BI10.1-7 | Molecular Biology — Glossary

The basic structural unit of nucleic acids, consisting of a nitrogenous base, a pentose sugar, and a phosphate group

Double-ring nitrogenous bases (adenine and guanine) found in DNA and RNA

Single-ring nitrogenous bases (cytosine, thymine in DNA, uracil in RNA)

The covalent bond linking the 3' carbon of one nucleotide's sugar to the 5' carbon of the next via a phosphate group, forming the nucleic acid backbone

Phosphoribosyl pyrophosphate — the activated ribose-5-phosphate that donates the sugar-phosphate in nucleotide synthesis

Hypoxanthine-guanine phosphoribosyltransferase — the key salvage pathway enzyme that recycles hypoxanthine and guanine into IMP and GMP

An X-linked disorder caused by HGPRT deficiency, characterised by hyperuricaemia, self-mutilation, intellectual disability, and choreoathetosis

The enzyme that catalyses the final two steps of purine degradation: hypoxanthine → xanthine → uric acid

A metabolic arthropathy caused by deposition of monosodium urate crystals in joints, resulting from hyperuricaemia

A xanthine oxidase inhibitor used to treat gout by reducing uric acid production

Adenosine deaminase deficiency causing toxic accumulation of deoxyadenosine, leading to severe combined immunodeficiency (SCID)

The fundamental principle that genetic information flows from DNA → RNA → Protein, with replication copying DNA

The enzyme that synthesises new DNA strands by adding nucleotides complementary to the template strand, always in the 5'→3' direction

The enzyme that transcribes DNA into RNA by reading the template strand 3'→5' and synthesising mRNA 5'→3'

Short DNA fragments (100-200 bases in eukaryotes) synthesised on the lagging strand during replication, later joined by DNA ligase

A DNA repair mechanism that corrects base-pairing errors missed by polymerase proofreading; defective in Lynch syndrome

A repair mechanism that removes bulky DNA lesions (e.g., thymine dimers) by excising a patch of nucleotides; defective in xeroderma pigmentosum

A single nucleotide change in DNA that may be silent, missense, or nonsense depending on its effect on the protein product

An insertion or deletion of bases (not in multiples of 3) that shifts the entire reading frame, altering all downstream codons

Unstable amplification of three-nucleotide sequences causing diseases like Fragile X (CGG), Huntington (CAG), and myotonic dystrophy (CTG)

Heritable changes in gene expression without altering the DNA sequence, including DNA methylation and histone modifications

Bacterial endonucleases that cut DNA at specific palindromic sequences, producing fragments used in recombinant DNA technology

Polymerase Chain Reaction — a technique that amplifies specific DNA sequences exponentially through repeated thermal cycling (denaturation, annealing, extension)

A gene-editing system using guide RNA to direct Cas9 endonuclease to cut DNA at a specific target sequence for gene knockout or correction

Fluorescence In Situ Hybridisation — a technique using fluorescent probes to detect specific DNA sequences on chromosomes for diagnosing translocations and amplifications