Basque PAU Biology key terms

A protein (or occasionally RNA) that speeds up a biochemical reaction by lowering its activation energy, without being consumed. It binds specific substrates at its active site and is sensitive to temperature, pH and inhibitors.

The small region of an enzyme where substrate molecules bind and the chemical reaction takes place. Its shape and chemical groups determine substrate specificity and catalytic activity.

The study of how reaction rate depends on substrate concentration, enzyme concentration, pH and temperature. Key parameters include Vmax, the maximum rate, and Km, the substrate concentration giving half of Vmax.

A reversible inhibition in which an inhibitor resembling the substrate binds the active site, blocking substrate access. It raises the apparent Km but leaves Vmax unchanged because high substrate concentration can outcompete the inhibitor.

Loss of a protein's three-dimensional shape and function caused by heat, extreme pH, salts or solvents. Hydrogen bonds and other weak interactions break, though the peptide bonds of the primary structure remain intact.

The four levels of organisation of a polypeptide: primary (amino acid sequence), secondary (alpha helices and beta sheets), tertiary (overall 3D folding) and quaternary (assembly of several polypeptide chains).

The covalent bond formed between the carboxyl group of one amino acid and the amino group of the next, releasing water. It links amino acids into polypeptide chains.

Water's polarity lets it surround and dissolve ions and polar molecules through hydrogen bonding, forming hydration shells. This makes it the medium in which most cellular reactions occur.

A weak attraction between a partially positive hydrogen atom and a partially negative atom such as oxygen or nitrogen. It stabilises water's properties, protein folding and nucleic acid base pairing.

The net movement of water across a semipermeable membrane from a region of lower solute concentration to one of higher solute concentration. It drives turgor in plant cells and shapes animal cell volume.

The phospholipid bilayer with embedded proteins, cholesterol and glycolipids that surrounds every cell. It regulates the entry and exit of substances and carries receptors for signalling.

Passive transport of polar or charged solutes across a membrane through specific channel or carrier proteins, down their concentration gradient. It needs no ATP but is saturable.

Movement of substances across a membrane against their concentration gradient, using energy from ATP hydrolysis or an ion gradient. The sodium-potassium pump is a classic example.

A double-membraned organelle where pyruvate oxidation, the Krebs cycle and oxidative phosphorylation occur. Its inner membrane folds into cristae that hold the electron transport chain and ATP synthase.

The plant and algal organelle containing thylakoids and stroma where photosynthesis takes place. Chlorophyll in the thylakoid membranes captures light energy to produce ATP and NADPH.

Division of a eukaryotic nucleus producing two genetically identical daughter nuclei, usually followed by cytokinesis. It underpins growth, repair and asexual reproduction and proceeds through prophase, metaphase, anaphase and telophase.

A two-stage reduction division producing four haploid cells from one diploid cell. Crossing over in prophase I and independent assortment in metaphase I generate genetic variation.

The ordered sequence of interphase (G1, S and G2 phases, when DNA replicates) and the mitotic phase that a cell passes through before dividing into two daughter cells.

The anaerobic breakdown of glucose to two pyruvate molecules in the cytoplasm, yielding a net two ATP and two NADH per glucose. It is the first stage of both aerobic and anaerobic respiration.

A series of reactions in the mitochondrial matrix in which acetyl-CoA is oxidised to carbon dioxide, generating NADH, FADH2 and GTP per turn. It is also called the citric acid or tricarboxylic acid cycle.

ATP production driven by a proton gradient built by the electron transport chain on the inner mitochondrial membrane, as electrons from NADH and FADH2 pass to oxygen. Oxygen is the final electron acceptor.

Anaerobic regeneration of NAD+ from NADH by reducing pyruvate to lactate or ethanol plus carbon dioxide. It lets glycolysis continue with a small ATP yield when oxygen is scarce.

The light-dependent stage of photosynthesis in the thylakoid membranes, where water is split, oxygen is released and light energy is stored as ATP and NADPH for the Calvin cycle.

The light-independent stage of photosynthesis in the stroma, where CO2 is fixed by the enzyme rubisco and reduced to sugar using ATP and NADPH from the light reactions.

The monomer of nucleic acids, made of a phosphate group, a five-carbon sugar (deoxyribose or ribose) and a nitrogenous base. Nucleotides also act as energy carriers such as ATP.

The specific hydrogen bonding between complementary nitrogenous bases: adenine with thymine in DNA (uracil in RNA), and guanine with cytosine. It allows accurate copying and stable double-stranded structure.

Semiconservative copying of the double helix in S phase, in which each strand acts as a template for a new complementary strand built by DNA polymerase. Each daughter molecule keeps one original strand.

Synthesis of an RNA molecule from a DNA template, catalysed by RNA polymerase. In eukaryotes it occurs in the nucleus and the mRNA is processed before leaving for translation.

Assembly of a polypeptide at the ribosome, where mRNA codons are read and matched to transfer RNA carrying specific amino acids. It begins at a start codon and ends at a stop codon.

A sequence of three mRNA bases that specifies one amino acid or a stop signal during translation. The genetic code is degenerate, meaning several codons can code for the same amino acid.

A permanent change in the DNA sequence, such as a substitution, insertion or deletion. Mutations may be silent, change one amino acid, or shift the reading frame and alter the protein drastically.

Principles derived from Mendel's pea experiments: alleles segregate so each gamete receives one per gene, and different genes assort independently. They explain predictable ratios in monohybrid and dihybrid crosses.

The random orientation of homologous chromosome pairs at metaphase I, so alleles of genes on different chromosomes are distributed to gametes independently of one another.

Exchange of DNA segments between non-sister chromatids of homologous chromosomes during prophase I of meiosis. It creates new allele combinations and increases genetic variation.

The particular combination of alleles an organism carries for a gene or set of genes. It is distinct from the phenotype, the observable trait produced by interaction with the environment.

An infectious particle made of a nucleic acid genome enclosed in a protein capsid, sometimes with a lipid envelope. It can only replicate inside a host cell using that cell's machinery.

A Y-shaped protein produced by plasma cells that binds a specific antigen. Binding can neutralise pathogens or mark them for destruction by phagocytes and the complement system.

A preparation of weakened, inactivated or fragmentary pathogen material that stimulates an immune response and creates memory cells, giving protection against later infection.

The differential survival and reproduction of individuals whose inherited traits make them better adapted to their environment. Over generations it changes allele frequencies in a population.

The formation of new species when populations become reproductively isolated and diverge genetically. Isolation may be geographic (allopatric) or arise within one area (sympatric).

A feeding position in a food chain, such as producer, primary consumer or secondary consumer. Energy transfer between levels is inefficient, so biomass usually decreases at higher levels.

The maximum population size of a species that an environment can sustain indefinitely given available resources. Growth slows as the population approaches this limit.

The variety of life at genetic, species and ecosystem levels. It supports ecosystem stability and is reduced by habitat loss, pollution, overexploitation and invasive species.