Biological Molecules

monomers and polymers

• Polymers - molecules made from a large number of monomers joined together.

• Monomer examples - monosaccharides, amino acids and nucleotides.

• Condensation reaction - joins two molecules together with a chemical bond and removes a molecule of water

• Hydrolysis reaction - breaks a chemical bond between two molecules and involves the addition of a water molecule.

define metabolism

all the chemical processes that happen in a living organism

why is life based on carbon?

• readily form bonds with other carbon atoms

• varied carbon atom sequences

• forms ‘back bone’ where other atoms are attached to

what are organic molecules?

carbon-containing molecules

carbohydrates

• Monosaccharides - monomers from which larger carbohydrates are made.

• Examples - glucose (alpha and beta), galactose and fructose.

• Glucose = two isomers →alpha + beta

• Properties - sweet tasting

• Condensation reaction between two monosaccharides → a glycosidic bond.

• Disaccharides - the condensation of two monosaccharides:

1. maltose = alpha two glucose

2. sucrose = glucose and fructose

3. lactose = glucose and galactose

• Polysaccharides - formed by the condensation of many monosaccharides.

• Polysaccharide examples - starch, glycogen and cellulose

define isomer

Polysaccharide - starch

• found - plants in small grains

• job - energy store

• made - alpha glucose

• structure -

• important - insoluble (X water potential), large (X diffuse out), compact (lots stores), hydrolysis alpha glucose (easy transported), branched (many ends, enzymes, monomer released fast)

Polysaccharide - glycogen

• found - animals and bacteria

• job - energy store

• made - alpha glucose

• structure -

• important - insoluble (X osmosis), insoluble (X diffuse out), compact (many stores), highly branched (many ends, enzymes, monomers, use fast in respiration, more active)

Polysaccharide - cellulose

• found - plants

• job - structural strength in cell wall

• made - beta glucose

• structure - straight unbranched chains, run parallel, h-bonds form cross links adjacent chains, forms microfibrils

• important - beta glucose (long straight chains), h-bonds (strength), microfibrils and fibrils (more strength)

What id the test for reducing sugars?

• add 2cm cubed of food sample (liquid - grind in water)

• equal volume benedicts reagent

• heat in water bath 5 minutes

• result - turns orange/brown

what is the test for non-reducing sugars?

• liquid form (grind add water)

• follow negative reducing sugar test

• 2cm cube food sample to equal hydrochloric acid (hydrolyses disaccharide present)

• water bath 5 minutes

• add sodium hydrogencarbonate solution (neutralises acid so benedicts works)

• use reducing sugar test

• result - turns orange/brown

what is the test for starch?

• 2cm cube of food sample in depression on spotting tile

• add two drops iodine

• shake/stir

• result - blue/black from orange

what are lipids?

• Triglycerides and phospholipids are two groups of lipids.

• Triglycerides - formed condensation of one glycerol and three fatty acid molecules.

• A condensation reaction + glycerol and a fatty acid (RCOOH) = ester bond.

• The R-group of a fatty acid may be saturated or unsaturated.

• Phospholipids - two fatty acid molecules and a phosphate-containing group

• chain = no carbon-carbon double bonds - saturated

• chain = carbon-carbon double bonds - unsaturated

what are lipids important?

• cell membrane - contributes to flexibility and transfer of lipid-soluble substances across them

• energy source - oxidised, more twice than carbohydrates, releases water

• waterproof - insoluble (plants - waxy cuticle, animals - oily secretion from sebaceous glands in skin) to conserve water

• insulation - slow conductors of heat and retains it, electrical insulators for myelin sheath

• protection - around delicate organs like kidneys

what are triglycerides?

• three fatty acids with one glycerol

• each fatty acid forms ester bond in condensation reaction

• glycerol - same, fatty acids - different with different properties

• fatty acids - carboxyl group with hydrocarbon chain

properties of triglycerides

• low mass: energy - lots energy in small volume

• high carbon-hydrogen bonds: carbon atoms - energy

• large + nonpolar - insoluble, X water potential

• high hydrogen: oxygen - release water when oxidised, good for desert animals

what are phospholipids

• one glycerol + two fatty acids + one phosphate molecule + condensation reaction = ester bonds

• hydrophilic head - phosphate molecule interacts with water

• hydrophobic tail - fatty acids repels water

• in water = heads close to water and tails away due to different poles

properties of phospholipids

• polar - forms bilayer in aqueous place in cell surface membrane, hydrophobic barrier

• heads - hold at the surface of cell-surface membrane

• form glycolipids - carbohydrates in cell-surface membrane, in cell recognition

test for lipids

• dry test tube

• 2 cm3 sample and 5 cm3 ethanol

• shake well

• add 5 cm3 water

• shake gently

• positive - white emulsion

• control - test with water and should be clear

amino acids

• ^{Amino acids are the monomers from which polypeptides are made.}

• ^{The twenty amino acids that are common in all organisms differ only in their side group.}

• ^{A condensation reaction + two amino acids = peptide bond.}

• ^{Dipeptides = condensation of two amino acids.}

• ^{Polypeptides = condensation of many amino acids.}

• ^{Polypeptides join = protein}

• ^{central carbon atom}

• ^{amine group - NH2, basic group}

• ^{carboxyl group - COOH, acidic group}

• ^{hydrogen atom - H}

• ^{R side group - different chemical groups (20 occurring differ in this group)}

what is the structure of a protein

• polymerisation - many amino acids joining via a condensation reaction and peptide bonds

• primary = specific sequence of amino acids in a polypeptide chain

• secondary = H from amine group (positive) and O from carboxyl (negative) form hydrogen bonds, polypeptide chain in an alpha helix or beta pleated sheet.

• tertiary = secondary structure twisted to tertiary shape, hydrogen, disulphide and ionic bonds form

• quaternary = the joining of multiple polypeptide chains