Microbiology chapter 8 Nester

Mutagens increase the frequency of

mutations.

Nonsense Mutation

occurs when the base substitution creates a stop codon, resulting in a shorter and often non functional protein.

Mismatched repair fixes errors missed by?

proofreading mechanism; methlyation distinguishes the template strand.

Transposons

provide a mechanism for transferring genes. An insertion sequence encodes only transposase. A composite transposon has one or more genes flanked by insertion sequences.

Generalized transduction

results from a rare error that sometimes occurs during the construction of phage particles.

Missense mutation

results when the altered codon codes for a different amino acid. The effects depends on the positon and nature of the change.

Base analogs

structurally resemble nucleobases but have different hydrogen bonding properties.

Severe damage can be overcome by?

the SOS repair system

Frame shift Mutation as a Result of Nucleotide Addition.

the addition of a nucleotide pair to the DNA results in a shift in the reading freame when the sequence is transcibed and translated. Deletion of a single nucletide pair in the DNA would have a similar effect

A phage infects a bacterium by attaching to?

the cell and then injecting its nucleic acid into that cell

Base subtitution

the most common type of mutation occurs during DNA synthesis when an incorrect nucleotide is incorporated.

Phenotype

the observed characteristic of a cell

Every 24 hrs the genome of every cell in the human bod is damaged more than?

10,000 times

Staphlyococcus aureus

A gram positive coccus commonly called staph. It is a frequent cause of skin and wound infection. It was once treated with penicilin but some straing gained ability to destroy that antibiotic.

Auxtroph

A microorganism that requires an organic growth factor

Prototroph

A mircoorganism that does not require any organic growth factors.

Auxtroph

A mutant that requires a growth factor

Base subsitutuion

A replication error results in a mismatch bewteen the two DNA strand. Subsequent DNA replication using the altered strand as template results in a point mutation.

E. coli strain..

A wild type and a prototroph

Plasmid

An extrachromosomal DNA molecule that replicates independently of the chromosome.

Chemicals that modify Nucleobases

An umber of different chemicals modify the nucleobases in DNA, changing their base pairing properties.

Null or knockout mutation

Any mutation that totally inactivates the gene.

Transduction is the transfer of?

Bacterial DNA from one cell to another by the means of bacteriophage. It results form an error that occurs during the infection cycle of the bactriophage.

Why can a change have a significant impact on bateria?

Because bacteria are haploid, meaning they contain only a single set of genes.

Competent cells do what?

Bind DNA and take up single strand; that strand then integrates into the genome by homologous recombination.

What other structures can transfer DNA through conjugation?

Both plasmid DNA and Chromosomal DNA

Non-Homologous Recombination

DNA recombination that does not require extensive nucleotide sequence similarity in the stretches that recombine.

Conjugation requires contact between donor and recipient cells. A donor cell that synthesizes an F pilus transfers the?

DNA to one that does not.

Horizontal Gene Transfer

DNA transfer from one bacterium to another by conjugation, DNA mediated transformation or transduction.

Prototroph

Does not require growth factors

Some bacteria have an enzyme that recognizes the major distortions in DNA that result from thymine dimer formation.

Excision Repair - the enzyme removes the DNA strand with the damaged region.

Mismatch repair

Fixes errors missed by the proofreading of mismatched nucleobase, directing an enzyme to cut the sugar phosphate backbone of the new DNA strand. A short stretch of that strand is then degraded and DNA polymerase synthesizes a replacement.

Wild Type

Form of the cell or gene as it typically occurs in nature.

Removing or adding nucleotides can cause?

Frameshift Mutations

Example of horizontal gene transfer

Fungal genes have been found in an aphids DNA

What can remove modified nucleobases?

Glycosylases

Competence

In order for transformation to occur, the recipient cells must be competent. It is a specific physiological state that allows the cell to take up DNA.

The Mobile Gene pool

Includes plasmids, tranposons, genomic islands, and phage DNA.

Replica plating is used for?

Indirect selection, sometimes preceded by penicillin enrichment.

Cells can not repair all types of mutations, such as?

Insertions inactivation caused by transposition.

Repair of Modified nuecleobases in DNA

Modified nucleobases can result in base substitution if they are not repaid before the DNA is replicated.

