MATSEC AM Biology key terms

A reaction in which a water molecule is used to split a large molecule into smaller ones, as when a glycosidic, ester or peptide bond is broken by the addition of water.

A reaction that joins two molecules together with the release of one water molecule, forming a covalent bond such as a glycosidic, ester or peptide linkage.

The covalent link formed between the hydroxyl groups of two monosaccharides by condensation, joining them into a disaccharide or, when repeated, a polysaccharide chain.

The covalent bond between the carboxyl group of one amino acid and the amino group of the next, formed by condensation and giving a polypeptide its repeating backbone.

A large polymer built from many monosaccharide units joined by glycosidic bonds, such as starch, glycogen or cellulose, used for storage or structure.

The exact sequence of amino acids in a polypeptide chain, held by peptide bonds, which determines all higher levels of folding and the protein's eventual function.

The overall three-dimensional shape of a single polypeptide, stabilised by hydrogen bonds, ionic interactions, disulfide bridges and hydrophobic clustering of side chains.

The arrangement of two or more folded polypeptide subunits into one functional protein complex, as in haemoglobin, held together by the same kinds of bonds as tertiary structure.

Loss of a protein's specific three-dimensional shape caused by heat, extreme pH or chemicals, which breaks the weak bonds holding the folds and usually destroys biological function.

A globular protein that acts as a biological catalyst, lowering the activation energy of a specific reaction by binding substrates at its active site without being used up.

The small region of an enzyme, formed by a few specific amino acid side chains, that binds the substrate and where catalysis takes place; its shape is complementary to the substrate.

The minimum energy that reactant molecules must possess before a reaction can proceed; enzymes reduce this barrier, so reactions occur faster at normal cell temperatures.

A reversible form of inhibition in which a molecule similar in shape to the substrate binds the active site, blocking substrate access; its effect is reduced by raising substrate concentration.

The double layer of phospholipid molecules that forms the core of every cell membrane, with hydrophilic heads facing outwards and hydrophobic tails facing inwards.

The description of the membrane as a fluid phospholipid bilayer in which proteins, cholesterol and glycoproteins are embedded and can move laterally.

The net movement of water across a partially permeable membrane from a region of higher water potential to one of lower water potential, down the water potential gradient.

The tendency of water to move from one place to another, measured in kilopascals; pure water at atmospheric pressure has a value of zero and solutions have negative values.

Passive movement of a substance across a membrane down its concentration gradient through specific carrier or channel proteins, requiring no metabolic energy.

Movement of ions or molecules across a membrane against their concentration gradient by carrier proteins that use energy from ATP hydrolysis, for example the sodium-potassium pump.

The first stage of respiration, occurring in the cytoplasm, in which one glucose molecule is split and oxidised to two pyruvate molecules with net gain of two ATP and two reduced NAD.

The three-carbon product of glycolysis; in aerobic conditions it is decarboxylated and oxidised to acetyl coenzyme A, while in anaerobic conditions it is converted to lactate or ethanol.

A cycle of reactions in the mitochondrial matrix that oxidises acetyl coenzyme A, releasing carbon dioxide and reducing NAD and FAD, whose electrons later drive ATP synthesis.

A membrane protein complex that makes ATP from ADP and phosphate as protons flow through it down their electrochemical gradient, as occurs across the inner mitochondrial membrane.

The stage of photosynthesis in the thylakoid membranes in which light energy drives the photolysis of water, producing oxygen, reduced NADP and ATP for the next stage.

The Calvin cycle in the stroma of the chloroplast, in which carbon dioxide is fixed by the enzyme rubisco and reduced using ATP and reduced NADP to form triose phosphate.

A separation technique in which pigments or other molecules dissolved in a solvent move at different rates over a stationary phase, allowing them to be identified by their Rf values.

Nuclear division that produces two genetically identical daughter nuclei with the same chromosome number as the parent cell, used in growth, repair and asexual reproduction.

A reduction division producing four haploid cells from one diploid cell through two successive divisions, generating genetic variation by independent assortment and crossing over.

Exchange of corresponding sections of chromatids between non-sister chromatids of a homologous pair during prophase I of meiosis, producing recombinant chromosomes and new allele combinations.

The random alignment and separation of homologous chromosome pairs during meiosis I, so that alleles of different genes are distributed to gametes independently of one another.

One of two or more alternative versions of the same gene, occupying the same locus on homologous chromosomes and differing slightly in base sequence.

The particular combination of alleles an organism carries for a gene or set of genes, whether expressed or not, for example homozygous dominant or heterozygous.

The observable characteristics of an organism resulting from the interaction between its genotype and the environment in which it develops.

An in vitro technique that copies a DNA fragment many times using primers, nucleotides and a heat-stable DNA polymerase through repeated cycles of denaturation, annealing and extension.

A technique that separates DNA fragments by size, since negatively charged fragments move towards the positive electrode through a gel, with shorter fragments travelling further.

A group of organisms with similar morphology and physiology that can interbreed to produce fertile offspring, and which is reproductively isolated from other such groups.

The process by which individuals with inherited variations better suited to their environment survive and reproduce more, so allele frequencies in the population change over generations.

The position an organism occupies in a food chain, such as producer, primary consumer or secondary consumer, defined by the number of energy-transfer steps from the start.