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Infectious Agents > Exam 1: Bacterial Genetics > Flashcards

Exam 1: Bacterial Genetics Flashcards

1
Q

What is a phenotype?

A

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

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2
Q

What is a genotype?

A

They sequence of nucleotides in the DNA of a cell

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3
Q

What does phenotype result from?

A

Gene expression

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4
Q

What is a mutant?

A

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

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5
Q

What is an isogenic mutant?

A

Bacteria with only a single gene difference compared to parent strain

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6
Q

What is the gene organization of bacterial chromosomes?

A

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

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7
Q

What are the types of extrachromosomal DNA?

A

Plasmids
Bacteriophage
Transposable elements/transposons
Integrons

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8
Q

What are plasmids?

A

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

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9
Q

What do plasmids typically carry?

A

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

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10
Q

What do the genes that plasmids carry offer?

A

A selective advantage for the host bacteria under certain environmental conditions

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11
Q

What is bacteriophage similar to?

A

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

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12
Q

What is the lytic phase?

A

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

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13
Q

What is the lysogenic phase?

A

Bacteriophage inserts in host DNA

Can be subsequently induced to enter lytic phase

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14
Q

What are transposable elements/transposons?

A

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

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15
Q

What can transposable elements be carried in?

A

Chromosome of plasmid

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16
Q

What happens when transposition of transposable elements occurs?

A

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

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17
Q

What can transposable elements cause?

A

An insertion mutation if it inserts a gene

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18
Q

What are composite transposons?

A

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

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19
Q

What are integrons?

A

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

20
Q

What can a single integron capture?

A

Many antimicrobial resistance genes

21
Q

What can integrons be carried in?

A

Chromosome or on plasmids

22
Q

What are features of bacterial reproduction?

A

Asexual reproduction

Short generation time

23
Q

What is the generation time of E. coli?

A

20 minutes during log phase growth

24
Q

What does a generation time of 20 minutes mean?

A

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

25
Q

What is the normal mutation rate in E. coli?

A

1/2000 progeny will have a mistake in DNA

26
Q

What are the possible mutations like in bacteria?

A

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

27
Q

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

A

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

28
Q

How is adaptation possible for bacterial progeny?

A

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

29
Q

How can bacteria control gene expression?

A

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

30
Q

What is some evidence for DNA exchange between bacteria?

A

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

31
Q

What are genomic islands?

A

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

32
Q

What are mechanisms of DNA exchange?

A

Transformation
Transduction
Conjugation

33
Q

What is transformation?

A

Uptake of naked DNA

Natural transformation occurs in only a few species

34
Q

What is transduction?

A

Transfer of DNA by bacteriophage

35
Q

What can bacteriophages sometimes carry during transduction?

A

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

36
Q

What is conjugation?

A

Transfer of plasmid DNA by mating of 2 bacterial cells

37
Q

What is DNA transferred from and to in conjugation?

A

From a donor bacteria to a recipient

38
Q

What is conjugation pili?

A

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

39
Q

What are genes for conjugation pili usually carried by?

A

Plasmid

40
Q

What are host ranges like in conjugation?

A

Some plasmids are narrow (1 bacterial species or family)

Some are broad

41
Q

Why are broad host ranges dangerous?

A

They can move around even more than narrow ranges

42
Q

How is exchanges DNA maintained?

A

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

43
Q

How can exchanged DNA be inserted into the chromosome?

A

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

44
Q

What mediates homologous recombination?

A

Bacteria that have recombinases (RecA)

45
Q

What does homologous recombination require?

A

A similar sequence already in the chromosome

Infectious Agents (38 decks)

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