Direct Selection

Mutants that can grow under conditions in which the parent cells cannot are usually easy to isolate by directe selectionl

Genetic change in bacteria occurs by two mechanisms?

Mutation and horizontal gene transfer.

Transposon

Segment of DNA that can move from one site to another in a cells genome.

Can mutations change an organisms phenotype?

Yes

Silent mutation

The mutation is referred to as silent because the amino acid sequence of the protein remain unchanged. IE genetic code redundancy means that most amino acids are coded for by more than one codon.

Mutation

changes the existing nucleotide sequence of a cells DNA, which is then passed on to the progen (daughter cells) through vertical gene transfer.

Following transfer, plasmids replicate, but?

chromosomal DNA must be integrated into a replicon to replicate.

Homologous Recombination

chromosomal fragement is transferred then it must become intergraed into replicon to be maintain in a population.

DNA-Mediated Transformation

commonly referred to as transformation involves the uptake of naked DNA by recipient cells. Naked DNA is DNA that is free in the cells surroundings. Not contained with in a cell or virus.

Mutants can be either selected in either?

direct or indirect techniques.

Conjugative plasmids

direct their own transfer from donor to recipient cells. the most thoroughly studied example of the F plasmid.

The Ames test is used to screen chemicals to determine?

which one are possible carcinogens.

Formation of tranducing particle

1. A bacteriophage attaches to a specific receptor on a host cell. 2. The phage DNA enter the cell. The empty phage coat remains on the outside of bacterium. 3.Enzymes encoded by the phage genome cut the bacterial DNA into small pieces. 4.Phage nucleic acid is replicated and coat proteins synthesized. 5. During construction of viral particles, bacterial DNA can mistakenly enter a protein coat. this creates a transducing particle that carries bacterial DNA instead of phage DNA

Genes can be transferred from a donor to a recipient by three different mechanisms.

1. DNA mediated transformation - naked DNA is taken up from the environment by a bacterial cell. 2. Transduction: DNA is tranferred from one bacterial cell to another by a bacteriophage (a virus that infects bacteria) 3. Conjugation: DNA is transferred furing cell to cell contact.

DNA mediated Transformation Process

1. Double stranded DNA bin to the surface of a competent cell 2. Single strand enters the cell; the other strand is degraded. 3.The strand integrates into the recipient cells genome by homologous recombination. The strand it replaced will be degraded. 4.After replicating the DNA, the cell divides. 5. Non transformed cell die on streptomycin containing medium whereas transformed cell can multiply.

Conjugation F plasmid transfer

1. making contact - The F pilus of the donor cell binds to a specific receptor on the cell wall of the recipient. 2. Initiating transfer - after contact the F pilus retracts pulling the two cells together. A plasmid encoded enzyme cuts one strand of the plasmid at the specific nucleotide sequence, the origin of transfer. 3. Transferring DNA - a single strand of the F plasmid enter the F- cell. Once inside the recipent cell, the strand serves as a template for synthesis of the complementary strand, generating an F plasmid. 4.Transfer complete - both the donor and recipient cells are now F+ so they can act as donor of the F plasmid.

In DNA mediated transformation

DNA is released from donor cells and taken up by competent recipient cells.

What are the two mechanisms that are used for "proofreading"?

DNA polymerase and mismatch repair

Repair of errors in nucleotide incorporation

DNA polymerase sometimes incorporates the wrong nucleotide as its replicates DNA. Resulting mispairing of nucleobases result in in a slight distortion in the DNA helix which can be recongnized by enzymes within the cell that then repair the mistake. By quickly repairing the error before the DNA is replicated, the cell prevents the mutation.

Proofreading by DNA polymerase

DNA polymerases are complex enzymes that not only synthesize DNA, but also check the accuracy of their actions. The process called proofreading

A change in an organisms DNA alters?

It's genotype - the sequence of nucleotides in the DNA.

DNA Mediated Transformation

Mechanism of horizontal gene transfer in which the bacterial DNA is transferred as naked DNA.

conjugation

Mechanism of horizontal gene transfer in which the donor cell physically contacts the recipient cell.

Transduction

Mechanism of the horizontal gene transfer in which bacterial DNA is transferred inside a phage coat.

MRSA

Methicillin resistant S. aureus developed all resistance to all penicillin derivatives. Vancomycin is normally used for infections, but as a last resort.

A knockout mutation results in?

