Chapter 2: Biological molecules

Water

A polar molecule with hydrogen bonds; has high specific heat capacity

Hydrogen Bond

A weak electrostatic attraction between a slightly positive hydrogen atom and a slightly negative atom

Cohesion

The attraction between water molecules due to hydrogen bonding

Adhesion

The attraction between water molecules and other polar surfaces

Polarity

Unequal charge distribution within a molecule; polar molecules like water interact with other charged or polar substances.

Inorganic Ion

Charged atoms or molecules involved in biological functions

Monosaccharide

Simple sugar and monomer of carbohydrates

α-glucose

Isomer of glucose with the -OH group on carbon 1 below the ring; forms starch and glycogen.

β-glucose

Isomer of glucose with the -OH group on carbon 1 above the ring; forms cellulose.

Disaccharide

Two monosaccharides joined by a glycosidic bond

Polysaccharide

Polymer of many monosaccharides; used for storage (starch

Glycosidic Bond

Covalent bond between two monosaccharides formed by a condensation reaction.

Condensation Reaction

A reaction where two molecules join together with the removal of a water molecule.

Hydrolysis

A reaction where a molecule is broken down by the addition of water.

Starch

Plant storage polysaccharide of α-glucose; made of amylose and amylopectin

Glycogen

Animal storage polysaccharide of α-glucose; highly branched for rapid energy release.

Cellulose

Structural polysaccharide of β-glucose; forms strong fibres for plant cell walls.

Benedict’s Test

Test for reducing sugars; positive result turns brick-red after heating with Benedict’s reagent.

Lipid

Non-polar biological molecule used for energy storage

Triglyceride

A lipid made from one glycerol and three fatty acids joined by ester bonds.

Fatty Acid

Long hydrocarbon chain with a carboxyl group; can be saturated (no double bonds) or unsaturated (has double bonds).

Glycerol

A three-carbon alcohol that forms the backbone of triglycerides and phospholipids.

Ester Bond

Bond formed between glycerol and a fatty acid during condensation.

Phospholipid

Lipid with two fatty acids and a phosphate group; forms bilayers in cell membranes.

Hydrophobic

Repelled by water; non-polar molecules or parts of molecules.

Hydrophilic

Attracted to water; polar molecules or groups.

Emulsion Test

Test for lipids; positive result is a cloudy white emulsion after mixing with ethanol and water.

Amino Acid

Monomer of proteins; contains an amine group

Peptide Bond

Covalent bond between amino acids formed by condensation.

Polypeptide

Chain of amino acids joined by peptide bonds.

Primary Structure (Protein)

The specific sequence of amino acids in a polypeptide chain.

Secondary Structure (Protein)

Folding of polypeptide into α-helices and β-pleated sheets via hydrogen bonding.

Tertiary Structure (Protein)

3D shape of a polypeptide due to interactions between R groups

Quaternary Structure (Protein)

Structure formed when two or more polypeptides join

Globular Protein

Compact, circular and carry out functions

Fibrous Protein

Long, string like and provide structural support. Not soluble in water

Hydrogen Bond (Protein)

Weak bond between polar groups that stabilises protein structure.

Ionic Bond (Protein)

Attraction between oppositely charged R groups in protein structure.

Disulfide Bridge

Strong covalent bond between sulfur atoms in cysteine amino acids.

Biuret Test

Test for proteins; turns purple in presence of peptide bonds.

Enzyme

Biological catalyst that speeds up reactions by lowering activation energy.

Active Site

Region on an enzyme where the substrate binds and the reaction occurs.

Substrate

Molecule that fits into an enzyme’s active site to be transformed.

Enzyme-Substrate Complex

Temporary combination of enzyme and substrate during catalysis.

Induced Fit Model

Model where the enzyme changes shape slightly to better fit the substrate.

Lock and Key Model

Model where enzyme active site fits substrate exactly.

Activation Energy

Minimum energy needed for a chemical reaction to occur; lowered by enzymes.

Denaturation

Loss of enzyme structure and function due to changes in temperature or pH.

Optimum Temperature / pH

The temperature or pH at which an enzyme’s activity is highest.

Competitive Inhibitor

Molecule that competes with the substrate for the active site.

Non-Competitive Inhibitor

Molecule that binds elsewhere on the enzyme