FY12CE Biology key terms

A protein, or occasionally an RNA molecule, that speeds up a specific chemical reaction in a cell by lowering the activation energy needed, without being consumed by the reaction itself.

The small region of an enzyme where the substrate binds and the reaction takes place; its shape and chemical properties determine which molecules the enzyme can act on.

The minimum energy that reacting molecules must possess before a chemical reaction can proceed; enzymes reduce this barrier so reactions occur at body temperature.

Loss of a protein's functional three-dimensional shape caused by heat, extreme pH, or chemicals, which breaks bonds holding the structure together and usually destroys enzyme activity irreversibly.

The property by which an enzyme binds only particular molecules, because the active site's shape and charge complement only certain substrates, like a key fitting one lock.

The four-level organisation of a polypeptide: primary sequence of amino acids, local secondary folds such as helices and sheets, overall tertiary shape, and assembly of several chains into a quaternary complex.

The building block of proteins; about twenty standard types each share an amino group and a carboxyl group but differ in a side chain that determines chemical properties such as charge and polarity.

The covalent bond formed between the carboxyl group of one amino acid and the amino group of the next, releasing water and linking amino acids into a polypeptide chain.

The double layer of molecules with water-loving heads facing outward and water-fearing tails facing inward that forms the core of every cell membrane and limits passage of most substances.

The net movement of particles from a region of higher concentration to one of lower concentration, driven by random molecular motion and requiring no energy input from the cell.

The diffusion of water across a selectively permeable membrane from a region of higher water concentration, meaning lower solute concentration, toward a region of lower water concentration.

Movement of ions or molecules across a membrane against their concentration gradient, using energy from ATP hydrolysis and usually a carrier protein embedded in the membrane.

Adenosine triphosphate, the universal energy currency of cells; breaking its terminal phosphate bond releases usable energy that powers transport, synthesis, and movement.

The set of reactions, beginning with glycolysis and continuing in mitochondria, that release energy from glucose and store it in ATP, producing carbon dioxide and water as waste.

The process in chloroplasts by which plants, algae, and some bacteria use light energy to convert carbon dioxide and water into glucose and oxygen, storing energy in chemical bonds.

The green pigment inside chloroplasts that absorbs mainly red and blue light and reflects green, providing the energy that drives the light-dependent reactions of photosynthesis.

Nuclear division producing two daughter nuclei with the same chromosome number as the parent cell, used for growth, repair, and asexual reproduction in multicellular organisms.

Two successive nuclear divisions that halve the chromosome number and shuffle genes through crossing over and independent assortment, producing gametes for sexual reproduction.

One of the alternative versions of a gene at a given locus on a chromosome; different alleles may produce different traits, and an organism inherits one from each parent.

The particular combination of alleles an organism carries for a gene or set of genes, which together with environmental influences determines the observable phenotype.

The observable characteristics of an organism, such as flower colour or blood type, resulting from the interaction between its genotype and the environment.

An allele whose effect appears in the phenotype even when only one copy is present, masking the expression of a recessive allele paired with it in a heterozygote.

An allele whose trait is expressed only when two copies are present, because its effect is hidden by a dominant allele in a heterozygous individual.

Exchange of corresponding segments between paired homologous chromosomes during prophase of meiosis, which creates new combinations of alleles on a single chromosome.

Genes located close together on the same chromosome that tend to be inherited together rather than assorting independently, though crossing over can separate them.

The random orientation of each homologous chromosome pair at meiosis, so that alleles of genes on different chromosomes are distributed to gametes independently of one another.

A permanent change in the DNA sequence of a gene or chromosome, which may be silent, harmful, or beneficial and is the ultimate source of new genetic variation.

A long thread of DNA wrapped around histone proteins, carrying many genes in a linear order; humans have 46 in body cells, arranged as 23 pairs.

The process by which individuals with inherited traits that improve survival or reproduction leave more offspring, so those traits become more common in later generations.

An inherited feature of a population that improves its members' ability to survive and reproduce in a particular environment, arising over generations through natural selection.

The relative contribution an individual makes to the next generation's gene pool, measured by how many surviving offspring it produces compared with other individuals in the population.

The total collection of alleles present in all members of a population at a given time, whose frequencies can shift through selection, mutation, migration, and genetic drift.

Random change in allele frequencies from one generation to the next, especially strong in small populations, occurring by chance rather than because of any survival advantage.

The formation of new species when populations become reproductively isolated and diverge genetically, for example through geographic separation followed by accumulated differences.

The maintenance of a stable internal environment, such as constant body temperature or blood glucose, through feedback mechanisms that detect and correct deviations from a set point.

A control mechanism in which a change in a body variable triggers a response that counteracts the change, returning the variable toward its normal range and keeping conditions steady.

A chemical messenger secreted by an endocrine gland into the bloodstream, travelling to target cells with matching receptors where it alters their activity.

The maximum population size of a species that a given environment can support indefinitely, determined by available resources such as food, water, and space.

Any resource or condition, such as light, nutrients, or predation, that is in shortest supply and therefore restricts growth, population size, or distribution of organisms.

A group of individuals of the same species living in the same area at the same time, able to interbreed and sharing a common gene pool.