10.1-10.2 Step 0 of citrate cycle Flashcards
where does the citrate cycle take place?
in the mitochondria
what has to happen before the citrate cycle begins related to where it takes place?
pyruvate must be transported into the mitochondria
how does pyruvate get to the mitochondria?
via a transmembrane transporter protein
what happens when energy charge is low regarding the citrate cycle?
pyruvate is metabolized by pyruvate dehydrogenase to form acetyl CoA and CO2
what are the 5 coenzymes needed for pyruvate dehydrogenase’s function os converting pyruvate to acetyl-CoA
- NAD+/NADH
- FAD/FADH2
- CoA/CoAsh
- TPP
- alpha-lipoic acid
what does NAD stand for?
nicotinamide adenine dinucleotide
what is NAD+/NADH derived from?
niacin (vitamin B3)
how many reactions is NAD+/NADH involved in?
over 200
what does NAD+/NADH do? (how work?)
transfers to electrons at once as a hydride ion
what is a niacin deficiency called?
pellagra
what are 3 symptoms of pellagra? (niacin deficiency)
- diarrhea
- skin rash
- neurologic problems
what 3 food sources contain niacin?
- fish
- vegetables
- poultry
what does FAD stand for?
flavin adenine dinucleotide
what is FAD/FADH2 derived from?
riboflavin (vitamin B2)
what does FAD/FADH2 contribute to?
flavoproteins
how is FAD reduced to FADH2? what is an advantage of this?
one electron at a time with a semiquinone intermediate; gives flexibility
what is a riboflavin deficiency called?
cheliosis
what are 2 symptoms of cheilosis (riboflavin deficiency)
swelled lips, cracked lips
what foods contain riboflavin? (3)
- almonds
- meat
- dairy
what destroys riboflavin? how can this be applied to dairy storage?
light destroys riboflavin; this is why all dairy products are stored in opaque containers
what is CoA/CoAsh derived from?
pantothenic acid (vitamin B5)
what does CoA/CoAsh do?
serves as a cofactor in production of fatty acids, acetylcholine, heme, and cholesterol
what is CoA/CoAsh required for?
required for energy conversion in the citrate cycle
what is the explicit function of CoA/CoAsh?
removes acetyl group from lipoamide
is a pantothenic acid deficiency common? why or why not?
rare, found in most foods inclduing chicken, yogurt, and avocado
can CoA cross the cell membrane? what must be done if not?
nope; CoA must first be degraded by enzymes to pantothenic acid, which travels through the circulatory system and can cross cell membranes; once inside the cell the pantothenic acid is converted back to CoA by ATP and cysteine addition
what is TPP?
thiamine pyrophosphate
where is TPP derived from?
thiamine (vitamin B1)
what happens to TPP?
it is absorbed in the gut and then phosphorylated
what is the function of TPP?
pulls the acetyl group off of pyruvate
what is a thiamine deficiency called?
Beriberi
what are 3 symptoms of beriberi?
- anorexia
- cardiovascular problems
- neurologic problems
where can thiamine be found naturally?
in brown rice and fortified grains
what does milling rice do?
removed the bran and thiamine
what does thiaminase do? where is it found?
degrades thiamine; found in raw fish and raw silkworms
where is alpha-lipoic acid/lipoamide found? (2)
- synthesized in plants and animals
- also found in broccoli, liver, spinach, and tomato
what does lipoamide do?
provides reactive disulphide for redox reactions
what is the explicit function of lipoamide?
transfers acetyl group to CoA (the ball in the mechanism)
give the full reaction equation for step 0 of the citric acid cycle
pyruvate + CoA + NAD+ double arrow (reversible rxn) acetyl-CoA + CO2 + NADH + H+
describethe 6 steps of the pyruvate dehydrogenase mechanism
- pyruvate migrates from the cytoplasm to the mitochondria, where it is free floating until it meets E1
- the acetyl group is transferred from pyruvate to TPP and CO2 leaves
- the TPP with the acetyl group reacts with lipoamide and gives the acetyl group to the lipoamide
4.the lipoamide then gives the acetyl group to CoA, making acetyl-CoA that leaves - lipoamide gives 2 H from its SH to reduce FAD to FADH2, which then gives its electron tto reduce NAD+ to NADH, which leaves
- FADH2 is reoxidized back to FADH, which helps regnerate lipoamide for the next pyruvate
describe how lipoamide acts like the ball in the ball and chain pyruvate dehydrogenase mechanism
the E2 lipoamide picks up the acetyl group from the E1 TPP and then delivers the acetyl group to CoA in the E2 catalytic domain (swings back and forth)
what is oxidation?
loss of electrons
what is reduction?
gain of electrons
what is an oxidant? (3)
- a compound that oxidizes other molecules
- accepts electrons
- is reduced
what is a reductant? (3)
- a compound that reduces other molecules
- donates electrons
- is oxidized
what is reduction potential? (E)
the tendency of a molecule to gain electrons
describe the free energy of the citric acid cycle and what this means?
highly exergonic! low delta G so very favorable
what is reduction potential driven by?
free energy
describe the relationship between reduction potential (E) and free energy (G); then state the sign for each in favorable and unfavorable reactions
inverse
favorable: +delta E, -delta G
unfavorable: -deltaE, +delta G
how is reduction potential determined?
using half reactions, on a table where their E is listed
describe coupled redox reactions
combining two half-reactions with a common intermediate
what equation is used to related free energy to reduction potential?
the nernst equation, will be given
give the general process for calculating change in reduction potential
- combine 2 half reactions with a common intermediate
- get the delta E for each half reaction from the chart
- flip one of the reactions (all are given as reductions, need one to be an oxidation) and flip the sign of the delta E of whichever half reaction was flipped
- add the two delta E values
why do you not multiply the delta E with reaction stoichiometry?
the potential of the reaction did not change, just the amount of molecules in the reaction
