Microbio Ch: 8.2 - 8.4, Operons, Mutations, and Gene Transfer

As a group

In bacteria, genes encoding enzymes are regulated -

Operon

Set of operator and promoter sites and the structural genes they control

Promoter

Segment of DNA where RNA polymerase initiate transcription of structural genes

Operator

Segment of DNA that controls transcription of structural genes

Operon

“A” is the -

Promoter

“B” is the -

Operator

“C” is the -

Structural genes

“D” is the -

Operon

What helps bacteria in mRNA efficiency by bunching up genes together and saving resources

Repression genes

Inhibit gene expression and decreases enzyme synthesis

• mediated by repressors (proteins that block transcription)

• Default position is “on”

Induction gene

Will turn on gene expression

• Initiated by an inducer

• Default position is “off”

Inducer

Inducible operon will not have its structural genes transcribed unless an - is present

Lac operon

Example of an inducible operon

Repressor

An inducer will bind to the - so that it will not bind to the operator

Repressor, inactive

This - has become -

Repressible operons

Structural genes are transcribed until they are turned off

Tryptophan operon

Example of a repressible operon

Repressor

Co-repressors will bind to the - protein to activate it so that it bind to the operon and repress gene expression

Repressor, active

This - has become -

Constitutive genes

Genes that are expressed at a fixed rate, these do not appear to be regulated and are always “on”

Antibiotics

Example of external selection

Spontaneously

Bacteria can develop resistance to antibiotics irrespective of antibiotics by occuring -

Mutagens

Agents that cause mutations

Spontaneous mutations

Occurred in an absence of a mutagens. Natural errors the DNA polymerase makes unprovoked.

Silent mutations

Mutations that doesn’t affect activity of the product, may go undetected or when a change in one base still makes the same protein without changing the meaning of the codon.

Base substitution

Change in one base in DNA that will result in mRNA to carry the incorrect base in that position. Incorrect amino acid may be incorporated into the resulting protein.

Missense mutation

When a base substitution results in a change in an amino acid

Missense mutation

What mutation happened here

Nonsense mutation

Base substitution that results in a nonsense stop codon. A more serious mutation that results in a premature stop code on in a sequence of amino acid.

Nonsense mutation

What mutation is this?

Frameshift mutation

Mutation that results by the insertion or deletion of one or more nucleotide pairs.

• Causes a shift in the translational reading frame

• Every codon of amino acids are altered downstream

Frameshift mutation

What mutation is this?

Chemical mutagents

Chemicals that directly or indirectly cause mutations

Nitrous acid

An example of a chemical mutation that causes adenine to bind with cytosine instead of thymine

Nucleoside analog

Example of a chemical mutation that is structurally similar to normal nitrogenous bases, when incorporated into DNA in place of a normal base will cause mistakes in base pairing

Carcinogens

What is an example of a nucleotide analog?

Frameshift mutagens

An example of a chemical mutagens where chemicals will cause small deletions or insertions, resulting in frame shifts

Aflatoxin

An example of a frameshift mutagen

Ionizing x-ray and gamma rays

A radiation mutagen that causes formation of ions that can oxidize nucleotides and break the deoxyribose phosphate backbone

UV radiation

A radiation mutagen that cause thymine dimmers, which prevent proper replication and transcription of DNA. This can lead to deletion when section affected with thymine dimmers are omitted because of altered shape in the DNA backbone

Photolyases

An enzyme that uses light to separate thymine dimmers and repair UV induced damage in bacteria

Nucleotide excision repair

An enzyme that will cut out incorrect bases and fill in correct bases, and can also repair UV induced damage in bacteria

10^9

What is the mutation rate of spontaneous mutations for replicated base pairs?

10^6

What is the mutation rate of spontaneous mutations for a replicated genes?

10 to 1000 times

By how much can a mutagen increase the mutation rate?

Vertical gene transfer

Genetic transfer of genes from an organism to its offspring

Horizontal gene transfer

Transfer of genes between cells of the same generation

Donor cell, recipient cell

All horizontal transfer mechanisms involve a - that gives some of its DNA to a -

Horizontal gene transfer

Resistance mutations/ genes that can also be acquired from other cells/species via

Plasmids

Self replicating circular pieces of DNA. With an origin of replication that can activate whenever it chooses to

Plasmids

Where could coding for resistance factors and proteins that enhance their pathogenicity of a bacterium take place?

Transposons

Segments of DNA that can move from one region of DNA to another

Insertion sequences

What do transposons have that code for transposase that cut and reseal DNA

Transformation

Genetic exchange where genes are transferred from one bacterium to another as naked DNA

Transformation

This genetic transfer mechanism is what Griffith’s experiment determined how disease-causing genes can be taken up by bacteria

From heat-killed capsulated bacteria

How did non-capsulated bacteria get the genetic information to replicate as capsulated bacteria in Griffith’s experiment

Conjugation

Plasma transferred from one bacterium to another through cell to cell contact. These cells must be opposite mating types, where the donor has a conjugative plasmid and the recipient lacks the conjugative plasmid

Transduction

When DNA is transferred from a donor cell to a recipient via a bacteriophage