Lipid Structure and Classification_Molecules Flashcards Preview

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Flashcards in Lipid Structure and Classification_Molecules Deck (78):
1

What is a lipid?

1) A heterogenous class of naturally occurring organic compounds on the basis of common solubility properties

2

What are the common solubility properties of lipids?

1) Non polar/hydrophobic - soluble in organic solvents but NOT water
2) largely hydrocarbon in nature
3) Can be amphipathic (mainly non polar/hydrophobic but with some hydrophilic/polar groups)

3

What are the major classes of lipid?

1) Fatty acids (and their derivates)
2) Triacylglycerols (triglycerides)
3) (Glycero) phospholipids
4) Sphingolipids
5) Cholesterol

4

What are the 5 major functions that lipids have physiological importance for humans?

1) Serve as structural components of biological membrane
2) Provide energy reserves, predominantly in the form of Triacylglycerols
3) Both lipids and lipid derivatives serve as vitamins and hormone
4) Bile acids aid in lipid solubilisation
5) Biological signalling molecules

5

What are examples of lipids and lipid derivatives serving as vitamins and hormone?

1) Fat soluble vitamins
2) Eicosanoids (e.g. prostaglandins)
3) Steroid hormones

6

What are fatty acids composed of?

Long hydrocarbon chains (C10-C24) with a terminal carboxylate (COO-) group

7

Most naturally occurring FA have how many numbers of C atoms?

Even number of C atoms

8

Most fatty acids are branched or unbranched?

Branched

9

What are the properties of Fatty Acids?

1) Highly reduced (energy dense)
2) C-C double bonds in naturally occurring FA are cis (not trans)
3) Soem FA are essential and must be consumed in our diet
4) May be saturated (all C-C bond are single) or unsaturated (one or more C-C double bonds)

10

If there is 1 C-C double bond, what is it called?

Monounsaturated (MUFA)

11

If there are 2 or more C-C double bond, what is it called?

Polyunsaturated (PUFA)

12

What is the general structure of a fatty acid?

Position of C-C double bond may be denoted in relation to the C number (with 1 being the C atom of the -COO- group)
OR
Position of C-C double bond may be denoted in relation to omega C atom e.g. omega3, omega6, omega9 etc.

13

A saturated Fatty Acid doesn't have what?

No C = C double bonds

14

Most naturally occurring double bonds are what confirmation?

Cis
(Trans isomer is some but rare)

15

Chemical/Industrial production of MUFA and PUFA (hydrogenated fats) yield what? What is the effect?

Yield trans isomer (dietary trans FA)
Effect: Appear to increase risk of coronary heart disease in party by raising LDL cholesterol

16

Unsaturated FA have how many C=C double bond?

1 or more C=C double bond

17

What do trans FA do?

Makes fat more solid or 'spreadable', helps to prolong the shelf life of the food and maintain flavour stability

18

What are the effects of FA (De)saturation on structure of lipid aggregates?

- Saturated FA chains pack tightly and form more rigid, organised aggregates
- Cis unsaturated FA chains bend and pack in a less ordered way, with greater potential for motion i.e. more fluid - trans unsaturated chains are more straighter

19

Why is FA saturation important?

Important déterminant of membrane fluidity

20

What are essential fatty acids?

PUFAs with >= 2 double bonds at least 1 of which is beyond C9

21

Why is PUFAs with >= 2 double bonds at least 1 of which is beyond C9 considered an essential fatty acid?

As human and animal species cant introduce double bonds into FA after C9, some FA are essential and must be consumed in our diet

22

What are examples of essential fatty acids?

Linolenic acid (C18:3) - omega 3 fatty acid
Linoleic acid (C18:2) - omega 6 fatty acid

23

How do FA with double bonds after C9 become consumed in our diet to become beneficial to our body?

Converted by elongation and desaturation to PUFA with essential biological roles

24

What are examples of FA converted by elongation and desaturation to PUFA with essential biological roles?

Linoleic acid -> arachidonic acid (C20:4) - ARA
Linolenic acid -> eicosapentaeonic acid (C20:5) - EPA

25

What are ARA and EPA

Serve as precursors for synthesis of eicosanoids

26

What is a fatty acid derivatives?

Eicosanoids

27

What is eicosanoids derived from?

From C20 conditionally essential PUFAs

28

What are the C20 conditionally essential PUFA is needed to make eicosanoids?

1) C20:3 eicosatrienoic acid (ESA)
2) C20:4 arachadonic acid (ARA)
3) C20:5 eicosapentaenoic acid (EPA)
can be synthesised from essential FAs - linoleum acid (C18:2) and linolenic acid (C18:3)

29

What are the synthetic pathways that can create eicosanoids?

Cyclooxygenase (COX) pathway (prostaglandins and thromboxane)
Lipooxygenase (LOX) pathway (leukotriene)

30

What do eicosanoids do?

Exert their actions by binding to specific plasma membrane receptors

31

What are examples of a subclass of Eicosanoids, essentially a metabolite of arachidonic acid?

LT (Leukotrienes) and PG (Prostaglandins)

32

What do LT and PG do?

Function as local signalling molecules and play important roles in:
1) inflammation (COX2) inhibitors are widely prescribed NSADs e.g. aspirin)
2) regulation of vascular tone
etc.

33

What is a triacylglycerols (triglycerides)?

3C alcohol (glycerol) esterified to 3 FA through -COOH group

34

What is triacylglycerols used for?

A major energy storage form in animals
1) stored in adipose tissue,
2) highly reduced (energy dense) form of carbon,
3) no solvation (take up less space than highly hydrated CHO)

35

What are other advantages of triacylglycerols?

