lecture 19 biochem citric acid cycle

What is the part of the citrate synthase that is most exergonic and provides the driving force for the reaction?

• the breaking of thioester bonds (thioester hydrolysis)

• after the first step from acetyl coA+Oxaloacetate

what is the least abundant intermediates in the mitochondria

oxaloacetate (most oxidized)

why is the intermediate the least abundant

Acetly CoA is used up to drive reaction for citrate synthase

what enzyme from the citric acid cycle is most similar to pyruvate dehydrogenase?

α-ketoglutarate dehydrogenase

what happens to the two carbons that enter the citric acid cycle as acetyl CoA

Neither of the two carbons that enter the citric acid cycle as acetyl CoA are removed as CO2 in the first round of citric acid cycle.

how many carbons enter and leave the citric acid cycle

• 2 enter from acetly CoA

• 2 are released as CO2

in what steps of the citric acid cycle are CO2 produced

• isocitrate oxidized to α-ketoglutamine

• α-ketoglutarate is further oxidized to succinyl-CoA

Which reactions in the citric acid cycle produces ATP in heart muscle by substrate level phosphorylation?

Succinyl-CoA synthetase

what is substrate level phoshorolation

ATP is formed by the direct transfer of a phosphate group to ADP from a substrate or reactive metabolite

Which enzymes of the citric acid cycle is an integral membrane protein

 

Succinate dehydrogenase

What compound inhibits many steps in the citric acid cycle

NADH

what determines where regulation occurs

steps with the largest free energy drops

what are the 3 regulators

• citrate synthase

• isocitrate dehydrogenase

• α-ketoglutarate

what are the activators of citrate synthase

ADP

what are the inhibitors of citrate synthase

• citrate

• NADH

• succinyl CoA

• ATP

activators of isocitrate dehydrogenase

• Ca2+

• ADP

inhibitors of isocitrate dehydrogenase

ATP

activator of α-ketoglutarate

Ca2+

inhibitors of α-ketoglutarate

• NADH

• succinyl CoA

how many electrons are lost in the cycle

8

to what electron carriers are the lost electrons transffered to

3 NADH, 1 FADH2 (4 pairs), allow complete oxidation of acetyl CoA to co2

which enzymes are producing the reducing agents

icocitrate dehydrogenase (NADH), a-ketoglutarate dehydrogenase (NADH), succinate dehydrogenase (FADH2), malate dehydrogenase (NADH)

cataplerotic

removes/depletes intermediates from the cycle (mito). are precursors for other compounds

anaplerotic

build up intermediates, needed when the cycle is depleted from other biosynthetic pathways

pyruvate carboxylase

replenishes the cycle by converting pyruvate to oxaloacetate (anaplerotic)

what does the glycerophosphate shuttle do

• restored NAD+ for glycolysis

• uses 1 of 2 NADH from NADH produced in the cytoplasm by glycolysis

• done in the skeletal muscle and brain

where does the glycerophosphate shuttle occur

cytosol, inner mitochondrial matrix

what does 3-phosphoglycerol dehydrogenase do in the glycerophosphate shuttle

• oxidizes NADH to restore NAD+ for glycolysis

• simultaneously reduces dihydroxyacetone phosphate to 3-phosphoglycerol

what does flavoprotein dehydrogenase do in the glycerophosphate shuttle

reduces FAD to FADH2 (2 e- gained)

where do the 2e- from FADH2 get transferred to in the glycerophosphate shuttle

to the ETC at complex II

what does the malate aspartate shuttle do

• shuttle for NADH that does not cost ATP from the cytosol into the mitochondria

• uses 1 of 2 NADH from NADH produced in the cytoplasm by glycolysis

• important in the heart and liver

malate shuttle function

from cytosol into matrix, malate is exchanged for a-ketoglutamine (an antiporter = passive transporter)

aspartate shuttle function AGC

from matrix to cytosol, aspartate is exchanged for glutamate (AGC aspartate glutamate carrier, antiporter)

role of oxaloacetate in the malate aspartate shuttle

key intermediate in the cytosol reduced to malate to enter the matrix, oxidized back to oxaloacetate to regenerate NADH for the ETC