Lipids

Question 1

Classification of lipids

Answer 1

Simple and complex

Question 2

Simple lipid definition

Answer 2

An ester of fatty acids with alcohol and no other molecule

Question 3

Complex lipid definition

Answer 3

An ester of fatty acids with alcohol and other molecules such as phosphates, nitrogenous base,

Question 4

General structure of fatty acids

Answer 4

Follow general formula Ch3-(CH2)n-COOH

Saturated fatty acid with no double bond, straight chains.

Unsaturated fatty acid with double bond, forming a kink. . If more than one fatty acid is present then a methylene group often separates them.

Question 5

Alternatives to structure of fatty acids and where are they found?

Answer 5

Cyclic structure found in microorganisms and seeds, branched fatty acids in wax

Question 6

How are the carbons numbered?

Answer 6

Numbered 1-n from the carbon in the carboxyl group.

Question 7

What is an essential fatty acid?

Answer 7

One that cannot be synthesised by the body and must be supplied with the diet. Examples include polyunsaturated linoleic, linolenic and arachidonic FAs.

Question 8

Sources of fatty acid

Answer 8

Diet and de-novo synthesis

Question 9

Where in diet?

Answer 9

Present in animal fats such as duck fat, lard and butter or vegetable fats such as coconut oil, sunflower oil and rapeseed oil.

Question 10

De-novo synthesis explained

Answer 10

The synthesis of complex molecules from simple molecules such as sugars. Enzyme Acetyl CoA carboxylase introduces a carboxyl group to acetyl CoA, forming malonyl CoA. Fatty Acid Synthase enzyme then turns malonlyl-CoA into fatty acid chains.

Question 11

Key complex lipid examples

Answer 11

phospholipids, phosphatidyls, sphingolipids and sterols

Question 12

Phospholipid structure

Answer 12

Constituted by an alcohol, Fatty Acids and phosphoric acid.

Question 13

What is the most abundant phospholipid? + location

Answer 13

Glycerophospholipid, where the alcohol is a glycerol molecule. Found in high abundance in cell membranes and small quantities in fat stores

Question 14

Glycerophospholipid structure

Answer 14

2 hydroxyl groups esterase by fatty acids, with the one at C2 commonly an arachidonate. Third hydroxyl esterified by phosphoric acts. C2 of the glycerol moiety is asymmetric, producing stereoisomerism

Question 15

How does a phosphatidyl vary?

Answer 15

One of the OH groups on the phosphate moiety is esterified with another component, generating diffing glycerophospholipids .

Question 16

Different classes of phospholipids

Answer 16

Phosphatidic Acid (PA), Phosphatidylethanolamine (PE), Phosphatidylcholine (PC), Phosphatidylserine (PS), Phosphatidylinositol (PI) and Cardiolipin (CL)

Question 17

Phosphatidic acid structure + function

Answer 17

Compounds formed of a molecule of glycerol with two hydroxyl esterified by fatty acids and the other by phosphoric acid. Due to small highly charged head group lipid introduces high curvature in lipid bilayers. Produced as intermediates in the synthesis of triacylglycerols and glycerophospholipids.

Question 18

Phosphatidylethanolamine structure + function

Answer 18

Primary amine phospholipid, ethanol amine added to head group. Major structure in cell membranes

Question 19

Phosphatidylcholine structure + function

Answer 19

Amino acid choline esterified as head group. Important in packing cell membranes due to its can shape and zwitterionic (overall neutral) existence.

Question 20

Phosphatidylserine structure + function

Answer 20

Amino acid serine esterified as head group. Especially present in enriched brain tissue, considered to be involved in cognitive development. Also anchors proteins to the cell membrane, including PKC

Question 21

Phosphatidylinositol structure + function

Answer 21

Cyclic hexalcohol is head group. Important in signalling, especially in the brain. Commonly in the structure of phosphatodylinositol biphosphates, with C4 and C5 on the inositol groups being phosphorylated.

