cellular respiration

Question 1

cellular respiration

Answer 1

consumption of O2 and the output of CO2 within cells

Question 2

3 stages of respiration

Answer 2

1) organic fuels oxidized to acetyl-CoA; also releases NADH
- fuels: glucose, fatty acids, some AAs
2) acetyl group enters TCA & is oxidized to CO2
- energy released conserved in reduced electron carriers: coenzymes NADH & FADH2; also releases ATP
3) reduced coenzymes are oxidized; give up protons and electrons
- electrons transferred to O2 (via respiratory chain)
- energy released conserved as ATP

Question 3

two functions of TCA cycle

Answer 3

1) oxidative function (energy)
2) synthetic function ( intermediates used in fatty acid synthesis, gluconeogenesis, heme, and nonessential AA synthesis

Question 4

stage 1 of cellular respiration

Answer 4

pyruvate to acetyl-CoA
oxidative decarboxylation and activation of acetyl group
enzyme: pyruvate dehydrogenase (PDH) complex
irreversible in animals– highly regulated

Question 5

structure of PDH complex

Answer 5

3 different enzymes:
E1: pyruvate dehydrogenase
E2: dihyrolipoyl transacetylase
E3: dihydrolipoyl dehydrogenase
5 different coenzymes:
FAD-E3
- reversible reduction
- accepts 1 or 2 electrons (FADH+ or FADH2)
NAD-E3
- reversible reduction
- accepts 1 electron (NADH)
TPP-E1
lipoic acid-E2
- oxidized form has a disulfide bond
coenzyme A- E2
- reactive thiol group on terminal end

Question 6

mechanism of PDH complex

Answer 6

1. (E1) pyruvate undergoes decarboxylation when reacted with bound TPP of E1
   - step called oxidative carboxylation
   - rate limiting step
   - TPP derived from thiamine (vitamin B1)
2. (E2) hydroxyethyl group oxidized to acetate
   - lipoate and disulfide bond are reduced
   - thioester linkage formed on E2
   - whole structure derived from lipoic acid and lysine
3. (E2) transesterification
   - principal reaction here is formation of acetyl-coA
   - CoA constituted by SH group + pantothenic acid + ribose + adenine
   - at the final of this stage, lipoyllysine is completely reduced
4. (E3) reduced lipoyllsine group is oxidized thru electron transfer from FAD to FADH2 on E3 and the reoxidation of E2
5. electrons from FADH2 are transferred to NAD+ to give NADH

Question 7

control of PDH complex

Answer 7

allosteric inhibition: NADH, ATP, and acety-CoA inhibits PDH complex
allosteric activation: AMP, CoA-SH and NAD activates PDH complex
covalent modification: E1 is inactivated by phosphorylation of one of its Ser residues
- rxn catalyzed by pyruvate dehydrogenase kinase (activated by PKA)
- pyruvate dehydrogenase kinase is activated by ATP (so activates inhibition)
- can be deactivated by pyruvate and ADP
E1 is activated by dephosphorylation
- rxn catalyzed by pyruvate dehydrogenase phosphatase
- pyruvate dehydrogenase phosphatase is activated by low ATP concentration, Ca2+ (in muscle) and insulin (in liver)