Lipids part 1

Question 1

What are lipids?

Answer 1

Heterogeneous organic molecules

Insoluble in water (hydrophobic), soluble in organic solvents

Exist in cell membranes, as lipid droplets in adipocytes (adipose tissue), in blood lipoproteins

Question 2

What are the functions of lipids?

Answer 2

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

Question 3

What are the classes of lipids?

Answer 3

Fatty acids (1 or 2 acyl chains and phosphate group)
Triacylglycerol (3 acyl chains)
Phospholipid
Glycolipid (acyl chains linked to carb mol)
Steroids (ring structure)

Question 4

Types of fatty acids?

Answer 4

Saturated FA are solid, no double bonds (high Tm)

Unsaturated FA – one or more double bonds that kink the hydrocarbon chain, liquid (low Tm)

Question 5

What does 18:1(9) mean?

Answer 5

18 carbons and one double bond at position 9

Question 6

What are the essential fatty acids?

Answer 6

Linoleic and a-linolenic; must get these from plants

Question 7

What are the ‘good’ fats? (cardiovascular)?

Answer 7

high in polyunsaturated fatty acids: e.g. vegetable oils, like olive oil, sunflower oil, etc

Question 8

What are the ‘bad fats’ (cardiovascular)?

Answer 8

high in saturated fatty acids: e.g. stearic (beef). (Saturated -major role in myelination of nerve fibres and hormone production important in maintaining health).

Question 9

What are the really bad fats?

Answer 9

trans fatty acids, result from hydrogenation of vegetable oils e.g. hard margarine (man-made)

Question 10

Why are essential fatty acids essential?

Answer 10

Humans cannot introduce double bonds beyond carbon 9
Must ingest essential FA

Question 11

What other fatty acids are made from linoleic and linolenic acids?

Answer 11

Arachidonic acid, a precursor of eicosanoids can be synthesized from linoleic acid

Omega-3 fatty acids are derived from linolenic acid as essential FAs.
Omega-3 FA lowers plasma cholesterol prevents atherosclerosis, lowers TAG prevents obesity, reduces inflammation.

Question 12

Effects of essential fatty acid deficiency?

Answer 12

Rare, occurring most often in infants fed dietsdeficientin EFAs.
Signs include scaly dermatitis, alopecia, thrombocytopenia, and, in children, intellectual disability.

People with chronic intestinal disorders

Can result in depression-deficiency of lipid signalling molecules

ADHD –lower levels of omega3 leads to behavioural problems

Question 13

Characteristics of triaglycerols?

Answer 13

3 carbon backbone (glycerol) and 3 acyl chains

Esters of FAs and glycerol

Esters are neutral uncharged lipids

Water insoluble TAG coalesce into lipid droplets in adipose tissue (major lipid component of adipose tissue)

Dietary fuel and insulation

Question 14

What does it mean by a phopsholipid being amphipathic?

Answer 14

Composed of glycerol bonded to two fatty acids and a phosphate group.
Charged phosphate ‘head’ group of a phospholipid is hydrophilic (attracted to water).
Hydrophobic ‘tails’ repel water.

Question 15

Functions of phospholipids?

Answer 15

Membranes
Lipid droplets
Local signalling molecules

Question 16

What are the 3 main classes of steroids?

Answer 16

Cholesterol is the starting material for the synthesis of bile salts, steroid hormones and other components

Steroid hormones are substances that serve as chemical messengers in the body (corticosteroids, sex hormones).

Bile salts: sodium salts of steroids used for emulsification

Question 17

What are the functions of cholesterol, where it is made and where found?

Answer 17

-component of cell membranes
-precursor to other substances like sterol hormones, vitamin D and bile acids
-mainly made in liver and found only in animal foods

Question 18

What are function of statins?

Answer 18

Inhibit HMG-CoA reductase that is essential in cholesterol synthesis
Lowers Low Density Lipoprotein (LDL) levels
Reduce risk of developing cardiovascular disease

Question 19

Characteristics of Eicosanoids?

Answer 19

Lipid class derived from 20-carbon unsaturated fatty acids (eicosanoic acids) and are synthesized throughout the body

Signaling molecules derived from omega-3 or omega-6 fatty acids.

