Molecular Genetics and DNA Processes

Vocabulary flashcards generated from lecture notes covering DNA replication, chromosome structure, transcription, translation, gene regulation, and DNA repair mechanisms.

Semiconservative Replication

The mode of DNA replication in which each daughter double helix contains one intact parental strand and one newly synthesized strand.

Origin of Replication (ORI)

A specific sequence of nucleotides where DNA replication begins; bacterial chromosomes possess only one ORI.

Initiator Protein

The first protein to recognize and bind to the origin of replication, preparing the DNA for localized unwinding.

DNA Helicase

An enzyme attracted by initiator proteins that catalyzes the localized unwinding of the DNA double helix.

Topoisomerase

An enzyme that relaxes supercoils during DNA unwinding by nicking, unwinding, and suturing the DNA, and separates entwined daughter chromosomes.

Telomeres

Inert chromosomal ends containing long stretches of short repeating sequences that protect intact eukaryotic chromosomes from improper fusion or degradation.

Telomerase

A ribonucleoprotein enzyme containing an RNA template that synthesizes telomeric DNA on the $3'$ G-rich tail to prevent chromosome shortening.

Histones

Positively charged proteins rich in lysine and arginine that associate with eukaryotic chromosomal DNA.

Histone Octamer

A protein complex formed by an H3-H4 tetramer combined with two H2A-H2B dimers, around which $147$ base pairs of DNA wrap to form a nucleosome core.

Euchromatin

Uncoiled and decondensed regions of eukaryotic chromatin that are transcriptionally active.

Heterochromatin

Condensed areas of eukaryotic chromatin that remain mostly transcriptionally inactive.

Frameshift Mutation

A genetic mutation caused by nucleotide insertions or deletions that shift the triplet reading frame and alter downstream codons.

Pribnow Box

The conserved $-10$ region consensus sequence (TATAAT) found within bacterial gene promoters.

Poly-A Tail

A sequence of $100-200$ adenine nucleotides added to the $3'$ end of eukaryotic pre-mRNA by poly-A polymerase following cleavage downstream of the AAUAAA signal.

Polyribosome

A structure consisting of a single mRNA strand being translated concurrently by multiple ribosomes in the $5'$ to $3'$ direction.

Operon

A group of functionally related genes in prokaryotes controlled by a single operator switch within a promoter.

trp Operon

A repressible operon that directs tryptophan synthesis and is turned off when tryptophan acts as a corepressor to activate the trp repressor.

Photoreactivation Repair

A light-dependent DNA repair pathway in which photoreactivation enzyme absorbs blue light to directly cleave bonds in thymine dimers.

Base Excision Repair

A DNA repair pathway where DNA glycosylase excises an damaged base, AP endonuclease nicks the backbone, and DNA polymerase and ligase fill the gap.

Transposase

An enzyme encoded by DNA transposons that cleaves DNA at inverted terminal repeats (ITRs) and integrates the transposon into a new target site.