TCA cycle

Question 1

NADPH in biosynthesis of cholesterol

Answer 1

NADPH helps catalyse the final reaction of several

the C=C bond is reduced by transfer of a hydride ion

Question 2

acetyl CoA

Answer 2

thioester bond - high energy linkage
readily hydrolysed
can donate the 2C to other molecules

Question 3

describe the steps in the TCA cycle

Answer 3

2C from acetyl CoA to oxyloacetate - citrate
isomerisation of citrate to give isocitrate
oxidation of isocitrate to give a-ketoglutarate
similar to reaction by pyruvate dehydrogenase
CoA displaced by phosphate molecule - then phosphate transferred to GDP
oxidation of succinate - FADH2
addition of water breaking double bond
dehydration of malate to give oxaloacetate

Question 4

what is produced by a turn of the TCA cycle

Answer 4

2 CO2
3 NADH
1 GTP
1 FADH2

Question 5

Location of TCA cycle enzymes

Answer 5

soluble in matrix

except succinate dehydrogenase

Question 6

What is a necessary condition for the krebs cycle

Answer 6

aerobic

NAD+ and FAD only regenerated by transfer of electrons to O2 in ox phos

Question 7

degradation of AA

Answer 7

remove amino group - secreted as urea
carbon skeleton - into krebs/produce glucose
gives rise to: pyruvate, acetyl CoA, acetoacetyl CoA, a-ketoglutarate, succinyl CoA, fumarate and oxaloacetate

Question 8

What are transamination reactions

Answer 8

amine group transferred from 1 AA to keto acid - form new AA and keto acid

Question 9

Alanine transamination

Answer 9

enzyme - alanine aminotransferase
alanine and a-ketoglutarate – pyruvate and glutamate
pyruvate enter TCA
glutamate back to a-ketoglutarate by glutamate dehydrogenase - NH4+ - urea
persistently high levels - sign of hepatic disorders like Hep C

Question 10

why are shuttles needed

Answer 10

NADH from glycolysis need to enter mt for ox phos

Question 11

describe the glycerol-phosphate shuttle

Answer 11

electrons move not NADH
cytosolic GP dehydrogenase transfers electrons from NADH to dihydroxyacetone phosphate - GP
membrane bound GP dehydrogenase transfers electrons to FAD - passed to coenzyme Q

Question 12

The malate aspartate shuttle

Answer 12

2 membrane carriers and 4 enzymes
net reaction: NADH (cytoplasmic) + NAD+ (mt) – NAD+ (cyt) + NADH (mt)
hydride ion NADH ct to oxaloacetate - malate
catalysed by malate dehydrogenanse
malate transported into mitochondria
malate reoxidised by NAD+ - oxaloacetate and NADH
catalysed by malate dehydrogenase mt
a-ketoglutarate transporter exchange a-ketoglutarate for malate
glutamate aspartate transporter - glutamate for aspartate
transamination: glutamate + oxaloacetate – a-ketoglutarate + aspartate