Microbial Genetics

Question 1

What is a spontaneous mutation?

Answer 1

Mutations that occur naturally as the result of errors in replication or ambient radiation sources

Question 2

What is a mutation?

Answer 2

A heritable change in the nucleotide sequence of an organism’s genome

Question 3

What is a frame-shift mutation?

Answer 3

Insertions or deletions that result in a shift in the reading frame (whole protein is affected)

Question 4

What is conditional mutations?

Answer 4

Missense mutations in essential proteins (need to be made) that render them sensitive to temperature, salt, or other stresses
-NOTE: Can perform normal function unless put in a stressed environment

Question 5

What do mutations produce in a population? Are they harmful or beneficial to organisms?

Answer 5

-Spontaneous mutation creates variety/ genetic diversity (an advantage for evolution)

Question 6

Describe the Fluctuation Test (how it was conducted and how it was demonstrated)

Answer 6

-Taking advantage of mutations that provide resistance to a virus, called a bacteriophage.
-Luria set up a series of cultures with a small number of bacteria in each allowing them to evolve, and then plated them with the virus.
-If a mutation was random then the number of plates with resistant bacteria would vary between cultures. A “jackpot” would be a culture that picked up a mutation early and had a large number of survivors
-If mutations were directed, then the number of survivors would be the same in each culture
-white: dead
-red: alive

Question 7

What is each state in the lytic cycle of bacteriophages?

Answer 7

1) Attachment
2)Entry of phage DNA and degradation of host DNA
3)Synthesis of viral genomes and proteins
4)Assembly (head, tails, or tail fibers)
5) Release (cell is killed)

Question 8

What is tRNA?

Question 9

What are suppressor tRNAs and what do they do?

Question 10

What are the variations of tRNA and their purpose

Question 11

Do suppressor tRNAs result in longer or shorter proteins than normal? Why? How does this impact the health of cells that encode for suppressor RNA?

Question 12

What are inversions? Where do they tend to come from?

Answer 12

Mutations in which the orientation of a segment of DNA is reversed (result from mistakes in replication and recombination)

Question 13

What are translocations? Where do they tend to come from?

Answer 13

Large sections of chromosomal DNA are moved to a new position (result from mistakes in replication and recombination)

Question 14

How can you calculate the mutation frequency?

Answer 14

Number of mutants/ Total number of cells

Question 15

What mutations occur more commonly: missense or nonsense? Why? How are they different?

Answer 15

Nonsense mutations occur less frequently than missense mutations because nonsense leads to cell death which does not replicate.
-Missense mutations still have viable cells

Question 16

What kinds of genes are hard to identify using microbial genetics techniques? Why?

Answer 16

If the gene is essential to growth and replication you can not screen for it because the cells will be dead.

Question 17

How much can mutagens alter the mutation rate? Do they increase or decrease it? how do they do this? (give an example of chemical mutagens and one physical mutagen)

Question 18

What is SOS DNA repair and what induces it? When does a cell do it?

Answer 18

-Happens when there is a double-stranded break
-If wild type template isn’t available the SOS proteins make do (guess), which often results in errors and an increase in mutation rates

Question 19

What are the pros and cons of SOS DNA repair

Question 20

What is transposon mutagenesis? Define the process

Answer 20

-disrupt genes by adding additional genetic information that cannot replicate under certain conditions.
-insert in a what that disrupts the chromosome (unfunctional gene)
1)insert transposon
2)each cell has insertion at a different site
3)plate on medium

Question 21

How do we do microbial genetics in a lab or research setting?

Answer 21

1) Identify the question you are interested in answering
2) Develop a strategy for identifying mutations in the process of interest (screening)
3) Increasing your probability of success
4) Cloning
5) Make a null mutation in the gene you identified

Question 22

Are bacteria asexually or sexually reproducing organisms? Explain

Answer 22

-Asexual
-bacteria happily exchange DNA through multiple mechanisms

Question 23

Define conjugation

Answer 23

Genetic information exchanged between two bacteria (type IV secretion)

Question 24

What are F plasmids> What do they encode for> What does F+/F- mean?

Answer 24

-F+: F plasmid that can be sent to the other bacteria through the pilus (able to make the pilus bridge)
-F-: able to receive the plasmid

Question 25

Describe the process of conjugation step by step

Answer 25

-transfer antibiotic resistance plasmids while keeping their same plasmid
-does not need to be the same species
-The proteins required for pilus formation are encoded on the F plasmid
-Fusion forming conjugation bridge. F plasmid nicked in one strand
-Transfer of one strong from F+ cell to F- cell
-F plasmid simultaneously replicated in F+ cell
-synthesis of complementary strand begins in the recipient cell
-Completion of DNA transfer and synthesis.
-cells separate

Question 26

What is an Hfr strain

Answer 26

• Are routinely used for mapping the rough locations of mutations of interest via interrupted mating
  -The F-factor has become integrated into the bacterial chromosome
  -During conjugation, it transfers itself along with a copy of the chromosome
  -recombination follows conjugation
  -interrupted mating experiments led to a genetic map (what genes are transferred and in what order)

Question 27

What is transduction

Answer 27

Host DNA derived from any portion of the genome is packaged into a mature virus particle and transferred to a new host (bacteria-> virus-> bacteria)
-when the phage replicates its DNA in a bacterium, some bacterial DNA may be packaged in phage heads and the phage particle injects bacterial DNA into new bacterial cell

Question 28

What is transformation

Answer 28

-Double0stranded DNA forced through cytoplasmic membrane
-integration of linear fragments by homologous recombination or replication of plasmids(environment-> bacteria)

Question 29

Define horizontal gene transfer.

Answer 29

The non-sexual movement of genetic information between genomes

Question 30

What happens when bacteria are exchanging DNA? What are the evolutionary consequences of this?

Answer 30

-bacteria being able to transfer DNA to completely different species can create species that can be hard to distinguish between.