MOL100H23 lecture 9 DNA replication and repair

Cell cycle

The program that eukaryotic cells use to divide, consisting of gap phase 1 (G1), synthesis phase (S), gap phase 2 (G2), and mitosis (M).

DNA replication

The process of synthesizing a complementary strand of DNA using the existing DNA double helix as a template.

Conservative replication

A type of DNA replication where both strands are copied, resulting in two double strands consisting of the two parental strands and the two daughter strands.

Semiconservative replication

A type of DNA replication where both strands are copied, resulting in each of the two double strands consisting of one parental strand and one daughter strand.

Transcription

The process of synthesizing RNA from a DNA template.

RNA polymerase

The enzyme responsible for synthesizing RNA during transcription.

DNA polymerase

The enzyme responsible for synthesizing the new DNA strand during DNA replication.

Helicase

An enzyme that unwinds the DNA double strand during DNA replication.

Topoisomerase

An enzyme that cuts and re-seals the DNA backbone to relieve torsion during DNA replication.

Replication fork

The unwound DNA region at which the replication machinery assembles during DNA replication.

Leading strand

The DNA strand that is synthesized continuously during DNA replication.

Lagging strand

The DNA strand that is synthesized in short fragments as the parental DNA unwinds during DNA replication.

Primase

An enzyme that generates an RNA primer during DNA replication.

DNA Replication

The process of synthesizing a new DNA strand using an existing DNA strand as a template.

Lagging strand

The DNA strand that is synthesized discontinuously in short fragments called Okazaki fragments.

Okazaki fragments

Short DNA fragments (100-200 base pairs) that are synthesized on the lagging strand during DNA replication.

Leading strand

The DNA strand that is synthesized continuously in the 5' to 3' direction during DNA replication.

DNA polymerase

An enzyme that catalyzes the synthesis of DNA by adding nucleotides to the growing DNA strand.

Primase

An enzyme that synthesizes a short RNA primer on the lagging strand during DNA replication.

RNA primer

A short segment of RNA that serves as a starting point for DNA synthesis on the lagging strand.

DNA ligase

An enzyme that joins the Okazaki fragments on the lagging strand during DNA replication.

Helicase

An enzyme that unwinds the DNA double helix during DNA replication.

DNA damage

Changes in the DNA sequence caused by endogenous or exogenous factors.

Mutation

A permanent change in the DNA sequence, often caused by DNA damage.

Proofreading

The process by which DNA polymerases correct their own errors during DNA synthesis.

Base excision repair

A DNA repair mechanism that corrects single nucleotide mutations by removing and replacing damaged bases.

Nucleotide excision repair

A DNA repair mechanism that corrects DNA damage that distorts the shape of the DNA, such as thymine dimers caused by UV light.

Nucleotide excision repair

A DNA repair mechanism that corrects damage that distorts the shape of the DNA, such as thymine dimers caused by UV light.

Thymine dimer

The dimerization of two adjacent thymine residues on the same DNA strand, caused by UV light.

Bulging of the DNA

The distortion of the DNA caused by thymine dimers or other types of damage.

Protein complexes

Complexes of proteins that slide along the DNA double helix and detect bulging or other distortions.

Helicase

An enzyme that opens the double strand of DNA during nucleotide excision repair.

Endonucleases

Enzymes that cleave the damaged section of DNA during nucleotide excision repair.

DNA polymerase

An enzyme that fills the gap left after the damaged section is excised during nucleotide excision repair.

Double strand breaks (DSB)

Severe forms of DNA damage where both strands of the DNA double helix are broken.

Non-homologous end joining (NHEJ)

A mechanism for repairing DNA double strand breaks where the ends are joined without using a template.

Homologous recombination

A high precision DNA repair mechanism that uses a template, often the sister chromatid, to repair single strand breaks or double strand breaks.

KU80/KU70 heterodimer

A protein complex that binds to free DNA ends during non-homologous end joining.

DNA-dependent protein kinase (DNA-PK)

An enzyme that is part of the protein complex bound to free DNA ends during non-homologous end joining.

DNA ligase

An enzyme that joins the ends of DNA during non-homologous end joining.

Exonucleases

Enzymes that generate single stranded 3' ends (3' overhangs) after a double strand break.

Rad51

A protein that mediates the hybridization of a single strand to the homologous chromosome during homologous recombination.

Holliday structure

The point at which the strands switch from one chromosome to the other during homologous recombination.

Robin Holliday

A scientist who proposed the Holliday structure in 1964.

Resolution of the Holliday structure

The process of cleaving the single strands and re-ligating the ends to restore two separate DNA double strands.

Recombinant chromosomes

Chromosomes that contain DNA from both original chromosomes after cleavage of the single strands during homologous recombination.