6 lipids and biological membrane 1

Question 1

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What is the defining feature of lipids?

Answer 1

insolubility in water

Question 2

What are the 3 types of lipids

Answer 2

• fats and oils - major stored forms of energy
• phospholipids and steroids - major structrual element of biological membranes
• other lipids - present in small quantities, crucial role in enyme cofactors, eectron carriers, hormones etc

Question 3

What are the stored forms of lipids?

Answer 3

Fats and oils

Question 4

What are fats and oils a derivative of?

Answer 4

Fatty acids

Question 5

what are fatty acids?

Answer 5

carboxylic acids with hydrocarbon chains
range from 4 to 36 carbon long
* some chains are unbranched and fully saturated (no DB)
* others contain one or mroe double bond

Question 6

what does R-COOH refer to?

Answer 6

structure of fatty acid

R = a hydrocarbon chain that can vary in legnth
-COOH = terminal carboxyl group

Question 7

Diff between short, medium, long and very long chain?

Answer 7

short = 2-4
medium = 6-12
long = 14-20
very long = >20

Question 8

What do fatty acid properties depend on?

Answer 8

• length of hydrocarbon chain
• degree of saturation (no. of DB)

determine whether its melting point, solid or liquid in room temp

longer chain + saturated = higher MP, solid at room temp cuz packed more closely

Question 9

Saturated vs unsaturated FA

Answer 9

sat - no more hydrogens can be added
unsat - FA with one or more DB, contain less hydrogen atoms than sat FA

Question 10

What are the 2 possible position of double bonds?

Answer 10

cis and trans

Question 11

What are cis-unsaturated FA?

Answer 11

Hydrogen on the double bond carbons are on the same side
= bend fatty acid

Question 12

What configuration are nearly all naturally occuring unsaturated FA in?

Answer 12

cis-configuration

Question 13

What are trans-unsaturated FA?

Answer 13

Hydrogen on the carbon-carbon double bond are on opposite sides
= straight fatty acid

Question 14

Where can trans fatty acid be obtained?

Answer 14

from dairy products and meats
also produced during hydrogenation (adding H) of fish or vegetable oils

Question 15

what do the numbers of this nomenclature refer to?

Answer 15

chain length:number of DB
position of any DB are specific by △ followed by superscript numbers

e.g. 18:3(△⁸)

Question 16

How does the FA structure affect packing?

Answer 16

Packing affect the physical property - solid of liquid form when in room temp

trans - straight line, can be packed very orderly and closely = easier to solidify, more dense
Mixture - create more space between fatty acids, less dense, more fluid at room temperature

Question 17

Question 18

What are triacylglycerols made from?

Answer 18

3 fatty acids and a glycerol molecule

Question 19

In what way are most naturally occuring triacylglycerol mixed?

Answer 19

contain at least 2 diff types of fatty acid

Question 20

What are the properties of triacylglycerol?

Answer 20

non polar, hydrophobic molecules
essentially insoluble in water

Question 21

How do triacylglycerol used as storage fuel in body and in plants?

Answer 21

Body
* large amount of triacylglycerols as fat droplets in adipocytes or fat cells in vertebrate stores (nearly fill the cell)

Plants
* seeds store triacylglycerol as oils = provide energy and biosynthetic precursors duing seed germination

Question 22

what are 4 advantages of using triacylglycerol as storage fuel?

Answer 22

1. carbons of FA are more reduced than those in polysaccharide = oxidation of triacylglycerol yields 2x more energy than oxidation of polysaccharide
2. since they are hydrophobic and therefore unhydrated, they do not carry extra water weight, every gram of polysaccharide stored with 2g of water
3. store more energy in triacylglycerol, less than a days energy supply in glycogen
4. triacylglycerol stored beneath the skin can searve as insulation = penguins are padded with triacylglycerol

Question 23

What are biological membranes made of?

Answer 23

double layer of lipids

Question 24

What do the structural lipids in membrane do?

Answer 24

act as barrier to the passage of polar molecules and ions

Question 25

How are membrane lipids amphipathic?

Answer 25

hydrophillic end and hydrophobic end
hydrophobic interactions with each other and hydrophilic interact w water
= packs into sheets called membrane bilayer

Question 26

What are 2 categories of membrane lipids?

Answer 26

phospholipids and glycolipids

Question 27

What are 2 phospholipids?

Answer 27

glycerophospholpids
sphingolipids

Question 28

What are glycerophospholipids?

Answer 28

• membrane lipid with 2 FA linked to C1 and C2 of glycerol
• a highly polar or charged group linked to C3 via a phosphodiester linkage
• are named as derivatives of the parent counpound, phosphatidic acid, according to the polar alcohol in the head group

Question 29

what are sphingolipids?

Answer 29

• also have polar head group and 2 nonpolar tails
• but no glycerol
• contains one molecule of sphingosine or derivative, one molecule of fatty acid, and a polar head joined by glycosidic or phosphodiester linkage
• C1, C2, C3 of sphingosine molecule is analogous to the 3 carbons of glycerol in glycerophospholipid

Question 30

what are 3 subclasses of sphingolipids?

Answer 30

1. sphingomyelins
2. glycosphingolipids
3. gangliosides

Question 31

What are glycosphingolipids?

Answer 31

glycophingolipids are determinants of blood groups

Question 32

what are sterols?

Answer 32

• structural lipids present in most membranes of eukarotic cells
• steroid nucleus consists of 4 fused carbon rings, 3 with 6 carbons, 1 with 5 carbons (ABC= 6C D = 5C)
• this steroid nucleus is almost planar and fairly rigid

Question 33

what is a major sterol in animal tissues?

Answer 33

cholesterol

Question 34

What is cholesterol and what does it do?

Answer 34

• amphipatic = polar head and a nonpolar body
• modulates the fluidity of animal cell membrane (more cholesterol = less fluid)
• precursor of steroid hormones such as progesterone, estradiol and cortisol (used to make diff steroid hormones)

Question 35

What are a few examples of steroids derived from cholesterol?

Answer 35

Testosterone
cortisol
beta-estradiol

remember 3 i guess

Question 36

What are 4 roles of biological membranes?

Answer 36

• define cellular boundaries
• divide cells into compartments
• organise complex reaction sequences
• play a role in signal reception and energy transformaiton

Question 37

How do lipid composition of membrane vary by?

Answer 37

organism
tissues
organelles

Question 38

What lipid composition varies in membranes?

Answer 38

• ratio of lipid to protein
• type of phospholipid
• abundance and type of sterols varies

Question 39

What is the effect of more sterols on the membrane?

Answer 39

more rigid membrane

Question 40

How are membrane bilayers asymmetric?

Answer 40

2 leaflets have different lipid composition
the outer leaflet (exposed to extracellular enviornment) is often more positively charged