Brock Biology Of Microorganisms Chapter 10

Front 1

Mutation

Back 1

an inherited change in a nucleotide base or base sequence in the DS DNA of the genome

can be beneficial or harmful

Front 2

Genetic recombination

Back 2

genes from two separate genomes that are brought together

a larger degree of genetic change occurs through recombinationt han through mutation

Front 3

Genetic Change in Prokaryotes

Back 3

do not reproduce sexually

prokaryotes can undergo genetic change due to gene transfer

Front 4

Later Gene Flow

Back 4

mechanisms that allow for gene transfer and recombination are based on this

genes are transferred from donor to recipient horizontally rather than vertically from mother to daughter cell

Front 5

Mutant

Back 5

a strain carrying a mutation

Front 6

Wild type strain

Back 6

A strain isolated from nature

mutant derviatives can be derived from this

Front 7

Genotype of organism designated by this

Back 7

three lowercase letters followed by a capital letter all in italics

Front 8

Phenotype of organism is designated by this

Back 8

capital letter follwed by two lower case letters with either a plus or minus subscript indicating the presence of absence of a property

Front 9

Selectable mutations

Back 9

confer somee type of an advantage to the organisms possessing them

example of this is srug resistance

Front 10

Unselectable mutations

Back 10

no selective advantage is incurred

example of this is the loss of color in a pigmented organism

Front 11

Spontaneous Mutations can occur because of this

Back 11

1) exposure to nautral forms of radiation

2) oxygen radicals

3) base pairing errors during DNA replication

Front 12

Point Mutation

Back 12

if a mutaiton affects just a single base pair

if point mutations are carried through transcription and translation they can end up altering the protein sequence

can have severe implications or can be unharmful

Front 13

Reversion

Back 13

point mutations may be reversed by this process

Front 14

Same site revertants

Back 14

site that is mutated that reverts back to the original base

Front 15

Second Site revertants

Back 15

second mutation occurs at a second site in the sequence

compensates for the effect produced by the first mutation

Front 16

Transition Changes

Back 16

occur when a base mutation involves the substitution of one purine base for another purine base or one pyrimidine base for another

Front 17

Transversion Changes

Back 17

purine for pyrimidine or vice versa

Front 18

Base insertions

Back 18

mutations involving the addition of a base or bases

Front 19

Base deletions

Back 19

mutations involving the deletion of a base or bases from the nucleotide sequence

Front 20

Frameshift Mutations

Back 20

alter the reading frame of the mRNA by mvoing the reading frame up or down a single base or several bases

Front 21

Mutations in RNA genomes

Back 21

occur at a level that is 1000 fold higher than in DNA genomes

there are no repair mechanisms but there are proof reading functions

leads to a heightened mutation rate in the RNA genomes of RNA viruses

makes RNA viruses able to eveolve more rapidly

Front 22

Mutagenesis

Back 22

induced by agents called mutagens

Front 23

Nucleotide base analogs

Back 23

molecules that resemble DNA purine and pyrimidine bases in structre yet display faulty base pairing properites

result in mismatched base pairs

Front 24

Alkylating Agents

Back 24

react with amino, carboxyl, and hyroxyl groups in proteins and nucleic acids and substitute alkyl groups in their place

can induce changes even in nonreplicating DNA

Front 25

Radiation

Back 25

1) ionizing

2) nonionizing

both are used to create mutations

Front 26

Nonionzing radiation

Back 26

more widely used

used in the form of UV light

maximum absorption is at 260 nm

Front 27

Pyrimidine dimers

Back 27

one of the effects of UV light on DNA is the formation of this

when two adjacent pyrimidine bases become covalently bonded to one another such that the probability of the DNA polymerase misreading the sequence is greatly increased

Front 28

Ionizing

Back 28

1) more powerful form of radiation than UV light

cause the ionization of compounds which brings about the formation of potent chemical species such as free radicals

has greater penetrating power than UV light and is potentially more destructive

Front 29

Free radicals

Back 29

react with DNA causing "hits" to occur that result in mutations

Front 30

Examples of short wavelength

Back 30

1) X-rays

2) Cosmic Rays

3) Gamma Rays

Front 31

DNA Repair

Back 31

if an error in DNA synthesis is correct before the cell divides, no mutation occurs

if DNA replication stalls, teh cell will die

Front 32

SOS regulatory system

Back 32

an example of DNA repair process that has some aspects that occur in the absence of template instruction

Front 33

Hyperaccurate Phenotype

Back 33

where an organism has an extremely efficient system of DNA fidelity repair and replication

can be advantageous or disadventageous

Front 34

Advantageous

Back 34

when making repairs caused by exposure to radiation

Front 35

Disadvantggeous

Back 35

when it prevents an organism from evolving at a apce that is dictated by a changing environment

Front 36

Homologous Recombination

Back 36

genetic exchange between homologous DNA dequences from two different sources

invovles crossing over

uses RecA protein

occurs only after the transfer when DNA from the host is in the recipient cell

Front 37

Transformation

Back 37

occurs in BActeria and some archae

process by which free DNA is incorporated into a recipient cell and bring about genetic change

occurs in B. subtilis fragmented DNA

only 1% of certain strains and species of prokaryotes are naturally competent (can be transformed)

Front 38

incorporation of donor DNA into recipient cell

Back 38

requires the activity of a single-stranded binding protein, RecA protein, and several other enzymes

SS binding proteins prevent transforming DNA from degradation by nucleases

Front 39

RecA

Back 39

allows homologous recombination to occur which allows transforming DNA to be integrated into the genome of the recipient

