Microbiology Chapter 9

How does conjugation between Gram positive bacteria differ from Gram negative?

Gram-positive bacteria do not make a conjugation pilus; instead they form a conjugation bridge, or mating bridge, where the DNA is transferred

Explain how a point mutation can be a missense, nonsense, or silent mutation.

Point mutations: incorrect base is incorporated into the DNA •Missense mutation: codes for a different amino acid •Silent mutation: the codon is changed, the amino acid is not •Nonsense mutation: changes an amino acid codon to a stop codon

What is a mutation?

a change in the DNA code

Point mutation

a change that involves the loss, substitution, or addition of one or a few nucleotides

Chromosomal DNA

a chromosome is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences

Describe the main features of conjugation in Gram-negative bacteria.

a conjugation pilus is formed which joins two cells. The plasmid DNA (with F pilus gene and other genes) is replicated and one DNA strand is transferred to the adjoined cell, where enzymes use complementary nucleotides to produce a double stranded DNA plasmid.

Spontaneous mutation

a mutation in DNA caused by random mistakes in replication and not known to be influenced by any mutagenic agent

Thymine dimer

a pair of abnormally chemically bonded adjacent thymine bases in DNA, resulting from damage by ultraviolet irradiation

Plasmid DNA

a plasmid is an extra- chromosomal DNA molecule separate from the chromosomal DNA

DNA recombination

a type of genetic transfer in which DNA from one organism is donated to another

What types of cells are able to form a conjugation pilus?

an F+ cell is able to form a conjugation pilus because it has the genes on a plasmid that code for the pilus. It can only conjugate with an F-

Frame shift mutation

an insertion or deletion mutation that changes the codon reading frame from the point of the mutation to the final codon. Almost always leads to a nonfunctional protein. Normal: THE FAT CAT ATE THE RAT Deletion: THE F_T CAT ATE THE RAT Insertion: THE FAT ACA TAT ETH ERA T

Induced mutation

any alteration in DNA that occurs as a consequence of exposure to chemical or physical mutagens

Base analogue

chemical that can substitute for a normal nucleobase in nucleic acids. They are categorized in two separate groups, purine analogues and pyrimidine analogues

What type of DNA is transferred and where does it come from?

pieces of double stranded DNA from cells that have died and lysed

What is different about Hfr conjugation?

the F pilus gene is integrated into the chromosomal DNA is transferred to the F- cell

Conjugation pilus (also called F pilus or sex pilus)

the connection between donor and recipient cells associated with the transfer of genetic material such as plasmids. Can involve special (sex) pili. Also a form of sexual recombination in ciliated protozoans

Generalized transduction: What type of DNA is transferred and how?

usually chromosomal DNA 1.Bacteriophage infects first cell 2.Phage causes the degradation of the host cell DNA 3.During assembly of new viral particles, the virus inserts random pieces of host cell DNA in the capsid 4.Host cell lyses, virions are released 5.Virus infects a new host cell 6.The DNA can be integrated into the recipient cell's chromosome

What type of DNA is transferred during conjugation?

usually plasmid DNA

How can mutations be beneficial to microbes?

•Mutations sometimes allow organisms to be more fit for their environment •Able to adapt to changes, survive, and reproduce

Describe the process of bacterial transformation.

•Uptake of DNA from the environment •DNA released from dead cells and degraded into small pieces •DNA binds proteins on recipient cell and is transported across the membrane •Chromosomal integration