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Microbiology pt.1 > genetics of bacteria and viruses > Flashcards

genetics of bacteria and viruses Flashcards

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Biology 101 flashcards
1
Q

Of what type of genome does a virus consist?

A

DNA or RNA

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2
Q

How can viral DNA be organized?

A

single-stranded, double-stranded or linear or circular

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3
Q

What does ambisense mean?

A

containing + and - regions of RNA attached end to end

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4
Q

The genome of influenza virus is special because

A

its viral RNA genome is segmented into pieces with each piece containing one or more genes

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5
Q

Double stranded viral RNA contain…

A

positive and negative regions

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6
Q

where is the bacterial chromosome located?

A

in the nucleoid

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7
Q

How can the bacterial chromosome be organized?

A

single, double stranded or circular

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8
Q

what are plasmids?

A

small genetic elements that can replicate independently of the bacterial chromosome

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9
Q

How are most plasmids structured?

A

circular, double stranded DNA molecules

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10
Q

How many base pairs can a bacterial genome have?

A

from 1500 to 400,00 base pairs

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11
Q

How can a bacterial genome be transferred from one bacterium to another?

A

horizontally

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12
Q

What kind of virulence factors can they encode?

A

toxins, enzymes for breakdown of antibiotics

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13
Q

what are replicons?

A

plasmids that can autonomously replicate like bacterial chromosomal DNA

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14
Q

What are episomes?

A

plasmids that can integrate into host bacterial chromosome such as E.coli F plasmid

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15
Q

what is an operon?

A

DNA sequence that includes several structural genes

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16
Q

for what are tenges coding?

A

for proteins which are functionally related

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17
Q

How is the transcription of an operon often activated or repressed?

A

by product of a regulator gene located elsewhere on the chromosome

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18
Q

What is the basic mechanism behind transcription of bacterial genes?

A

copying of the sense strand of the DNA into mRNA

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19
Q

How is the genetic nucleotide sequence transcribed?

A

colinearly

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20
Q

name the three phases of transcription process?

A
  • promoter recognition
  • elongation
  • termination
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21
Q

what is the promoter region?

A

site where RNA polymerase begins reading DNA sequence

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22
Q

what is crucial for binding of the promoter?

A

the sigma factor

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23
Q

What is a sigma factor?

A

proteins that associate temporarily with the RNA polymerase (core enzyme) to form a holoenzyme

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24
Q

When does the sigma factor dissociate itself?

A

once the transcription process has begun (can associate once again)

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25
Q

additional sigma factors are important for what?

A

facilitate the transcription of special determinants

depends on the physiological status of the cell

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26
Q

What is known as an operon?

A
  • genes that code for functionally related proteins which are often arranged sequentially at specific locations on the chromosome or plasmid
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27
Q

What does polycistronic mean?

A

mRNA synthesized by the transcription of an operon

- contains information sequences of several genes

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28
Q

what is transformation?

A

mechanism of gene transfer between bacteria
- process by which bacteria actively take up fragments of exogenous or foreign DNA and incorporate them into their genomes

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29
Q

Where does the uptake of the DNA take place?

A

free DNA via cell wall

30
Q

name the steps of transformation process

A
  1. through the cell membrane (only competent bacteria)
  2. combination of new DNA material with bacterial pre-existing DNA
  3. degradation of unused DNA
  4. expression of new genes → transformation process
31
Q

Which bacteria can do this? why

A

only competent bacteria because their cell wall is permeable to extracellular DNA

32
Q

how can a non-competent bacteria become competent?

A
  • under natural conditions (e.g. starvation)

- or through lab interventions (heat shock or chemical treatment

33
Q

What could be extracellular genetic material in transformation?

A

free DNA from dead bacterium that has lysed or a plasmid

34
Q

Which bacteria perform transformation?

A

neisseria, haemophilus influenza type b and streptococcus pneumonia

35
Q

define transduction

A

transfer of genetic material from one bacterium to another by a bacteriophage (bacterial virus)

36
Q

who can bacteriophages infect?

A

only bacteria

37
Q

What can infection lead to?

A

either production of new virus with destruction of bacterium (lytic phage) or integration of phage DNA in the bacterial genome (prophage)

38
Q

what could result from the integration of phage DNA?

