AQA A Level Biology Topic 1: Biological Molecules

Comprehensive vocabulary flashcards covering monomers, polymers, carbohydrates, lipids, proteins, enzymes, nucleic acids, ATP, water, and inorganic ions based on AQA A Level Biology Topic 1 notes.

Monomers

Smaller / repeating molecules from which larger molecules / polymers are made.

Polymer

A molecule made up of many identical / similar molecules / monomers.

Condensation reaction

A reaction where 2 molecules join together, forming a chemical bond and releasing a water molecule.

Hydrolysis reaction

A reaction where 2 molecules are separated by breaking a chemical bond and using a water molecule.

Monosaccharides

Monomers from which larger carbohydrates are made, such as glucose, fructose, and galactose.

Isomers (Alpha & Beta glucose)

Molecules with the same molecular formula but differently arranged atoms; in $\alpha\text{-glucose}$ the $OH$ group is below carbon 1, while in $\beta\text{-glucose}$ it is above.

Disaccharides

Molecules formed by two monosaccharides joined together with a glycosidic bond via a condensation reaction.

Maltose

A disaccharide formed from the condensation of two glucose molecules.

Sucrose

A disaccharide formed from the condensation of a glucose molecule and a fructose molecule.

Lactose

A disaccharide formed from the condensation of a glucose molecule and a galactose molecule.

Polysaccharides

Many monosaccharides joined together with glycosidic bonds, formed by many condensation reactions.

Amylose

A component of starch made of $\alpha\text{-glucose}$ with 1,4-glycosidic bonds, structured as an unbranched helix.

Amylopectin

A component of starch made of $\alpha\text{-glucose}$ with 1,4- and 1,6-glycosidic bonds, resulting in a branched structure.

Glycogen

An energy store in animal cells made of $\alpha\text{-glucose}$ with 1,4- and 1,6-glycosidic bonds, which is highly branched for fast hydrolysis.

Cellulose

A polysaccharide of $\beta\text{-glucose}$ with 1,4-glycosidic bonds forming straight, unbranched chains linked by hydrogen bonds.

Microfibrils

Strong fibres formed by many hydrogen bonds linking parallel strands of cellulose, providing strength to plant cell walls.

Benedict's test

A test for reducing sugars where a sample is heated with Benedict's solution; a positive result is a green, yellow, orange, or red precipitate.

Triglycerides

Lipids formed by the condensation of 1 glycerol molecule and 3 fatty acids, creating 3 ester bonds and releasing 3 water molecules.

Saturated fatty acid

A fatty acid with no $C=C$ double bonds in the hydrocarbon chain; all carbons are fully saturated with hydrogen.

Unsaturated fatty acid

A fatty acid with one or more $C=C$ double bonds in the hydrocarbon chain, creating a bend or kink.

Phospholipids

Lipids consisting of one glycerol, two fatty acids, and a phosphate-containing group; they form a bilayer in cell membranes.

Emulsion test

A test for lipids involving the addition of ethanol followed by water; a positive result is a milky white emulsion.

Amino acids

The monomers of proteins, consisting of a carboxyl group ($-COOH$), an amine group ($-NH_2$), and a variable side group ($R$).

Peptide bond

A chemical bond formed by a condensation reaction between the carboxyl group of one amino acid and the amine group of another.

Primary structure

The specific sequence of amino acids in a polypeptide chain.

Secondary structure

The folding of a polypeptide chain into patterns like $\alpha\text{-helices}$ or $\beta\text{-pleated sheets}$ due to hydrogen bonding between $NH$ and $C=O$ groups.

Tertiary structure

The 3D folding of a polypeptide chain caused by interactions between amino acid $R$ groups, including hydrogen bonds, ionic bonds, and disulfide bridges.

Quaternary structure

A structure formed by the interaction of more than one polypeptide chain.

Biuret test

A test for proteins using sodium hydroxide and copper (II) sulphate; a positive result is a purple or lilac colour.

Induced-fit model

A model of enzyme action where the active site changes shape slightly as the substrate binds to become complementary, distorting bonds and lowering activation energy.

Competitive inhibitors

Inhibitors with a similar shape to the substrate that compete for and block the enzyme's active site.

Non-competitive inhibitors

Inhibitors that bind to an allosteric site, changing the enzyme's tertiary structure and active site shape so it is no longer complementary to the substrate.

DNA (Deoxyribonucleic acid)

A polynucleotide that holds genetic information; its nucleotides contain deoxyribose, a phosphate group, and bases A, T, C, or G.

RNA (Ribonucleic acid)

A polynucleotide that transfers genetic information from DNA to ribosomes; its nucleotides contain ribose, a phosphate group, and bases A, U, C, or G.

Phosphodiester bond

A bond that joins adjacent nucleotides in a polynucleotide chain, formed between a phosphate group and a pentose sugar.

DNA helicase

The enzyme that breaks hydrogen bonds between complementary bases to unwind the DNA double helix during replication.

DNA polymerase

The enzyme that joins adjacent nucleotides on a new strand by condensation reactions, forming phosphodiester bonds.

Semi-conservative replication

Refers to DNA replication where each new DNA molecule consists of one original template strand and one new strand.

ATP (Adenosine triphosphate)

A nucleotide derivative formed from ribose, adenine, and three phosphate groups; used as an immediate energy source.

ATP hydrolase

The enzyme that catalyses the hydrolysis of ATP into ADP and an inorganic phosphate ($P_i$), releasing energy.

ATP synthase

The enzyme that catalyses the condensation reaction of ADP and $P_i$ to resynthesise ATP during respiration or photosynthesis.

Cohesion (Water)

The property where hydrogen bonds cause water molecules to stick together, supporting columns of water like the transpiration stream.

Specific heat capacity (Water)

The ability of water to absorb or lose significant heat without large temperature changes, buffering aquatic environments and internal body temperatures.

Inorganic ions

Ions such as $H^+$, $Fe^{2+}$, $Na^+$, and $PO_4^{3-}$ found in organisms, occurring in solution in the cytoplasm and body fluids.