Chapter 8 Bacterial Genectics

Errors and DNA polymerase can be repaired

the wrong nucleotide is incorporated during DNA synthesis 1. Near the mismatched base an enzyme cuts the sugar-phosphate backbone of the unmethylated strand 2. An enzyme degrades a short stretch of the strand that had the error 3.DNA polymerase synthesizes a new stretch incorporating the correct nucleotide

X rays damage DNA

Deletions-cause single and double strand to break in DNA

UV light damage DNA

Errors during repair process-causes thymine to form

Plasmids

Independent of chromosome and generally encodes only non-essential genetic information

mobile gene pool

Variable genes in a species that can move from one DNA molecule to another - on mobile genetic elements

prototroph

a microorganism that does not require any organic growth factors

auxotroph

a microorganism that requires an organic growth factor

Base substitution: Missence

alter codon codes for a different amino acid

chemical mutagens: base analogs

base pairing properties differ from those of nucleobases normally found in DNA-Nucleotide sustitution

Base substitution: Nonsense

base substitution creates a stop codon

Consequence of removing or adding nucleotides

causes frameshift mutation-changes reading frame-different codon is translated

direct selection

cells inoculated onto medium that supports growth of mutant but not parent

chemicals that modify nucleobases

change base pairing properties of nucleobases- nucleotide substitution

Mutation

change in existing nucleotide sequence

intercalating agents

insert between base pair pushing them apart- Addition or subtraction nucleotides

indirect selection

isolates auxotroph from prototrophic parent strain

How transporosons cause mutation

jumping genes; DNA that can move from one location to another

genomic islands

large DNA segments in a cell's genome that originated in other species

horozontal gene transfer

movement of DNA from one organism to another

Phage DNA

phage genome; may encode additional genes

CRISPR system

recognizes foreign DNA sequences that have previously entered the cell and directs the Cas proteins to destroy them.

Transporons

segments of DNA that directs its own movement to another location in plasmid DNA

genotype

sequence of nucleotides in DNA

Base substitution: Silent

the change generates a codon that translates into the same amino acid as original

core genome

the part of a genome shared by all strains of a species

Modified nucleobases repair

1. DNA contains oxidized guanine as a result of oxidization damage 2.Glycosylase removes the oxidize nucleobase from the sugar phosphate back bone 3.site of missing nucleobase, an enzyme cuts the sugar phosphate backbone 4.DNA polymerase degrades a short stretch of the strand 5.Combined action of DNA polymerase and DNA ligase fill in and seal gap

the process of transformation

1. Double stranded DNA binds to the surface of a competent cell 2.single strand the cell the other strand is degraded 3.the strand integrates into the recipient cells genome by homologous recombination. the strand it replace will be degraded 4.After replicating DNA cell divides 5. Non transformed cell dies on streptomycin medium wheres transform cell multiply

repair of thymine dimers- Photoreactivation

1. Thymine dimer distorts the DNA molecule 2.enzyme uses visible light to break the covalent bond of thymine dimer restoring the DNA

Repair of Thymine Dimers- Excision Repair

1.Thymine dimers distort the DNA molecules 2. an enzyme removes the damage section by cutting the DNA backbone on either side of the thymine dimer 3. the combined actions of DNA polymerase and DNA ligase fill in and seal the gap

phenotype

Physical expression of the genes

restriction modification system

Primary defense Involves 2 types of enzymes 1. Restriction enzymes (restriction endonucleases) 2. Modification enzymes