7/28/2019 Discussion 13- Microbial Genetics

1/24

Microbial Genetics

7/28/2019 Discussion 13- Microbial Genetics

2/24

Replica Plating

negative/indirect

selection

selects a cell which

cannot perform a

specific function

7/28/2019 Discussion 13- Microbial Genetics

3/24

7/28/2019 Discussion 13- Microbial Genetics

4/24

7/28/2019 Discussion 13- Microbial Genetics

5/24

Selective and differential

medium

Used for growing non-

fastidious G(-) rodsPresence of bile salts

and crystal violet

7/28/2019 Discussion 13- Microbial Genetics

6/24

Usually contain the

minimum nutrients

possible for colony

growth, generally

without the presence of

amino acids

2 Uses:

1. to grow "wild type"

microorganisms

2. to select for or againstrecombinants

7/28/2019 Discussion 13- Microbial Genetics

7/24

Three components:

1. carbon source (e.g.: sugar)

2. various salts

3. water

7/28/2019 Discussion 13- Microbial Genetics

8/24

Lost

capability to

synthesize

an amino

acid

7/28/2019 Discussion 13- Microbial Genetics

9/24

Prototroph- The ability to synthesize all needed

amino acid

Wild type

Antibiotic resistant- Gained resistance to anantibiotic

7/28/2019 Discussion 13- Microbial Genetics

10/24

7/28/2019 Discussion 13- Microbial Genetics

11/24

7/28/2019 Discussion 13- Microbial Genetics

12/24

Are agents in the environment, such as certain

chemicals and radiation, that directly or indirectly

bring about mutations

Almost any agent that can chemically or physicallyreact with DNA can potentially cause mutations.

7/28/2019 Discussion 13- Microbial Genetics

13/24

Nitrous Acid

7/28/2019 Discussion 13- Microbial Genetics

14/24

7/28/2019 Discussion 13- Microbial Genetics

15/24

Still, other chemical mutagens cause small deletionsor insertionsFRAMESHIFTS

Ex: benzopyrene (smoke and soot)

aflatoxin (Aspergillus flavus)- mold in peanutand grain

acridine dyes used experimentally against

herpes virus infections

7/28/2019 Discussion 13- Microbial Genetics

16/24

X rays and gamma rays potent mutagens because of

their ability to ionize atoms and molecules.

Electrons pop out of usual shells

electronsbombard other molecules and cause more

damage ions and free radicals may combine

with bases in DNA errors in replication and repair

that produce mutations

Breakage of covalent bonds in the sugar-phosphate

backbonephysical breaks in chromosomes.

7/28/2019 Discussion 13- Microbial Genetics

17/24

Ultraviolet (UV) light- a nonionizing component of

ordinary sunlight

Most mutagenic component of UV light (wavelength

260 nm) is screened out by the ozone layer of the

atmosphere

Formation of harmful covalent bonds between

certain basesTHYMINE DIMERS

May cause serious damage or even death because itcannot properly transcribe or replicate such DNA

7/28/2019 Discussion 13- Microbial Genetics

18/24

Photolyases- also known as light-repair enzymes,use visible light energy to separate the dimer back to

the original two thymines

Nuc1eotide excision repairand action ofmethylases

(Hamilton Smith, 1970)

Enzymes cut out incorrect base and fill in the gap with

newly synthesized DNA that is complementary to the

correct strand

Methylases add methyl group to selected bases soonafter DNA is made.A repair endonuclease then cuts

the nonmethylated strand.

7/28/2019 Discussion 13- Microbial Genetics

19/24

7/28/2019 Discussion 13- Microbial Genetics

20/24

Two ways in which DNA can become mutated:

Inherited- if a parent has a mutation in his or her

DNA, then the mutation is passed on to his or her

children.

Acquired-happens when environmental agents

damage DNA, or when mistakes occur when a cell

copies its DNA prior to cell division.

7/28/2019 Discussion 13- Microbial Genetics

21/24

Base substitution/point mutation-singlebase at one

point in the DNA sequence is replaced with a

different base

May cause amino acid substitution in the synthesized

proteinmissense mutation

or

creation of a nonsense (stop) codon in the middle of

an mRNA moleculenonsense mutation

7/28/2019 Discussion 13- Microbial Genetics

22/24

Frameshift mutations-where one or a few

nucleotide pairs are deleted or inserted in the DNA

Can shift the translational reading frame

Spontaneous mutations may occur due to occasionalmistakes made during DNA replication.

- apparently occur in the absence of any mutation-causing agents

7/28/2019 Discussion 13- Microbial Genetics

23/24

7/28/2019 Discussion 13- Microbial Genetics

24/24