was removed from the alcohol to form the ketone) (NADH drives the cell to make 3 ATP)
- oxidative decarboxylation - alpha-ketoglutarate → succinyl-CoA (further reduction of NAD+ to from NADH)
11
Q
What happens during the Krebs Cycle stage 2 (4)
A
- Cleavage of thioester bond in succinyl-CoA → succinate (side reaction: GTP + ADP → ATP + GDP)
- Oxidation of succinate → fumarate
- Hydration of fumarate → malate
- Oxidation of malate → oxaloacetate
