biomolecules 2

carbohydrates

molecules that contains carbon, hydrogen and oxygen atoms

also known as a saccharide

single saccharide (monosaccharide), two monosaccharides (disaccharide), few linked monosaccharides (oligosaccharide), many monosaccharide (polysaccharide)

monosaccharide

simple sugar units

they have the empirical formula = (CH₂O)_n where n = 3-7 carbons

they are poly-hydroxy aldehydes or ketones

n = 3 carbons: triose

n = 5 carbons: pentose

n = 6 carbons: hexose

triose

glyceraldehyde (aldose) - aldehyde is on carbon 1

dihydroxyacetone (ketose) - ketone is in the middle

pentoses

important pentoses in biology:

• ribose, deoxyribose - nucleotides (ATP, NAD), nucleic acid (DNA/RNA)

• ribulose, xylulose - hexose-monophosphate shunt

• xylose - glycoproteins

hexose

same chemical formula but different structures

these structures are called isomers

glucose: fruit juices, starch, glycogen, lactose, maltose, cane sugar

fructose: fruit juices, honey, cane sugar

galactose: milk (lactose)

mannose: plants and gums

cyclisation of monosaccharides

in an aldose, the carbonyl group is at C1

C1 in cyclized aldose = anomeric carbon

beta = OH group in up, alpha = OH group is down

in a ketose it all happens at carbons 2

glycosidic bond

the name or type of bond depends on the number of the connected carbons, the position of the anomeric hydroxyl group

• if the OH group is in the alpha configuration it is an alpha bond and vice versa

example: lactose = beta-galactose + glucose

• bod is between carbon 1 of beta-galactose and carbon 4 of glucose

• bond is beta(1→4) glycosidic bond)

carbohydrates can also bond to non carbohydrate structures (purines, aromatic rings, proteins, lipids)

disaccharides

maltose: glucose alpha(1→4) glucose

lactose: galactose beta(1→4) glucose

polysaccharides

n > 12-hundreds

variations can occur in the chain: monosaccharides, glycosidic bonds, branch points, structure

example: amylopectin branched every 24-30 residues

polysaccharide functions

storage in animals

• glycogen: a homopolymer of glucose. branched every 12-14 residues (alpha1-4, alpha1-6)

storage in plants:

• starch: a homopolymer of glucose; composed of amylose(non branches helical structure)

• amylopectin (branched every 24-30 residues)

structure in plants

• cellulose: homopolymer of glucose, long straight chains (beta1-4)

lipids

heterogeneous group of water insoluble (hydrophobic) organic molecules

functions:

• major source of energy in the body

• structural components of cells and organelles

• involved in cellular signaling events e.g. steroids

fatty acid

hydrophobic hydrocarbon chain with terminal carboxyl group (unsaturated and saturated)

cis configuration means that two hydrogen atoms adjacent to the double bond stick out on the same side of the chain

saturated FAs

carbon to carbon bonds are single

contain no double bonds

fully reduced or saturated with hydrogen atoms

highly flexible due to free rotation around single bonds

unsaturated FAs

contain double bonds - one db = monosaturated, more than one = polysaturated

if 2 or more db bonds: bond is spaced at 3 carbon intervals

position is specified by distance from carboxy end: e.g. ▲⁶ (delta 6) double bond is between carbon 6 and 7

omega FA

omega refers to the position of the double bond from the omega end of the FA chain

omega 3 refers to the position of the final double bond, which is three carbons from the omega or tail end of FA

classification of lipids

fatty acids and their derivatives

lipids containing glycerol

• neutral lipids: mono, di, tri-acylglycerol

• charged lipids: phospholipids

lipids not containing glycerol

• steroids, sphingolipids

lipoproteins and lipopolysaccharides

essential FAs

nutritionally essential as we cannot synthesize them in the body

linoleic acid (omega-6 FA)

alpha-linolenic acid (omega-3 FA)

triglycerides

made up of 3 FAs and glycerol

the principal storage form of energy in the body

stored in adipose tissue

diglycerol and monoacylglycerol

DAG

• potent intracellular signaler

• mobilization of calcium

MAG

• breakdown product of TAG in fat digestion

phospholipids

major component of cell membrane

they are amphipathic: hydrophilic head and hydrophobic tails

the hydrophilic head is negatively

sphingolipids

sphingosine + FA + R

when R if hydrogen → ceramide

when R is phosphocholine → sphingomyelin

when R is sugar → glycosphingolipid

steroids

contain a characteristic fused ring with a hydroxyl or keto group on carbon 3

one of the most essential steroids is cholesterol

functions as a metabolic precursor of vitamin D, bile acids, steroid hormone

plays a key role in structure of membranes

other major steroid classes: bile acids (24 carbons), progesterone (21 carbons) androgens (19 carbons), estrogens (18 carbons)

lipoprotein

spherical particles found in plasma that transport lipids including cholesterol

hydrophobic core of triacylglycerols and cholesterol esters

phospholipid layer associated with cholesterol and protein