Non functional protein.

Spontaneous mutation happen during?

Normal cell processes and can change the properties of the cell.

Point Mutation

Only one base pair is changed the mutation is called a point mutation.

Natural Selection

Orangisms need to adapt in order to survive and mulitply. If they fail to do this, competing orgainisms more fit to thrive in the new setting will soon predominate.

A leaky mutation results in?

Partially functional protein.

A change in genotype alter the organisms observable characteristic which is the?

Phenotype. (what you see) But Phenotype can be influenced by environmental conditions.

Repair of thymine Dimers - Bacteria have several mechanisms to prevent the DNA damaging effects of UV light such as sunlight?

Photoreactivation - light is required for this mechanism. An enzyme uses the energy of visible light to break the covlaent bonds of the thymine dimer, restoring the DNA to its original state.

What structures are replicons?

Plasmidds and chromosomes are replicons, but fragments of chromosomal DNA is not.

Homologous Recombination

Process by which a cell replaces a stretch of DNA with a segment that has a similar nucleotide sequence.

DNA polymerases have what type of ability?

Proofreading.

Bacteria have two general means by which they routinely adjust to new circumstances?

Regulating gene expression and genetic change.

Replica plating

Replica plating is a clever method for indirect selection of auxotrophic mutants.

Chemical Mutagens

Some chemical mutagens cause base substitutions and others cause frameshift mutations.

Vertical Gene Transfer

Transfer of genes from parent to offspring

Mutation

a change in the nucleotide seques of a cells DNA that passed on to daghter cells.

What is plasmid?

a genetic structure in a cell that can replicate independently of the chromosomes, typically a small circular DNA strand in the cytoplasm of a bacterium or protozoan. Plasmids are much used in the laboratory manipulation of genes.

Framshift Mutation

adding or sutracting one or two nucleotides pair.

Deletion or addition of nucleotieds during DNA replication?

also results in spontaneous mutations

Spontaneous mutations

are genetic changes that result from normal cell processes. They occur randomly, and genes mutate spontaneously at infrequent but characteristic rates.

Genomic islands

are large DNA segments in a cells genome that orginated in other species.

Plasmid transfer

are most frequently transferred to another cells by conjugation. These DNA molecules are replicons.

Transposons

are pieces of DNA that can move from one location to another in a cells genome, a process called transposition.

Plasmids

are replicons that code for non essential information; many are readily transferred by conjugation. R plasmids code for anitbiotic resistance.

Intercalating Agents

increase the frequency of framshift mutations.

In human defects either mismatch repair or repair of modified nucleobases?

increase the incidence of certain cancers

Indirect selection

indirect selection is used to isolate an auxotrophic mutant from the prototrophic parent strain.

Some chemical mutagen cause base substitution, but?

intercalating agents cause framshift mutations.

Conjugation

is a complex process that requires contact between donor and recipient bacterial cells. Gram positive and gram negative bacteria can both transfer DNA this way.

SOS repair

is last effort attempt that bacteria use to repair extensively damaged DNA. the enzyme that carry out this repair are induced when DNA is so heavily damaged by UV light that photoreactivation and excision repair may not be able to correct all the damage.

Penicillin Enrichment of mutants

is something used before replica plating to increase the proportion of auxotrophs in a broth culture.

Horizontal gene transfer

is the moviemnt of DNA from one organism to another. changes are then passed on to progeny through vertical transfer.

Transduction

is the process by which DNA is transferred from one bacterium to another by a virus . It also refers to the process whereby foreign DNA is introduced into another cell via a viral vector. Bacterial viruses (phages) can transfer bacterial genes from a donor to a recipient by transduction.

Transposons can?

jump from one location to another in a cells genome.

Replicon

meaning it has an origin of replication.

Thymine dimers can be repaired through?

photoreactivation and excision repair;

Base Substitutions Outcomes include

silent, missense, and nonsense mutations.

Base subsitutions that occur during DNA synthesis can lead to?

sillent, missense, and nonsend mutations.

Genotype

the sequence of nucleotide is an organisms DNA

Following a gene transfer, recipient cells must replicate the DNA to pass it on to daughter cells.

this can happen only if DNA is a Replicon

The properties of Bacteria can change either?

through mutation of horzontal gene transfer.

Both plasmid and chromosomal DNa ca be?

transferred