Genes, Transcription & Translation, DNA Replication, and Cell Cycle

A comprehensive vocabulary review of gene structure, transcription, translation, semiconservative DNA replication, and cell cycle phases and checkpoints.

Centromere

A specialized region of DNA where two sister chromatids are held together, producing a pinched or constricted appearance.

Kinetochore

A protein complex located at the centromere that serves as the attachment site for microtubules during cell division.

Gene

A segment of DNA that carries information needed to produce an RNA molecule which is usually involved in protein synthesis.

Open Reading Frame (ORF)

The region within a gene structure that contains the protein-coding sequence.

Exons

Sequences within a gene that code for proteins and are retained in mature mRNA.

Introns

Non-coding sequences in primary RNA transcripts that get removed during RNA processing.

Promoter

A regulatory sequence on DNA that tells RNA polymerase where to begin transcription.

Primary Transcript (Pre-RNA)

The initial RNA strand synthesized directly from DNA before undergoing RNA processing to remove introns.

Alternative Splicing

An RNA processing mechanism where different combinations of exons are joined together, allowing one gene to produce more than one protein.

Start Codon

The mRNA codon (AUG) that tells the ribosome where to begin translation and codes for the amino acid methionine.

Acceptor Site (A Site)

The site on the ribosome where incoming tRNA carrying an amino acid arrives during translation elongation.

Peptidyl Site (P Site)

The ribosomal site that holds the tRNA carrying the growing polypeptide chain and where peptide bonds are formed.

Exit Site (E Site)

The site on the ribosome from which an empty (deacylated) tRNA leaves during translation.

Release Factor

A protein that binds to the A site instead of tRNA when a stop codon (UAG, UAA, or UGA) is reached, initiating translation termination.

Semiconservative Replication

The model of DNA replication where each newly replicated DNA molecule consists of one strand from the original parent DNA molecule and one new strand.

DNA Helicase

An enzyme that unzips and unwinds the double-stranded DNA molecule during replication.

Primase

An enzyme that lays down a short RNA sequence (primer) to initiate DNA replication.

DNA Polymerase

An enzyme that adds complementary bases to synthesize new DNA strands in the $5' \rightarrow 3'$ direction and performs proofreading.

DNA Ligase

An enzyme that seals fragments together and closes gaps in the newly synthesized DNA strand.

Leading Strand

The strand of DNA that is replicated continuously during DNA replication.

Lagging Strand

The strand of DNA that is replicated discontinuously in small sections during DNA replication.

Interphase

The period of the cell cycle encompassing all phases ($G_1$, S, and $G_2$) between cell divisions.

$G_0$ Phase

A non-dividing resting phase of the cell cycle.

$G_1$ Checkpoint

The restriction point in the cell cycle that determines whether a cell enters the S phase or transitions into $G_0$.

$G_2$ Checkpoint

The cell cycle control checkpoint that determines if the cell can proceed to mitosis after checking for errors in duplicated chromosomes.

M Checkpoint

The regulatory checkpoint occurring at the transition from metaphase to anaphase that determines if a cell can enter anaphase and separate sister chromatids.