Biochem Lecture 12- Citric Acid Cycle

Citric Acid Cycle

Completes the breakdown of glucose by oxidizing a derivative of pyruvate to carbon dioxide, including the biproducts of NADH and FADH2

Acetyl CoA

the entry compound for the citric acid cycle in cellular respiration, formed from a fragment of pyruvate attached to a coenzyme.

Pyruvate Dehydrogenase Complex

Pyruvate is converted to Acetyl CoA by this enzyme omplex (made up of E1, E2, E3)

TPP

This reacts with pyruavte in E1 on way to form Acetyl CoA

NAD+, NADH

In the process of turning pyruvate into Acetyl CoA, _________ is reduced to __________

inactive

Regulation of pyruvate dehydrogenase happens on E1, if the E1 is phosphorylated, then it is ____________(active/inactive)

Active

Regulation of pyruvate dehydrogenase happens on E1, if the E1 is dephosphorylated, then it is ____________(active/inactive)

Thioester

the formation of the ______________ on Acetyl coA makes it "activated"

Acetyl-CoA, Oxaloacetate, citrate

"Step 1" of CAC starts with _____________-________ reacting with ____________________ to form ________________

Rate limiting step

Acetyl CoA + Oxaloacetate -> Citrate is the __________ _______________ _____ of the CAC

C-C

Acetyl CoA + Oxaloacetate -> Citrate is the only reaction with a __-___ bond formation

favorable, irreversible

Acetyl CoA + Oxaloacetate -> Citrate is highly ___________(favorable/not favorable) and _________________(reversible/irreversible)

Isocitrate

In the next step of CAC, Citrate is isomerized to _____________

Not favorable

Citrate -> Isocitrate is energetically _______________(favorable/not favorable)

Reactant

Citrate -> Isocitrate is driven by a very high ________________(reactant/product) concentration

alpha-ketoglutarate, NADH, CO2

After isomerization, isocitrate reacts to form ____-_______________________, and has biproducts of ___________ and _____

Isocitrate dehydrogenase

enzyme that converts isocitrate to alpha-ketoglutarate

6, 5

Citrate and Isocitrate have ___(how many?) carbons, but after it is converted to alpha-ketoglutarate, that molecule has ___(how many?) carbons

Succinyl-CoA, NADH, CO2

after alpha-ketoglutarate is formed, it is converted into ________________-______, and gives biproducts of ________ and _____

6, 5, 4

Citrate and Isocitrate have ___(how many?) carbons, but after it is converted to alpha-ketoglutarate, that molecule has ___(how many?) carbons, and after that is converted to succinyl-CoA, it has ____(how many?) carbons

Favorable, irreversible

Alpha-ketoglutarate -> succinyl CoA is highly thermodynamically ____________(favorable/not favorable) and is ______________(reversible/irreversible)

Succinate, GTP

Succinyl-CoA is converted into ___________, and gives off a molecule of _________ in the process

Product, low

Succinate formation is only slightly thermodynamically favorable, and it is driven forward by keeping the ______________(reactant/product) concentration _______(low/high)

Fumarate, FADH2

After succinate is formed, it is converted into ______________ and gives off one molecule of ___________ in the process

not favorable, product, low

Succinate -> Fumarate is thermodynamically _______________(favorable/not favorable) and it is driven forward by keeping the ___________(product/reactant) concentration ______(high/low)

L-Malate, Fumarase

Fumarate is then converted to __-_________ by the enzyme ___________

Reversible, product, low

Fumarate -> L-Malate is ______________(reversible/irreversible) and it is driven forward by keeping the ______________(reactant/product) concentration _______(high/low)

Oxaloacetate, NADH

The "final" step of the CAC convertes L-Malate into __________________, and gives off one molecule of __________ in the process

Unfavorable, Acetyl-CoA, favorable

L-Malate -> Oxaloacetate is highly thermodynamically ______________(favorable/unfavorable) and this reaction is driven forward because oxaloacetate is immediately reacts with ___________-_____ in the next step of the CAC, which his highly ___________(favorable/unfavorable)

3 NADH, 1 FADH2, 1 GTP

In one turn of the citric acid cycle, how many NADH, FADH2, and GTP are made?

4 NADH, 1 FADH2, 1 GTP

From one molecule of pyruvate, how many NADH, FADH2, and GTP are made from the formation of Acetyl-CoA and 1 turn of CAC?

NADH and ATP

these are the two regulators of the CAC

Activated

At very low levels of NADH and ATP, the CAC is ____________(activated/inhibited)

Inhibited

At very high levels of NADH and ATP, the CAC is ____________(activated/inhibited)

Activated

At high levels of NAD+ and AMP, the CAC is ___________(activated/inhibited)

acetyl-Coa

CO2

One turn of the CAC oxidized 1 ____ ____ and releases 2 ____

pyruvate dehydrogenase (pyruvate → acetyl coa)

citrate synthase (oxaloacetate → citracte)

isocitrate dehydrogenase (isocitrate → AKG)

AKG dehydrogenase (AKG -> succinyl coA)

what are the energetically favorable/regulated steps of the CAC

Irreversible, negative

regulated steps of the CAC are _____ (reversible/irreversible) and have a (positive/negative) delta G

acetate becomes activated when it is attached to CoA —→ Acetyl-CoA

occurs through the formation of a thioester bond

How is acetate activated?

substrate

CAC is activated by _____ availability

replenishes the CAC intermediates that are drawn off for biosynthesis (fill up cycle)

anaplerotic reaction

remove intermediates for use in other pathways (drain cycle)

cataperotc reaction