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52 Cards in this Set

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  • Back
____ and _____ both result in changes in the content of bacterial chromosomes.
mutation and recombination
alteration in bacterial chromosome as a result of a PERMANENT DNA CHANGE
chromosomal alteration by the acquisition of new DNA from another organism (transformation, conjugation, transduction)
Whats the difference between mutation and recombination?
mutation occurs as a result of a PERMANENT DNA CHANGE, whereas recombination occurs as a result of ACQUISITION OF DNA from another organism.
what are the three types of recombination?
transformation, conjugation, transduction
Transformation refers to the uptake of ______.
naked DNA
Does transformation have to occur within the same species?
What happens in natural transformation?
- Dead donor DNA is picked up by live recipient.
- Recipient incorporates donor DNA into chromosome.
What happens in laboratory transformation?
- Chemically 'competent' cells are forced to take up plasmid DNA.
- Transformants selected by using some trait encoded by plasmid (antibiotic resistance)
transfer of genetic information through direct cell-to-cell contact
What are F factors?
fertility plasmids

They encode genes for pilus, etc (20-30 genes required for conjugation)
What do F factors encode?
genes for PILUS
For cell-to-cell contact, the donor cell, F+, produces the conjugation pilus that makes contact with the recipient cell, known as an F- cell. The donor cell is called F+ because?
it contains an F plasmid

F+ transfers a copy of itself (possibly including resistance genes)
Does conjugation require the activity of the bacterial chromosome?
NO. only plasmid!
Can conjugation occur between bacteria of different genera?

ex: RK2 plasmid goes into all gram-hegatives
Transduction requires a virus to carry the DNA fragment from donor to recipient cell. In transduction, genetic transfer is mediated by ____
bacteriophage- the virus that participates in transduction
What are the two types of transduction?
1) generalized
2) specialized
lytic cycle
after viral replication, host bacterium broken open

- phage invades the bacterium, then replicates itself and destroys the bacterium as new phages are released.
What does a virulent phage do?
causes lysis
virus integrates into bacterial chromosome
____ phages are lysogenic
integrated viral DNA
Generalized Transduction is carried out by ___ phage
virulent phages that have a lytic cycle of infection
What happens in generalized transduction?
- virulent bacteriophage attaches to surface of a host bacterial cell.

- DNA from virulent phage enters the cytoplasm of the bacterium. Viral DNA multiplies and host DNA is fragmented into small pieces

- Random pieces of host chromosome get accidentally packaged by virulent phage

- Transferred to a second host

- Recombined into second host's chromosome
Give two examples of virulent phages that have a lytic cycle of infection and carries out generalized transduction.
P1 infects E. coli

P22 infects S. typhimurium
What does phage P22 infect?
S. typhimurium
What does phage P1 infect?
E. coli
Specialized transduction occurs as a result of ____ and unlike generalized transduction, results in the transfer of specific genes. It is carried out by ____ phages

What happens in specialized transduction?
- temperate bacteriophage attaches to the surface of a host bacterial cell

- DNA of temperate phage enters the bacterial cytoplasm

- Viral DNA integrates into the bacterial DNA. Now it is called a prophage.

- Some type of stress induces lysogenic phage to enter lytic cycle

- imprecise excision of phage occurs

- because of capsid size, some bacterial genes taken, some phage genes left behind

- resulting phage infects a second host and transduces it with genes from first host
Alteration in bacterial chromosome as a result of a permanent DNA change
Silent mutation
nucleotide change does not result in amino acid change.

- GAG --> GAA, G-->A transition (purine to purine). GLU stays as GLU
- Genetic code is degenerate

AG are purines
CT are pyrimidines
Nonsense mutation
amino acid changed to stop codon

- GAG --> TAG, G --> T transversion (purine to pyrimidine)
Missense mutation
amino acid changed to another amino acid (GLU to VAL)

- GAG --> GTG, A -->T transversion
Frameshift mutation
insertion or deletion of nucleotides resulting in a change in the reading frame
Spontaneous mutations happens every 1 in 10^9 nucleotides. It is caused by?
natural errors in replication

These mutations may end up being advantageous to an organism

- No identifiable cause
- No added mutagens (things that cause mutations)
What causes induced mutations?
an identifiable source such as UV light or chemical mutagen
What does ultraviolet light induce?
thymine dimers
What do thymine dimers, induced by ultraviolet light, cause?
Thymine dimers cause localized distortion of the DNA helix--any activity involving DNA messed up.

Direct exposure to UV light used to disinfect surfaces--kills bacteria by mutating their DNA
Name a Chemical Mutagen.
Nitrous acid
Nitrous acid is a chemical mutagen that converts DNA's ____ molecules to _____ molecules.


- Hypoxanthine pairs with C instead of T
-Results in a T-C transition mutation

Nitrous acid is a chemical mutagen that converts DNA's adenine molecules to hypoxanthine molecules. Adenine will normally base pair with thymine during DNA replication, but hypoxanthine base pairs with cytoosine. Later, when protein synthesis thakes place, the new DNA molecule having cytosine substituted for thymine will code for guanine in the mRNA instead of the normal adenine.
Mutations also can be induced by a series of BASE ANALOGS that bear a chemical resemblance to nitrogenous bases. One such base analog, ______, is taken up by cells and incorporated into DNA where thymine should be positioned.
true or false?

DNA with base analog in place functions poorly.
Base analogs may be used to treat diseases such as viral infections. DNA viruses such as herpesviruses can be treaded with ___, a base analog.

_____ induce changes in reading frame

-Fungal toxin from Aspergillus flavus
How does Frameshift mutations work?
FLAT PLANAR STRUCTURE intercalates into DNA to cause frameshifts
Frameshift mutations are found where?
peanuts, wheat, animal products
DNA is the only macromolecule that is ____, not degraded
What is mismatch repair?
- Normal part of replication
- DNA polymerase has proofreading function
- Removes and replaces mismatched nucleotides

Mismatch repair during DNA replication. As a result of an incorrectly paired nucleotide, DNA polymerase removes (excises) the nucleotide and adds the correct complementary nucleotide.
What is excision repair?
- General repair system for distortions in DNA (T-T dimers, intercalating agents)
- UvrABC endonuclease cuts out distorted part
- DNA pol and DNA ligase fill and seal gap

Excision repair to DNA damage. Thymine dimer distortion triggers nuclease repair enzymes that excise the damaged DNA and permit resynthesis of the correct nucleotides.
What are the components of the Ames test?
- Salmonella typhimurium histidine auxotroph
~ inactive excision repair => accumulate DNA mutations
~ mutated lipopolysaccharide coat to increase permeability

- Liver extract to approximate effects of mammalian metabolism
In the Ames test, 'Strength' of carcinogen measured by ____
number of revertants (his+ colonies)
Name two mutagens found by the Ames Test
- Tris (2,3-dibromopropyl) phosphate
Chemical used to make pajamas flame retardant

- Furylfuramide
Antibacterial food additive used to increase shelf life of packaged foods