DNA/RNA Metabolism
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DNA/RNA Metabolism. Blackburn & Gait, Ch. 5 Neidle, Ch. 4 Recombination • understand basics of the reaction • know advantages/disadvantages of recombination • understand how recombinase protein works • know structure of Holliday junction (X-shaped) • know different types of recombination.

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DNA/RNA Metabolism

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Dna rna metabolism

DNA/RNA Metabolism

Blackburn & Gait, Ch. 5

Neidle, Ch. 4

Recombination

• understand basics of the reaction

• know advantages/disadvantages of recombination

• understand how recombinase protein works

• know structure of Holliday junction (X-shaped)

• know different types of recombination


Dna rna metabolism

Recombination

• Enables the limited exchange of genetic material between paired chromosomes

• Occurs between intact double helices

• Damage to DNA can stimulate recombination

• Enables the immune system to generate a diversity of protein antibodies from a limited set of genes

• Enables viruses to integrate their genetic material into a host’s genome

• Enables host organism to assort alleles (differing copies of same gene) into novel groups - favorable & unfavorable alleles can be shuffled randomly

• Enables repair of a damaged gene in an otherwise favorable chromosome

• Enables regulation of gene expression

• Enables rearrangement of antibody genes

• Can lead to cancers - example: Burkitt’s lymphoma caused by translocation between ch. 8 and 14


Dna rna metabolism

Recombination

  • • THREE main categories

  • 1. Homologous recombination

  • takes place between similar sequences

  • Site-specific recombination

    Limited sequence similarity between recombining DNAs

  • 3. Transposition

  • movement of a DNA element from one position to another, little sequence similarity needed

  • called “illegitimate recombination”


Dna rna metabolism

1. Homologous Recombination


Dna rna metabolism

1. Homologous Recombination

Recombinase protein

• One example is that of Cre recombinase from a bacteriophage (virus that infects bacteria)

• The enzyme mediates strand cleavage and exchange between two pieces of DNA

• An intermediate (half reacted) configuration of the DNA is called a Holliday junction (X-shaped)


Dna rna metabolism

1. Homologous Recombination

Recombinase protein


Dna rna metabolism

1. Homologous Recombination


Dna rna metabolism

2. Site-specific Recombination

Lambda phage integration and excision


Dna rna metabolism

2. Site-specific Recombination

VDJ rearrangement in antibody production


Dna rna metabolism

3. Transposition - Recombination

Bacterial antibiotic resistance


Dna rna metabolism

3. Transposition - Recombination

Eukaryotic transposable elements

Barbara McClintock - Noble prize

Normal maize

Active C causes synthesis of purple pigment

Mutant maize

Ac allows Ds to transpose out of C in many cells, results in purple pigmented spots on kernels

Mutant maize

Mutant C

Ds insertion inactivates C and prevents pigment synthesis


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