TCA cycle

Question 1

what does TCA cycle stand for

Answer 1

tricarboxylic acid cycle (krebs cycle)

Question 2

what is TCA cycle in short

Answer 2

catabolism of proteins/fats/carbohydrates in 3 stages of cellular respiration

1. acetyl CoA production
2. acetyl CoA oxidation
3. electron transfer and oxidative phosphorylation

Question 3

how does pyruvate enter the TCA cycle

Answer 3

decarboxylation of pyruvate/pyruvate converts to acetyl CoA using pyruvate dehydrogenase complex that contains 3 distinct protein groups

Question 4

what cofactors are involved

Answer 4

TPP (thiamine pyrophosphate), lipoic acid, coenzyme A, FAD, NAD+

(tender loving care for nancy)

Question 5

what is the PDH complex

Answer 5

pyruvate dehydrogenase complex, large multi enzyme complex, contains 60 individual protein molecules which require 5 different cofactors in 5 consecutive steps, derived from 4 different vitamins

Question 6

describe the 5 cofactors that pyruvate dehydrogenase complex needs

Answer 6

thiamine pyrophosphate- functions in electron transfer, requires vitamin B1 (thiamine)

lipoic acid- has 2 thiols that can form disulfide bonds

coenzyme A- acyl carrier with reactive thiol, often acetyl CoA, requires vitamin B5 (pantothenate)

FAD- electron carrier, requires vitamin called riboflavin

NAD+- electron carrier, requires vitamin B3 (niacin)

Question 7

what are some symptoms of vitamin B5 deficiency

Answer 7

impaired energy production, fatigue, irritability, hypoglycaemia, increased sensitivity to insulin

Question 8

what is vitamin B3 deficiency called and what are the risk factors of it

Answer 8

pellagra, caused by dietary deficiency, chronic alcoholism, hartnup disease

Question 9

symptoms of pellagra (vit B3 deficiency)

Answer 9

photo sensitive dermatitis, diarrhoea, dementia, death

sore skin, sensitive to UV light

Question 10

what is nixtamalisation

Answer 10

process of corn soaked and cooked in alkaline substances like lime or wood ash, treats vitamin B3 deficiency i think

Question 11

advantages of nixtamalisation

Answer 11

unlocks niacin, reduces mycotoxins, adds calcium, improves taste, more easily ground, removal or pericarp

Question 12

where does krebs’ cycle occur

Answer 12

mitochondria

Question 13

describe what happens in the 8 steps of krebs cycle

Answer 13

1. acetyl CoA (C6) reacts with oxaloacetate (C4), catalysed by citrate synthase, C6 unit made, 3 carboxy groups, tricarboxylic acid

2, rearrangement of OH group to C4 to give isocitrate to prepare molecule for decarboxylation

3. oxidative decarboxylation to lose a CO2 group to form a C5, oxidation of OH and reduction of NAD to make NADH
4. another oxidative decarboxylation and reduction to give another NADH and produce succinyl CoA
5. high energy bond so some energy transfers to GDP, all NADH used in ETC, GTP and succinate produced, directly generates energy (transferring energy from thioester bond to molecule of GDP to make GTP)
6. succinate oxidised by succinate dehydrogenase, reduction to give FADH, enzyme embedded in inner membrane of mitochondria, all other enzymes are soluble within matrix
7. fumarate (C4 dicarboxylic acid with double bond) hydrates double bond to make malate
8. oxidised OH group to carbonyl group to give NADH and regenerates oxaloacetate

Question 14

describe the conformational changes by oxaloacetate binding

Answer 14

oxaloacetate binds to enzyme to cause conformational changes from open to closed form, the changes create a binding site for the second acetyl CoA, citroyl CoA is formed and another conformational change puts an Asp side chain to cleave citroyl-CoA

Question 15

what is the overall outcome of TCA cycle/what does 1 acetyl CoA produce

Answer 15

2 CO2
3 NADH
1 FADH2
1 ATP (GTP)

Question 16

other than generating energy, krebs’ cycle has other uses (what are some of the products used for)

Answer 16

citrate- fatty acid synthesis

ketoglutarate- glutamate synthesis, makes other amino acids and nucleotides

succinyl CoA- heme biosynthesis