microbial genetics. terminology genetics genetics study of what genes are study of what genes are...
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TerminologyTerminology
GeneticsGenetics Study of what genes areStudy of what genes are how they carry informationhow they carry information how information is expressedhow information is expressed how genes are replicatedhow genes are replicated
GeneGene Segment of DNA that encodes a Segment of DNA that encodes a
functional product, usually a functional product, usually a proteinprotein
TerminologyTerminology
GenomeGenome All of the genetic material in a cellAll of the genetic material in a cell
GenomicsGenomics Molecular study of genomesMolecular study of genomes
GenotypeGenotype Genes of an organismGenes of an organism
PhenotypePhenotype Expression of the genesExpression of the genes
Polymer of nucleotides: Polymer of nucleotides: adenine, thymine, adenine, thymine, cytosine, guaninecytosine, guanine
Double helix associated Double helix associated with proteinswith proteins
"Backbone" is "Backbone" is deoxyribose-phosphatedeoxyribose-phosphate
Strands held together by Strands held together by hydrogen bonds hydrogen bonds between AT and CGbetween AT and CG
Strands are antiparallelStrands are antiparallel
DNADNA
Figure 8.4
DNA is copied by DNA polymeraseDNA is copied by DNA polymerase In the 5In the 5 3 3 direction direction Initiated by an RNA primerInitiated by an RNA primer Leading strand synthesized continuouslyLeading strand synthesized continuously Lagging strand synthesized Lagging strand synthesized
discontinuously discontinuously Okazaki fragments Okazaki fragments RNA primers are removed and Okazaki RNA primers are removed and Okazaki
fragments joined by a DNA polymerase fragments joined by a DNA polymerase and DNA ligase and DNA ligase
DNADNA
mRNA is mRNA is translated in translated in codons (3 codons (3 nucleotides)nucleotides)
Translation of Translation of mRNA begins at mRNA begins at the start codon: the start codon: AUGAUG
Translation ends Translation ends at a STOP at a STOP codon: UAA, codon: UAA, UAG, UGAUAG, UGA
TranslationTranslation
Figure 8.2
Change in the genetic materialChange in the genetic material Mutations may beMutations may be
neutralneutral beneficialbeneficial or harmfulor harmful
Mutagen: Agent that causes Mutagen: Agent that causes mutationsmutations
Spontaneous mutations: Occur in the Spontaneous mutations: Occur in the absence of a mutagenabsence of a mutagen
MutationMutation
Base substitution Base substitution (point mutation)(point mutation)
Missense mutationMissense mutation
MutationMutation
Figure 8.17a, b
•Change in one Change in one basebaseResult in change in Result in change in amino acidamino acid
Nonsense Nonsense mutationmutation
MutationMutation
• Results in a Results in a nonsense codonnonsense codon
Figure 8.17a, c
Frameshift Frameshift mutationmutation
MutationMutation
Figure 8.17a, d
•Insertion or deletion of Insertion or deletion of one or more nucleotide one or more nucleotide pairspairs
Ionizing radiation Ionizing radiation formation of ions that can react with formation of ions that can react with
nucleotides and the deoxyribose-nucleotides and the deoxyribose-phosphate backbone.phosphate backbone.
Nucleotide excision repairs Nucleotide excision repairs mutationsmutations
MutagenMutagen
UV radiationUV radiation causes causes thymine thymine dimersdimers
Light-repair Light-repair separates separates thymine thymine dimersdimers
MutagenMutagen
Figure 8.20
Spontaneous mutation rate = 1 in Spontaneous mutation rate = 1 in 101099 replicated base pairs or 1 in 10 replicated base pairs or 1 in 1066 replicated genesreplicated genes
Mutagens increase to 10Mutagens increase to 10–5–5 or 10 or 10–3–3 per replicated geneper replicated gene
The Frequency of The Frequency of MutationMutation
SelectionSelection
Positive (direct) selection detects Positive (direct) selection detects mutant cells because they grow or mutant cells because they grow or appear different.appear different.
Negative (indirect) selection detects Negative (indirect) selection detects mutant cells because they do not mutant cells because they do not grow.grow.
Vertical gene Vertical gene transfertransfer
Horizontal gene Horizontal gene transfertransfer
Genetic Transfer and Genetic Transfer and RecombinationRecombination
•Occurs during Occurs during reproduction, reproduction, between between generations of cellsgenerations of cells•Transfer of genes Transfer of genes between cells of the between cells of the same generationsame generation
Segments of Segments of DNA that can DNA that can move from move from one region of one region of DNA to DNA to anotheranother
Contain Contain insertion insertion sequences for sequences for cutting and cutting and resealing DNA resealing DNA (transposase)(transposase)
Complex Complex transposons transposons carry other carry other genes genes
TransposonsTransposons
Figure 8.30a, b
Constitutive enzymes are expressed Constitutive enzymes are expressed at a fixed rateat a fixed rate
Other enzymes are expressed only Other enzymes are expressed only as neededas needed Repressible enzymesRepressible enzymes Inducible enzymesInducible enzymes
Regulation of Bacterial Regulation of Bacterial Gene ExpressionGene Expression