Precursors to prostaglandins, thromboxanes, and leukotrienes.

Short half life (metabolised rapidly), produced and act locally

Question 20

What do eicosanoids regulate?

Answer 20

Lipid Inflammatory response (e.g. joints, skin, eyes)
Pain & fever (prostaglandins)
Blood pressure regulation (prostacyclin)
Blood clotting induction/platelet homeostasis (thromboxanes)
Many reproductive functions (e.g. labour induction) & menstrual cramps, sperm mobility (prostaglandins)
SMC constrictions & bronchioconstriction (leukotrienes)
Mucus production in the stomach (prostaglandins)

Question 21

What is the main dietary lipid and other lipids ?

Answer 21

triaglycerol and phospholipids, cholesterol, cholesterol ester, free fatty acids

Question 22

Where is main site of digestion?

Answer 22

small intestine

Question 23

What is the main enzyme to break down lipids?

Answer 23

pancreatic enzymes (lipases) promoted by emulsification (dispersion) by bile salts and peristalsis (mixing)

Question 24

Characteristics of bile salts?

Answer 24

Act as biological detergents to form emulsions and mixed micelles
Saves lipids coalescing in an aqueous environment
Derivatives of cholesterol

Question 25

Steps of the digestion of lipids? (small intestine)

Answer 25

Most TAG degraded in small intestine by pancreatic lipase to monoacylglycerol and two fatty acids (FA)

Cholesterol esters digested to cholesterol and free FA

Phospholipids hydrolysed to FA and lysophospholipid

Question 26

Digestion of lipids steps (basic)?

Answer 26

fat to emulsified fat through bile acids

emulsified fats to fatty acids and glycerol through lipases

Question 27

How are digested lipids uptaken into cells?

Answer 27

Products of lipid digestion form mixed micelles with bile salts. Mixed micelles approach brush border membranes of enterocytes and release lipid products which enter cells by diffusion.
Short and medium chain FA do not require micelles for absorption

Question 28

What is steatorrhea?

Answer 28

Lipid malabsorption due to defects in bile secretion, pancreatic function or intestinal cell uptake results in steatorrhea

Steatorrhea is excess fat in faeces. Stools float due to excess lipid, have an oily appearance and are foul smelling

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

Question 29

What happens to absorbed fatty acids?

Answer 29

Intestinal cells resynthesize TAG, PL, CE (lipids) for export

FAs are insoluble so packaged with apoB-48 (solubilising protein) into chylomicrons for export

Chylomicrons are released by exocytosis into lymph then blood

Question 30

What happens when blood chylomicrons reach tissue?

Answer 30

TAG in chylomicrons is hydrolysed to FA and glycerol by lipoprotein lipase

Lipoprotein lipase is found primarily in capillaries of skeletal muscle and adipose tissue

Resulting free FA used for energy or re-esterified to TAG for storage

Chylomicrons depleted of TAG are called chylomicron remnants which go to the liver

Glycerol is used by liver to produce glycerol-3-phosphate (glycolysis & gluconeogenesis)

Question 31

How are fatty acids transported in blood?

Answer 31

Free fatty acids transported through blood in complex with serum albumin
(sometimes called non-esterified fatty acids or NEFA)

Albumin most abundant plasma protein with 2-7 binding sites for FA

Most FA (>90%) is esterified (ie not free)
Esterified FA are carried in lipoproteins

Question 32

Characteristics of lipoproteins?

Answer 32

Hydrophobic core: TGs, chloesteryl esters

Hydrophillic surfaces: Unesterified cholesterol, phospholipids, apolipoproteins e.g.B100

Question 33

Lipoprotein classes?

Answer 33

Classified by density (least to most)

most dense are smallest

Chylomicrons: TAG rich (TAG from intestine to tissues).
VLDL: TAG rich (transports TAG from liver to tissue)
LDL: Cholesterol rich (cholesterol to extrahepatic tissue = BAD cholesterol)
HDL: Protein & cholesterol rich (cholesterol from tissue to liver for elimination = GOOD cholesterol)

Question 34

What leads to atherosclerosis?

Answer 34

Too much LDL (obesity or genetic defect in LDL receptors) leads to atherosclerosis
Lipid develops into fatty streaks and plaque within artery