CAPE Biology Unit 1 key terms

Small, single units that join end to end in long chains, such as amino acids forming proteins or nucleotides forming nucleic acids. Their structure determines the properties of the polymer built from them.

A large molecule made of many similar subunits linked in sequence, such as starch from glucose or a protein from amino acids. Its behaviour depends on chain length, branching and folding.

A joining reaction in which two molecules bond and a small molecule, usually water, is released. It builds glycosidic, peptide and ester bonds when monomers are assembled into polymers.

A splitting reaction in which a water molecule is used to break a bond between subunits. Digestion of starch, proteins and lipids depends on it, and it reverses condensation.

The bond formed between the hydroxyl groups of two monosaccharides with the loss of water. Its orientation, alpha or beta, changes whether a polysaccharide coils or forms straight strands.

A storage polysaccharide of alpha-glucose found in plant cells, made of amylose and amylopectin. It is compact, insoluble and easily hydrolysed to release glucose for respiration.

A structural polysaccharide of beta-glucose forming straight chains held by hydrogen bonds into microfibrils. It gives plant cell walls tensile strength and cannot be digested by most animals.

A sugar with a free carbonyl group able to donate electrons, so it reduces copper(II) ions to a brick-red precipitate when heated in Benedict's reagent. All monosaccharides and most disaccharides qualify.

The covalent link formed between the amino group of one amino acid and the carboxyl group of another, releasing water. It is rigid and planar, which constrains how a polypeptide chain can fold.

The exact sequence of amino acids in a polypeptide, held by peptide bonds. It is coded by DNA and ultimately determines the three-dimensional shape and function of the protein.

Local regular folding of a polypeptide into alpha-helices or beta-pleated sheets, stabilised by hydrogen bonds between backbone groups. These patterns arise without involving side chains.

The overall three-dimensional shape of a single polypeptide, held by interactions between side chains such as hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic attractions. It determines the protein's specific function.

The arrangement of two or more polypeptide chains into one functional protein complex, as in haemoglobin with four subunits. Each chain keeps its own tertiary shape within the assembly.

Loss of a protein's three-dimensional shape when bonds holding its folding are broken by heat, pH change or chemicals. The primary structure remains intact but function is usually lost, often irreversibly.

A protein that speeds up a specific metabolic reaction by lowering activation energy, acting as a biological catalyst. Its active site binds substrates temporarily and is reused unchanged.

The small region of an enzyme where substrate binds, formed by a few key amino acids folded into a precise shape. Its shape and charge distribution give the enzyme specificity.

The minimum energy reactants need before they can be converted into products. Enzymes lower this barrier by providing an alternative reaction pathway, so reactions proceed faster at the same temperature.

A molecule with a shape similar to the substrate that binds the active site and blocks substrate entry. Its effect is reduced by raising substrate concentration because the two compete.

The tendency of water to move from one region to another, measured in kilopascals and highest in pure water at zero. Water moves down a gradient from less negative to more negative values.

The net movement of water across a partially permeable membrane from a region of higher water potential to one of lower water potential. It is passive and driven by the water potential gradient.

The component of water potential caused by dissolved solutes, always negative or zero. More concentrated solutions have more negative solute potentials and so attract water.

Shrinking of the protoplast away from the plant cell wall when a cell loses water in a hypertonic solution. It occurs because the protoplast contracts while the rigid wall stays in place.

Passive movement of polar or large molecules across a membrane through channel or carrier proteins, down a concentration gradient. No energy from ATP is used at any stage.

Movement of substances across a membrane against a concentration gradient using carrier proteins and energy from ATP hydrolysis. It allows cells to accumulate ions or nutrients far above external levels.

The description of membranes as a phospholipid bilayer with proteins and other molecules embedded in or attached to it, able to move laterally. It explains selective permeability and membrane flexibility.

The first stage of mitosis, when chromosomes condense, the nuclear envelope breaks down and spindle fibres begin to form. Each chromosome is already duplicated into two sister chromatids.

The mitotic stage in which condensed chromosomes line up along the cell equator, attached to spindle fibres at their centromeres. This alignment ensures one chromatid from each pair goes to each pole.

The mitotic stage in which spindle fibres shorten and pull sister chromatids apart to opposite poles. Each pole therefore receives one complete set of identical chromosomes.

The final mitotic stage, when chromosomes reach the poles, decondense and new nuclear envelopes form. Cytokinesis usually follows, dividing the cytoplasm to produce two separate cells.

Nuclear division producing two daughter nuclei genetically identical to the parent cell and to each other. It underlies growth, repair and asexual reproduction in eukaryotes.

Two successive nuclear divisions that halve the chromosome number and produce four genetically varied haploid cells. Crossing over and independent assortment create new allele combinations.

Exchange of corresponding segments between non-sister chromatids of homologous chromosomes during prophase I. It breaks linkages between alleles and produces recombinant chromosomes.

Random orientation of homologous chromosome pairs at the equator in meiosis I, so maternal and paternal chromosomes are distributed independently into gametes. It generates many possible allele combinations.

A pair of chromosomes of similar size and shape carrying the same gene loci, one inherited from each parent. They pair during meiosis but may carry different alleles at a locus.

One of the two identical DNA copies of a replicated chromosome, joined at the centromere. Chromatids separate at anaphase so each daughter nucleus receives one copy of every chromosome.

The constricted region of a chromosome where the two sister chromatids are held together and where spindle fibres attach. It ensures correct segregation of chromatids during nuclear division.