Lecture 5: Bacterial Mutation And Recombination

Front 1

____ and _____ both result in changes in the content of bacterial chromosomes.

Back 1

mutation and recombination

Front 2

Mutation

Back 2

alteration in bacterial chromosome as a result of a PERMANENT DNA CHANGE

Front 3

recombination

Back 3

chromosomal alteration by the acquisition of new DNA from another organism (transformation, conjugation, transduction)

Front 4

Whats the difference between mutation and recombination?

Back 4

mutation occurs as a result of a PERMANENT DNA CHANGE, whereas recombination occurs as a result of ACQUISITION OF DNA from another organism.

Front 5

what are the three types of recombination?

Back 5

transformation, conjugation, transduction

Front 6

Transformation refers to the uptake of ______.

Back 6

naked DNA

Front 7

Does transformation have to occur within the same species?

Back 7

yes

Front 8

What happens in natural transformation?

Back 8

- Dead donor DNA is picked up by live recipient.
- Recipient incorporates donor DNA into chromosome.

Front 9

What happens in laboratory transformation?

Back 9

- Chemically 'competent' cells are forced to take up plasmid DNA.
- Transformants selected by using some trait encoded by plasmid (antibiotic resistance)

Front 10

conjugation

Back 10

transfer of genetic information through direct cell-to-cell contact

Front 11

What are F factors?

Back 11

fertility plasmids

They encode genes for pilus, etc (20-30 genes required for conjugation)

Front 12

What do F factors encode?

Back 12

genes for PILUS

Front 13

For cell-to-cell contact, the donor cell, F+, produces the conjugation pilus that makes contact with the recipient cell, known as an F- cell. The donor cell is called F+ because?

Back 13

it contains an F plasmid

F+ transfers a copy of itself (possibly including resistance genes)

Front 14

Does conjugation require the activity of the bacterial chromosome?

Back 14

NO. only plasmid!

Front 15

Can conjugation occur between bacteria of different genera?

Back 15

Yes

ex: RK2 plasmid goes into all gram-hegatives

Front 16

Transduction requires a virus to carry the DNA fragment from donor to recipient cell. In transduction, genetic transfer is mediated by ____

Back 16

bacteriophage- the virus that participates in transduction

Front 17

What are the two types of transduction?

Back 17

1) generalized
2) specialized

Front 18

lytic cycle

Back 18

after viral replication, host bacterium broken open

- phage invades the bacterium, then replicates itself and destroys the bacterium as new phages are released.

Front 19

What does a virulent phage do?

Back 19

causes lysis

Front 20

Lysogeny

Back 20

virus integrates into bacterial chromosome

Front 21

____ phages are lysogenic

Back 21

temperate

Front 22

prophage

Back 22

integrated viral DNA

Front 23

Generalized Transduction is carried out by ___ phage

Back 23

virulent phages that have a lytic cycle of infection

Front 24

What happens in generalized transduction?

Back 24

- virulent bacteriophage attaches to surface of a host bacterial cell.

- DNA from virulent phage enters the cytoplasm of the bacterium. Viral DNA multiplies and host DNA is fragmented into small pieces

- Random pieces of host chromosome get accidentally packaged by virulent phage

- Transferred to a second host

- Recombined into second host's chromosome

Front 25

Give two examples of virulent phages that have a lytic cycle of infection and carries out generalized transduction.

Back 25

P1 infects E. coli

P22 infects S. typhimurium

Front 26

What does phage P22 infect?

Back 26

S. typhimurium

Front 27

What does phage P1 infect?

Back 27

E. coli

Front 28

Specialized transduction occurs as a result of ____ and unlike generalized transduction, results in the transfer of specific genes. It is carried out by ____ phages

Back 28

lysogeny

temperate

Front 29

What happens in specialized transduction?

Back 29

- temperate bacteriophage attaches to the surface of a host bacterial cell

- DNA of temperate phage enters the bacterial cytoplasm

- Viral DNA integrates into the bacterial DNA. Now it is called a prophage.

- Some type of stress induces lysogenic phage to enter lytic cycle

- imprecise excision of phage occurs

- because of capsid size, some bacterial genes taken, some phage genes left behind

- resulting phage infects a second host and transduces it with genes from first host

Front 30

Mutation

Back 30

Alteration in bacterial chromosome as a result of a permanent DNA change

Front 31

Silent mutation

Back 31

nucleotide change does not result in amino acid change.

