Chapter 12 Flashcards
Where does the citric acid cycle occur within the cell?
Mitochondria
Where are mitochondria most abundant in the body?
Muscle and liver cells
Why cant RBCs generate energy from the CAC?
They lack of mitochondria
Where do RBCs get energy from?
Glycolosis
Where are the enzymes for CAC located?
In the mitochondrial matrix
Why is the CAC considered part of the aerobic metabolic process?
Because of its link to the electron transport chain and oxidative phosphorylation
What coenzymes are generated by the CAC?
NADH and FADH2
they pass their electrons to oxygen to generate energy for the cell
Where do the reduced coenzymes from CAC go?
Electron transport chain
Where does glycolysis occur in the cell?
Cytoplasm
Where is succinate dehydrogenase located?
In the inner membrane of the mitochondria
Where must pyruvate travel to for the CAC?
From the cytosol into the mitochondrial matrix through a transporter in the inner membrane
Where does oxidative phosphorylation occur?
Inner membrane of the mitochondria
What must be activated for it to enter the CAC?
Pyruvate must be activated to acetyl-CoA
reactive thiol group that has higher energy bonds
What happens during conversion of pyruvate to Acetyl-CoA?
Oxidative decarboxylation of pyruvate (irreversible oxidation)
First carbons of glucose to be fully oxidized
What catalyzes the conversion of pyruvate to acetyl-coa?
Pyruvate dehydrogenase complex (3 enzyme complex)
What are the prosthetic groups of the pyruvate dehydrogenase complex?
TPP
Lipoyllysine
FAD
What are the co-substrates for pyruvate dehydrogenase complex?
NAD+ and CoA-SH
What is removed from pyruvate as CO2 by pyruvate dehydrogenase?
Carboxyl group
How many coenzymes are required by pyruvate dehydrogenase complex?
5 coenzymes
Is conversion of pyruvate to Acetyl-CoA reversible?
No it is irreversible
What are the products of converting pyruvate to acetyl-CoA?
Acetyl-CoA
NADH
What do the 5 coenzymes of pyruvate dehydrogenase complex do?
Assist in transfer of functional groups
What do the 5 coenzymes for pyruvate dehydrogenase complex act as?
Oxidants or carriers for intermediates of this enzyme complex
What kind of complex is PDC?
A large multienzyme complex
What are the three enzymes in PDC?
Pyruvate dehydrogenase (E1) Dihydrolipoyl transacetylase (E2) Dihydrolipoyl dehydrogenase (E3)
What are the advantages of a multienzyme complex?
Short distance between catalytic sites allows channeling of substrates from one catalytic site to another
Channeling minimizes side reactions
The regulation of activity of one subunit affects the entire complex
What is the first step of CAC?
The C-C bond formation between acetate(2C) and oxaloacetate(4C) to make citrate (6C)
Releases CoA-SH
Claisen condensation
What is the second step in the CAC?
Isomerization via dehydration/rehydration to make isocitrate
Release water
What does steps 3-4 of CAC do?
Oxidative decarboxylations to give 2 NADH
Release of 2 CO2
Makes alpha-ketoglutarate (3)
and Succinyl CoA
What happens in step 5 of CAC?
Substrate-level phosphorylation to make succinate
Gives GTP from GDP
Makes CoA-SH
What does step 6 of CAC do?
Dehydrogenation to give FADH2 to make fumerate
What does step 7 of CAC do?
Hydration to make malate
What happens in step 8 of CAC?
Dehydrogenation to give NADH
Makes oxaloacetate
What is the mnemonic for CAC?
Citrate Is Krebs Starting Substrate For Making Oxaloacetate
In step one how is acetyl-CoA and Oxaloacetate combined?
By condensation
Is step one favorable or unfavorable?
Favorable and irreversible
What is step 1 of CAC regulated by?
Substrate availability
What is step one of CAC inhibited by?
Increased concentrations of ATP, NADH, Citrate, Succinyl CoA
What is step 1 of CAC stimulated by?
ADP
What is unique about step 1 of CAC?
It is the only reaction with a C-C bond formation
What does the activity of Step 1 of CAC depend on?
Oxaloacetate
What is the first part of step 2 of CAC?
Loss of water (dehydration) from citrate to give a cis C-C double bond
What kind of alcohol is citrate?
A tertiary alcohol
poor substrate for oxidation so needs to be changed
What is the second part of step 2 of CAC?
Inserting water to cis-aconitate to make isocitrate
What kind of alcohol is isocitrate?
A secondary alcohol
good substrate for oxidation
What kind of reaction is the second step in CAC?
Dehydration - hydration reaction
Is step 2 favorable?
No it is unfavorable and reversible
What pulls step 2 forward?
Product concentration kept low
What is produced in step 3?
NADH is produced
What inhibits step 3 of CAC?
high levels of ATP or NADH
What kind of reaction is step 3 ?
Oxidation and decarboxylation
What stimulates step 3 of CAC?
ADP and Ca+2
What is released in step 3 of CAC?
Carbon dioxide
