kreb cycle

what is the Krebs cycle what helps run it

8 step process, each step catalyzed by an ENZYME

Why kind of process is it (name) + why is it that?

CYCLIC PROCESS

• because oxaloacetate (product of step 8) is the reactant in step 1

What happens to the entire glucose molecule? What is preserved?

it is ENTIRELY consumed, 6 carbon atoms LEAVE the process as a six low energy CO2

Preserved:

• most of its energy (4 ATP, 10 NADH, 2 FADH₂)

What will happen to some of the products?

• NADH and FADH2 will be converted to ATP at the e.t.c by chemiosmosis

What happens before the kreb cycle? What happens during this step and what is the purpose of it?

Pyruvate oxidation

purpose: convert pyruvate into acetyl coA so it can enter the kreb cycle

Process:

1) pyruvate enters the mitochondrion from the cytoplasm

2) Decarboxylation: pyruvate loses ONE carbon → REMOVED AS CO2

3) Electron (H+) is removed by NAD+ (carries to ETC)

4) Coenzyme A attaches to the 2 carbon molecule FORMS ACETYL CO A that enters krebs

What are the products in pyruvate oxidation per glucose molecule?

Per ONE glucose (2 pyruvates):

• 2 Acetyl-CoA

• 2 NADH

• 2 CO₂

What are the steps in kreb cycle?

Step 1: Acetyl CoA + Oxaloacetate → citrate

• acetyl coA brings 2 carbons into the cycle

• oxaloacetate has 4 carbons

• they combine to form citrate (6 carbons)

• coenzyme A is released

Step 2: Citrate → isocitrate

• isomerization into isocitrate

Step 3: Isocitrate → alpha-ketoglutarate

• One carbon is lost as Co2

• Nad+ gains electrons

OXIDATIVE (NAD) DECARBOXYLATION (CARBON REMOVED)

step 4: same as step 3, coenzyme A is attached to the remaining 4 carbon molecule

• succinyl co A is formed

Step 5: substrate level phosphorylation

• coenzyme A is removed

• ATP is produced through substrate-level phosphorylation.

step 6: FAD STEP

• Succinate is oxidized.

  FAD accepts electrons and hydrogen.

  FAD becomes FADH₂.

Step 7; hydration

• The enzyme is fumarase.

  Water (H₂O) is added to fumarate.

  This produces malate.

step 8:

• Malate is oxidized.

  NAD⁺ accepts electrons and becomes NADH.

  Oxaloacetate is regenerated.