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Endocrine System > 320-326. Lipid Metabolism > Flashcards

320-326. Lipid Metabolism Flashcards

1
Q

Name the three types of dietary lipids.

A
  1. Triglycerides
  2. Cholesterol
  3. Phospholipids
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2
Q

What are triglycerides made of?

A

Glycerol and 3 fatty acids

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3
Q

What are the three types of fatty acids?

A

Saturated
Monounsaturated
Polyunsaturated

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4
Q

What type of bond is present between glycerol and fatty acids in triglycerides?

A

Ester bond

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5
Q

Where does lipid digestion occur in the GI tract?

A

Small intestine

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6
Q

What are the two enzymes involved in lipid digestion?

A

Pancreatic lipase and colipase

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7
Q

What is the role of lipases in lipid digestion?

A

Breaks down triglycerides into 2 fatty acids and MAG (monoglyceride)

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8
Q

What are bile salts synthesised from?

A

Cholesterol

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9
Q

What secretes bile salts?

A

Liver through the bile duct

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10
Q

What is the role of bile salts?

A

EMULSIFY fats into micelles (water soluble tiny fat droplets)

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11
Q

Describe how lipids are absorbed into the lymphatics system once they enter the intestinal cell (3)

A

TAG re-forms in intestinal cell

TAG is packaged with cholesterol, lipoproteins and other lipids to form CHYLOMICRONS

CHYLOMICRONS released into lymphatic system by exocytosis

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12
Q

What enzyme causes the release of fatty acids from chylomicrons to enter adipose tissue?

A

Lipoprotein lipase

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13
Q

What are the three fates of fatty acids once they are taken up by adipose tissue?

A
  1. Oxidised (for ATP)
  2. Used structurally e.g. phospholipids
  3. Storage (TAG)
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14
Q

Describe what beta oxidation is with regards to fatty acid metabolism

A

Generation of energy from fatty acids

Fatty acids first added to acetyl CoA to form fatty acyl-CoA

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15
Q

Where does beta oxidation of fatty acids occur?

A

Within the mitochondrion

Must cross the inner mitochondrial membrane

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16
Q

What carrier molecule is required for fatty acids to cross the inner mitochondrial membrane?

A

Carnitine (carnitine palmitoyl transferase on membrane itself)

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17
Q

What is carnitine derived from?

A

Lysine and methionine

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18
Q

What type of tissue has high levels of carnitine?

A

Muscle

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19
Q

What degrades Fatty acyl CoA in beta oxidation?

A

The beta carbon

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20
Q

Beta oxidation of the fatty acyl chain occurs in rounds. How many carbons are reduced per round?

A

2 carbons

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21
Q

What is produced per turn of beta oxidation?

A

FADH2, NADH, and acetyl CoA (2 carbons)

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22
Q

What is the final product of beta oxidation (the last turn)?

A

A final acetyl CoA

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23
Q

After beta oxidation to acetyl CoA, how can fatty acids be further oxidised?

A

Kreb’s cycle/oxidative phosphorylation

24
Q

What is the ATP yield of palmitate (hence showing how fatty acids are an excellent source of ATP)?

A

106 ATP

25
Q

What is the basis of triglyceride synthesis?

A

The esterification of glycerol and three fatty acids

26
Q

What is the role of lipoprotein lipase (LPL) in triglyceride synthesis?

A

Hydrolyses TAG in chylomicrons/VLDL

27
Q

What is the role of Diacylglycerol Acyl Transferase (DGAT) in triglyceride synthesis?

A

Re-esterifies to TAG using glycerol obtained from glycolysis

28
Q

Describe in general terms, triglyceride breakdown (lipolysis), including the enzyme involved

A

Breakdown of the triglyceride into glycerol and 3 fatty acids

Hormone sensitive lipase in adipose tissue

29
Q

What activates hormone-sensitive lipase, leading to lipolysis in adipose tissue?

What inhibits hormone-sensitive lipase?

A

cAMP-dependent phosphorylation in response to adrenaline in fasted state

Hormone-sensitive lipase is inhibited by insulin

30
Q

How many carbons at a time can be added to fatty acids during fatty acid synthesis?

A

2

31
Q

What is the limit for the number of carbons that can be added during fatty acid synthesis?

A

16

32
Q

What are the key regulatory enzymes for fatty acid synthesis?

