Molecular Genetics Glossary

An alternative form of a gene at a particular locus on a chromosome. Different alleles can produce variations in the inherited trait.

A three-nucleotide sequence on tRNA that is complementary to a specific codon on mRNA, ensuring the correct amino acid is incorporated during translation.

The complex of DNA and histone proteins that packages DNA within the nucleus. Exists as euchromatin (loosely packed, active) or heterochromatin (tightly packed, silent).

A three-nucleotide sequence in mRNA that codes for a specific amino acid or serves as a start or stop signal during translation.

The specific hydrogen bonding between nucleotide bases in nucleic acids: adenine pairs with thymine (or uracil in RNA) via two hydrogen bonds, and guanine pairs with cytosine via three hydrogen bonds.

Clustered Regularly Interspaced Short Palindromic Repeats. A bacterial adaptive immune system adapted as a genome editing tool. The CRISPR-Cas9 system enables precise, targeted modifications to genomic DNA.

An enzyme that catalyzes the formation of phosphodiester bonds between adjacent DNA fragments, sealing nicks in the sugar-phosphate backbone. Essential in replication (joining Okazaki fragments) and molecular cloning.

An enzyme that synthesizes new DNA strands by adding nucleotides complementary to a template strand, working in the 5' to 3' direction. Also has proofreading (3' to 5' exonuclease) activity.

A regulatory DNA sequence that can increase transcription of a gene when bound by specific transcription factors. Enhancers can act over long distances and in either orientation relative to the gene.

A segment of a gene that is represented in the mature mRNA product after splicing. Exons typically contain the coding sequences that are translated into protein.

The process by which information encoded in a gene is used to synthesize a functional product, typically a protein. Includes transcription, RNA processing, translation, and post-translational modification.

The genetic constitution of an organism, specifically the combination of alleles at a particular locus or across the entire genome.

An enzyme that unwinds the double-stranded DNA helix at the replication fork by breaking the hydrogen bonds between complementary base pairs, creating single-stranded templates for replication.

A non-coding sequence within a gene that is transcribed into pre-mRNA but removed by splicing before translation. Introns are found primarily in eukaryotic genes.

A permanent alteration in the nucleotide sequence of DNA. Mutations may be spontaneous or induced and can range from single nucleotide changes to large chromosomal rearrangements.

The monomer unit of nucleic acids, consisting of a nitrogenous base (A, T/U, G, or C), a five-carbon sugar (deoxyribose in DNA, ribose in RNA), and one or more phosphate groups.

A functional unit of prokaryotic gene regulation consisting of a cluster of genes under the control of a single promoter and operator. Transcribed as a single polycistronic mRNA.

The observable physical, biochemical, or behavioral characteristics of an organism, resulting from the interaction of its genotype with the environment.

A small, circular, double-stranded DNA molecule found in bacteria that replicates independently of chromosomal DNA. Widely used as a cloning vector in recombinant DNA technology.

A DNA sequence upstream of a gene where RNA polymerase and transcription factors bind to initiate transcription. Common elements include the TATA box in eukaryotes and the -10/-35 regions in prokaryotes.

The Y-shaped region of a replicating DNA molecule where the parental strands are being unwound and new daughter strands are being synthesized.

A molecular machine composed of rRNA and proteins that catalyzes protein synthesis by reading mRNA and linking amino acids into a polypeptide chain. Consists of a large and small subunit.

An enzyme that synthesizes RNA from a DNA template during transcription. Prokaryotes have one type; eukaryotes have three (Pol I for rRNA, Pol II for mRNA, Pol III for tRNA and small RNAs).

A large complex of snRNPs (small nuclear ribonucleoproteins) and proteins that removes introns from pre-mRNA and joins exons together in eukaryotic cells.

A protein that binds to specific DNA sequences (such as promoters and enhancers) to regulate the rate of transcription. General transcription factors are needed for all genes; specific ones activate particular genes.