A
  • uptake of pathogenicity factors
39
Q

name the types of transduction

A

generalized transduction and specialized transduction via excision

40
Q

which cycle takes place in generalized transduction?

A

lytic cycle

41
Q

how is the bacterial DNA transferred from one to another?

A

via a bacteriophage

42
Q

name the steps of generalized transduction

A

bacteriophage infects bacterium → cleavage of bacterial DNA (this DNA does not incorporate into DNA of infected bacterium) → viral DNA is packaged into phage capsid (bacterial DNA may also be incorporated) → lysis of infected bacteria → new bacteriophage infects other bacteria

43
Q

Where does the bacteriophage attach?

A

at the cell Wall of the bac

44
Q

which cycle does the specialized transduction include?

A

lysogenic and lytic cycle via temperate phages

45
Q

what happens after the first cycle of specialized transduction?

A

a restricted set of bacterial genes is transferred to another bacterium (incl. new virulence factors)

46
Q

describe the process of specialized transduction

A

bacteriophage has injected its DNA into bacterium → viral DNA is incorporated into the bacterial genome at a specific location → remains inactive as a prophage (lysogenic phase)

47
Q

what activates viral DNA replication in specialized transduction

A

heat or radiation

48
Q

the genes for which toxins are transferred from one bacterium to another by specialized?

A 
erythrogenic toxin (streptococcus pyogenes) 
cholera toxin
diphteria toxin (corynebacterium diphtheria) and shiga toxin (shigella spp.)
49
Q

explain conjugation

A

transfer of DNA from a donor bacterial cell to a recipient bacterial cell in the conjugational process involving cell to cell contact

50
Q

What is F?

A

fetility factor which enables bacterial plasmid to transfer genetic material between bacteria

51
Q

F+ means?

A

bacteria with a plasmid that contain genes for sex pilus ( to attach to recipient cell) and F factor → acts as donors

52
Q

F- means?

A

bacteria without F factor and sex pilus -> act as recipients

53
Q

How do F+ and F- bacteria connect?

A

via the sex pilus

54
Q

How is a single strand of plasmid DNA transferred?

A

from the F+ bacteria to the F- bacteria (mating bridge) -> result F+ bacteria

55
Q

what are Hfr cells?

A

high frequency recombination cells which are bacteria with a conjugative plasmid (e.g. F factor) integrated into their chromosomal DNA

56
Q

With whom do they connect?

A

with F- bacteria via sex pilus

57
Q

What happens if Hfr cells and F- bacteria connect?

A

transfer and replication ofDNA material on recipientF-bacteria (only the leading part of theplasmidand some adjacentgenesaretransferred)→F-bacteria have newgenes

58
Q

result of Hfr bacteria and F- cell connection

A

F- cell has new genetic material

59
Q

what are mutations in microorganisms?

A

any changes in base sequence of DNA

60
Q

Describe transition

A

single base change -> one purine is replaced by another purine or pyrimidine replaced by another pyrimidine

61
Q

describe transversion

A

purine is replaced by a pyrimidine and vice versa

62
Q

describe silent mutation

A

change at the DNA level which doesn’t result in any change of amino acid in the encoded protein → occurs because more then one codon may encode an amino acid

63
Q

missense mutation is…

A

different AA being inserted in the protein but may be a conservative mutation if the new AA has similar properties

64
Q

describe nonsense mutation

A

changes codon encoding an AA to a stop codon -> ribosome will fall off the mRNA and end the synthesis of protein prematurely

65
Q

conditional mutations are

A

temperature sensitive mutations that change the structure or function of an important protein at elevated temperatures

66
Q

conditional mutations may result from

A

conservative mutation

67
Q

small deletion or insertion produces

A

a frameshift mutation

68
Q

small deletion or insertion results in

A

a change in the reading frame and useless peptide and premature truncation of protein

69
Q

null mutations arise when

A

there is an extensive insertion, deletion or gross rearrangement of chromosome structure

70
Q

null mutations lead to

A

the complete destroying of the gene function

71
Q

what could cause null mutations?

A

insertion of long sequences of DNA by recombination, by transposition, or during genetic engineering by separating the parts of a gene and inactivating the gene

Microbiology pt.1 (10 decks)

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