Insulation

36

What does it mean for there to be highly reduced form of carbon?

1 g of triacylglycerols yields about 38 kJ of energy (twice as much as CHO or protein)

37

What is triglyceride structure?

1) Lipases cleave ester bonds and release the FA
2) FA may all be the same or different and may be saturated, unsaturated or both

38

What is the simplest GPL [(Glycerol)Phospholipids]?

Phosphatidate

39

What is the structure of the simplest GPL which is phosphatidate?

Glycerol 3 phosphate esterified with 2 FA (diacylglycerol with a PO4 at 3rd -OH Group)

40

If GPL contains an unsaturated FA, where would it be?

Be at C2

41

What is unique about (glycerol)phospholipids (GPL)?

A variety of polar alcohol compounds can be esterified to the PO4 group of phsophatidate

42

What are the variety of polar alcohol that can be esterified to the PO4 group of phosphatidate?

1) Choline (phosphatidylcholine aka lecithin)
2) Serine (phosphatidylserine)
3) Ethanolamine (phosphatidylethanolamine)
4) Inositol (phosphatidylinositol)
5) Glycerol (Phosphatidylglycerol)

43

What is do venoms of poisonous snakes like the Indian cobra contain

Venoms of poisonous snakes contain large amounts of phospholipase A2

44

What is lysolecithin?

A breakdown product of this reaction (phospholipase breakdown of GPL)

45

What does lysolecithin do?

Acts as a biological detergent and dissolves the membranes of red blood cells, causing them to rupture

46

What are (glycerol)phospholipid properties?

GPLS are amphipathic molecules
- polar head: PO4 and alcohol groups
- non polar tail: hydrophobic FA chains

47

What are the benefits of the GPL having amphipathic properties?

Integral to the role of GPL in biological membranes

48

What does unsaturated fatty acids do?

Change the fluidity and permeability of membrane

49

What does phospholipid bilayer with many unsaturated fatty acids have?

High fluidity
High permeability

50

What is an important determinant of membrane fluidity?

Temperature

51

What is the effect of temperature and membrane fluidity?

Increase in temperature, increase in fluidity
- Lipids acquire thermal energy when they are heated up; energetic lipids move around more, arranging and rearranging randomly, making the membrane more fluid

52

What does cholesterol do to membrane fluidity?

1) Cholesterol decreases membrane fluidity near membrane surface
2) acts as a 'spacer' allowing greater fluidity deeper inside the lipid bilayer

53

What do the main class of glycolipids contain?

Contain sphingosine and one or more sugars (glycophingolipids - GPL)

54

What is the simplest glycosphingolipids?

Ceramide

55

What is glycosphingolipids particularly abundant in?

In nerve cell membrane

56

What does glycosphingolipids being particularly abundant in nerve cell membrane help with?

1) Nerve impulse transmission
2) Cell-cell recognition
3) Molecular recognition (binding glycoprotein homeones and bacterial toxins)

57

What are genetic defects in glycosphingolipid metabolism respsonsible for?

For several fatal neurological disorders (sphingolipidoses)

58

What are sphingolipids?

Membrane lipids based on an 18C amino alcohol (sphingosine) rather than glycerol

59

What is the parent compound of sphingolipids?

Ceramide

60

What is ceramide consisted of?

Sphingosine
FA joined to the nitrogen of sphingosine in an amide linkage

61

What are categories under Glycosphingolipids?

1) Cerebrosides
2) Globosides
3) Gangliosides

62

What are cerebrosides?

Ceramide + 1 sugar

63

What are examples of cerebrosides?

Glucosylceramide
Galactosylceramide

64

What are Globosides?

Ceramide + 2 or more sugars not including NANA

65

What are examples of globosides?

Lactosylceramide
Trihexosylceramide
Globoside

66

What are gangliosides?

Ceramide + 3 or more sugars one of which is N acetylneuraminic aka NANA

67

What are sphingomyelin?

Abundant membrane lipid in nerve cells phosphorylcholine or phosphorylethanolamine esterified to C1 -OH of ceramide

68

What does sphingomyeline have and don't have?

Phospholipid but not glycerophospholipid

69

What is the core structure of cholesterol?

Consists of three 6 membered rings and one 5 membered ring with 8C side chain

70

What type of molecule is cholesterol?

Hydrophobic molecule apart from weakly polar -OH group on C3 (amphipathic lipid)

71

What is cholesterol comprised of?

30-40% of plasma membrane lipids,

72

What is the cholesterol do?

1) playing a critical role in regulating membrane fluidity
2) Serves as a precursor for synthesis of many other biological molecules such as steroid hormones and bile salts

73

What are the major cholesterol derivatives and what is the hormone they play apart of?

1) Mineralocorticoids - Aldosterone
2) Glucocorticoids - Cortisol
3) Androgens - Testosterone
4) Estrogens - Estradiol
5) Progestagens - Progesterone
6) Calciferols - 1,25 dihydroxy vitamin D2
7) Bile salts- chalk acid/deoxycholic acid

74

What type of molecule are lipids?

Lipids are predominantly hydrophobic molecules that can be esterified but cannot polymers

75

Which is more dense fatty acid or carbohydrates?

Fatty acids are more energy dense than carbohydrates and can be stored in a more compact form

76

What type of molecules are glycerophospholipids?

Amphipathic molecules that can form the lipid bilayer component of cell membrane

77

What is bilayer fluidity dependent on?

On length and saturation of its lipids and on the presence of cholesterol

78

What are glycolipids?

Abundant membrane lipids in cells of the CNS