Biology Lecture 9: Cell Cycle & DNA Replication

Vocabulary flashcards defining core terms, structures, and enzymes involved in the cell cycle and DNA replication based on lecture notes.

Cell Cycle

The life of a cell from the time it is first formed from a dividing parent cell until its division into two daughter cells.

Mitosis

The phase of cell division responsible for nuclear division.

Cytokinesis

The phase of cell division responsible for the division of cytoplasm.

Genome

The total content of DNA and genetic information within a cell.

Chromatin

The complex of DNA and proteins that serves as the building material of chromosomes.

Human Somatic Cell

A non-reproductive body cell containing 46 chromosomes, arranged as 2 sets of 23 inherited from each parent.

Germ Cells

Reproductive cells (sperm and ovum) containing one set of 23 chromosomes.

Interphase

The non-dividing stage between two successive cell divisions that accounts for about 90% of the cell cycle duration.

G1-phase

The first gap phase of interphase where the cell grows, duplicates centrosomes, and forms enzymes required for DNA synthesis.

G0 Phase

A non-cycling state entered by cells that stop dividing, such as nerve cells, skeletal muscle cells, and RBCs.

S-phase

The synthesis phase of interphase where DNA replication, duplication of chromosomes, and synthesis of chromosomal proteins occur.

G2-phase

The second gap phase of interphase in which protein synthesis and cell growth continue to prepare the cell for M-phase.

Generation Time

The amount of time taken to complete one full cell cycle, which is 24 hours in a human cell.

Semi-conservative Model

The model of DNA replication where two parent strands unwind and separate, each serving as a template to form two double helices containing 50% new and 50% old DNA.

DNA Helicase

An enzyme that unwinds and separates the two strands of the DNA double helix at the replication fork.

Single-strand Binding Protein

A protein that prevents the rejoining of the two separated DNA strands during replication.

RNA Primase

An enzyme that synthesizes an RNA primer to provide a $3' \text{-OH}$ end for new DNA strand extensions.

RNA Primer

A segment of RNA synthesized by RNA-primase that provides the $3' \text{-OH}$ end required for DNA strand extension.

DNA Polymerase III

The main enzyme of replication that builds new DNA strands in the $5'$ to $3'$ direction using nucleoside triphosphates.

Topoisomerase

An enzyme that prevents knotting and tangling in the unwound DNA double helix during replication.

Replication Fork

The Y-shaped structure formed by DNA helicase from which DNA synthesis takes place.

Leading Strand

A newly synthesized continuous DNA strand built in the direction toward the replication fork.

Lagging Strand

A newly synthesized discontinuous DNA strand composed of short fragments grown away from the replication fork.

Okazaki Fragments

Short fragments of DNA synthesized discontinuously along the lagging strand during DNA replication.

DNA Polymerase I

An enzyme that replaces the RNA primer with a DNA fragment after strand synthesis.

DNA Ligase

An enzyme that seals Okazaki fragments together to form a complete DNA strand.

Telomerase

An enzyme that maintains telomere length and extends chromosomes to their original length at the end of replication.