Lipids and Carbohydrates

Question 1

what is the empirical formula of carbohydrates?

Answer 1

(CH2O)n

Question 2

what are:
monosaccharides
oligosaccharides
polysaccharides

Answer 2

simple sugars
short chains of monosaccharides, less than 20 residues
consists of hundreds or thousands of monosaccharide units

Question 3

properties of monosaccharides

Answer 3

colourless, crystalline solids
water soluble
sweet tasting
open chain or ring structures
aldoses or ketoses

Question 4

monosaccharide aldoses

Answer 4

6 carbon sugar
carbonyl group at the end of the chain - aldehyde
reducing sugars
asymmetric, chiral centres at C2,3,4,5
L and D configuration based on orientation of C5 groups
16 isomers

Question 5

monosaccharide ketoses

Answer 5

6 carbon sugar
carbonyl group at C2 position - ketone
reducing sugars
asymmetric, chiral carbins at C3,4,5
L and D configuration based on orientation of C5 groups
8 isomers

Question 6

monosaccharide ring formation

Answer 6

in aqueous solutions aldotetroses with five or more carbons exist as cyclic structures
covalent bond formed between carbonyl group and oxygen atom of a hydroxyl group
produces chiral centre
anomers

Question 7

what is the conformation of pyranose rings?

Answer 7

tetrahedral geometry of saturated carbons produce non-planar structures
axial substituents sterically hinder each other
chair from of beta D-glucopyranose predominates as all axial positions are occupied by H atoms

Question 8

what is the conformation of furanose rings?

Answer 8

furanose rings like pyranose rings are not planar
conformation is known as envelope form
in ribose wither C2 or C3 is out of the plane

Question 9

monosaccharide glycosidic bond formation

Answer 9

O-glycosidic bonds are formed when a hydroxyl group reacts with the anomeric carbon
determines structure of oligo and polysaccharides
non-reducing sugar

N-glycosidic binds are formed when anomeric carbon reacts with a nitrogen atom

Question 10

oligosaccharides

Answer 10

disaccharides that are natural are not normally a source of energy
O-glycosidic bonded monosaccharides
includes:
lactose, trehalose, maltose, sucrose

Question 11

polysaccharides - glycans

Answer 11

found commonly in nature
vary by monosaccharide units involved, type of bonds linking units, degree of branching
homopolymer-identical monosaccharides
heteropolymer-variable monosaccharides

Question 12

name some roles of sugars

Answer 12

energy sources
structural
information

Question 13

why are polysaccharides good?

Answer 13

compact
bonding means less osmotic pull
little water associated

Question 14

cellulose

Answer 14

abundant
unbranched
joined by beta1-4 linkages
long straight chain
parallel can form hydrogen bonds forming fibrils - high tensile strength

Question 15

chitin

Answer 15

N-acetylglucosamine linked by beta1-4 glycosidic bonds
differs to cellulose by replacement of C2 hydroxyl group with an acetylated amino group
parallel chains interact by hydrogen bonds

Question 16

proteoglycans

Answer 16

glycans with a bit of protein
polysaccharide chains - glycosaminoglycan (GAG)
GAG are anionic polysaccharide chains made up of repeating disaccharide units
can from crosslink meshwork for extra strength and resilience

monosaccharide + amino sugar = N-acetylglucosamine or N-acetylgalactosamine

Question 17

sugar fingerprint

Answer 17

sugar residues of our cell surafces unique to us can recognise self to non-self
sugars allow more variety than proteins structurally
important for tissue typing
define blood groupings
mount immune response

Question 18

blood group -oligosaccharide assembly

Answer 18

synthesised by specific enzymes - glycosyltransferases
specific to sugars being linked
blood groups are good examples - carbo attached to proteins and lipids on cell surface
common foundation known as the O antigen
A and B differ by 1 monosac
O is a result of mutation resulting in no active glycosyltransferases

Question 19

lectins

Answer 19

proteins that recognise and bind to specific carbohydrate structures
used in cell-cell recognition
they remove old erythrocytes and remove them

Question 20

fatty acids

Answer 20

present often as components of more complex lipids
long chains with non polar hydrocarbon tail
carboxyl group at 1 end with pKa 4.7-5.0
variables that change the melting point include length and saturation

Question 21

what form are biological FA in?

Answer 21

cis form (hydrogen is on the same side of the double bond)
always 3Cs apart
PUFA - poly unsaturated FA
omega 3 - food products
omega 6 - plants

Question 22

name some examples of common FAs

Answer 22

stearic acid
palmitic acid - most common saturated FA
oleic acid - most common monounsaturated FA, cis-9

Question 23

name some essential FAs

Answer 23

alpha linolenic acid
linoleic aicd

arachidonic essential in deficient in linoleic acid because humans can’t insert double binds beyond carbon 9

Question 24

give examples of precursors

Question 25

triacylglycerols (TAG)

Answer 25

non-polar usually variable FAs on each glycerol if mostly saturated so solid at room temp (e.g: animal fats) if mostly unsaturated they are liquids at room temp (e.g: vegetable oil)

Question 26

what is the function of TAGS

Answer 26

insulation protection energy storage: complete oxidation FAs - 38kJ/g complete oxidation of carbohydrate - 17kJ/g so 9 fold difference in energy presenting FAs store more energy than carbohydrates

Question 27

phospholipids

Answer 27

glycerophospholipids 3rd position point on glycerol s occupied by phosphate phosphoglyceride is amphiphilic

Question 28

what are the most common phosphate head groups?

Answer 28

phosphatidylinositol phosphatidylserine phosphatidylcholine

Question 29

sphingolipids

Answer 29

membrane lipids sphingosine instead of glycerol - an amine alcohol two other positions: 1 -FA via amino group to form ceramide 2- phosphate

Question 30

sphingomyelin

Answer 30

25% all lipid in humans phosphorylcholine usually 2 straight chains tighter packaging stable membrane alters fluidity myeline sheath

Question 31

glycolipids

Answer 31

cerebrosides, sphingoglycolipids, glycosphingolipids contains a carbohydrate amphipathic specialised membrane movement common in plant cells or nervous cells acts as recognition molecules

Question 32

steroids

Answer 32

eukaryotes hopanoids in eukaryotes 4 fused rings relatively non-polar cholesterol as an example common steroid amphipathic major component animal plasma membranes lesser in organelle membranes structure rigid and flat simvastatin helps with membrane fluidity acts as precursor for sex hormones, glucorticoids, mineralocorticoids, vit D, bile salts

Question 33

terpenoids

Answer 33

synthesised from isoprenes precursor for vit A, vit K and ubiquinone