Molecular Biology Glossary Table

Term	Definition
Transformation	Uptake of foreign DNA by a bacterium, causing heritable phenotypic change
Transcription	Synthesis of RNA from DNA template by RNA polymerase
Translation	Synthesis of protein from mRNA sequence at the ribosome
Semiconservative	Each daughter DNA molecule contains one parental and one new strand
Codon	Three-nucleotide sequence in mRNA that specifies one amino acid
Anticodon	Three-nucleotide sequence on tRNA that base-pairs with the mRNA codon
Okazaki fragment	Short DNA fragment synthesized discontinuously on the lagging strand template
Operator	DNA sequence in an operon where the repressor binds to block transcription
Inducer	A molecule that inactivates the repressor, allowing gene expression
Repressor	A protein that binds the operator to inhibit transcription
Nucleosome	Basic chromatin unit: ~200 bp DNA + histone octamer (2×H2A, H2B, H3, H4)
Operon	A cluster of co-regulated genes with a shared promoter, transcribed as one mRNA
Polycistronic	An mRNA encoding more than one protein (common in prokaryotes)
Intron	Non-coding intervening sequence in eukaryotic genes, spliced out from pre-mRNA
Exon	Expressed coding sequence in eukaryotic genes, retained in mature mRNA
VNTR	Variable Number Tandem Repeat — polymorphic repetitive DNA used in fingerprinting
CsCl gradient	Cesium chloride density gradient centrifugation — separates DNA by density
Degenerate code	Multiple codons can encode the same amino acid
Non-ambiguous	Each codon specifies only one amino acid (never two)
Allolactose	Isomer of lactose; the actual inducer of the Lac operon
Template strand	DNA strand read by RNA polymerase (3'→5'); also called antisense/non-coding strand
Coding strand	DNA strand with same sequence as mRNA (5'→3'); also called sense strand
Peptidyl transferase	Catalytic activity of 23S rRNA in large ribosomal subunit; forms peptide bonds
Release factor	Protein that recognizes stop codons and terminates translation
Telomerase	Ribonucleoprotein enzyme that extends telomeres using built-in RNA template