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 and wield it as a defense against future attacks, DNA from a phage attack will integrate into a cells genome, and will then encode for RNA enzymes that disable that sequence if recognized again in the future, CRISPR Region, encodes for single guide RNA (sgRNA) used to identify/compare phage information to find and destroy, Not a scientist developed process, but was recognized by Emmanuelle Charpentier and Jennifer Doudna

Effects of Gene Transfer Spreads useful genes among bacteria like antibiotic resistance genes, pathogenicity islands, genes to degrade special metabolites

Mutant Organism that is the direct offspring of a normal member of species but is different, contains mutations. Generates new variations in populations> Extremly usefu in understanding the nature of genes.

Mutation Heritable changes in nucleic acid bases in the genome of an organism, they are rare and can be either spontaneous or induced, they provide novel functions and can become fixed in populations when they create an advantage

Point Mutation Change in a single base

Insertion Addition of one or more bases

Deletion Subtraction of one or more bases

Inversion DNA is flipped in orientation

Reversion DNA mutates back to og sequence

Silent Mutation Does not change amino acid sequence

Missense Mutation Changes one amino acid sequence to another

Nonsense Mutation Changes the amino acid sequence to a stop codon

Frame-shift mutation Changes the open-reading frame of the gene

Spontaneous Mutations Arise at a low rate in any cell in the absence of any added agent, Errors in DNA replication

Induced Mutation Created by treating the organism with an added mutagen. Caused by chemicals, physical factors like radiation of heat, or biological insertion of transposons

Radiation Mutagen A physical mutagen where UV and ionizing radiation cause the formation of toxic oxygen radicals, which cause adjacent pyrimidine bases to connect (called a dimer), which prevents DNA replication and gene transcription

Base Analogs as a Chemical Mutagen The use of base analogs which are similar structures to natural bases. Incorporated during DNA replication. Leads to a point mutation because of a incorrect base pair. Changes a bases structure and pairing characteristics

Intercalating agents Distort DNA to induce single nucleotide insertion or deletion

Ames test A test for how strong a mutagen is as it uses a bacterial mutant that cannot synthesize histidine on a medium without histidine + a mutagen. If the mutagen causes a reversion of the mutant to now produce hisG, its strength is determined by the number of colonies. It can also show how cancerous something can be, as a strong mutagen is more likely to become cancerous

Proofreading Correction of mismatch by DNA polymerase III during DNA replication

Methyl mismatch repair Use DNA methylation as an indicator for the newer strand containing the error

Photoreactivation A way to repair as the enzyme photolyase bins to the pyrimidine dimer and cleaves the cyclobutane ring

Nucleotide excision repair A endonuclease removes a patch of a single-stranded DNA containing certain types of damaged bases, including dimers

Base excision repair Specialized enzymes can recognize specific damaged bases and remove them without breaking the phosphodiester bonds, creating an AP site which is recognized and cleaved by a specific AP endonuclease. DNA Poly I then synthesizes a replacement strand containing the proper base

SOS Regulatory System If there is extensive DNA damage, the SOS regulatory system is induced. SOS genes are expressed, as the LexA that typically represses the expression of SOS genes is inactivated by RecA, so that it doesnt further create error prone DNA repair

Transposons (transposable elements) Jumping genes discovered by Barbara McClintock in corn. These are segments that can hop from one place in DNA to another (transposition). Contain transposases which are enzymes that promote transposition. They are a large amount of transposons is all living organisms and are widely used in molecular genetics to generate mutants

Non-replicative transposition Transposable elements jump from one site to another

Replicative transposition Transposable element is copies and one copy remains in og site