GATE BT key terms

A model describing enzyme-catalysed reaction rate as a function of substrate concentration, yielding the maximum velocity Vmax and the Michaelis constant Km, the substrate level giving half of Vmax.

Km is the substrate concentration at which an enzyme works at half its maximal rate and inversely reflects substrate affinity; Vmax is the highest rate reached when enzyme is fully saturated with substrate.

A double-reciprocal graph of 1/rate against 1/substrate concentration that linearises Michaelis–Menten data; intercepts and slopes reveal Km, Vmax and the type of inhibition.

Reduction of enzyme activity by a molecule binding the enzyme or its substrate complex; classified as competitive, uncompetitive, non-competitive or mixed according to which kinetic parameters change.

The number of substrate molecules converted to product by one enzyme active site per unit time when the enzyme is fully saturated; also called catalytic constant kcat.

Control of protein activity by a molecule binding at a site distinct from the active site, shifting the protein between active and inactive conformations and often producing sigmoidal kinetics.

Binding of a ligand at one site on a multimeric protein that alters the affinity of other sites for the same ligand, giving a sigmoidal saturation curve and sharpened physiological response.

The cytosolic pathway that converts one glucose into two pyruvate molecules with net production of two ATP and two NADH, supplying energy and biosynthetic precursors to the cell.

The mitochondrial cycle in which acetyl-CoA is oxidised to carbon dioxide, generating NADH, FADH2 and GTP while supplying intermediates for biosynthesis; also called the citric acid or Krebs cycle.

Synthesis of ATP driven by a proton gradient across the inner mitochondrial membrane, generated by electron transport through respiratory complexes and used by ATP synthase.

The number of molecules of ATP formed per pair of electrons transferred to oxygen through the respiratory chain, a measure of coupling efficiency in oxidative phosphorylation.

A compound such as 2,4-dinitrophenol that carries protons across the inner mitochondrial membrane, dissipating the gradient so electron transport continues but ATP synthesis falls.

The flow of genetic information from DNA to RNA to protein, with DNA replication as the copying step; reverse transcription is a known exception in retroviruses.

Enzyme-catalysed synthesis of an RNA molecule from a DNA template by RNA polymerase, initiated at a promoter and terminated at a specific signal.

Ribosome-mediated synthesis of a polypeptide in which mRNA codons are decoded by aminoacyl-tRNAs according to the genetic code, beginning at a start codon.

A cluster of co-transcribed genes under one promoter and operator, regulated as a unit; the lac and trp operons are classic examples of inducible and repressible control.

Reduction of transcription of catabolic genes when a preferred carbon source such as glucose is present, mediated in bacteria by low cAMP and inactive CRP.

The property that most amino acids are encoded by more than one codon, because several triplets differ at the third position while specifying the same residue.

The proposal that a single tRNA anticodon can pair with more than one mRNA codon because the third base pair tolerates non-standard geometry, explaining degeneracy.

A bacterial enzyme that cleaves DNA at a specific recognition sequence, protecting the host via methylation; widely used in cloning to cut vector and insert DNA.

A DNA sequence that reads the same on the complementary strand when both are read in the same direction, forming the typical recognition site of type II restriction enzymes.

Short single-stranded overhangs produced by staggered cleavage of DNA, which base-pair with complementary overhangs and allow efficient joining of fragments.

Joining of two DNA molecules by forming phosphodiester bonds between them, catalysed by DNA ligase and used to insert a fragment into a vector.

A small self-replicating DNA molecule such as a plasmid, phage or artificial chromosome that carries an inserted fragment into a host cell for propagation or expression.

Introduction of free DNA into a bacterial cell, either naturally when competence develops or artificially by chemical treatment or electroporation.

A gene carried on a vector that lets host cells containing it survive under a selective condition, typically an antibiotic-resistance gene used to identify transformants.

A colony assay in which insertional inactivation of lacZ prevents a chromogenic substrate from being cleaved, so recombinant colonies stay white while non-recombinants turn blue.

In vitro amplification of a DNA segment by repeated cycles of denaturation, primer annealing and extension with a thermostable polymerase, doubling the target each cycle.

A short single-stranded oligonucleotide that provides a free 3'-hydroxyl end for a polymerase to extend, defining the start and boundaries of amplification.

The temperature at which PCR primers hybridise to their complementary template; it is set a few degrees below the primer melting temperature to balance specificity and yield.

An antibody population of identical specificity produced by a single B-cell clone, usually via hybridoma technology, binding one epitope of an antigen.

A fused cell line made from an antibody-producing B lymphocyte and a myeloma cell, combining specific antibody secretion with indefinite growth in culture.

An enzyme-linked immunosorbent assay that detects an antigen or antibody by a colour-producing enzyme reaction, run in direct, indirect, sandwich or competitive formats.

A technique in which proteins separated by gel electrophoresis are transferred to a membrane and detected with specific antibodies, revealing size and abundance.

Sodium dodecyl sulfate polyacrylamide gel electrophoresis, which denatures proteins and gives a negative charge proportional to mass, so migration reflects molecular weight.

The pH at which a molecule carries no net electrical charge; proteins are least soluble and do not migrate in an electric field at this pH.

Separation of charged molecules by reversible binding to a resin bearing opposite charges, eluted by changing salt concentration or pH.

Purification based on a specific reversible interaction between a target molecule and an immobilised ligand, giving high selectivity in few steps.

An enzyme fixed to a solid support or entrapped in a matrix, allowing reuse, continuous operation and easier separation of product from catalyst.

Two-phase growth in a batch culture on two carbon sources, where the preferred substrate is consumed first and a lag precedes use of the second.

An empirical expression relating specific growth rate to the concentration of a limiting substrate through a maximum rate and a half-saturation constant.