Lecture #11 | Genetic Change and Genome Evolution

CRISPR

Clustered Regularly Interspaced Short Palindromic Repeats, an adaptive system where an organism that manages to survive a phage attack captures a piece of the invaders genome to wield it as a defense against future attacks, effectively creating a form of acquired immunity.

DNA from a phage attack

Integrates into a cell's genome, encoding RNA enzymes that can disable that sequence if it is recognized again, thus providing a method for defense against repeated viral infections.

CRISPR Region

Encodes for single guide RNA (sgRNA) used to identify and compare phage information, allowing the organism to find and destroy such invaders more efficiently.

Mutation

Heritable changes in nucleic acid bases in the genome of an organism. They are rare and can occur spontaneously during DNA replication or can be induced by external factors and provide novel functions which can become advantageous.

Point Mutation

A change in a single base within the DNA sequence, which can affect the amino acid sequence of proteins formed during translation.

Insertion

The addition of one or more bases into a DNA sequence, which can lead to significant changes in the resulting protein structure.

Deletion

The removal of one or more bases from a DNA sequence, affecting the downstream reading frame and possibly the resulting protein function.

Inversion

A mutation where a segment of DNA is flipped in orientation, potentially disrupting gene function.

Reversion

A mutation where DNA mutates back to its original sequence, restoring the typical function.

Silent Mutation

A mutation that does not change the amino acid sequence of a protein, therefore typically having no effect on function.

Missense Mutation

This type of mutation changes one amino acid in a protein to another, potentially altering the protein's function or stability.

Nonsense Mutation

A mutation that changes the amino acid sequence to a stop codon, causing premature termination of protein synthesis.

Frame-shift mutation

This mutation alters the open-reading frame of the gene, potentially altering all downstream amino acids and resulting in a nonfunctional protein.

Spontaneous Mutations

Arise at a low rate in any cell without added agents, often due to errors in DNA replication; these mutations contribute to genetic diversity.

Induced Mutation

Mutations created by treating the organism with an added mutagen, which can be chemical, physical (like radiation), or biologically induced by transposons.

Radiation Mutagen

A physical mutagen where UV and ionizing radiation lead to the formation of toxic oxygen radicals, resulting in adjacent pyrimidine bases connecting to form dimers, which hinder DNA replication and gene transcription.

Base Analogs as a Chemical Mutagen

The use of base analogs mimicking natural bases during DNA replication, leading to point mutations due to incorrect incorporation.

Intercalating agents

Chemicals that insert themselves between the base pairs of DNA, distorting the helix and leading to single nucleotide insertions or deletions during replication.

Ames test

A biological assay for determining the mutagenicity of compounds that uses a bacterial mutant incapable of synthesizing histidine. If a mutagen causes reversion to histidine synthesis, its strength is assessed based on the number of colonies that grow.

Proofreading

The mechanism by which DNA polymerase III corrects mismatches during DNA replication, ensuring high fidelity in DNA replication.

Methyl mismatch repair

This system utilizes DNA methylation as an indicator to identify the newly synthesized strand containing the error, facilitating targeted repair.

Photoreactivation

A repair mechanism where the enzyme photolyase binds to pyrimidine dimers caused by UV light and cleaves the cyclobutane ring to restore original DNA structure.

Nucleotide excision repair

An essential DNA repair mechanism in which an endonuclease removes a section of single-stranded DNA containing damaged bases, including pyrimidine dimers, followed by DNA synthesis.

Base excision repair

Specialized enzymes recognize specific damaged bases, excise them without breaking phosphodiester bonds, and initiate repair at an AP site, allowing replacement by DNA Poly I.

SOS Regulatory System

In instances of extensive DNA damage, the SOS regulatory system is activated, leading to the expression of SOS genes and overcoming the repression typically exerted by LexA.

Transposons (transposable elements)

DNA sequences known as jumping genes, discovered in corn by Barbara McClintock, that can move within and between chromosomes, facilitating genetic diversity.

Non-replicative transposition

A process where transposable elements jump from one genomic site to another without creating a copy, often disrupting existing genes.

Replicative transposition

A process that results in the duplication of a transposable element, where one copy remains at the original site while the other moves to a