BIOL 1000 - Lecture 22: DNA Replication and the Cell Cycle

Comprehensive vocabulary flashcards covering the cell cycle, origins of replication, replication machinery, enzymes, and the mechanisms of leading- and lagging-strand DNA synthesis.

Interphase

The cell cycle stage preceding mitosis, consisting of the $G_1$, S (DNA synthesis), and $G_2$ phases.

Mitotic (M) Phase

The division phase of the cell cycle consisting of mitosis and cytokinesis.

Daughter Cells

Cells resulting from division that are identical copies of the parent cell, containing the exact same heritable material (DNA).

Origin of Replication

A specific nucleotide sequence recognized by initiating proteins where the DNA replication process begins, activated once during the S phase.

Bacterial Origin of Replication

A single origin of replication present in bacterial chromosomes from which replication proceeds bidirectionally.

Eukaryotic Origins of Replication

Hundreds to thousands of replication origins present on eukaryotic chromosomes that permit faster replication.

Replication Bubble

The open structure formed when double-stranded DNA unwinds and separates at the origin of replication.

Replication Fork

The Y-shaped junction where the parental DNA double helix is unwound and separated into single strands.

Bidirectional Replication

The process by which DNA synthesis proceeds in both directions ($5' \rightarrow 3'$) away from each origin of replication.

Helicase

An enzyme that unwinds and separates parental DNA strands at the replication forks by breaking hydrogen bonds between base pairs.

Single-Strand DNA-Binding Proteins (SSBPs)

Proteins that attach to and stabilize separated single-stranded DNA to prevent the strands from reforming a double helix.

Topoisomerase

An enzyme that breaks, twists, and rejoins the DNA double helix to relieve twisting forces and pressure ahead of the replication fork.

Template Strand

An unwound parental DNA strand that serves as a guide for synthesizing a new, complementary daughter strand.

RNA Primer

A short sequence of complementary RNA synthesized on the template strand that provides a $3'$ end for DNA polymerase to begin synthesis.

Primase

An enzyme that catalyzes the synthesis of an RNA primer on the leading strand and for each Okazaki fragment on the lagging strand.

DNA Polymerases

Enzymes that catalyze the addition of new nucleotides complementary to the template strand, starting at the $3'$ end of the RNA primer.

5' to 3' Direction

The exclusive biochemical orientation in which all new complementary DNA strands are elongated.

3' to 5' Direction

The direction in which DNA polymerase travels along the parent template DNA strand during synthesis.

Sliding Clamp

A ring-shaped protein structure that holds DNA polymerase in place on the template strand during strand extension.

DNA Polymerase III (Leading Strand)

The enzyme that continuously extends the leading strand from the RNA primer toward the replication fork.

Leading Strand

The new DNA strand synthesized continuously toward the replication fork in the $5' \rightarrow 3'$ direction, requiring only a single RNA primer.

Continuous Elongation

The uninterrupted synthesis process characteristic of the leading strand as it follows the unwinding replication fork.

Lagging Strand

The new DNA strand synthesized discontinuously in segments away from the replication fork, requiring multiple RNA primers.

Discontinuous Elongation

The segmented synthesis mechanism characteristic of the lagging strand, progressing away from the replication fork.

Okazaki Fragment

A segment of newly synthesized DNA nucleotides along with its initiating RNA primer formed during lagging-strand synthesis.

DNA Polymerase III (Lagging Strand)

The enzyme that extends an Okazaki fragment from an RNA primer until it reaches the $5'$ end of the preceding RNA primer.

DNA Polymerase I

The enzyme that removes the RNA primer from synthesized fragments and replaces the ribonucleotides with DNA nucleotides.

DNA Ligase

An enzyme that joins Okazaki fragments into a continuous strand by linking sugar-phosphate backbones via phosphodiester bonds.

Phosphodiester Bond

The covalent chemical linkage created between the $3'$ hydroxyl group of a growing DNA strand and the $5'$ phosphate of an incoming deoxyribonucleotide.

Replisome

A multi-protein complex and DNA-synthesizing machine wherein two DNA polymerases work together following helicase along the DNA.