Chapter 8 - Bacterial Genetics Flashcards
How do bacteria adapt to changing environments?
Mutations and Horizontal gene transfer
Are bacteria haploid or diploid?
haploid
What are the three mechanisms of gene transfer?
Transformation, Transduction, and Conjugation
What is transformation?
naked DNA uptake by bacteria
What is transduction?
bacterial DNA transfer by bacteriophages
What is conjugation?
direct DNA transfer between bacterial cells
Which mechanism is sensitive to deoxyribonuclease?
transformation
Which mechanism requires cell-to-cell contact?
conjugation
Can DNA without an origin of replication replicate?
NO
What are replicons?
plasmids, chromosomes
How are some DNA fragments added to chromosomes?
homologous recombination
What is generalized transduction?
any genes of donor cell are transferred
What is specialized transduction?
specific genes are transferred
What cells are pathogenic in pneumococci?
Only encapsulated cells
What is special about the host cell in transformation?
The recipient cell must be competent
*some accept only from closely related bacteria (DNA sequence)
What kind of plasmids direct their own transfer in conjugation?
conjugative plasmids
What are the two types of conjugation?
Plasmid transfer and Plasmid + chromosome transfer
What is the process of plasmid transfer?
- use the F plasmid of E. coli
- F+ cells have, F- do not
1) pili bring cells into contact
2) enzyme cuts plasmid
3) single strand transferred
4) complementary strands synthesized
5) both cells are now F+
What is the process of Chromosomal DNA transfer?
1) Hfr cells involved (high frequency recombination cells)
2) F plasmid is integrated into chromosome via homologous recombination
3) process is reversible
a) Hfr cell produces F pilus
b) transfer begins with genes on one side of origin of transfer of plasmid (in chromosome)
c) part of chromosome transferred to recipient cell
d) chromosome usually breaks before full transfer (~100 minutes)
e) recipient cell remains F- since incomplete F plasmid transferred
What is the Start codon and amino acid?
AUG and Methionine (Met)
What are the Stop codons?
UAA, UAG, UGA
What are the two major types of mutations?
Base substitution mutations and Addition/Deletion (frameshift)
What is the basis of base substitution mutations?
incorrect nucleotide/s incorporated during DNA synthesis
What is a point mutation?
change of a single base pair
What are the three possible outcomes of base substitution mutations?
Silent mutation, missense mutation, and nonsense mutation
What is a silent mutation?
wild-type amino acid is still made
What is a missense mutation?
Different amino acid or effect on protein depends upon role played by changed amino acid
What is a nonsense mutation?
Specifies stop codon or nonsense codon and yields shorter protein
What is a mutation called that inactivates a gene?
A null or knockout mutation
Why are base substitutions more common in aerobic environments?
Reactive oxygen species (ROS) produced from O2 and can oxidize nucleobase guanine which DNA polymerase often mispairs with adenine
What effects the outcome of Addition/deletion mutations?
the number of nucleotides involved
What yields a frameshift mutation?
one or two nucleotide changes
What does a frameshift mutation do?
results in a different set of codons translated and often results in a nonfunctional protein
What does a three nucleotide change do?
adds or removes one amino acid and the impact depends on where the addition/deletion takes place
What are transposons?
- “Jumping genes”
- can move from one location to another through a process called transposition
- usually inactivates the gene to which it inserts
Can transposons replicate independently?
NO
Who discovered transposons and how did they study them?
Barbara McClintock and she observed color variation in corn kernels
What are Spontaneous Mutations and how often do they occur?
Mutations that occur randomly at infrequent but characteristic rates
Rate = 10^-6 for a given gene
-mutations are passed to progeny
What is it called when a mutation changes back to its original state?
Reversion
What are induced mutations?
Mutations that result from outside influence
What is the agent that induces mutation?
Mutagen
What do mutagens do to the mutation rate?
increase it
rate = 10^-3
What are the two general types of mutagens?
Chemical and radiation
What does nitrous acid do?
Causes a nucleotide substitution by converting cytosine to uracil
-base pairs with adenine instead of guanine
What do alkylating agents do?
Cause nucleotide substitutions by adding alkyl groups (CH3 and others) to nucleobases
- nitrosoguanidine adds methyl group to guanine
- -Changes GC to GT
What do base analogs (5-bromouracil) do?
Cause nucleotide substitutions by being used in place of normal nucleobases in DNA
–resembles thymine and often pairs with cytosine
What do intercalating agents (ethidium bromide) do?
Add or subtract nucleotides by inserting between base pairs
- -push nucleotides apart, producing space and causes errors during replication
- –likely carcinogen
What do transposons do?
insertionally inactivate DNA by randomly inserting themselves
What does UV light do?
Causes errors during repair process by creating intrastranded thymine dimers to form
- -distorts molecules at the covalent bonding
- –cells die if not repaired
What do x-rays do?
Cause deletions by causing single and double-stranded breaks in DNA
- -double stranded breaks often cause lethal deletions
- -alter nucleobases
What is non ionizing radiation?
UV
What is ionizing radiation?
X-ray and Gamma ray
What is the “Mobile Gene Pool”
plasmids found in most bacteria, archaea
- some Eucarya
- usually double stranded DNA with origin of replication
- generally nonessential; cells can be cured
- Few to thousands of genes
- most have a narrow host range (single species)
- some broad host range (include G- and G+)
- one or a few or many per cell
Which organisms have plasmid coded traits for antibiotic resistance?
E. coli, Salmonella sp, Neisseria sp, Staphylococcus sp, and Shigella sp
Which organisms have plasmid coded traits for pilus synthesis?
E. coli, Pseudomonas sp
Which organisms have plasmid coded traits for tumor formation in plants?
Agrobacterium sp
Which organisms have plasmid coded traits for nitrogen fixation?
Rhizobium sp
Which organisms have plasmid coded traits for Oil degradation?
Pseudomonas sp
Which organisms have plasmid coded traits for Gas vacuole production?
Halobacterium sp
Which organisms have plasmid coded traits for Insect toxin synthesis?
Bacillus thuringiensis
Which organisms have plasmid coded traits for plant hormone synthesis?
Pseudomonas sp
Which organisms have plasmid coded traits for antibiotic synthesis?
Streptomyces sp
Which organisms have plasmid coded traits for Increased virulence?
Yersinia sp
Which organisms have plasmid coded traits for toxin production?
Bacillus anthracis
