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Science for Medicine > Lipids 1 > Flashcards

Lipids 1 Flashcards

1
Q

What are lipids?

A

Heterogeneous organic molecules that are insoluble in water but soluble in organic solvents.

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2
Q

What forms can lipids take?

A
  • Phospholipids in cell membranes
  • Lipid droplets in adipose tissue
  • Lipoproteins in blood
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3
Q

What are the biological functions of lipids?

A
  • Stored form of energy
  • Structural element of membranes
  • Enzyme cofactors
  • Hormones
  • Vitamins A,D,E,K
  • Signalling molecules
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4
Q

What are the 5 lipid classes?

A
  • Fatty acids
  • Tracylgycerol
  • Phospholipid
  • Glycolipid
  • Steroids
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5
Q

Describe unsaturated FA.

A
  • Contain one or more double bonds that kink the hydrocarbon chain
  • Liquid
  • Low Tm
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6
Q

Describe saturated FA.

A
  • No double bonds
  • Solid
  • High Tm
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7
Q

What does 18:1 mean in FA nomenclature?

A

18 carbons and 1 double bond

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8
Q

What is the terminal methyl group?

A

Omega carbon

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9
Q

What are the 4 kinds of FA?

A
  • Essential FA
  • Good fats
  • Bad fats
  • Really bad fats
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10
Q

What are essential FA/

A

Linoleic and a-linolenic which we must get from plants

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11
Q

What are good fats?

A
  • High in polyunsaturated FA

- Vegetable oils, olive oil, sunflower oil

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12
Q

What are bad fats?

A
  • High in saturated FA

- stearic (beef)

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13
Q

What are really bad fats?

A
  • Trans FA which are a result of hydrogenation of vegetable oils
  • Hard margarine
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14
Q

What do saturated fats play a huge role in?

A

Myelination of nerve fibres and hormone production

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15
Q

Why must we ingest essential FA?

A

Humans are not capable of introducing double bonds beyond carbon 9

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16
Q

What is arachnoid acid?

A

A precursor of eicosanoids which can be synthesised from linoleic acid.

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17
Q

What is linoleic acid a substrate for?

A

Prostaglandins

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18
Q

What is omega-3 FA derived from?

A

Linolenic acid

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19
Q

What are examples of Omega-3 FA?

A
  • Eicosapentaenoic acid

- Docosahexaenoic acid

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20
Q

What do Omega-3 FA do?

A
  • Lowers plasma cholesterol preventing atherosclerosis

- Lowers TAG preventing obesity

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21
Q

What are Omega-6 FAs?

A
  • Derived from linoleic

- Essential but not the same benefits as omega-3

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22
Q

What are the symptoms of essential fatty acid deficiency?

A
  • Growth retardation
  • reproductive failure
  • Skin lesions
  • Kidney and liber disorders
  • Subtle neurological and visual problems
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23
Q

What conditions are linked to essential FA deficiency?

A
  • Chronic intestinal diseases
  • Depression
  • ADHD
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24
Q

What is TAG?

A
  • Triacylglycerol/ triglyceride
  • Esters of FAs and glycerol
  • Dietary fuel and insulation
  • Esters are neutral uncharged lipids
  • Water insoluble, TAG coalesce into lipid droplets in adipose tissue
25
Q

What are phospholipids composed of?

A

-Glycerol bonded to 2 FA and a phosphate group

26
Q

Amphipathic

A

Charged phosphate group head of a phospholipid id hydrophilic whereas the hydrophobic tails repel water

27
Q

What is the main dietary lipid?

A

TAG

28
Q

What are other dietary lipids/

A
  • Phospholipids
  • Cholesterol
  • Cholesterol ester
  • Free FA
29
Q

What is the main site of lipid digestion?

A

Small intestine

30
Q

What are the main mechanisms involved in the digestion of lipids?

A

Lipid digestion by pancreatic enzymes (lipases) is promoted by emulsification (dispersion) by bile salts and peristalsis

31
Q

What do bile salts do?

A
  • Act as biological agents to form emulsions
  • Saves lipid coalescing in an aqueous environment
  • Derivatives of cholesterol
32
Q

How is TAG broken down?

A

Most TAG is degraded in the small intestine by pancreatic lipase to monoacylglycerol and 2 FA

33
Q

What are cholesterol esters digested to?

A

Cholesterol and free FA

34
Q

What are phospholipids hydrolysed to?

A

FA and lysophospholipid

35
Q

What do the products of lipid digestion from?

A

Mixed micelles with bile salts

36
Q

What happens to the mixed micelles?

A

They approach the brush border membranes of enterocytes and release lipid products which enter cells by diffusion

37
Q

What do not require micelles for absorption?

A

Short and medium chain FA

38
Q

What is steatorrhea?

A

Excess fat in faeces. Stools float due to excess lipid and have an oily appearance and foul smell

39
Q

What causes steatorrhea?

A

Lipid malabsorption due to defects in bile secretion, pancreatic function or intestinal call uptake

40
Q

What role does the gallbladder play in lipid absorption?

A

It secretes bile. Removal of the gallbladder inhibits digestion and absorption fats

41
Q

What happens to absorbed FA?

A
  • The intestinal cells resynthesize TAG, phospholipids and cholesterol esters for export.
  • They are insoluble so are packaged with apoB-48 into chylomicrons for export.
  • Chylomicrons are released by exocytosis into lymph then blood
42
Q

What is apoB-48?

A

Solubilising protein

43
Q

What does lipoprotein lipase do?

A

Hydrolyses TAG in chylomicrons to FA and glycerol

44
Q

Where is lipoprotein lipase found?

A

Primarily in capillaries of skeletal muscle and adipose tissue

45
Q

What happens to the FA TAG is hydrolysed?

A

Used for energy or re-esterified to TAG for storage

46
Q

What happens to chylomicrons depleted of TAG?

A

They are call chylomicron remnants and they go to the liver

47
Q

What does the liver do to glycerol?

A

Uses it to produce glycerol-3-phosphate for us in glycolysis and gluconeogenesis

48
Q

What is TAG stored as in adipose tissue?

A

Droplets that constitute depot fat

49
Q

Why is TAG the most efficient form of storage fuel?

A

It is highly reduced and nearly anhydrous

50
Q

How are FA released from stored TAG?

A

By the action of HSL (hormone sensitive lipase)

51
Q

What activates HSL?

A

Phosphorylation in response to epinephrine

52
Q

What promotes the dephosphorylation and consequent inactivation of lipase?

A

High plasma glucose and insulin

53
Q

How are free FA transported in the blood?

A

In a complex with serum albumin

54
Q

What is albumin?

A

The most abundant plasma protein

55
Q

What are esterified FA in the blood carried in?

A

Lipoproteins

56
Q

Describe the structure of a lipoprotein.

A
  • Hydrophobic core made of TAG and cholesterol esters

- Hydrophilic surface made of unesterfied cholesterol, phospholipids and apolipoproteins

57
Q

Liporotein classes according to density.

Least dense to Most dense

A
  • Chylomicrons: TAG rich (TAG from intestine to tissues)
  • VLDL: TAG rich (TAG from liver to tissue
  • LDL: cholesterol rich (cholesterol to extrahepatic tissue)
  • HDL: protein/cholesterol rich (transports cholesterol from tissue to liver for elimination)
58
Q

What does too much LDL lead to?

A
  • Artheroscolosis

- Lipid develops into fatty streaks and plaque within artery

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