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Microbiology > Lecture 5: Bacterial Genetics > Flashcards

Lecture 5: Bacterial Genetics Flashcards

1
Q

What is a mutant

A

Offspring from a normal member of a species but genetically distinct from wild type

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2
Q

What is a mutation

A

Any heritable change in DNA sequence

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3
Q

What is an allele

A

Different forms of the same gene

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4
Q

What are isogenic strains

A

Two linages of the same bacterium that have a single change

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5
Q

Do mutations occur spontaneously or are they driven by selective pressures

A

Occur spontaneously but if you apply selective pressure you will create mutations that are resistant

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6
Q

What is selection

A

Growth condition that allows for growth of only a specific kind of mutant

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7
Q

What is a spontaneous base pair change

A

Occurring by insertion of incorrect base during replication

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8
Q

What is an induced base pair change

A

Addition of external factors (mutagens) that alter chemical bonds in DNA and need repair

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9
Q

What happens to base pairs with UV exposure

A

Form thymine dimer (T-T instead of T-A)

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10
Q

CCC encodes for ___

A

Proline

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11
Q

What is a silent or synonymous mutation and example

A

Change in base pair that doesn’t change coding of amino acid

CCC- encodes proline but so does CCA, CCG, CCU

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12
Q

What is a missense or nonsynonymous mutations

A

Changes in AA
CCU codes for proline but CGC codes arginine, GCC codes alanine

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13
Q

What is a null mutation

A

Loss of function of gene being altered

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14
Q

Does a nonsynonymous mutation always lead to a change in phenotype

A

No

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15
Q

Is mutation always beneficial to bacterium

A

No

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16
Q

How does transcription and translation occur in prokaryotes

A

Occurs simultaneously (CTT) because lack nucleus and nuclear membrane so mRNA is produced and ribosomes are immediately added

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17
Q

What is polycistronic

A

In prokaryotes there are multiple translation start sites, multiple genes controlled by one promoter

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18
Q

What is monocistronic

A

In eukaryotes single translation start site, 1 gene/1 promoter

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19
Q

Describe how transcription termination can occur with Rho

A

Rho binds rut sites that are not covered by ribosomes, progresses up to the mRNA strand until it hits RNA polymerase and dislodges it

Controls genes produced

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20
Q

What type of mutation is a mutation that changes from coding an amino acid to coding a stop codon- lead to early translation termination

A

Nonsense mutation

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21
Q

What are the two stop codons

A

UAG and UAA

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22
Q

What type of mutation can cause both early termination of transcription and translation

A

Non-sense mutation

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23
Q

What are frame shift mutations

A

Base deletions or additions that alter the reading frame of the mRNA

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24
Q

What is vertical gene transfer

A

DNA replication provides Daugherty cells with copy of parental DNA

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25
Q

What is horizontal gene transfer

A

Evolutionary process that distributes genes between divergent prokaryotic linages

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26
Q

What is transformation

A

Uptake of naked DNA from the environment and stable incorporation into genome

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27
Q

What is transduction

A

Transfer of DNA by virus or viral vector (bacteriophage)

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28
Q

What is transposition

A

Transposon genes are transferred from one organism to another through copying and insertion processes

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29
Q

What is conjugation or mating

A

Transfer of genetic material between bacteria by direct cell to cell contact between two cells

30
Q

Why do we care that bacterial cells share DNA

A

Because can turn avirulent pathogen to virulent

31
Q

What is natural competence

A

Ability of bacterium to take up DNA

32
Q

What are some examples of bacterium with natural competence

A

Streptococcus pneumoniae, Neisseria gonorrhoeae, Haemophilius influenza

33
Q

How does DNA uptake in gram negative cells

A
  1. Binding dsDNA to outer membrane surface
  2. Moving dsDNA across outer membrane
  3. Degradation of one DNA strand
    4, translocation of ssDNA molecule into cell
34
Q

How does DNA uptake in gram positive cells

A
  1. Binding dsDNA to outer cell surface
  2. Degradation of one DNA strand
  3. Translocation of ssDNA molecule into cell
35
Q

How do bacteria regulate competence

A

Quorum sensing

36
Q

What is quorum sensing

A

Bacterial communication, relays number of cells in an environment based on secreted protein or product

37
Q

Describe the example of quorum sending with Streptococcus pneumoniae

A
  1. Build up of competence stimulating peptide (CSP) due to S. Pneumoniae population increased leads to induction of competence
  2. Fratricide- killing of neighboring non-competent cells as sources of DNA
  3. CSP1 producing builds up, triggers competence in CSP1, CSP2 remains non-competent
  4. Will lyse non-competent and take up DNA that may contain antibiotic resistance genes
38
Q

