L12: TCA Cycle

Question 1

what does TCA stand for

Answer 1

TriCarboxyclic Acid (cycle)

Question 2

what is degraded to acetyl-CoA

Answer 2

carbon skeletons of fatty acids, glucose, amino acids degraded to acetyl-CoA

Question 2

what stage of fat catabolism is TCA cycle

Answer 2

stage 2

Question 3

where does the TCA cycle occur

Answer 3

mitochondria

Question 4

is it a catabolic or anabolic cycle

Answer 4

both

Question 5

acetyl-CoA structure

Answer 5

CoA added on covalently to acetyl grp making thiol bond

Question 6

how does pyruvate
enter mitochondria
(glycolysis entry into TCA cycle)

Answer 6

in presence of O2 pyruvate enters mitochondria via Mitochondrial Pyruvate Carrier protein (MPC)

Question 7

how is pyruvate converted to acetyl-CoA (glycolysis entry into TCA cycle)

Answer 7

using pyruvate dehydrogenase enzyme (PDH)

Question 8

where does the oxidisation & decarboxylation of pyruvate to acetyl-CoA occur

Answer 8

mitochondrial matrix

Question 9

how is PDH regulated

Answer 9

• allosterically/covalently (phosphorylation)
• PDH off when sufficient fuel available, off when cells energy is low

Question 10

what does a deficiency in PDH genes or thiamine result in

Answer 10

pyruvate build up -> energy dysfunction -> loss of brain function

Question 11

the metabolic intermediates

Answer 11

1. oxaloacetate
2. citrate
3. isocitrate
4. ketoglutarate
5. succinyl-CoA
6. succinate
7. fumarate
8. malate
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Question 12

how much energy does the condensation rxn of acetyl-CoA w oxaloacetate produce

Answer 12

3NADH, 1FADH2, 1GTP, 2CO2

Question 13

what sort of rxn is step 1 TCA cycle

Answer 13

condensation rxn

Question 14

step 1 enzyme

Answer 14

citrate synthase

Question 15

what happens in step 1

Answer 15

• acetyl-CoA (2C) condenses with oxaloacetate (4C) to form citrate (6C)
• citrate a tricarboxcylic acid - high energy nature

Question 16

what kind of rxn is step 2

Answer 16

isomerisation rxn

Question 17

step 2 enzyme

Answer 17

citrate aconitase

Question 18

what happens step 2

Answer 18

• citrate isomerises to isocitrate by removal and addition of H2O
• sets up bond structure for next rxn

Question 19

what kind of rxn is step 3

Answer 19

first oxidative decarboxylation

Question 20

step 3 enzyme

Answer 20

isocitrate dehydrogenase

Question 21

what happens step 3

Answer 21

• first key exergonic step
• isocitrate (6C) oxidised to alpha-ketoglutarate (5C)
• first CO2 released
• NADH formed

Question 22

what kind of rxn is step 4

Answer 22

second oxidative decarboxylation

Question 23

enzyme step 4

Answer 23

alpha-ketoglutarate dehydrogenase complex

Question 24

what happens step 4

Answer 24

* second key exergonic step * addition of CoA and oxidation of alpha-ketoglutarate (5C) to succinyl-CoA (4C) * second CO2 released * second NADH formed

Question 25

enzyme step 5

Answer 25

succinyl-CoA synthetase

Question 26

what happens step 5

Answer 26

* conversion of succinyl-CoA (4C) to succinate (4C) * removal of CoA -> energy of this forms 1GTP which converts to ATP

Question 27

what kind of rxn step 6

Answer 27

oxidation

Question 28

enz step 6

Answer 28

succinate dehydrogenase (SDH), a flavoprotein

Question 29

what happens step 6

Answer 29

* oxidation of succinate (4C) to fumarate (4C) * removal of 2H * formation of 1FADH2

Question 30

what kind of rxn is step 7

Answer 30

hydration

Question 31

enz step 7

Answer 31

hydratase (fumarase)

Question 32

what happens step 7

Answer 32

addition of H2O to fumarate (4C) to get malate (4C)

Question 33

what kind of rxn is step 8

Answer 33

oxidation

Question 34

enz step 8

Answer 34

malate dehydrogenase

Question 35

what happens step 8

Answer 35

* oxidation of malate (4C) to oxaloacetate (4C) * removal of 2H+ * formation of NADH + H+ * cycle starts again

Question 36

what is reduced for 1 acetyl-CoA input

Answer 36

* 3NAD+ reduced to 3NADH * 1FAD+ reduced to 1FADH2 * 1GTP converted to 1ATP

Question 37

what delivers electrons to stage 3 resp chain

Answer 37

3NADH & 1FADH2

Question 38

what is TCA cycle coordinated with for effective bioenergy transfer

Answer 38

coordinated with oxidative phosphorylation