Lipids

Question 1

TAG

Answer 1

Triglycerides

Question 2

PAG

Answer 2

Phospholipids

Question 3

General structure

Answer 3

Straight hydrocarbon chain with methyl -CH3 (water-hating) and carboxyl group -COOH (water-loving)

Question 4

If the acid contains double bonds it is …

Answer 4

Unsaturated

Question 5

Each double bond inserts a … in the chain, in either … or … conformation

Answer 5

Bend and cis or trans

Question 6

Cis bond inserts a … angle into the hydrocarbon chain

Answer 6

30 degree

Question 7

Linoleic acid example 18:2 n-6

Answer 7

No. C atoms = 18
No. Double bonds = 2
Position of 1st double bond from methyl end = 6

Question 8

Only short chain fatty acids occur …

Answer 8

Free

Question 9

Long chain fatty acids are always…

Answer 9

Saturated, monounsaturated or polyunsaturated

Question 10

Fatty acids are the building blocks for…

Answer 10

Acylglycerols

Question 11

What affects the melting point and susceptibility to oxidation of fatty acids?

Answer 11

Structure

Question 12

What is the normal end point for fatty acid synthesis in cell cytoplasm?

Answer 12

Palmitic acid (C16:0)

Question 13

Where do chain lengthening and desaturation take place?

Answer 13

Smooth endoplasmic reticulum

Question 14

What enzymes add 2C to the carboxyl end of the fatty acid chain?

Answer 14

Elongase

Question 15

What enzymes remove 2H in the presence of O2 to form H20?

Answer 15

Denaturase

Question 16

Animals do not have a denaturase to insert double bonds further from carboxyl end than …

Answer 16

C9

Question 17

Fatty acids are amphiphilic meaning…

Answer 17

They have hydrophilic (COOH) and hydrophobic (CH2) regions

Question 18

Synthesis requires…

Answer 18

High levels of acetyl co-A in cytoplasm
High levels of NADPH (from Pentose phosphate pathway)
Occurs in cytosol

Question 19

When fats are used as energy storage molecules they are stored as…

Answer 19

Triacylglycerols

Question 20

Fatty acid synthesis mainly occurs in … and …

Answer 20

Liver and adipose tissue

Question 21

What type of fatty acids are essential for the maintenance of health?

Answer 21

Polyunsaturated fatty acids as they cannot be formed through normal synthetic pathways

Question 22

Fatty acids that are essential in the diet

Answer 22

Essential fatty acids

Question 23

What are the two essential fatty acids

Answer 23

Linoleic acid (n-6)
a-Linolenic acid (n-3)

Question 24

Most important fatty acids synthesised from Linoleic acid

Answer 24

n-6 series

Question 25

Most important fatty acids synthesised from a-linolenic acid

Answer 25

n-3 series

Question 26

The … fatty acids are precursors of eicosanoids which act as local hormones

Answer 26

C20

Question 27

What are triacylglycerols?

Answer 27

Esters of glycerol and fatty acids

Question 28

Fats are … derived and oils are … derived

Answer 28

Animal and plant

Question 29

Fats have … melting points than oils due to a … number of saturated fatty acids

Answer 29

Higher and higher

Question 30

What are major components of biological membranes?

Answer 30

Phospholipids

Question 31

What are phospholipids made up of?

Answer 31

Esters of glycerol with 2 FA and phosphoric acid

Question 32

How do phospholipids affect the fluidity of membranes?

Answer 32

More polyunsaturated fat means more fluid membrane

Question 33

Polyunsaturated fats are prone to undergoing oxidation which can result in

Answer 33

Membrane damage and cell death

Question 34

Phosphate head is … and fatty acid tail is …

Answer 34

Hydrophilic and hydrophobic

Question 35

What are sterols?

Answer 35

Ampipathic ring structures that are synthesised from acetyl-CoA

Question 36

What are sterols stored as?

Answer 36

Cholesteryl esters

Question 37

Steroid hormones are derived from …

Answer 37

Cholesterol

Question 38

Cholesterol is needed for the production of what?

Answer 38

Bile acid

Question 39

3 types of major lipids in the diet

Answer 39

Triacylglycerols Phosphoacylglycerols Cholesterol and cholesterol esters

Question 40

Lipid in the diet is a source of…

Answer 40

Energy and essential fatty acids

Question 41

Excess lipid intake over energy requirements is stored as … in adipose tissue

Answer 41

Triacylglycerols

Question 42

TAGs are major dietary lipids and non-polar so do not dissolve in

Answer 42

Aqueous environments

Question 43

Lipid digestion - mouth

Answer 43

Lingual lipase released from serous glands pH optimum 4-5 so not active until stomach Gastric lipase secreted by chief cells in stomach Lingual and district lipase both active in stomach

Question 44

Lipid digestion - stomach

Answer 44

Gastric and lingual lipase remove fatty acids at sn-3 position Primarily get DAG formed Do not need bile salts Primarily active against short and medium chain FA

Question 45

Lipid digestion - small intestine

Answer 45

More mechanical mixing and emulsification before further digestion Bile synthesised in liver and secreted into SI via bile duct in response to cholecytokinin Bile salts are ampipathic so emulsify lipids Lipolytic enzymes secreted into pancreas e.g. pancreatic lipase Needs colipase for full activity

Question 46

Lipid digestion continued

Answer 46

Fat entering duodenum stimulates CCK release CCK stimulates secretion of pancreatic enzymes and procolipase Procolipase made into active colipase by trypsin CCK also stimulates gall bladder contraction to expel bile into duodenum Cholesterol esterase hydrolyses cholesterol esters to release free cholesterol

Question 47

Bile

Answer 47

Bile salts derived from cholesterol Ampipathic so assist in formation of micelles Liver synthesises approx 600mg per day Total bile acid pool = 2-4g May need this twice to emulsify a single meal Re-circulated throughout day

Question 48

Absorption of lipids into enterocyte

Answer 48

Micelles containing lipid digestion products pass through water layer Some passively absorbed Some dependant on specific transport proteins Within enterocyte, FA reincorporated into TAG Esterify with glycerol or MAG Incorporated into chylomicrons Secreted across basolateral membrane and enter lymph