Cell Cycle and DNA Replication

Flashcards covering key concepts related to the cell cycle, DNA replication, and repair mechanisms.

Cell Cycle

A series of phases that ensures cells grow, accurately replicate their DNA, and divide into two genetically identical daughter cells.

G1 Phase

The first phase of the cell cycle where the cell grows and prepares for DNA replication.

S Phase

The phase of the cell cycle where DNA replication occurs, resulting in two identical sister chromatids for each chromosome.

G2 Phase

The second gap phase where the cell continues to grow and prepares for mitosis.

M Phase

The phase of mitosis and cytokinesis where the nucleus divides and the cytoplasm is split into two daughter cells.

G0 Phase

A non-dividing resting state that some cells may enter.

Semiconservative DNA Replication

A type of DNA replication where each new DNA molecule consists of one original parental strand and one newly synthesized strand.

Bidirectional Replication

Describes how DNA replication proceeds outward in both directions from the origin of replication.

Replication Fork

Y-shaped regions at each end of the replication bubble where DNA strands separate and new strands are synthesized.

Helicase

An enzyme that unwinds the DNA double helix by breaking hydrogen bonds between bases.

Single-Strand Binding Proteins

Proteins that stabilize separated DNA strands and prevent them from reannealing.

Topoisomerase

An enzyme that relieves torsional strain ahead of the replication fork by cutting and rejoining DNA strands.

Primase

An enzyme that synthesizes short RNA primers, providing a starting point for DNA synthesis.

DNA Polymerase

The enzyme that adds nucleotides to the growing DNA strand in the 5’→3’ direction.

Leading Strand

The strand of DNA synthesized continuously toward the replication fork.

Lagging Strand

The strand of DNA synthesized discontinuously away from the replication fork.

Okazaki Fragments

Short segments of DNA synthesized on the lagging strand.

Proofreading

The process by which DNA polymerase checks newly added bases and removes mismatches using exonuclease activity.

End-Replication Problem

The issue where DNA polymerase cannot fully replicate the ends of linear chromosomes after primer removal.

Telomeres

Repetitive DNA sequences at chromosome ends that protect coding regions.

Telomerase

An enzyme that extends telomeres using an RNA template.

Mismatch Repair

A repair system that corrects replication errors that were missed by proofreading.

Base Excision Repair

A repair process for damaged or abnormal single bases.

Nucleotide Excision Repair

A DNA repair mechanism that removes bulky DNA lesions such as thymine dimers.

Thymine Dimers

Covalent bonds formed between adjacent thymine bases due to UV radiation.

Homologous Recombination

An accurate repair mechanism that uses a sister chromatid as a template.

Nonhomologous End Joining

A repair process that directly joins broken DNA ends, often introducing mutations.

Cell Cycle Checkpoints

Surveillance mechanisms that halt cell cycle progression if errors or damage are detected.

Cyclins

Regulatory proteins whose concentrations fluctuate throughout the cell cycle.

Cyclin-Dependent Kinases (CDKs)

Enzymes activated by cyclins that phosphorylate target proteins to promote cell cycle progression.

Maturation-Promoting Factor (MPF)

A cyclin-CDK complex that triggers the onset of mitosis.

Ubiquitin-Mediated Proteolysis

A process that tags proteins for degradation to regulate transitions in the cell cycle.

p53

A tumor suppressor protein that halts the cell cycle when DNA damage is detected.

Apoptosis

Programmed cell death that eliminates damaged or unnecessary cells.

Proto-Oncogenes

Normal genes that stimulate cell division when needed.

Oncogenes

Mutated or overactive proto-oncogenes that lead to uncontrolled cell division.

Tumor Suppressor Genes

Genes that restrain cell division and promote DNA repair or apoptosis.

Metastasis

The process by which cancer cells spread to distant tissues.

Replication Fork Diagram

Illustration showing helicase activity, leading strand synthesis, lagging strand synthesis, and primer initiation.

Checkpoint Regulation Diagram

Illustration illustrating cyclins activating CDKs and checkpoint progressions.

DNA Repair Diagram

Illustration showing how damaged DNA is recognized, removed, replaced, and sealed.