AQA A Level Biology Topic 1 Biological molecules

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

Monomers

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

Polymers

Molecules made from many (a large number of) identical / similar monomer molecules.

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, breaking a chemical bond using a water molecule.

Monosaccharides

The monomers from which larger carbohydrates are made, with common examples being glucose, fructose, and galactose.

Isomers

Molecules with the same molecular formula but differently arranged atoms, such as $\alpha$-glucose and $\beta$-glucose.

$\alpha$-glucose vs $\beta$-glucose structure

In $\alpha$-glucose, the OH group is below carbon 1, while in $\beta$-glucose, the OH group is above carbon 1.

Disaccharides

Two monosaccharides joined together with a glycosidic bond, formed by a condensation reaction.

Maltose

A disaccharide made from the condensation of two glucose molecules.

Sucrose

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

Lactose

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

Polysaccharides

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

Starch

An energy store in plant cells consisting of a polysaccharide of $\alpha$-glucose; includes unbranched amylose ($1,4$-glycosidic bonds) and branched amylopectin ($1,4$- and $1,6$-glycosidic bonds).

Glycogen

An energy store in animal cells made of $\alpha$-glucose with $1,4$- and $1,6$-glycosidic bonds, making it highly branched.

Cellulose

A polysaccharide of $\beta$-glucose with $1,4$-glycosidic bonds that forms straight, unbranched chains linked by hydrogen bonds to form microfibrils.

Reducing sugars test

Add Benedict's solution and heat in a boiling water bath; a positive result is a green, yellow, orange, or red precipitate.

Non-reducing sugars test

Heat with acid to hydrolyse, neutralise with alkali, then heat with Benedict’s solution to get a positive coloured precipitate.

Iodine test

A test for starch using iodine dissolved in potassium iodide; a positive result is blue-black.

Triglyceride

A lipid formed from 1 glycerol molecule and 3 fatty acids joined by 3 ester bonds via condensation reactions.

Saturated fatty acid

A fatty acid with no $C=C$ double bonds in the hydrocarbon chain, where 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.

Phospholipid

A lipid where one of the fatty acids of a triglyceride is substituted by a phosphate-containing group.

Emulsion test

A test for lipids where ethanol is added and shaken to dissolve the lipid, followed by water; a positive result is a milky white emulsion.

Amino acid structure

Consists of a carboxyl group ($COOH$), an amine group ($NH_2$), and a variable side chain ($R$) group.

Peptide bond

A chemical bond formed between the carboxyl ($COOH$) group of one amino acid and the amine ($NH_2$) group of another during a condensation reaction.

Primary structure

The specific sequence of amino acids in a polypeptide chain, joined by peptide bonds.

Secondary structure

The folding of a polypeptide chain (e.g., alpha helix or beta pleated sheets) due to hydrogen bonding between $NH$ and $C=O$ groups.

Tertiary structure

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

Quaternary structure

A functional protein consisting of more than one polypeptide chain formed by interactions between polypeptides.

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 substrate binding causes the active site to change shape slightly to become complementary, distorting bonds and lowering activation energy.

Competitive inhibitor

A molecule with a similar shape to the substrate that competes for and blocks the active site.

Non-competitive inhibitor

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

DNA vs RNA nucleotides

DNA nucleotides contain deoxyribose and thymine, while RNA nucleotides contain ribose and uracil.

Phosphodiester bond

A bond formed by a condensation reaction between the phosphate group of one nucleotide and the sugar of another.

Semi-conservative replication

The process where DNA helicase breaks hydrogen bonds and both strands act as templates for new strands, resulting in DNA molecules with one original and one new strand.

DNA polymerase

An enzyme that joins adjacent nucleotides on a new DNA strand by forming phosphodiester bonds.

ATP (Adenosine triphosphate)

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

ATP hydrolase

An enzyme that catalyses the hydrolysis of ATP into ADP and inorganic phosphate ($P_i$) to release energy.

ATP synthase

An enzyme that catalyses the resynthesis of ATP from ADP and $P_i$ during respiration and photosynthesis.

Specific heat capacity of water

The ability of water to gain or lose significant heat without changing temperature, allowing it to buffer temperature changes.

Latent heat of vaporisation

The amount of energy required to evaporate water, providing an effective cooling mechanism via evaporation.

Cohesion

Strong attraction between water molecules due to hydrogen bonding, supporting columns of water in plant transport cells.

Iron ions ($Fe^{2+}$)

A component of the haem group in haemoglobin that allows oxygen to bind for transport.

Phosphate ions ($PO_4^{3-}$)

Components of DNA, RNA, and ATP, and used to phosphorylate other compounds to make them more reactive.