Exam 1: Bacterial Genetics

Question 1

What is a phenotype?

Answer 1

The identifiable characteristics of a cell that can be altered by mutation

Question 2

What is a genotype?

Answer 2

They sequence of nucleotides in the DNA of a cell

Question 3

What does phenotype result from?

Answer 3

Gene expression

Question 4

What is a mutant?

Answer 4

Bacteria with altered genetic sequence; may or may not have altered phenotype

Question 5

What is an isogenic mutant?

Answer 5

Bacteria with only a single gene difference compared to parent strain

Question 6

What is the gene organization of bacterial chromosomes?

Answer 6

Genes have no introns
Several genes can be expressed on a single mRNA molecule: operon
Gene expression is regulated by specific sequences and gene products
Sets of genes and operons are coordinately regulated in response to the environment

Question 7

What are the types of extrachromosomal DNA?

Answer 7

Plasmids
Bacteriophage
Transposable elements/transposons
Integrons

Question 8

What are plasmids?

Answer 8

Smaller DNA molecules that are separate and replicate independently from the chromosome
Close circular, supercoiled, double stranded DNA molecules, similar to chromosome except smaller

Question 9

What do plasmids typically carry?

Answer 9

Genes that ensure copies are maintained in each daughter cell as the parent divides

Question 10

What do the genes that plasmids carry offer?

Answer 10

A selective advantage for the host bacteria under certain environmental conditions

Question 11

What is bacteriophage similar to?

Answer 11

Eukaryotic viruses. It can replicate lytic phase or enter quiescent lysogenic phase

Question 12

What is the lytic phase?

Answer 12

Bacteriophage directs the host cell to manufaccture copies of the phage and the host cell is lysed

Question 13

What is the lysogenic phase?

Answer 13

Bacteriophage inserts in host DNA

Can be subsequently induced to enter lytic phase

Question 14

What are transposable elements/transposons?

Answer 14

Genes that can move from one location in bacterial DNA and insert randomly in the same or a different DNA molecule

Question 15

What can transposable elements be carried in?

Answer 15

Chromosome of plasmid

Question 16

What happens when transposition of transposable elements occurs?

Answer 16

The gene removes itself and randomly inserts in either the same DNA molecule or a different one

Question 17

What can transposable elements cause?

Answer 17

An insertion mutation if it inserts a gene

Question 18

What are composite transposons?

Answer 18

They carry genes that offers a selective advantage, such as antibiotic resistance

Question 19

What are integrons?

Answer 19

Mobile DNA elements with the ability to capture genes, notably those encoding antibiotic resistance, by site-specific recombination

Question 20

What can a single integron capture?

Answer 20

Many antimicrobial resistance genes

Question 21

What can integrons be carried in?

Answer 21

Chromosome or on plasmids

Question 22

What are features of bacterial reproduction?

Answer 22

Asexual reproduction

Short generation time

Question 23

What is the generation time of E. coli?

Answer 23

20 minutes during log phase growth

Question 24

What does a generation time of 20 minutes mean?

Answer 24

1 cell can produce more than 2000 progeny in less than 4 hours

Question 25

What is the normal mutation rate in E. coli?

Answer 25

1/2000 progeny will have a mistake in DNA

Question 26

What are the possible mutations like in bacteria?

Answer 26

Some are silent Some are lethal Some cause a detectable phenotypic change

Question 27

What leads to mutations that can cause a detectable phenotypic change?

Answer 27

Nutrient requirement (auxotrophy) Failure to grow under certain environmental conditions (conditional lethal) Adaptation to new environment Resistance

Question 28

How is adaptation possible for bacterial progeny?

Answer 28

Bacteria still have the ability to control gene expression to their environment Random mutations and short generation type Exchange of DNA between bacteria

Question 29

How can bacteria control gene expression?

Answer 29

Genes are located close together and do not have interrupting sequences (introns) No nuclear membrane (transcription and translation occur simultaneously) Adapt to their environment

Question 30

What is some evidence for DNA exchange between bacteria?

Answer 30

Genomic sequencing of bacteria has revealed large differences in gene makeup within bacterial species Genomic islands

Question 31

What are genomic islands?

Answer 31

Clusters of genes, often located near phage remnants or other evidence of lateral exchange, that have different G+C content of codon usage than the rest of the chromosome

Question 32

What are mechanisms of DNA exchange?

Answer 32

Transformation Transduction Conjugation

Question 33

What is transformation?

Answer 33

Uptake of naked DNA | Natural transformation occurs in only a few species

Question 34

What is transduction?

Answer 34

Transfer of DNA by bacteriophage

Question 35

What can bacteriophages sometimes carry during transduction?

Answer 35

Chromosomal DNA from an infected bacterium and transfer it into an uninfected bacterium

Question 36

What is conjugation?

Answer 36

Transfer of plasmid DNA by mating of 2 bacterial cells

Question 37

What is DNA transferred from and to in conjugation?

Answer 37

From a donor bacteria to a recipient

Question 38

What is conjugation pili?

Answer 38

Specialized surface structures on a donor cell that attach to a recipient cell and transfer DNA

Question 39

What are genes for conjugation pili usually carried by?

Answer 39

Plasmid

Question 40

What are host ranges like in conjugation?

Answer 40

Some plasmids are narrow (1 bacterial species or family) | Some are broad

Question 41

Why are broad host ranges dangerous?

Answer 41

They can move around even more than narrow ranges

Question 42

How is exchanges DNA maintained?

Answer 42

Exchanged DNA must have its own origin of replication that is recognized by the host strain OR It must be inserted into the chromosome

Question 43

How can exchanged DNA be inserted into the chromosome?

Answer 43

Transposition (transposons only) Lysogeny (phage only) Integron integration Homologous recombination (allelic exchange)

Question 44

What mediates homologous recombination?

Answer 44

Bacteria that have recombinases (RecA)

Question 45

What does homologous recombination require?

Answer 45

A similar sequence already in the chromosome