A

Acetyl CoA carboxylase - forms malonyl CoA

Fatty acid synthase

33
Q

Other than aiding fatty acid synthesis, what is the other role of malonyl CoA?

A

Inhibits fatty acid oxidation

34
Q

Where does fatty acid synthesis occur in the cell?

A

Cytoplasm

35
Q

What leads to the formation of ketones?

A

As beta oxidation leads to a substantial amount of acetyl CoA production, ketone body formation is the “overflow” pathway for acetyl CoA use

36
Q

When does acetyl CoA get converted into ketones?

A

If there is no oxaloacetate, then acetyl CoA does not go through the Kreb’s cycle and is converted to ketones instead

37
Q

Name 3 ketone bodies

A

Acetone
Beta-hydroxybutyrate
Acetoacetate

38
Q

Which ketone body can be converted into the other two ketone bodies in this list?

a) acetone
b) Beta-hydroxybutyrate
c) acetoacetate

A

c) Acetoacetate can be converted into acetone and beta-hydroxybutyrate

39
Q

Briefly describe how phospholipids are formed

A

Same as first steps of TAG synthesis to form DAG, then combined with an alcohol

40
Q

List 5 different phospholipids which can be formed by combining DAG with an alcohol

A
  1. Phosphatidylethanolamine
  2. Phosphatidylserine
  3. Phosphatidylglycerol
  4. Phosphatidylinositol
  5. Phosphatidylcholine
41
Q

Where do you find high levels of phospholipid synthesis?

A

In rapidly-dividing cells

42
Q

How are essential fatty acids obtained and name two types

A

Cannot be synthesised, obtained from diet (originally Vit F)

Polyunsaturated omega-3 or omega-6

43
Q

Name 4 functions of essential fatty acids

A
  1. Cell membrane formation
  2. Required for proper growth and development
  3. Required for brain and nerve function
  4. Precursors for eicosanoids - prostanoids & leukotrienes - inflammatory response
44
Q

How does omega-3 fatty acids affect cardiovascular disease?

A

Protects against heart and circulatory disease by reducing plasma TAG(?)

Not clear whether sources of omega-3 fatty acids other than oily fish provide the same benefits

45
Q

How does omega-6 fatty acids affect cardiovascular disease?

A

May lower LDL

High intakes may also lower HDL

46
Q

How does insulin regulate lipid metabolism?

A

Suppresses lipolysis

Stimulates TAG synthesis and FA synthesis

47
Q

How does noradrenaline regulate lipid metabolism?

A

Stimulates lipolysis

48
Q

What enzymes/transport systems are stimulated by insulin? (4)

A

GLUT-4 mediated transport of glucose

Acetyl CoA carboxylase activity

Expression of fatty acid synthase

Increase activity of lipoprotein lipase (in adipose)

49
Q

Noradrenaline stimulates lipolysis by stimulation of what 3 processes?

A
  1. cAMP synthesis
  2. cAMP-dependent protein kinase (PKA) activation
  3. PKA-mediated phosphorylation and activation of hormone sensitive lipase (HSL)
50
Q

How does insulin inhibit lipolysis?

A

Insulin stimulates breakdown of cAMP

Therefore noradrenaline is no longer able to stimulate lipolysis

51
Q

What happens to the levels of lipoprotein lipase synthesis and activity in the fed state in:

a) adipocytes
b) skeletal and heart muscle

A

a) Increases

b) decreases

52
Q

What happens to the levels of lipoprotein lipase synthesis and activity in the fasted/exercise state in:

a) adipocytes
b) muscle

A

a) Decreases

b) Increases

53
Q

What may lead to elevated fatty acid levels - lipotoxicity?

A

If lipolysis is overactive or if the adipose tissue has exceeded the storage capacity for TAG

54
Q

What happens to fatty acids in lipotoxicity? How does this affect hormonal regulation?

A

FA are taken up and stored as TG in the liver and muscle

Metabolites of FA impair insulin signalling

55
Q

What happens as a result of impaired insulin action in liver, muscle and adipose?

A

Increase: lipolysis, gluconeogenesis

Decrease: glucose uptake, glycogen synthesis

Impaired insulin secretion by beta-cells

HYPERGLYCAEMIA RESULTS

56
Q

Why are essential fatty acids important? List their functions.

A
  • Cell membrane formation
  • required for proper growth and development
  • required for brain and nerve function
  • are precursors for eicosanoids - prostanoids & leukotrienes - responsible for inflammatory response

Endocrine System (6 decks)

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