DNA, Chromosomes, and Cell Division

A comprehensive set of vocabulary flashcards covering DNA replication, protein synthesis processes (transcription and translation), and the detailed phases of the cell cycle, mitosis, and meiosis.

DNA Helicase

Enzyme that unwinds and separates the two DNA strands by breaking the weak hydrogen bonds.

Single-Strand Binding Proteins

Proteins that attach to and keep the two DNA strands separated and untwisted during replication.

Topoisomerase

Enzyme that attaches to the forks of the replication bubble to relieve stress and prevent the super-coiling of DNA as it separates.

Replication Fork

A Y-shaped structure at the active region of DNA separation originating at replication bubbles.

S phase

The specific phase of interphase during which DNA is copied or synthesized.

DNA Primase

The enzyme that synthesizes the RNA primer necessary to start the addition of new nucleotides.

DNA polymerase III

Enzyme that facilitates the addition of complementary nucleotides to the $3'$ end of a newly forming DNA strand.

Leading Strand

The DNA strand synthesized as a single strand from the point of origin toward the opening replication fork.

Lagging Strand

The DNA strand synthesized discontinuously against the overall direction of replication.

Okazaki Fragments

A series of short segments created on the lagging strand during DNA replication.

DNA ligase

Enzyme that joins Okazaki fragments together and rejoins exons during mRNA processing.

Semiconservative

A type of replication resulting in two identical DNA molecules, each consisting of one parent strand and one newly synthesized strand.

Transcription

The process where genetic information in DNA is used as a template to assemble complementary nucleotides into messenger RNA (mRNA).

TATA box

A specific region within the promoter where RNA Polymerase must bind to begin the transcription of RNA.

RNA capping

The addition of Guanosine triphosphate to the $5'$ end of the RNA to serve as a recognition signal for ribosomes.

Polyadenylation

The modification of the $3'$ end of the primary transcript by adding a string of $150$ or more adenine nucleotides for stability and transport.

Introns

Non-functional segments of DNA that are snipped out of the mRNA chain during processing.

Exons

Segments of DNA that code for proteins and are joined together after introns are removed.

Codon

A triplet or sequence of three nitrogenous bases in mRNA that codes for a specific amino acid.

Anticodon

A sequence of three nucleotide bases on tRNA that are complementary to a codon on mRNA.

Translation

The process of decoding mRNA into a polypeptide chain using ribosomes and tRNA.

Release factor

A protein that binds to the A site at a stop codon, adding water instead of an amino acid to release the polypeptide and disassemble the complex.

$G_1$ phase

A stage of interphase where the cell is metabolically active, protein synthesis occurs, and chromosomes exist as single chromatids.

$G_2$ phase

The final phase of interphase where the cell prepares to undergo cell division.

Prometaphase

The mitotic stage where the nuclear membrane disappears and chromosomes attach to spindle fibers at their kinetochores.

Metaphase

The stage where the mitotic spindle is complete, centrioles move to opposite poles, and chromosomes line up on the equatorial plate.

Anaphase

The stage where centromeres divide longitudinally and sister chromatids migrate to opposite poles.

Telophase

The stage where chromosomes uncoil, nucleoli reform, and the nuclear membrane is reconstructed, usually followed by cytokinesis.

Meiosis

A process involving one DNA duplication and two cell divisions that reduces the chromosome number from diploid ($2n = 46$) to haploid ($n = 23$).

Synapsis

The locus-for-locus pairing of homologous chromosomes occurring during the zygotene stage of prophase I.

Crossing-over

The exchange of homologous segments of DNA between nonsister chromatids during pachytene, resulting in genetic recombination.

Bivalents

Structures formed by paired homologs, also known as tetrads because they are composed of four chromatids.

Chiasmata

The points where homologous chromosomes are held together after repulsion begins, representing the locations where crossing-over occurred.

Diakinesis

The final stage of prophase I where chromosomes reach their greatest contraction.