CH 9

Silent point mutation

(seCreT)

T to C

Missense point mutation

(Miss my TA)

T to A

Nonsense point mutation

(Carpenter Girl)

C to G

Insertion frameshift

(AT&T)

AT after T

Inserts AT after the T of the TCC serine codon

Deletion frameshift

Removes 4 nucleotides

Inversion

Invert/Flip something

Duplication

DNA sequence is copied

What causes mutations

Mistakes during replication

Point Mutations

Change in one base pair

Transition mutation

Base replaced by another base of the same class

Ex: 

Adenine (A) -> Guanine (G)

Cytosine (C) -> Thymine (T)

Larger mutations (IID)

(Dinner In Italy)

Insertion of a section of DNA into

chromosome

Deletion of a portion of the chromosome

Inversion: flipping a portion of chromosome

Mutagens that cause mutations

Electromagnetic radiation -

• UV light

• x-rays

• gamma rays

Chemicals -

• Base analogs

• Base-modifying chemicals

• Intercalators

Base analogs

(Ana - con artist)

Chemical impostors that trick a cell into using them instead of normal DNA building blocks

Base-modifying chemicals

Substances that alter the chemical structure of normal DNA or RNA nucleotide bases

Intercalators

(In escalators)

Molecular wedge that slips between the rungs of a DNA ladder.

(causes frameshift mutations)

How do mutations affect phenotype ?

(No effect)

Most have no effect on the organism

How do mutations affect genotype

Permanent change in an organism's DNA sequence

How is mutagenicity accessed

(How do we know if this chemical damages DNA?)

Ames test

Ames test

Uses auxotrophic bacteria for histidine because they have hisG gene mutation (cant grown without histidine)

Chemical added, if causes reversion bacteria grow = mutagenicity

Most mutagens are carcinogens (cause cancer)

Mismatch repair

Cuts out mispaired base and puts correct one

BER (Base Excision Repair)

Replaced by DNA Polymerase I

Recombinational repair

Copies undamaged strand to replace damaged one after

rep

catalyzed by RecA recombinase

SOS repair

(Error prone)

Extensive DNA damage, turns off LexA, last resort

How do microbial genomes evolve

(Gain or loss of genetic material)

Gain or loss of genetic material

Small changes in a gene sequence cause…

Small changes = Slow changes

(no new func)

Slow changes in protein usually no new func

Large chromosome changes are

(ID)

Insertion of new material

Duplication of genes

Duplication of genes causes…

New functions for the cell (only if copied gene keeps doing its og func)

Base-modifying chemicals

CHANGE the base

Mutagens

CAUSE mutations

How do microbes exchange genetic material ?

Horizontal Gene Transfer

HGT: Transformation, Conjugation, and Transduction

What is Horizontal Gene Transfer (HGT)

Movement of genes between cells (besides cell division)

Plasmids

Carry genes between cells without having to become part of the chromosome

What is a plasmid ?

Extra piece of DNA outside chromosome

What is a secondary genome linked to ?

Plasmid acquisition or integration of an essential gene.

How can a secondary genome form ?

Through plasmid acquisition or integration of an essential gene.

What is one example of bacteria with two chromosomes ?

Vibrio cholerae.

What process can help bacteria acquire plasmids ?

Horizontal gene transfer.