Chapter 25 Flashcards

Flashcards on DNA Replication, Repair, and Recombination

Semi-conservative DNA Replication

Two molecules of duplex DNA are produced, each containing one polynucleotide strand from the parent molecule and a newly synthesized complementary strand.

DNA Polymerase Requirements

DNA polymerase requires a template and primers to synthesize DNA.

Semi-discontinuous Replication

Double-stranded DNA is replicated semi-discontinuously, resulting in Okazaki fragments.

Okazaki Fragments

DNA fragments of 1000 to 2000 nucleotides long in prokaryotes and 100 to 200 nucleotides long in eukaryotes, formed during discontinuous DNA replication.

DNA Polymerase Activity

Prokaryotic DNA polymerases possess 3’ → 5’ exonuclease activity, and Pol I also has 5’ → 3’ exonuclease activity, contributing to proofreading and repair.

Additional Proteins for DNA Replication

Proteins are required to separate DNA strands, unwind the helix, bind to single-stranded DNA, and synthesize RNA primers.

Sliding Clamp

Enhances the processivity of DNA polymerase by loading onto template DNA.

DNA Ligase

Required along with a termination factor and topoisomerases to complete DNA replication.

Accuracy of DNA Replication

Achieved through balanced nucleotide levels, the polymerase mechanism, its proofreading activity, and DNA repair enzymes.

Nick Translation

Uses DNA polymerase I to simultaneously remove RNA primers or damaged DNA and replace them with new DNA.

Klenow Fragment

A fragment of E. coli DNA polymerase I used as a model polymerase.

SSB Protein

Prevents single-stranded DNA from reannealing during replication in E. coli.

Primosome

Synthesizes new RNA primers on the lagging strand during replication.

Replisome

A complex molecular machine that carries out replication of DNA, containing helicase, primase, DNA polymerase, and other proteins.

Catenated Chromosomes

Interlinked chromosomes formed during termination of replication, separated by DNA topoisomerase IV.

Telomerase

Uses an RNA template to extend the 3’ ends of eukaryotic chromosomes, maintaining telomere length.

TERT

The catalytic subunit of telomerase.

DNA Damage

DNA is susceptible to damage from various sources, leading to mutagenicity and potentially carcinogenicity.

Cyclobutylthymine Dimer

A type of DNA damage caused by UV radiation.

Oxidative Deamination

A type of DNA damage where amino groups are removed oxidatively from bases.

Alkylating Agents

Chemicals that can modify DNA bases by adding alkyl groups.

DNA Methylation

The addition of methyl groups to DNA bases, influencing gene expression and genome stability.

Ames Test

A test to assess the mutagenicity of a compound using bacteria.

Base Excision Repair (BER)

Involves removing a damaged base by DNA glycosylase and replacing it.

Nucleotide Excision Repair (NER)

A repair pathway to correct pyrimidine dimers and other bulky DNA lesions.

Mismatch Repair (MMR)

Corrects insertion or deletion mutations and errors at the active site of DNA polymerase.

DNA Photolyase

Enzyme that repairs pyrimidine dimers through photoreactivation.

Alkyltransferases

Enzymes that directly repair DNA by reversing base methylation.

DNA Glycosylase

Enzyme involved in base excision repair that cleaves the glycosidic bond between a damaged base and the deoxyribose.