Biochem Of Met, Block 2, #2: Tca Cycle And Associated Reactions

Front 1

What's the first part of the TCA cycle? Why is it interesting?

Back 1

Combining oxaloacetate and acetyl co-A into Citrate, catalyzed by citrate synthase!

this commits acetyl Co-A to the TCA cycle, can't be reversed. CoASH is released from the reaction.

Front 2

What's the 2nd reaction of TCA?

Back 2

conversion of citrate to isocitrate by ACONITASE. This simply moves the hydroxyl group from the middle to the bottom, so it can be oxidized to a keto group next time.

Front 3

What's the 3rd reaction of TCA? Why is it special?

Back 3

this is the first redox of the TCA.

Isocitrate to alpha-ketogluterate, via ISOCITRATE DEHYDROGENASE.

NOTE: this makes a Co2, also NADH. Also irreversible.

Front 4

What is the 4th reaction of the TCA? Why special?

Back 4

Alpha-Ketogluterate to Succnyl-CoA bya Alpha Ketogluterate Dehydrogenase Complex. Requires catalyst.

Get an NADH out of it.

Front 5

What is the 5th reaction of TCA?

Back 5

Succnyl Co-A to Succinate, via Succinyl CoA Syntnthetase (or thiokinase).

Get production of GTP

Front 6

6th reaction of TCA: why weird?

Back 6

Succinate to Fumarate via Succinate Dehydrogenase. Get FADH2 produced.

NOTE: this is the only enzyme bound to the inner mito membrane, meaning the FADH2 electrons get put directly into the ETC without needing an intermediate.

Front 7

7 and 8 reactions: What's up?

Back 7

regenerating oxaloacetate.

Fumarate to malate via fumarase,

malate to oxaloacetate via malate dehydrogenase. (get NADH made here).

Front 8

Regulation of the TCA: what's up?

Back 8

Easy: main negative regulator is NADH, main positive regulator is ADP.

Note that citrate feeds back on the enzyme that made it, citrate synthase, in the 1st step.

Also note that the CAC can never be totally shut down - its intermediates are ingredients all over the cell.

Limited mostly by how fast E- can enter the ETC.

Front 9

How are ingredients in the TCA replaced, and what enzyme matters?

Back 9

these are anaplerotic reactions: pyruvate carboxylase is the most important re-generator of TCA intermediates. It's the same one used in gluconeogenesis and requires BIOTIN as a cofactor!!!

Glutemate can be reversed into alpha ketogluterate, and leucine/isoleucine can go back and be succnyl CoA.

Front 10

How are the NADH's made in glycolyis brought into the mito matrix?

Back 10

Can't go on their own, need to be shuttled.

Glycerol phosphate shuttle (1.5 ATP) and the malate-asparate shuttle (2.5 ATP).

Front 11

What's interesting about the glycerol phosphate shuttle?

Back 11

It's present in most tissues, yields 1.5 ATP because it generates FADH2.

Front 12

What's interesting about the malate asparate shuttle?

Back 12

found mostly in the liver, generates 2.5 ATP because it creates NADH.