Front 40

Transduction

Back 40

bacterial DNA is transferred from cell to cell by a bacterial virus

occurs by generalized transduction or specialized transduction

Front 41

Generalized transduction

Back 41

virus incorporates random fragments of the host bacteria cell's chromosomal DNA into the viral genome

efficiency is low

Front 42

Specialized transduction

Back 42

DNA from a specific region of the host bactera chromosome is integrated idrectly into the virus genome and ususally replaces some of the virus genes

efficiency may be very high

only occurs in some temperate viruses

Front 43

Plasmids

Back 43

small circular or linea DNA molcules that carry any of a variety of unessential genes

vary in size from 1kb to >1 mb

smaller than bacterial chromosome

double stranded (DS)

majority are circular and in a supercoiled conformation

present in cells in various copy numbers (few as 1 or as many as 100 copies present in a cell)

Front 44

Multiple Plasmid Types

Back 44

cells can contain more than one type of plasmid

each is genetically distinct

Front 45

Incompatible Plasmids

Back 45

if a plasmid is transferred to a cell that already carries another type of plasmid the second plasmid may not be maintained and consequently lost during subsequent cell replication

Front 46

F Plasmid

Back 46

found in E. coli

Front 47

Conjugation

Back 47

involves cell to cell contact

a replicative process whereby both cells end up with copies of the plasmid

process of genetic transfer

Front 48

Conjugative Cells

Back 48

Plasmids that govern their own transfer by cel to cell contact

not all plasmids are conjugative

Front 49

Resistance Plasmids

Back 49

Known as R plasmids

among the most widespread and well-studied groups of plasmids

confer risistance to antibiotics and other growth inhibitors

resistance is spread between bacteria through conjugation

Front 50

Colonziation factor antigen

Back 50

allows certain bacgterial pathogens to colonzie the small intestine prior to secreting endotoxins

Front 51

Bacteriocins

Back 51

plasmids may also allow code for genes that produce proteins that allow bacteria to kill or inhibit related or unrelated strains of bacteria

Front 52

Features of Conjugation

Back 52

sometimes other genetic elements such as all or parts of the host chromosome can be transferred during conjugation

DNA replication must take place during conjugation such that both the donor and recipient cells have fully formed plasmids at the conclusion of conjugation

Front 53

Pilus

Back 53

produced by the donor cell

allows for direct contact between the cells

Front 54

Rolling Circle Method

Back 54

Method of DNA replication during conjugation

Front 55

Episome

Back 55

it can integrate into the host chromosome

Front 56

Mobilization of F Plasmid

Back 56

When integrated into the chromosome, the chromosome becomes mobilized

this can lead to a transfer of chromosomal genes to a recipient cell

Front 57

F+ Plasmids

Back 57

Cells that have an unintegrated F plasmid

Front 58

Hfr Plasmids

Back 58

High frequency recombination

F plasmid integrated into the chromosome

Front 59

F' Plasmids

Back 59

previously integrated F plasmids that have deintegrated and excised some chromosomal genes

Front 60

Insertion Sequence (IS)

Back 60

integration of the F plasmid into the host chromosome occurs at this site

these sites are regions of DNA sequence homology between chromosomal and F plasmid DNA

Front 61

Complementation

Back 61

recombination takes place between the donor chromosome and the recipient chromosome

Front 62

How do we clone?

Back 62

1) isolating a gene of interest onto a fragment of DNA

2) experimentally control the replication

3) amplify copies

Front 63

Gene Cloning

Back 63

Involves molecular manipulation in vitro of vectors using PCR, RE, synthesizing DNA probes, DNA sequencing, gel electrophoresis etc.

purpose is to isolate multiple copies of specific genes or regions of a chromosome in pure form

Front 64

How are plasmids used as cloning vectors?

Back 64

1) they are easy to isolate and purify

2) can multiply to high copy numbers in bacterial cells

3) presence of selectable markers like antibiotic resistant genes

Front 65

Plasmid pBR322

Back 65

replicates in e. coli

small genome size

can be maintained stably in its host

can by amplifies to very high copy numbers

reasonable amount of foreign DNA can be inserted into it

Front 66

Insertional Activation

Back 66

foreign DNA is inserted into one of these restriction sites contained within an antibiotic resistant gene, antibiotic resistance will be lost

can be used as a means of selecting transformed bacterial clones that have picked up the insert

Front 67

Second Generation Plasmid Vectors

Back 67

Higher utility and even easier to use than pBR322

Example is pUC19

Front 68

pUC19

Back 68

contains a multiple cloning site

polylinker is contained within the coding region of the gene that encodes B galactosidase

Front 69

Blue colonies

Back 69

bacterial clones that contain pUC19 without the DNA insert (B galactosidase is not disrupted and remains active)

Front 70

White colonies

Back 70

contain pUC19 with the DNA insert (B galactosidase is disrupted and inactivated)

Front 71

Bacteriophage Lambda as a cloning vector

Back 71

modified bacterial phage

Front 72

Transfection

Back 72

introduces bacteriophage lambda into host cell


allows DNA fragments up to 20 kb to be clones into lambda

Front 73

Why are bacteriophages like lambda advantageous?

Back 73

1) transfection rate is greater than the transformation rate of plasmid vectors

2) can hold larger amounts of DNA than most plasmid vectors

Front 74

Five steps of cloning with lambda

Back 74

1) isolate vector DNA from phage particles and digest with the appropriate RE

2) connect the two lambda fragments with the fragments of foreign DNA using DNA ligase

3) packaging of DNA insert by adding cell extracts containing the phage head and tail proteins and allowing viable phage particles to form

4) transfecting E. coli and isolating phage clones by selecting plaques on a host strain

5) checking the recombinant phage for the presence of the foreing DNA insert sequence

Front 75

use of site directed mutagenesis

Back 75

comparison of wild type protein versus a mutated protein

examine the efficiency of porteins and/or enzymes with a particualr amino acid substitution

examine how mutation of a gene promoter affects transcription