Biological molecules - carbs, lipids, proteins

define a monomer

smaller units from which larger molecules are made

define polymer

large molecule that is made up of many smaller repeating units

condensation reaction - dehydration synthesis

when monomers are combined to form polymers by removing water (hydrolysis opposite)

monosaccharides

monomer of carbohydrates, sweet tasting, soluble

maltose

two glucose monomers

lactose

glucose + galactose

sucrose

glucose + fructose

alpha glucose structure

beta glucose structure

(switched on carbon 1)

define isomers

compounds with the same molecular formula but different structures and properties

whys galactose a different sugar

the H and hydroxyl on carbon 4 are switched from glucose

what does a condensation reaction create

glycosidic bond

starch

made of alpha glucose in the forms of amylose (1,4) and amylopectin (1,4 +1,6)

starch structure - amylose

an unbranched helix

starch structure - amylopectin

long, branched

starch function

energy storage in plants

starch - how structure fits function

• insoluble so doesn't affect water potential and is osmotically inactive

• too large to pass through membranes, so good for storage

• compact so can be stored in small place

• branched structure increases SA for rapid hydrolysis back to glucose

• when hydrolysed forms a-glucose which is easily transported and readily used for respiration

glycogen structure

alpha glucose, branched structure even more than starch with 1,4 linkage bonds and 1,6 branches

glycogen function

storage of glucose in animals

glycogen - how structure fits function

• stored mainly in liver and muscle cells important for regulating blood glucose levels

• branched structure increases SA for rapid conversion back to glucose when energy is needed, more important for animals as more active

• insoluble so won't affect water potential, no water draws into cell

• compact

cellulose structure

beta glucose, straight chains (1,4) with H-bonds linking adjacent chains forming microfibrils

cellulose function

structure in plants - provide support and rigidity

cellulose - how structure fits function

-long straight chains, and cross-linked hydrogen bonds add strength

-grouped to form microfibrils which then forms fibres to add strength

-cell walls need to be strong so that leaves are held in a position to absorb max sunlight and stems need to withstand wind etc

chitin

A structural polysaccharide, beta (1,4) with straight chains and H-bonds found in many fungal cell walls and in the exoskeletons of all arthropods.

test for reducing sugars

• add 2cm³ of food sample to a test tube

• add an equal volume of Benedict's Reagent

• heat the mixture in a gently boiling test tube for 5 mins

• brick red is a positive result - insoluble red precipitate of copper(1) oxide

test for non-reducing sugars

• heat with Benedict's

• if negative (stays blue), hydrolyse substance with HCl into constituent monosaccharides and neutralise with sodium hydrogencarbonate

• repeat original test with same outcome if positive

test for starch

• 2cm^3 of iodine solution

• shake or stir

• blue black colouration

structure of triglycerides

3 fatty acids and one glycerol molecule

structure of phospholipids

2 fatty acids, one glycerol molecule and a phosphate group

reaction to form triglycerides

condensation reaction, where carboxyl group of fatty acid reacts

what bond is formed in triglycerides

an ester bond and 3 water molecule is removed

what is saturated

no double bonds, usually solid at room temp, animals

what is unsaturated

at least one double bond, usually liquid at room temp, found in plants

what do fatty acids contain

hydrocarbon with a methyl group and carboxyl group

are fatty acids hydrophobic

yes, they’re the ‘tail’ and are uncharged so don’t interact with water

are phosphate groups hydrophobic

no, they’re hydrophilic because they have a negative charge and so form hydrogen bonds with water

emulsion test

-sample should be ground and in liquid form

-add 2cm³ of ethanol and shake

-add 2cm³ of deionised water

-gives a milky white emulsion

are lipids soluble in water

no

triglycerides have a higher ratio of energy storing C-H bonds to C atoms so

good source of energy

triglycerides have a low mass to energy ratio so

good storage molecule

triglycerides are large and nonpolar meaning they’re insoluble in water so

storage doesn’t affect osmosis of water potential in cells

triglycerides have a high ratio of H to O so

release water when oxidised so important source of water

phospholipids are polar molecules so

form a bilayer within membranes,which is hydrophobic as

what do phospholipid heads help

hold well at surface of cell membranes

phospholipid structure allows formation of glycolipids by combinging with carbs at cell membrane which is

important for cell recognition

what are the monomers of proteins

amino acids

structure of amino acid

what replaces the r group

one of the 20 amino acids that differ

what does a condensation reaction of amino acid form

a dipeptide or polypeptide with peptide bond(s)

what type of compound are proteins

amphoteric

buiret test

• add a little sodium hydroxide to clear solution and make alkaline

• add some copper (II) sulfate solution

• turns purple if present (stays blue if not)

primary structure for proteins

the sequence of amino acids in a polypeptide chain

secondary structure for proteins

3 dimensional folding arrangement of primary into coils or pleats held by H bonds

structure of alpha helix and beta pleaated sheet

what do groups in amino acids posess and why easy to H bond

NH has a positive charge and C=0 has a negative charge, readily forms weak H bonds which causes twists

tertiary structure for proteins

supercoiling of a helix to give 3D shape or ‘conformation’of protein due to bonding between R groups on chain

different types of bonds on tertiary structure

disulphide bridges - strong and form between sulhur atoms in cysteine amino acids

hydrogen bonds - numerous but easily broken

ionic bonds - formed between carboxyl + amino not involved in forming peptide bonds, weaker than D, easily broken by changes in pH

quaternary structure for proteins

the way polypeptide chains are assembled together

example of protein with quaternary structure

haemoglobin - has 4 polypeptide chains, each containing an iron containing HAEM group that binds to molecules of oxygen

fibrous protein

structural, insoluble, eg keratin, collagen - 3 polypeptide chains twisted like a rope

globular proteins

specific 3D shape, soluble, eg enzymes

why are globular proteins soluble

at tertiary structure level hydrophobic amino acids are bound in the interior of molecule and hydrophilic amino acids are bound towards exterior