Topic 11: Mechanisms of Gene Variation

viral assembly

During ________, fragements of host DNA mistakenly packaged into phage head.

transfer of genes

The ________ between bacteria that depends on.

Bacteriophage

________- mediated= prokaryotes to eukaryotes.

prokaryotes

In ________ usually produce phenotypic changes.

Phenotype changes

making capsules

ex

antibiotics resistance

ex

pathogenic vs. non-pathogenic, smooth vs. rough

mutagens increase mutation rate 10

1000x

mutagens

an agent, such as radiation or a chemical substance, which causes genetic mutation

ex

what if one survive in a rough environment and doubling time is 30 minutes, in 12 hours, there is 32 million cells

ex

mature culture = 10^9 cells / ml (US population x 4)

point mutations

base pair subsitution (silent, missense, nonsene)

frameshift mutations

insertion or deletion of one or more nucelotide pairs

chemical mutagens

nuceloside analogs have altered base-pairing properties; they can be …

HIV

only used by viral enzymes (e.g

nuceloside analog

nucleic acid analog and sugar

nucelotide analog

nucleic acid analog, sugar, and 1-3 phosphate group

fire fighters have 3 x higher level in blood

kidney and other cancers

teflon

we all have in our blood, cause kidney/testicular cancer, ulcerative colitis, thyroid disease, high cholesterol, pregnancy-induced hypertension (only 6 according to class action lawsuit investigation)

potent carinogens

distortion due to intercalating agent will lead to one or more base-pairs inserted or deleted during replication

Tautomerization

organic compounds interconverts

ex

single bond to double bond, normally A=T, G (triple bond) C

Transitions

A & G and C &T (normal pairing)

Transversions

A & C and G & T (not normal pairing)

ex

5-bromouracil

ex

methyl nitrosoguanidine

Ultraviolet (UV) damage of DNA

UV Radiation

Ionizing radiation (x-rays and y-rays)

lead to deletion mutations (ds breaks)

Photolyases

light repair enzymes (use energy from visible light to fix UV light damage)

Subsitution

during DNA synthesis, an incorrect nucelotide on the new strand pairs with a nucelotie on the template

Deletion

during DNA synthesis, a nucelotide is omitted in the formation of the new strand

Insertion

during DNA synthesis, a nucelotide is inserted at a point in the formation of the new strand where there was no opposite nucelotide in the template

silent mutation

change nuceloside sequence of codon but not the encoded amino acid

missense mutation

a single base substitution that changes codon for one amino acid into codon for another amino acid

nonsense mutation

converts a sense codon to a stop codon

conditional mutations

expressed only under certain environmental conditions

auxotrophic mutant

unable to make an essential macromolecule such as amino acid or nucleotide

Mutagen Identification

Ames Test

look for cells (colonies) that have reverted from his

to his+

Thymine Dimers

NER pathway

GG-NER

global genomic NER

TC-NER

transcription coupled NER

vertical gene transfer

occurs during reproduction between generations of cells

ex

human

horizontal gene transfer

the transfer of genes between cells of the same generation; leads to genetic recombination

ex

bacteria

three mechanisms of horizontal gene transfer

transformation, conjugation, transduction

mid 1980s, HGT prediciton was made

suggesting biological significance/evolutionary history of Earth

2007 HGT

played a major role in bacterial evolution, the role remains unclear in multicellular eukaryotes

spread of virulence factor

exotoxin adaptation in E. coli from Shigella via transduction (virus)

synthetic man-made chemicals (pesticides) degradation via adaptation

bacteria symbioetic relation to insects = live longer

exogenote

DNA that is transferred to recipient

endogenote

genome of recipient

merozygote

recipent cell that is temporarily diploid as results of transfer process

Class I (retrotransposons)

first they are transcribed fro DNA to RNA, and the RNA produced is then reversed transcribed to DNA

Class II (DNA transposons)

the cute and paste transposition mechanism of class II does not involve an RNA intermediate

Bacterial Plasmids

replicative transposition

number varies

1-30

donor genes are transferred to recipient cell (F

cell)

Why does exogenous DNA fragments (transformation experiment) have antibiotic resistance?

chemical, temperature, pH, dry condition resistances

What are mutations?

stable, hertiable changes in sequence of bases in DNA

Mutations in prokaryotes usually produce ___ changes such as pathogenic vs nonpathogenic or smooth vs rough.

phenotypic

How do mutations occur?

spontaneously or be induced by chemical mutagens or radiation

Metabolic errors are ___.

mutations

True or False: mutations can be beneficial, harmful or neutral (silent).

true

What is the spontaneous mutation rate?

1 in 10^8

What can increase mutation rate 10-1000x?

mutagens (i.e. radiation)

What are mutagens?

an agent, such as radiation or a chemical substance, which causes genetic mutation

What are point mutations?

base pair substitution (silent, missense, nonsense)

What are frameshift mutation?

insertion or deletion of one or more nucleotide pairs

What are chemical mutagens?

nucleoside analogs that have altered base-pairing properties such as randomly incorportating into growing cells

What are nucleoside analogs?

have nucleic acid analog and sugar

HIV is an example of a ___ mutagen.

chemical

Intercalating agents are ___ mutagens (type of chemical mutagen).

frameshift

What is an example of frameshift mutagens?

teflon

What does intercalating agents do?

distortion leading to one or more base-pairs inserted or deleted during replication

Potent carcinogens are examples of ___ agent.

intercalating

What are spontaneous mutation?

arise without exposure to external agents

What may cause spontaneous mutations?

errors in DNA replication or from the action of mobile genetic elements such as transposons (jumping genes)

What can cause errors in DNA replication?

due to base tautomerization or due to insertion or deletion of nucleotides

What does base tautomerization result in?

transition and transversion mutations

What is transition mutations?

similar type (purine or pyrimidine) bases are swapped - purine to purine

What is transversion mutations?

different type (purine or pyrimidine) bases are swapped - purine to pyrimidine

What are induced mutations?

caused by agents that directly damage DNA

What are examples of induced mutations?

base analogs, DNA modifying agents, intercalating agents

What are base analogs?

structurally similar to normal bases; mistakes occur when they are incorporated into growing polynucleotide chain

What are DNA modifying agents?

alter a base causing it to mispair

What are intercalating agents?

distort DNA to induce a single nucleotide pair insertion and deletion

5-bromouracil is an example of ___.

base analog

Methyl nitrosoguanidine is an example of ___.

DNA modifying agent

DNA modifying agents causes ___ changes so mismatch repair will miss it; it is used in cancer treatment.

subtle

Ultraviolet (UV) damage of DNA results in formation of ___ and the resulting DNA can no longer serve as a template.

thymine dimers

Ionizing radiation (x rays and gamma rays) lead to ___ mutations.

deletion

What can repair radiation mutations?

photolysases separate thymine dimers (UV) and nucleotide excision repair

What is a substitution mutation?

during DNA synthesis, an incorrect nucleotide on the new strand pairs with a nucleotide on the template

What is a deletion mutation?

during DNA synthesis, a nucleotide is omitted in the formation of the new strand

What is an insertion mutation?

during DNA synthesis, a nucloetide is inserted at a point in the formation of the new strand where there was no opposite nucleotide in the template

Substitution mutation is also called ___ mutation.

point

Insertion and deletion mutations are also called ___ mutation.

frameshift

Point mutations can cause which 3 mutations to possibly occur?

silent, missense, or nonsense