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

Vocabulary flashcards covering DNA structure, chromosome organization, transcription, translation, DNA replication, and cell cycle checkpoints based on the provided lecture notes.

5' phosphate and 3' hydroxyl

The functional groups attached to the terminal carbons of a DNA strand that determine its directionality and opposite strand orientation.

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 acts as the attachment site for microtubules.

Gene

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

Open reading frame (ORF)

The portion of a eukaryotic gene structure that contains the protein-coding sequence of exons.

Exons

Segments of DNA within a gene that code for proteins.

Introns

Non-coding segments within a eukaryotic gene that get removed during RNA processing.

Promoter

A regulatory DNA sequence located upstream of an open reading frame that tells RNA polymerase where to begin transcription.

Transcription

The process in which RNA polymerase binds to a promoter, unwinds DNA locally (~20 base pairs), reads the template strand, and builds complementary mRNA.

Primary transcript

The raw, precursor pre-RNA strand generated by transcription prior to RNA processing.

Alternative Splicing

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

Start codon

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

A site (Acceptor)

The ribosomal site where an incoming aminoacyl-tRNA delivering an amino acid arrives during translation elongation.

P site (Peptidyl)

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

E site (Exit)

The ribosomal site from which an empty or deacylated tRNA exits the ribosome.

Transfer RNA (tRNA)

RNA molecules that bring specific amino acids to the ribosomal A site during translation elongation.

Release factor

A protein that binds at the A site instead of tRNA when a stop codon (UAG, UAA, or UGA) is reached, causing ribosome subunits to dissociate and releasing the free polypeptide.

Semiconservative replication

The mode of DNA replication where each newly synthesized double strand retains one original strand from the parent DNA molecule.

DNA helicase

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

Primase

An enzyme that lays down a short RNA sequence (primer) required for DNA polymerase to initiate synthesis.

DNA polymerase

An enzyme that synthesizes new DNA by pairing complementary bases along the template strand in the $5' \rightarrow 3'$ direction.

DNA ligase

An enzyme that seals backbone nicks and joins DNA fragments together in the newly synthesized strand.

Leading strand

The strand of DNA that is replicated continuously in the $5' \rightarrow 3'$ direction toward the replication fork.

Lagging strand

The strand of DNA that is replicated discontinuously in small sections away from the replication fork.

G0 Phase

A resting phase in the cell cycle where cells exist outside the active cell division cycle.

Interphase

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

G1 Phase

The stage of interphase characterized by cell growth and performance of normal physiological tasks.

S Phase (Synthesis)

The phase of interphase during which DNA is replicated and centrioles are duplicated.

G2 Phase

The phase of interphase where the cell double checks duplicated chromosomes for errors, makes repairs, and prepares for mitosis.

G1 Checkpoint

The restriction point in the cell cycle determining whether a cell progresses into S phase or enters $G_0$.

G2 Checkpoint

A cell cycle checkpoint that verifies chromosome duplication accuracy before permitting entry into mitosis.

M Checkpoint

A cell cycle regulatory point occurring at the metaphase to anaphase transition to ensure proper spindle attachment before sister chromatid separation.