l4 - THE KREBS CYCLE

Question 1

Whats aceytyl co-a

Answer 1

a central molecule in the enrgy metablism
all molecules that are catbolized for energy are converted into aceytyl-coA including proteins lipids and carbs.
- can be used to produce atp or fat
- the pathway taken by aceytl COA depends on the levels of ATP in the cell.
low ATP means aceytl CoA goes into krebs
HIGH ATP means aceytl coA goes on to produce lipids

Question 2

The krebs cycle

Answer 2

it is a cyclical process in that oxaloacetate reacts with aceytl CoA to form citrate which starts a series of several other reactions
the final reacion in the series involves regeneration of oxloacetate
- the krebs cycle turns twice for EVERY MOLECULE OF GLUCOSE and once for every molecule of aceytl CO-A

Question 3

reaction 1 - condensation

Answer 3

the aceytl group 2-c of aceytl co-A condenses with oxaloacetate to form citrate (c-6)

Question 4

reaction 2 and 3: isomerization

Answer 4

in a two step reaction, citrate (6-c) rearranges to form isocitrate (6-C)

Question 5

reaction 4: the first oxidation

Answer 5

isocitrate (6-C) becomes ox-ketoglutarate (5-c) because:
- a carbon dioxide molecule is removed
isocitrate is oxidized and NAD+ is reduced to NADh

Question 6

reaction 5: the second oxidation

Answer 6

• ox-ketoglutarate (5-C) becomes succinyl-Coa )4-C) because:
  a carbon dioxide molecule is removed
  ox-ketoglutarate is oxidized and NAD+ is reduced to NADH
  coenzyme A is reattached

Question 7

reaction 6: substrate level phosphorylation

Answer 7

succinyl-coa becomes succinate (4-c)
the steps:
- a phosphate group is added to succinyl co a as a conenyzme a leaves
- the departure of coenzyme a provides the energy to attach the phosphate group to GDP producing GTP (an energy carrying mole,cule)
- the terminal phosphate group from GTP is then transferred to ADP to produce ATP

Question 8

7: the third oxidation

Answer 8

• succinate (4-c) is converted to fumarate (4-c) because:
  succinate is oxidized and FADD is reduced to FADH2

Question 9

reaction 8 : hydration

Answer 9

fumarate (4-c) reacts with water to produce malate (4-c)

Question 10

reaction 9 : the fourth oxidation

Answer 10

malate (4-c) is converted to oxaloacetate(4-c) because:
malate is oxidized and nad+ is reduced to NADH
- the final product is oxaloacetate. this makes thepathway cyclical, oxaloacetate is regenerated and ready to react with more acetyl co a entering the krebs cycle

Question 11

krebs cycle summary

Answer 11

for every turn,
1 ATP is produced, 3 NADH, 1FADH, 2 CO2 and 1 H2O
for every molecule of glucose, its double.

Question 12

what happens to the original glucose?

Answer 12

ultimately, the 6 carbon atoms of glucose are released in the form of 6 carbon dioxide molecules.
2 carbon dioxide were released in pyruvate oxidation
4 co2 was released in krebs cycle
the energy from the breakdown of glucose is in the form of:
- 4 atp molecules (2 from glycolysis, 2 from krebs)
- 10 NADH molecuels, (2 from glycolysis, 2 from pyruvate, and 6 from krebs)
2 FADH2 molecules(from krebs.
the 2 nadh molecuels from glyycolysis give up their electrons to FAD inside the mitochondria because nADH cannot get into the mitocondria, therefore, we will now say we have 8 NADH and 4 FADH2