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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)?

25
What is the basis of triglyceride synthesis?
The esterification of glycerol and three fatty acids
26
What is the role of lipoprotein lipase (LPL) in triglyceride synthesis?
Hydrolyses TAG in chylomicrons/VLDL
27
What is the role of Diacylglycerol Acyl Transferase (DGAT) in triglyceride synthesis?
Re-esterifies to TAG using glycerol obtained from glycolysis
28
Describe in general terms, triglyceride breakdown (lipolysis), including the enzyme involved
Breakdown of the triglyceride into glycerol and 3 fatty acids Hormone sensitive lipase in adipose tissue
29
What activates hormone-sensitive lipase, leading to lipolysis in adipose tissue? What inhibits hormone-sensitive lipase?
cAMP-dependent phosphorylation in response to adrenaline in fasted state Hormone-sensitive lipase is inhibited by insulin
30
How many carbons at a time can be added to fatty acids during fatty acid synthesis?
2
31
What is the limit for the number of carbons that can be added during fatty acid synthesis?
16
32
What are the key regulatory enzymes for fatty acid synthesis?
Acetyl CoA carboxylase - forms malonyl CoA Fatty acid synthase
33
Other than aiding fatty acid synthesis, what is the other role of malonyl CoA?
Inhibits fatty acid oxidation
34
Where does fatty acid synthesis occur in the cell?
Cytoplasm
35
What leads to the formation of ketones?
As beta oxidation leads to a substantial amount of acetyl CoA production, ketone body formation is the "overflow" pathway for acetyl CoA use
36
When does acetyl CoA get converted into ketones?
If there is no oxaloacetate, then acetyl CoA does not go through the Kreb's cycle and is converted to ketones instead
37
Name 3 ketone bodies
Acetone Beta-hydroxybutyrate Acetoacetate
38
Which ketone body can be converted into the other two ketone bodies in this list? a) acetone b) Beta-hydroxybutyrate c) acetoacetate
c) Acetoacetate can be converted into acetone and beta-hydroxybutyrate
39
Briefly describe how phospholipids are formed
Same as first steps of TAG synthesis to form DAG, then combined with an alcohol
40
List 5 different phospholipids which can be formed by combining DAG with an alcohol
1. Phosphatidylethanolamine 2. Phosphatidylserine 3. Phosphatidylglycerol 4. Phosphatidylinositol 5. Phosphatidylcholine
41
Where do you find high levels of phospholipid synthesis?
In rapidly-dividing cells
42
How are essential fatty acids obtained and name two types
Cannot be synthesised, obtained from diet (originally Vit F) Polyunsaturated omega-3 or omega-6
43
Name 4 functions of essential fatty acids
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
How does omega-3 fatty acids affect cardiovascular disease?
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
How does omega-6 fatty acids affect cardiovascular disease?
May lower LDL | High intakes may also lower HDL
46
How does insulin regulate lipid metabolism?
Suppresses lipolysis | Stimulates TAG synthesis and FA synthesis
47
How does noradrenaline regulate lipid metabolism?
Stimulates lipolysis
48
What enzymes/transport systems are stimulated by insulin? (4)
GLUT-4 mediated transport of glucose Acetyl CoA carboxylase activity Expression of fatty acid synthase Increase activity of lipoprotein lipase (in adipose)
49
Noradrenaline stimulates lipolysis by stimulation of what 3 processes?
1. cAMP synthesis 2. cAMP-dependent protein kinase (PKA) activation 3. PKA-mediated phosphorylation and activation of hormone sensitive lipase (HSL)
50
How does insulin inhibit lipolysis?
Insulin stimulates breakdown of cAMP | Therefore noradrenaline is no longer able to stimulate lipolysis
51
What happens to the levels of lipoprotein lipase synthesis and activity in the fed state in: a) adipocytes b) skeletal and heart muscle
a) Increases | b) decreases
52
What happens to the levels of lipoprotein lipase synthesis and activity in the fasted/exercise state in: a) adipocytes b) muscle
a) Decreases | b) Increases
53
What may lead to elevated fatty acid levels - lipotoxicity?
If lipolysis is overactive or if the adipose tissue has exceeded the storage capacity for TAG
54
What happens to fatty acids in lipotoxicity? How does this affect hormonal regulation?
FA are taken up and stored as TG in the liver and muscle Metabolites of FA impair insulin signalling
55
What happens as a result of impaired insulin action in liver, muscle and adipose?
Increase: lipolysis, gluconeogenesis Decrease: glucose uptake, glycogen synthesis Impaired insulin secretion by beta-cells HYPERGLYCAEMIA RESULTS
56
Why are essential fatty acids important? List their functions.
- 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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