6 lipids and biological membrane 1 Flashcards
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What is the defining feature of lipids?
insolubility in water
What are the 3 types of lipids
- 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
What are the stored forms of lipids?
Fats and oils
What are fats and oils a derivative of?
Fatty acids
what are fatty acids?
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
what does R-COOH refer to?
structure of fatty acid
R = a hydrocarbon chain that can vary in legnth
-COOH = terminal carboxyl group
Diff between short, medium, long and very long chain?
short = 2-4
medium = 6-12
long = 14-20
very long = >20
What do fatty acid properties depend on?
- 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
Saturated vs unsaturated FA
sat - no more hydrogens can be added
unsat - FA with one or more DB, contain less hydrogen atoms than sat FA
What are the 2 possible position of double bonds?
cis and trans
What are cis-unsaturated FA?
Hydrogen on the double bond carbons are on the same side
= bend fatty acid
What configuration are nearly all naturally occuring unsaturated FA in?
cis-configuration
What are trans-unsaturated FA?
Hydrogen on the carbon-carbon double bond are on opposite sides
= straight fatty acid
Where can trans fatty acid be obtained?
from dairy products and meats
also produced during hydrogenation (adding H) of fish or vegetable oils
what do the numbers of this nomenclature refer to?
chain length:number of DB
position of any DB are specific by △ followed by superscript numbers
e.g. 18:3(△⁸)
How does the FA structure affect packing?
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
What are triacylglycerols made from?
3 fatty acids and a glycerol molecule
In what way are most naturally occuring triacylglycerol mixed?
contain at least 2 diff types of fatty acid
What are the properties of triacylglycerol?
non polar, hydrophobic molecules
essentially insoluble in water
How do triacylglycerol used as storage fuel in body and in plants?
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
what are 4 advantages of using triacylglycerol as storage fuel?
- carbons of FA are more reduced than those in polysaccharide = oxidation of triacylglycerol yields 2x more energy than oxidation of polysaccharide
- since they are hydrophobic and therefore unhydrated, they do not carry extra water weight, every gram of polysaccharide stored with 2g of water
- store more energy in triacylglycerol, less than a days energy supply in glycogen
- triacylglycerol stored beneath the skin can searve as insulation = penguins are padded with triacylglycerol
What are biological membranes made of?
double layer of lipids
What do the structural lipids in membrane do?
act as barrier to the passage of polar molecules and ions
How are membrane lipids amphipathic?
hydrophillic end and hydrophobic end
hydrophobic interactions with each other and hydrophilic interact w water
= packs into sheets called membrane bilayer
What are 2 categories of membrane lipids?
phospholipids and glycolipids
What are 2 phospholipids?
glycerophospholpids
sphingolipids
What are glycerophospholipids?
- 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
what are sphingolipids?
- 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
what are 3 subclasses of sphingolipids?
- sphingomyelins
- glycosphingolipids
- gangliosides
What are glycosphingolipids?
glycophingolipids are determinants of blood groups
what are sterols?
- 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
what is a major sterol in animal tissues?
cholesterol
What is cholesterol and what does it do?
- 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)
What are a few examples of steroids derived from cholesterol?
Testosterone
cortisol
beta-estradiol
What are 4 roles of biological membranes?
- define cellular boundaries
- divide cells into compartments
- organise complex reaction sequences
- play a role in signal reception and energy transformaiton
How do lipid composition of membrane vary by?
organism
tissues
organelles
What lipid composition varies in membranes?
- ratio of lipid to protein
- type of phospholipid
- abundance and type of sterols varies
What is the effect of more sterols on the membrane?
more rigid membrane
How are membrane bilayers asymmetric?
2 leaflets have different lipid composition
the outer leaflet (exposed to extracellular enviornment) is often more positively charged