Competence is critical to the development of ____

A

Antibiotic resistance

39
Q

What is transduction

A

Bacteriophage- bacterial viruses infect and move DNA

40
Q

P1 bacteriophage infects what

41
Q

P22 bacteriophage infects what

A

Salmonella

42
Q

Phage lambda infects what

A

E. Coli and salmonella

43
Q

What is specialized transduction

A

Phage transfers small amount of bacterial DNA adjacent to phage DNA in chromosome- produces infections particles with phage DNA

44
Q

What is generalized transduction

A

Transduction phage- mutation leads to misreading pac sites, carries bacterial DNA

45
Q

DNA loaded into the phage head is recognized by ___

A

PAC sites bound by tail proteins on the phage

46
Q

What happens to tail protein in generalized transduction

A

Mutation in tail protein recognize alternate pac sites found commonly on bacterial chromosome so get a mixture of infection particles and bacterial DNA

47
Q

Generalized transduction must have a ___ marker

A

Selectable

48
Q

What is lytic growth

A

Phage replicates- produces phage proteins, generates functional viral particle

49
Q

What is lysogenic growth

A

Phage silently insert into bacterial chromosome and phage DNA is replicated during cell division as if it is bacterial DNA

50
Q

What is a prophage or lysogen

A

Lytic genes repressed, viral DNA remains silent in host

51
Q

What is a transposon

A

DNA element that “hop” or transpose from one place in DNA to another

52
Q

How does transposition work via insertion sequence/elements

A
  1. Inverted repeats with transposase in middle
  2. Cuts DNA and allows transposon to insert
53
Q

Insertion elements are called __DNA because they provide no benefit to host, only cut and paste

A

Selfish DNA

54
Q

What are composite transposons

A

Large transposable elements flanked by insertion sequences that may or may not be identical

55
Q

Composite transposons are typically carrying ___ markers

A

Antibiotic resistance markers

56
Q

What are noncomposite transposons

A

Genes involved in transpotion and non-transposition genes are clustered together and flanked by terminal inverted repeat sequences

57
Q

What is the mechanism of transposition

A
  1. Transposition initiated by DNA replicaition
  2. dsDNA break is left behind as transposon goes elsewhere to insert
  3. Break must be fixed for cell to be viable
  4. Repair mechanisms use the other chromosome copy as template- transposon repaired in donor DNA
58
Q

What is the conjugative transposons mechanism

A
  1. Transposon excises from the chromosome and circularizes
  2. Genes encoding proteins that form a channel connecting two cells allow for a transfer of ssDNA
  3. Each cell has one strand of DNA that is replicated and the transposon re-inserts
59
Q

What are the reasons for using transposons in molecular biology

A
  1. Transpose at high frequency
  2. Transpose randomly
  3. Easily selectable marker
  4. Broad host range
60
Q

What are the common transposons

A

Tn5 and Tn10

61
Q

T or F: F plasmid is a self-transmissible plasmid with tra genes- transfer apparatus

62
Q

What are the two functions of tra in F-plasmid

A
  1. Dtr- DNA transfer and conjugal replication- preparation of DNA for transfer
  2. Mpf-mating pair formation- supramolecular structure (pill) to pass DNA to recipient
63
Q

Describe the steps in F plasmid transfer

A
  1. Mating pair is established
  2. Single strand DNA is transferred
  3. DNA replication occurs in both donor and recipient
  4. Cells separate
64
Q

T or F: mobilizable plasmids have their own tra apparatus

A

False- depend on tra from self-transmissible plasmid or helper plasmid

65
Q

Describe high frequency recombination and F- mating for genetic mapping

A

F can be integrated into chromosome and use markers that will be moved into recipient cell, over time look for genes transferred to recipient

66
Q

T or F: the longer it takes for a gene to be transferred the further down the road in the chromosome it is located

67
Q

Original map of E. Coli chromosome was based on ___

68
Q

What are pathogenicity islands

A

Horizontally acquired selections of bacterial chromosome that encode genes primarily associates with virulence

69
Q

What are the pathogenicity islands associated with salmonella

A

Island 1 and 2

70
Q

How can you tell DNA was horizontally acquired

A
  1. Look at close relatives
  2. Look at GC content
  3. Repeat sequences flanking genes
71
Q

SPI2 in salmonella pathogenicity islands is required for what

A

Replication in macrophages

72
Q

what is the normal GC in salmonella and what is the SPI2 GC content

A

Normal GC: 52.7%
SPI2 GC content: 43%

Microbiology (31 decks)

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