Lipids 1

Question 1

What are lipids?

Answer 1

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

Question 2

What forms can lipids take?

Answer 2

• Phospholipids in cell membranes
• Lipid droplets in adipose tissue
• Lipoproteins in blood

Question 3

What are the biological functions of lipids?

Answer 3

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

Question 4

What are the 5 lipid classes?

Answer 4

• Fatty acids
• Tracylgycerol
• Phospholipid
• Glycolipid
• Steroids

Question 5

Describe unsaturated FA.

Answer 5

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

Question 6

Describe saturated FA.

Answer 6

• No double bonds
• Solid
• High Tm

Question 7

What does 18:1 mean in FA nomenclature?

Answer 7

18 carbons and 1 double bond

Question 8

What is the terminal methyl group?

Answer 8

Omega carbon

Question 9

What are the 4 kinds of FA?

Answer 9

• Essential FA
• Good fats
• Bad fats
• Really bad fats

Question 10

What are essential FA/

Answer 10

Linoleic and a-linolenic which we must get from plants

Question 11

What are good fats?

Answer 11

• High in polyunsaturated FA

- Vegetable oils, olive oil, sunflower oil

Question 12

What are bad fats?

Answer 12

• High in saturated FA

- stearic (beef)

Question 13

What are really bad fats?

Answer 13

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

Question 14

What do saturated fats play a huge role in?

Answer 14

Myelination of nerve fibres and hormone production

Question 15

Why must we ingest essential FA?

Answer 15

Humans are not capable of introducing double bonds beyond carbon 9

Question 16

What is arachnoid acid?

Answer 16

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

Question 17

What is linoleic acid a substrate for?

Answer 17

Prostaglandins

Question 18

What is omega-3 FA derived from?

Answer 18

Linolenic acid

Question 19

What are examples of Omega-3 FA?

Answer 19

• Eicosapentaenoic acid

- Docosahexaenoic acid

Question 20

What do Omega-3 FA do?

Answer 20

• Lowers plasma cholesterol preventing atherosclerosis

- Lowers TAG preventing obesity

Question 21

What are Omega-6 FAs?

Answer 21

• Derived from linoleic

- Essential but not the same benefits as omega-3

Question 22

What are the symptoms of essential fatty acid deficiency?

Answer 22

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

Question 23

What conditions are linked to essential FA deficiency?

Answer 23

• Chronic intestinal diseases
• Depression
• ADHD

Question 24

What is TAG?

Answer 24

• 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

Question 25

What are phospholipids composed of?

Answer 25

-Glycerol bonded to 2 FA and a phosphate group

Question 26

Amphipathic

Answer 26

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

Question 27

What is the main dietary lipid?

Answer 27

TAG

Question 28

What are other dietary lipids/

Answer 28

- Phospholipids - Cholesterol - Cholesterol ester - Free FA

Question 29

What is the main site of lipid digestion?

Answer 29

Small intestine

Question 30

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

Answer 30

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

Question 31

What do bile salts do?

Answer 31

- Act as biological agents to form emulsions - Saves lipid coalescing in an aqueous environment - Derivatives of cholesterol

Question 32

How is TAG broken down?

Answer 32

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

Question 33

What are cholesterol esters digested to?

Answer 33

Cholesterol and free FA

Question 34

What are phospholipids hydrolysed to?

Answer 34

FA and lysophospholipid

Question 35

What do the products of lipid digestion from?

Answer 35

Mixed micelles with bile salts

Question 36

What happens to the mixed micelles?

Answer 36

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

Question 37

What do not require micelles for absorption?

Answer 37

Short and medium chain FA

Question 38

What is steatorrhea?

Answer 38

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

Question 39

What causes steatorrhea?

Answer 39

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

Question 40

What role does the gallbladder play in lipid absorption?

Answer 40

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

Question 41

What happens to absorbed FA?

Answer 41

- 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

Question 42

What is apoB-48?

Answer 42

Solubilising protein

Question 43

What does lipoprotein lipase do?

Answer 43

Hydrolyses TAG in chylomicrons to FA and glycerol

Question 44

Where is lipoprotein lipase found?

Answer 44

Primarily in capillaries of skeletal muscle and adipose tissue

Question 45

What happens to the FA TAG is hydrolysed?

Answer 45

Used for energy or re-esterified to TAG for storage

Question 46

What happens to chylomicrons depleted of TAG?

Answer 46

They are call chylomicron remnants and they go to the liver

Question 47

What does the liver do to glycerol?

Answer 47

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

Question 48

What is TAG stored as in adipose tissue?

Answer 48

Droplets that constitute depot fat

Question 49

Why is TAG the most efficient form of storage fuel?

Answer 49

It is highly reduced and nearly anhydrous

Question 50

How are FA released from stored TAG?

Answer 50

By the action of HSL (hormone sensitive lipase)

Question 51

What activates HSL?

Answer 51

Phosphorylation in response to epinephrine

Question 52

What promotes the dephosphorylation and consequent inactivation of lipase?

Answer 52

High plasma glucose and insulin

Question 53

How are free FA transported in the blood?

Answer 53

In a complex with serum albumin

Question 54

What is albumin?

Answer 54

The most abundant plasma protein

Question 55

What are esterified FA in the blood carried in?

Answer 55

Lipoproteins

Question 56

Describe the structure of a lipoprotein.

Answer 56

- Hydrophobic core made of TAG and cholesterol esters | - Hydrophilic surface made of unesterfied cholesterol, phospholipids and apolipoproteins

Question 57

Liporotein classes according to density. | Least dense to Most dense

Answer 57

- 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)

Question 58

What does too much LDL lead to?

Answer 58

- Artheroscolosis | - Lipid develops into fatty streaks and plaque within artery