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Endocrinology > Lipid Metabolism > Flashcards

Lipid Metabolism Flashcards

1
Q

List the dietary lipids

A
  • Triglycerides
  • Cholesterol
  • Phospholipids
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2
Q

List the different types of FAs in triglycertides

A
  • Saturated (no-double bonds - usually solid at RT)
  • Monounsaturated (1 double bond - liquid)
  • Polyunsaturated (>1 double bond - liquid)

*the H

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3
Q

Structure of tryglycerides

A

Glycerol attached to 3 FA chains via ESTER BOND

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4
Q

Where does lipid digestion occur?

A

Small intestine

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5
Q

What enzymes digest lipids?

A

Pancreatic lipase and co-lipase

Enzymes also require bile salts which are formed from cholesterol; stored and secreted from the gall bladder and emulsify the large lipid droplet to smaller lipid droplets

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6
Q

What does the digestion of lipid yield?

A

triglyceride –> monoglyceride + 2FAs

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7
Q

How are lipids absorbed?

A
  1. Micelles breakdown forming FAs and MG at the apical surfaces of enterocytes
  2. Diffusion
  3. Triacytlglycerol (TAG) packaged with cholesterol, phospholipids, and others forming chylomicrons
  4. Chylomicrons are released into lymphatic system by exocytosis (into lacteal to thoracic duct into venous system)
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8
Q

How are lipids transported in the plasma after absorption?

A
  • Chylomicron binds to lipoprotein lipase
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9
Q

What is the fate of lipids absorbed?

A
  1. Storage - TAG
  2. Structural - phospholipid membrane bilayer
  3. Oxidation - ATP
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10
Q

How are lipids taken up by cells?

A

Via LDLrs

Low density lipoprotein receptors

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11
Q

How is fat-metabolised?

A

Beta-oxidation

  • Generation of ATP (energy) from FFAs
  • Oxidation of the beta-carbon (C3) facilitates sequential cleavage of acetyl units
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12
Q

What is beta-oxidation

Where does it occur?

A
  • Generation of ATP from FFAs
  • FAs first added to acetyl CoA to form fatty acytl-CoA
  • Occurs in the mitochondria

Therefore it must cross the inner mitochondrial membrane via carnitine (carrier molecule)

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13
Q

What is carnitine?

A

Carrier molecule
Carries FFA into mitochondria
Derived from lysine and methionine
High in muscle

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14
Q

Where is CPT I located?

A

Outer mitochondrial membrane

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15
Q

Where is CPT II located?

A

Inner mitochondria membrane

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16
Q

What does CPT stand form?

A

Carnitine Palmitoyl Transferase

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17
Q

What does B-oxidation yield?

A

FADH2
NADH
Acetyl CoA (2C)

Ends up with final Acetyl CoA —> ATP
(TCA cycle/oxidative phosphorylation)

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18
Q

How many C-atoms are oxidised at a time?

A

2

19
Q

How much is the ATP yield of palmitate (C16)

A

106ATP

20
Q

What is triglyceride synthesis?

A

Esterification of 3FAs and glycerol

21
Q

What are the intermediates and regulated enzymes of triglyceride synthesis in adipose tissue?

A
  • Esterification of 3FAs + glycerol
  • Lipoprotein lipase (LPL) hydrolyses TAG in chylomicroms
  • Diacylglycerol Acyl Transferase (DGAT) re-esterifies to TAG
  • Glycerol obtained from glycolysis
22
Q

What are the 2 enzymes involved in triglyceride synthesis?

A 
Lipoportein lipase (on surface)
DGAT (inside cell)
23
Q

What are intermediates and regulated enzymes of lipolysis in adipose tissue?

A

Lipolysis = Triglyceride breakdown of triglycertide into glycerol and 3FAs

  • Hormone sensitive lipase in adipose tissue
24
Q

What is hormone sensitive lipase and how is it activated?

A

HSL is involved in lipolysis

It is activated by cAMP-dependent phosphorylation in response to adrenaline in the fasted state

25
Q

What inhibits hormone sensitive lipase?

A

Insulin

26
Q

What triggers hormone sensitive lipase activity?

A

Adrenaline

27
Q

Describe the key intermediates and regulated enzymes of fatty acid synthesis

A

Stage 1: formation of precursor malonyl CoA by acetyl CoA carboxylase and biotin from acetyle CoA

Stage 2: coupling acetyl CoA to malonyl CoA elongation of chain 2Cs at a time by fatty acid synthase

  • requires NADPH via pentose phosphate pathway
  • 7 steps
28
Q

What is the significance of malonyl CoA?

A

Inhibits carnitine palmitoyl transferase (CPT) thus inhibiting FA b-oxidation

29
Q

Where does FA synthesis takes place?

A

Cytoplasm

30
Q

Where does FA oxidation takes place?

A

Mitochondria

31
Q

What is the product of b-oxidation?

A

Acetyl CoA

32
Q

How are ketone bodies formed from FA oxidation?

A
  • b-oxidation forms acetyl CoA
  • acetyl CoA enters Krebs

HOWEVERE

if oxaloacetate is NOT present then acetyl CoA is converted into ketone bodies

Ketone bodies are essentially and OVERFLOW of acetyl CoA
- they start joining together

acetyl-CoA + acetyl-CoA = acetoacetyl CoA
acetoacetyl CoA - CoA = acetoacetate

Acetoacetate can be converted into acetone or/and hydroxybutyrate

33
Q

Describe the formation of phospholipids

A

Same as triglyceride synthesis

Then combine with alcohol

34
Q

Where do you find high levels of phospholipid synthesis?

A

Rapidly dividing cells

35
Q

Explain the requirements for essential fatty acids

A
  • Cannot be synthesised
  • Must be obtained from diet
  • Polyunsaturated omega 3 and 6
36
Q

What are the functions of essential FAs

A
  • Cell membrane function
  • Required for proper growth and development
  • Required for brain and nerve function
  • Precursors for inflammatory mediators
37
Q

What are the key regulators of lipid metabolism?

A

Insulin - inhibits

Adrenaline - triggers

38
Q

How does insulin regulate lipid metabolism?

A

Stimulates FA and TAG synthesis

Suppresses lipolysis

39
Q

How does insulin suppress lipolysis?

A

Inhibits hormone sensitive lipase

40
Q

What does adrenaline do in lipid metabolism?

A

Stimulates lipolysis via hormone sensitive lipase

41
Q

Outline what insulin does during lipid metabolism

A

IN THE FED STATE

  • GLUT4 translocation
  • Activates acetyl CoA Carboxylase (FA synthesis first step)
  • Increases expression of FA synthase (FA synthesis 2nd step)
  • Increases activity of lipoprotein lipase
42
Q

Outline what adrenaline does during lipid metabolism

A
  • cAMP synthesis
  • cAMP-dependent phosphorylation of PKA
  • cAMP-PKA phosphorylation and activation of hormone sensitive lipase (HSL)
43
Q

What does insulin do to lipolysis?

A

Inhibits lipolysis by stimulating the breakdown of cAMP

44
Q

Describe the regulation of lipoprotein lipase

A

Lipoprotein lipase breakdown chylomicrons into FAs
Expressed on the cell surface

In the fed state:

  • LPL synthesis and activity is increased on adipocyte
  • LPL synthesis and activity is decreased on muscle and liver

In the fasting state:

  • LPL synthesis and activity decreases on adipocytes
  • LPL synthesis and activity increases on muscle and liver

Endocrinology (11 decks)

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