BB451 exam 1 - Citric Acid Cycle Flashcards
pyruvate dehydrogenase complex function
pyruvate from glycolysis –> acetyl CoA for citric acid cycle
pyruvate dehydrogenase complex occurs in the..
mitochondrion (pyruvate from cytoplasm transported into mitochondrion)
E1
pyruvate decarboxylase
decarboxylation and part of oxidation
E2
transfer of acetyl group to CoA –> acetyl CoA
E3
handles electrons and regenerates original enzyme
coenzymes used with pyruvate dehydrogenase complex
TPP, lipoamide, CoA, FAD, NAD
ultimate electron destination
NAD
mechanism of pyruvate dehydrogenase complex similar to…
alpha-keto-gluterate dehydrogenase complex of citric acid cycle
-both involve oxidation of alpha-keto acids
pyruvate dehydrogenase complex step 1
pyruvate decarboxylated –> 2C reactive intermediate attached to TPP
*catalyzed by E1
pyruvate dehydrogenase complex step 2
2C intermediate transferred to lipoamide molecules –> acetyl group
- oxidation (E1 and E2)
- single bond oxygen to double bond oxygen
- disulfide bond to sulfhydryl
- e’s passed to lipoamide
pyruvate dehydrogenase complex step 3
CoA grabs acetyl group –> acetyl CoA
- left reduced sulfhydryl compound
- E2
pyruvate dehydrogenase complex step 4
electrons –> FAD –> FADH2
- sulfhydryl back to disulfide bond of lipoamide
- E3
pyruvate dehydrogenase complex step 5
transfer of e’s from FADH2 –> NAD –> NADH
*NADH released
1 turn of pyruvate dehydrogenase complex cycle …
1 acetyl CoA and 1 NADH
glucose –> 2 pyruvate –> 2 CoA and 2 NADH
yeast fermentation stops at
decarboxylation step
no oxidation
yeast fermentation forms
acetaldehyde w/out gain/loss of e’s
acetaldehyde –> ethanol
when oxygen is present with yeast/bacteria…
fermentation does not occur
E2 and E3 catalyze reactions as in aerobic higher organisms –> acetyl CoA
first electron carrier in pyruvate dehydrogenase complex reactions
lipoamide
mitochondrial inner membrane
e-transport chain
proteins and enzymes for –> ATP
permeable to: water, CO2, oxygen, CO
cristae
infoldings of inner membrane
citric acid cycle occurs in
mitochondrial matrix
CAC: 2C added as ___, released as ___
added as acetyl CoA, released as CO2
1 acetyl CoA—>
3 NADH and 1 FADH2
1 high energy phosphate (GTP in animals, ATP in plants and bacteria)
1 glucose –> CAC –>
6 NADH, 2 FADH2, 2 GTP
acetyl CoA produced from…
fatty acid metabolism
aerobic oxidation of glucose
many amino acid metabolism
substrate level phosphorylation
directly make triphosphate from high energy intermediate (1 in CAC)
most triphosphates made by ….
oxidative phosphorylation in mitochondria
step 1 CAC
oxaloacetate + acetyl CoA –> citrate
4C + 2C –> 6C
enzyme = citrate synthase
very energetically favorable - pulls cycle
step 2 CAC
citrate isocitrate
isomerization
enzyme = aconitase
aconitase inhibited by
fluorocitrate
fluoroacitate is poison used by citrate synthase to make fluorocitrate
step 3 CAC
isocitrate --> alpha-KG 6C --> 5C NAD+ --> NADH enzyme = isocitrate dehydrogenase first decarboxylation (release CO2) isocitrate is oxidized
dehydrogenase means..
oxidation is occurring (losing e-)
alpha-KG
useful intermediate, convert to glutamic acid or back
step 4 CAC
alpha-KG + NAD + CoA –> succinyl CoA + NADH
enzyme: alpha-KG dehydrogenase
puts CoA onto succinate, driving force from oxidation
almost same as pyruvate dehydrogenase complex reactions
big band: very energetically favorable
step 5 CAC
succinyl CoA --> succinate 5C --> 4C GDP --> GTP enzyme: succinyl CoA synthetase substrate level phosphorylation (requires high energy from CoA)
step 6 CAC
succinate –> fumerate
enzyme= succinate dehydrogenase
add 2e- and 2H onto FAD –> FADH2
step 7 CAC
fumerate + H2O –> malate
enzyme = fumarase
step 8 CAC
malate --> oxaloacetate NAD --> NADH enzyme = malate dehydrogenase hydroxyl oxidized to ketone malate loses e- to NAD
step 8 is rare oxidation because…
not energetically favorable, delta G 0prime is positive
oxaloacetate pulled away by citrate synthase reaction –> pulls reaction forward
overall… CAC is energetically ___
favorable
most important regulation of CAC
availability of NAD+ and FAD
NADH and FADH2 turn cycle off
e- transport/oxidative phosphorylation regenerate NAD and FAD
exercising heavily..
low ATP, low O2 in muscle cells
high NADH and CAC stops
relaxed state..
high ATP, high NADH
NADH increase when cell can catch up –> CAC stops –> citrate accumulates –> acetyl CoA increases –> get fat (acetyl CoA to make fatty acids)
when all NADH and FADH2 of cycle –> ATP
30-38 ATPs / glucose
compare to 2 from glycolysis
limiting reagent needed to keep cycle turning
oxygen (ultimately convert NADH –> NAD)
NAD needed to 3 reactions is CAC
cant get around need for oxygen (like glycolysis does with fermentation)
anaplerotic reactions
“filling up” the intermediates of metabolism
intermediates involved in metabolism of amino acids, fatty acids, nucleotides, and sugars
arsenic poisoning
arsenic knocks out pyruvate dehydrogenase and alpha-KG dehydrogenase
treatment: BAL, takes arsenic away from lipoic acid
glyoxylate cycle in
plants, bacteria, and yeast
2 additional enzyme for glyoxylate cycle
isocitrate lyase
malate synthase
isocitrate lyase
cleavage of isocitrate –> glyoxylate and succinate
malate synthase
linkage of acetyl CoA to glyoxylate –> malate
glyoxylate cycle can
form glucose from acetyl CoA because bypass decarboxylation reactions of CAC
acetyl CoA converted to useful material (instead of just fatty acids)
glyoxylate cycle produces less ___ than CAC
less NADH, because skips decarboxylation
less ATP produced
____ influences CAC or glyoxylate cycle
energy state of cell
need energy: CAC
abundant energy: glyoxylate cycle
every turn of glyoxylate cycle –>
2 oxaloacetates instead of 1
