metabolic pathways and ATP production

Question 1

structure of a fatty acid

Answer 1

hydrophilic COO- head and hydrophobic hydrocarbon tail

Question 2

saturated vs unsaturated fatty acid

Answer 2

saturated have no C=C and are solid; unsaturated have C=C present and are liquid

Question 3

enzyme for desaturation

Answer 3

fatty acyl CoA desaturase

Question 4

where is fat obtained

Answer 4

diet, liver (de novo), adipocytes

Question 5

what does bile do

Answer 5

emulsify fats and increase their digestion and absorption

Question 6

what is steatorrhea and how is it used to treat obesity

Answer 6

fatty stool; inhibit lipases

Question 7

where does B-oxidation occur

Answer 7

mitochondria

Question 8

sources of fatty acids

Answer 8

triacylglycerols, adipose

Question 9

fatty acid to acyl CoA reaction

Answer 9

fatty acid + ATP + HSCoA → acyl CoA + AMP + PPi

Question 10

what enzyme catalyses the conversion of fatty acids to acyl CoA, and where in the mitochondria does it act

Answer 10

acyl CoA synthase in outer membrane

Question 11

how is acyl CoA transported into the matrix

Answer 11

via coupling to carnitine and entering via a translocase membrane

Question 12

reaction of acyl CoA with carnitine, and enzyme

Answer 12

acyl CoA + carnitine ⇌ acyl carnitine, by carnitine acyltransferases

Question 13

diagram of translocase

Answer 13

diagram from metabolism 6

Question 14

acyl CoA → acetyl CoA: first step

Answer 14

acyl CoA oxidised by dehydrogenase enzyme (FAD → FADH2)

Question 15

acyl CoA → acetyl CoA: second step

Answer 15

hydrated by hydrolase enzyme

Question 16

acyl CoA → acetyl CoA: third step

Answer 16

oxidised by dehydrogenase enzyme (NAD+ → NADH + H+)

Question 17

acyl CoA → acetyl CoA: fourth step

Answer 17

cleavage by reacting with HSCoA, catalysed by thiolase enzyme to form acetyl CoA and an acyl CoA

Question 18

how many fewer carbons does the new acyl CoA have

Answer 18

2

Question 19

acetyl CoA formation diagram

Answer 19

diagram from metabolism 6

Question 20

palmitoyl as example of fatty acid: reaction

Answer 20

palmitoyl CoA + 7 FAD + 7 NAD+ + 7 H2O + 7 CoA → 8 acetyl CoA + 7 FADH2 + 7 NADH

Question 21

how many B-oxidations required for palmitoyl

Answer 21

7 (16C → 8 acetyl CoA as last produces 2x acetyl CoA, as 4C intermediate)

Question 22

what is the maximum number of ATP molecules produced by palmitoyl B-oxidation

Answer 22

129 ATP as 131 but 2 bonds broken: ATP → AMP+PPi

Question 23

why can’t glucose be generated via gluconeogenesis in this pathway

Answer 23

pyruvate is not produced when fats are respired, so there is no conversion to oxaloacetate, so [oxaloacetate] decreases; therefore acetyl CoA from B-oxidation only enters TCA if balanced with carbohydrate metabolism

Question 24

what happens to acetyl CoA when B-oxidation is greater than glycolysis (e.g. when fasting)

Answer 24

converted to ketone bodies in the liver

Question 25

fat metabolism diagram

Answer 25

diagram from metabolism 9

Question 26

acetyl CoA → fatty acid (lipogenesis): what enymes are required and where does it occur

Answer 26

acetyl CoA carboxylase and fatty acid synthase (FAS); occurs in cytoplasm

Question 27

list the components associated with FAS

Answer 27

synthesising, transferring, dehydrating, reducing and hydrolysing; also contains acyl carrier protein (ACP), which is a swinging arm to move molecules (similar to PDH)

Question 28

acetyl CoA → fatty acid (lipogenesis): first stage

Answer 28

formation of malonyl CoA by acetyl CoA carboxylase (+ HCO3-) and biotin coenzyme; ATP → ADP + Pi

Question 29

acetyl CoA → fatty acid (lipogenesis): second stage

Answer 29

transfer of malonyl to ACP ro form malonyl-ACP (ACP → HSCoA)

Question 30

acetyl CoA → fatty acid (lipogenesis): third stage

Answer 30

transfer of acetyl from acetyl CoA to ACP to form acetyl-ACP (ACP → HSCoA)

Question 31

acetyl CoA → fatty acid (lipogenesis): fourth stage

Answer 31

condensation of malonyl-ACP and acetyl-ACP to form 4C fatty acid acetoacetyl-ACP

Question 32

acetyl CoA → fatty acid (lipogenesis): fifth stage

Answer 32

reduction of acetoacetyl-CoA to 3-hydroxybutyryl-ACP (NADPH → NADP+)

Question 33

acetyl CoA → fatty acid (lipogenesis): sixth stage

Answer 33

dehydration of 3-hydroxybutyryl-ACP to crotonyl-ACP

Question 34

acetyl CoA → fatty acid (lipogenesis): seventh stage

Answer 34

reduction of crotonyl-ACP to butyryl-ACP (NADPH → NADP+)

Question 35

how many times must stages 4 to 7 be repeated to form 16C palmitoyl-ACP

Answer 35

6

Question 36

final stage reaction of acetyl CoA → fatty acid (lipogenesis) for palmitate

Answer 36

hydrolysis of palmitoyl-ACP to palmitate and ACP

Question 37

summary reaction of acetyl CoA → palmitate (lipogenesis)

Answer 37

acetyl CoA (C2) + 7 malonyl CoA (C3) + 14 NADPH + 14 H+ → palmitate (C16) + 7CO2 + 6H2O + 8CoA-SH + 14 NADP+

Question 38

how many more carbons does the fatty acid have

Answer 38

2

Question 39

B-oxidation vs lipogenesis reaction sequences

Answer 39

B-oxidation: oxidation, hydration, oxidation, cleavage; lipogenesis: condensation, reduction, dehydration, reduction

Question 40

diagram showing B-oxidation and lipogenesis differences

Answer 40

diagram from metabolism 6

Question 41

B-oxidation and lipogenesis: difference in carriers

Answer 41

B-oxidation: CoA; lipogenesis: ACP

Question 42

B-oxidation and lipogenesis: difference in reducing power

Answer 42

B-oxidation: NADPH; lipogenesis: FAD/NAD+

Question 43

why is a family of acyl CoA dehydrogenases required

Answer 43

catalyse different lengths of fatty acids (fatty acids pocessed produce acyl CoA with 2 fewer carbons)

Question 44

inborn disorders of fatty acid oxidation: MCAD deficiency

Answer 44

C6-C12; can't break down FA beyond C6 so can't generate acetyl CoA; can be fatal (especially if fasting); treated with a high carb diet and IV glucose

Question 45

inborn disorders of fatty acid oxidation: primary carnitine deficiency

Answer 45

mutation in gene for carnitine transporter which lowers carnitine uptake; treated with carnitine supplements