Lecture 4 - DNA recombination and repair

Lecture 4 - DNA recombination and repair - DNA...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
DNA Recombination A general phenomenon during which two strands of DNA molecules are spliced together giving rise to a new DNA molecule that contains information from each strand. It’s a controlled “mixing” of DNA that increases genetic diversity. The control occurs as only suitable or closely related DNA molecules can recombine. DNA recombination and mutation are the two principal approaches by which cells create variation that is required for molecular evolution to occur . Examples: Chromosomal “crossing over” during meiosis. Integration of viral DNA into a host Transduction of “host cell” DNA into a recipient cell.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Types of recombination: Type Sequence Heterduplex Proteins DNA Homology sequences involved Synthesis __________________________________________________________________________ Homologous Extensive on both long RecA,RecBCD,RuvC Some strands; not sequence specific Site-Specific Short, short Recombinases Some specific DNA sequence on both strands Transpositional Homology not required none Transposases Minor specific DNA sequence is (only to fill gaps) required on one strand NHEJ NONE none DNA-PK Minor (only to fill gaps)
Background image of page 2
Recombination occurs between two homologous (largely complementary) slightly variant copies of a same chromosome spanning several thousand bases. Homologous Recombination There has been an equal, reciprocal exchange between them.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Features of holiday model: 1. Homology 2. Symmetry of both breaks and strand invasion 3. Four-stranded “Holiday junction” as a key intermediate. 1. Homologous alignment 2. Reciprocal invasion 3. Branch migration Holiday junction The gene arrangement does not change
Background image of page 4
Holliday model: The process occurs in several steps: 1. Single strand nicks occur at homologous positions in strands of the same polarity followed by a single strand invasion of the other chromosome. Strand invasion places the homologous chromosomes side by side in a process referred to as synapsis . This is a symmetrical and reciprocal event. 2. Homologous sequences begin to base pair, called Homologous Alignment . 3. The junction can migrate in either direction known as branch migration producing heterduplex regions of varying sizes. 4.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 30

Lecture 4 - DNA recombination and repair - DNA...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online