Unit 2 Topic 5

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Frederick Griffith's contribution to microbial genetics

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Demonstrated transformation through experiments with mice and Streptococcus pneumoniae.

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Oswald Avery, Colin MacLeod, and Maclyn McCarty's discovery

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Demonstrated that DNA was responsible for Griffith’s "transformation."

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Alfred Hershey and Martha Chase's experiment

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Demonstrated that DNA is the genetic material in the T12 bacteriophage.

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Characteristics of eukaryotic genomes

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- Sexual lifecycles involving 2n and n ploidy - Multiple linear chromosomes in nucleus - Complex packaging involving histone proteins - Up to 98% of the genome can be noncoding - Extrachromosomal DNA in mitochondria and chloroplast

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Characteristics of prokaryotic genomes

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- Asexual reproduction only; 2n and n do not apply - Typically 1 circular chromosome in nucleoid region - Packaging by simple supercoiling - Noncoding DNA only 12% of genome (average) - Extrachromosomal DNA as plasmids

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Features of plasmids

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- Small circular molecules of dsDNA - Carry genes necessary for their own replication and advantageous traits - Not essential for routine metabolism, growth, or reproduction - Often confer survival advantages under special circumstances

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Plasmid Inheritance

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Vertically: replicated and passed to daughter cells during cell division. Horizontally: transmitted via pilus during conjugation.

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Types of Plasmids

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Conjugative, R plasmids, Bacteriocin-encoding, Virulence, Metabolic, Cryptic.

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Viral Genomes Characteristics

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No chromosomes, far smaller than cellular genomes, 53% involve overlapping genes, DNA or RNA, single- or double-stranded, single or multiple molecules.

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Prokaryotic Chromosomal Replication

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Begins at the ori (origin of replication), is bidirectional, proceeds to ter (termination site) when present.