A-Level Biology 2.2 Biological Molecules

Condensation Reaction

a reaction that occurs when two molecules are joined together by the removal of water.

Hydrolysis Reaction

a reaction that occurs when a molecule splits into to smaller molecules with the addition of water.

Hydrogen Bond

a weak interaction between a polar hydrogen atom and another polar atom.

Maltose

a glucose + a glucose

Sucrose

a glucose + fructose

Lactose

B galactose + a glucose

Glycosidic Bond

a covalent bond formed between two monosaccharides by a hydrolysis reaction.

Amylose

long chain of a glucose molecules coiled into a spiral shape.

Amylopectin

long chain of a glucose molecules coiled into a spiral shape with branches emerging.

Glycogen

long chain of a glucose molecules with many branches in a compact structure.

Cellulose

long chains of B glucose with every other molecules rotated 180 degrees.

Lipid

a group of molecules that are soluble in alcohol but not water.

Triglyceride

lipid molecule made up of glycerol and three fatty acids.

Ester Bond

the bond formed as a result of a condensation reaction between a fatty acid and glycerol.

Phospholipid

lipid molecule consisting of glycerol, two fatty acids and a phosphate group.

Hydrophilic

attracted to water.

Hydrophobic

repelled by water.

Peptide Bond

covalent bonds that join amino acids by a condensation reaction.

Primary Structure

the sequence of amino acids found in a molecule.

Secondary Structure

the coiling or folding of an amino acid chain due to hydrogen bonds, forming an a helix or B pleated sheet.

Tertiary Structure

the overall 3D shape of the protein molecule due to HYDROGEN bonds, DISULFIDE bridges, IONIC binds and HYDROPHOBIC interactions.

Quaternary Structure

the protein structure where a protein consists of more than one polypeptide chain.

Fibrous Protein

protein that is relatively long and thin, insoluble in water and metabolically inactive, often playing a structural role.

Globular Protein

protein that is relatively spherical shaped, soluble in water and often has a metabolic role.

Cations

positive ions.

Anions

negative ions.

Iodine Test

tests for starch.
starch present = blue-black colour

Benedict's Test

tests for reducing or non-reducing sugars.
sugars present = orange-red colour
(low levels = yellow-green)

Emulsion Test (Ethanol)

tests for lipids.
lipids present = cloudy white emulsion

Biuret Test

tests for proteins.
proteins present = lilac colour