- GAG --> GAA, G-->A transition (purine to purine). GLU stays as GLU
- Genetic code is degenerate

AG are purines
CT are pyrimidines

Front 32

Nonsense mutation

Back 32

amino acid changed to stop codon

- GAG --> TAG, G --> T transversion (purine to pyrimidine)

Front 33

Missense mutation

Back 33

amino acid changed to another amino acid (GLU to VAL)

- GAG --> GTG, A -->T transversion

Front 34

Frameshift mutation

Back 34

insertion or deletion of nucleotides resulting in a change in the reading frame

Front 35

Spontaneous mutations happens every 1 in 10^9 nucleotides. It is caused by?

Back 35

natural errors in replication

These mutations may end up being advantageous to an organism

- No identifiable cause
- No added mutagens (things that cause mutations)

Front 36

What causes induced mutations?

Back 36

an identifiable source such as UV light or chemical mutagen

Front 37

What does ultraviolet light induce?

Back 37

thymine dimers

Front 38

What do thymine dimers, induced by ultraviolet light, cause?

Back 38

Thymine dimers cause localized distortion of the DNA helix--any activity involving DNA messed up.

Direct exposure to UV light used to disinfect surfaces--kills bacteria by mutating their DNA

Front 39

Name a Chemical Mutagen.

Back 39

Nitrous acid

Front 40

Nitrous acid is a chemical mutagen that converts DNA's ____ molecules to _____ molecules.

Back 40

adenine

hypoxanthine

- Hypoxanthine pairs with C instead of T
-Results in a T-C transition mutation

Nitrous acid is a chemical mutagen that converts DNA's adenine molecules to hypoxanthine molecules. Adenine will normally base pair with thymine during DNA replication, but hypoxanthine base pairs with cytoosine. Later, when protein synthesis thakes place, the new DNA molecule having cytosine substituted for thymine will code for guanine in the mRNA instead of the normal adenine.

Front 41

Mutations also can be induced by a series of BASE ANALOGS that bear a chemical resemblance to nitrogenous bases. One such base analog, ______, is taken up by cells and incorporated into DNA where thymine should be positioned.

Back 41

5-bromouracil

Front 42

true or false?

DNA with base analog in place functions poorly.

Back 42

true

Front 43

Base analogs may be used to treat diseases such as viral infections. DNA viruses such as herpesviruses can be treaded with ___, a base analog.

Back 43

acyclovir

Front 44

FRAMESHIFT MUTATIONS

_____ induce changes in reading frame

Back 44

Aflatoxins

-Fungal toxin from Aspergillus flavus

Front 45

How does Frameshift mutations work?

Back 45

FLAT PLANAR STRUCTURE intercalates into DNA to cause frameshifts

Front 46

Frameshift mutations are found where?

Back 46

peanuts, wheat, animal products

Front 47

DNA is the only macromolecule that is ____, not degraded

Back 47

repaired

Front 48

What is mismatch repair?

Back 48

- Normal part of replication
- DNA polymerase has proofreading function
- Removes and replaces mismatched nucleotides

Mismatch repair during DNA replication. As a result of an incorrectly paired nucleotide, DNA polymerase removes (excises) the nucleotide and adds the correct complementary nucleotide.

Front 49

What is excision repair?

Back 49

- General repair system for distortions in DNA (T-T dimers, intercalating agents)
- UvrABC endonuclease cuts out distorted part
- DNA pol and DNA ligase fill and seal gap

Excision repair to DNA damage. Thymine dimer distortion triggers nuclease repair enzymes that excise the damaged DNA and permit resynthesis of the correct nucleotides.

Front 50

What are the components of the Ames test?

Back 50

- Salmonella typhimurium histidine auxotroph
~ inactive excision repair => accumulate DNA mutations
~ mutated lipopolysaccharide coat to increase permeability

- Liver extract to approximate effects of mammalian metabolism

Front 51

In the Ames test, 'Strength' of carcinogen measured by ____

Back 51

number of revertants (his+ colonies)

Front 52

Name two mutagens found by the Ames Test

Back 52

- Tris (2,3-dibromopropyl) phosphate
Chemical used to make pajamas flame retardant

- Furylfuramide
Antibacterial food additive used to increase shelf life of packaged foods