Question 22

Cardiolipin structure + function

Answer 22

Essentially two Phosphatidic acids glued together by a glycerol. Found predominantly in the mitochondrial inner membrane and I important in stabilising proteins in the electron transport chain.

Question 23

Overall functions of phospholipids

Answer 23

Form phospholipid bilayers due to their amphipathic molecules, with a polar head comprised of the OH groups on the phosphoric acid moiety, while the non polar region comprises of the tails of the carbon chains of fatty acids. Allows the molecules to arrange as a double layer, with their polar heads facing towards the aqueous medium and the non polar acyl chains orientated towards the membrane interior. Enable organelles to function and cells.

Also act as detergents, reduce the water surface tension and stabilise the dispersion of hydrophobic compounds in aqueous solutions.

Question 24

Phospholipid degradation definition

Answer 24

Specific phospholipases hydrolyse bonds in phospholipids. Components can then be used in physiological functions and pathophysiological processes.

Question 25

Name three phospholipases

Answer 25

Phospholipase A1, A2 and C

Question 26

Roles of each phospholipase

Answer 26

A1- removes the 1-acyl, hydrolyse phospholipid into fatty acids, producing a fatty acid and a lysophospholipid. Act as digestive enzyme

A2- cleave fatty acid in position 2, recognises the sn-2 acyl bond, releasing arachidonic acid which is modified into eicosanoids including prostaglandins- inflammatory mediator.

C- removes phosphorylated head group, important in signal transduction pathways.

Question 27

Sphingolipid definition

Answer 27

A lipid composed of an alchohol called a sphingosine, a fatty acid, phosphoric acid and choline

Question 28

Most common sphingolipid

Answer 28

Sphingomyelin

Question 29

Sphingosine structure

Answer 29

18 carbon atoms, alcohol group at C1, amine at C2, secondary alcohol at C3 and a double bond between C4 and C5 and the rest is a saturated hydrocarbon chain.

Question 30

How are sphingolipids formed from spingoserine

Answer 30

FA binds to C2 amine via an amide function, forming a ceramide. Phosphoric acid esterifies the -OH at C1 and choline binds to the phosphate.

Question 31

Sphingomyelin function

Answer 31

Forms myelin sheaths of nervous tissues.

Question 32

Two most common types of glycolipids + original lipid

Answer 32

Derived from sphingomyelin- cerebrosides and gangliosides

Question 33

Cerebroside structure + function

Answer 33

Neutral compound formed of a ceramide (sphingosine and fatty acid) with a monosaccharide, usually galactose, bound to C1 of esfingol. Gallactose containing lipids are found in plasma membrane of neuronal cells, glucose in non neuronal cells.

Question 34

What is a globoside?

Answer 34

Glycosphingolipid with a more complex carbohydrate portion.

Question 35

Ganglioside structure

Answer 35

Ceramide with the carbohydrate portion at C1 being very complex, oligosaccharides composed of several hexoses and silica acid residues.

A chain of hexose monosaccharides, usually beginning with glucose, galactose, N-acetyl-galactosamine and another glucose or galactose.

Sialic acid is bound to one of the monosaccharides on the chain.

Question 36

Ganglioside function

Answer 36

Structural component of cell membranes and acts as a cell marker and specific binding site for interferons.

Question 37

Sterol definition

Answer 37

Cyclopentanoperhydrophenanthrene derivatives .All structures that have this chemical ring structure are called steroids.

Question 38

Cholesterol structure

Answer 38

Formed of 3 6 membered rings and one 5 membered ring a short aliphatic chain and hydroxyl group.

Amphiphillic nature due to hydroxyl group

Question 39

Cholesterol’s derivatives

Answer 39

steroid hormones and bile

Question 40

Steroid hormone synthesis

Answer 40

Synthesised from cholesterol in the gonads and adrenal glands.

Question 41

Bile synthesis

Answer 41

Bile salts are derived from cholesterol, then become conjugated in the liver with glycine and taurine to form bile acids.

Bile salts and acids have higher hydrophilicity than cholesterol so become excreted into the intestine to emulsify lipids to aid digestion.