Lecture 3 - Carbo. & Lipids

Question 1

Pyruvate does not directly enter the TCA. It undergoes a reaction first. What is the reaction? Desc. the product of the reaction, the enzyme, location and what affects it.

Answer 1

[Reaction: Pyruvate + CoA + NAD+ –> Acetyl CoA + CO2 + NADH + H+]

• Pyruvate converted to acetyl CoA
• Enzyme: Pyruvate Dehydrogenase (PDH)
• Location: Mitochondrial matrix
• Requires cofactor –> sensitive to Vit. B1 deficiency
• Reaction is irreversible = key regulatory step

Question 2

What inhibits and activates PDH?

Answer 2

Activate:

• Pyruvate
• NAD+
• ADP
• Insulin
• Dephosphorylation

Inhibit:

• Acetyl-coA
• NADH
• ATP
• Phosphorylation

Question 3

What occurs if there is a PDH deficiency?

Answer 3

Lactic acidosis

Question 4

What happens in stage 3 of carbohydrate metabolism?

name, products, location

Answer 4

• TCA/Krebs’ cycle
• Pyruvate –> Acetyl CoA –> X3 NADH, X1 GTP/ATP, X1 FADH2
  [so its x2 of everything because glucose –> x2 pyruvate]
• Occurs in mitochondria matrix
• Catalytic cycle = oxaloacetate is regenerated = no net synthesis or degradation of intermediates
• Acetate C-C bond is broken

Question 5

What is achieved at the end of the TCA cycle?

Answer 5

• All C-C and C-H bonds are broken
• All C atoms are oxidised to CO2
• X6 NADH, X2 FADH2, X2 GTP

Question 6

What is the use of reducing power in stage 4 of catabolism (ETC)?

Answer 6

Electrons of NADH & FADH2 transported through a series of electron carriers to O2 –> energy–> ATP (oxidative phosphorylation)

Question 7

Describe the ETC

Answer 7

• Electrons from NADH & FADH2 –> electron transport carriers –> energy –> move H+ across membrane –> p.m.f

Question 8

Which carrier transport H+ across mitochondrial membrane?

Answer 8

ATP synthase

Question 9

How many electrons/ATP does NADH & FADH2 each generate?

Answer 9

• NADH uses 3 PTCs (proton-transporting complexes) –> higher p.m.f =more ATP –> 2.5 moles of ATP each
• FADH2 uses 2 –> 1.5 moles of ATP each

Question 10

Desc. the regulation of oxidative phosphorylation

Answer 10

• Regulated by [ATP]
• High ATP = low ADP –> no substrate for ATO synthase –> inward flow of H+ stops –> [H+] ⬆️in intermembrane space –> ETC stops

Question 11

How does cyanide affect the ETC?

Answer 11

• Acts as an inhibitor
• Prevents oxidation of NADH and FADH2
• Prevents acceptance of electrons by O2

Question 12

How do uncouplers affect the ETC and oxidative phosphorylation? What are some examples of uncouplers?

Answer 12

• Increase the permeability of mitochondrial inner membrane to protons –> reduces p.m.f
• H+ enters mitochondria w/o ATP synthase –> heat
• No oxidative phosphorylation, ETC continues
• Examples: dinitrophenol, dinitrocresol, f.a

Question 13

What other thing can inhibit oxidative phosphorylation other than uncouplers and inhibitors?

Answer 13

• Ox/Phos disease

- Genetic defects in proteins coded by mtDNA –> ⬇️ETC

Question 14

What does brown adipose tissue contain? What is its function?

Answer 14

• Thermogenin (UCP 1): transport H+ back into mitochondria
• In response to cold –> noradrenaline (norepinephrine) activates:
  i) Lipase –> F.A from TAG
  ii) F.A oxidation –> NADH/FADH2 –> ETC
  iii) F.a activate thermogenin –> heat
• Found in neonates (x shiver)

Question 15

What are the differences between oxidative and substrate-level phosphorylation?

Answer 15

Oxidative:

• Required membrane-associated complexes (PTC)
• Energy coupling = indirect = p.m.f
• Need O2
• Major source of ATP (32)

Sub:

• Require enzymes
• Energy coupling = direct = hydrolysis of bonds
• Small ATP generated

Question 16

Describe the various classes of lipids

Answer 16

1. F.a = fuel molecules
2. TAG = Fuel storage and insulation
3. Phospholipid = Plasma membrane
4. Ketone bodies = Water sol. fuel mol.
5. Cholesterol = steroid hormone synthesis
6. Vitamin ADEK

Question 17

Desc. the metabolism of TAG

Answer 17

1. GI tract: Hydrolysis of lipids by pancreatic lipase –> F.a and glycerol
2. Packaged into chylomicrons –> lymphatic –> adipose tissue –> TAG (released when needed)

Question 18

Desc. F.A catabolism

Answer 18

• Occurs in mitochondria, requires O2
  1. FA is activated (linking coenzyme A outside mito., enzyme is hormone sensitive lipase)
  2. Transported into matrix via carnitine shuttle
  3. FA undergo oxidation, 2C removed each time
  4. FADH2, NADH, H2O released each 2C

Question 19

How does the activation of FA occur?

Answer 19

• In the cytoplasm
• FA link to coenzyme A by fatty acyl CoA synthase –> form fatty acyl CoA
• Activated FA X cross mitochondrial membrane readily –> carnitine shuttle

Question 20

What is the purpose of the carnitine shuttle?

What inhibits it?

Answer 20

• Transport activated FA
• Controls rate of FA oxidation
• Inhibited by malonyl CoA
• Defects can occur due to exercise intolerance

Question 21

Features of FA metabolism

Answer 21

• β-oxidation of FA
• Mitochondrial
• Require O2
• 2C removed each cycle
• No ATP synthesis (AMP + Pi)

Question 22

What can glycerol be metabolised into?

Metabolised in liver

Answer 22

• Glycerol –> G. P
  [Glycerol kinase]
• G.P –> TAG/ DHAP (NADH released when form DHAP)

Question 23

What is the function of acetyl CoA?

Answer 23

• Converted to F.A (form TAG/phospholipid)
• Converted to CO2
• Converted to HMG (form ketone bodies/cholesterol)

Question 24

What are the 3 types of ketone bodies and when are they formed?
(Normal range < 1mM)

Answer 24

• Acetoacetate, β-hydroxybutyrate, Acetone

- Produced in starvation or type 1 DM

Question 25

Where are ketone bodies synthesised and how?

Answer 25

• Made by liver mitochondria

Question 26

What do statin drugs inhibit?

Answer 26

• HMG-CoA reductase

- Prevent HMG-CoA to be converted to cholesterol

Question 27

How is the production of ketone bodies regulated?

Answer 27

• Insulin/glucagon ratio is high (fed state) –> lyase is inhibited, reductase is activated –> cholesterol
• When I/G ratio is low –> lyase is activated –> ketone bodies

Question 28

Is ketone bodies water sol. or X?

Answer 28

Water sol.