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

genetics of bacteria and viruses Flashcards

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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
additional sigma factors are important for what?
facilitate the transcription of special determinants | depends on the physiological status of the cell
26
What is known as an operon?
- genes that code for functionally related proteins which are often arranged sequentially at specific locations on the chromosome or plasmid
27
What does polycistronic mean?
mRNA synthesized by the transcription of an operon | - contains information sequences of several genes
28
what is transformation?
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
29
Where does the uptake of the DNA take place?
free DNA via cell wall
30
name the steps of transformation process
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
Which bacteria can do this? why
only competent bacteria because their cell wall is permeable to extracellular DNA
32
how can a non-competent bacteria become competent?
- under natural conditions (e.g. starvation) | - or through lab interventions (heat shock or chemical treatment
33
What could be extracellular genetic material in transformation?
free DNA from dead bacterium that has lysed or a plasmid
34
Which bacteria perform transformation?
neisseria, haemophilus influenza type b and streptococcus pneumonia
35
define transduction
transfer of genetic material from one bacterium to another by a bacteriophage (bacterial virus)
36
who can bacteriophages infect?
only bacteria
37
What can infection lead to?
either production of new virus with destruction of bacterium (lytic phage) or integration of phage DNA in the bacterial genome (prophage)
38
what could result from the integration of phage DNA?
- uptake of pathogenicity factors
39
name the types of transduction
generalized transduction and specialized transduction via excision
40
which cycle takes place in generalized transduction?
lytic cycle
41
how is the bacterial DNA transferred from one to another?
via a bacteriophage
42
name the steps of generalized transduction
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
Where does the bacteriophage attach?
at the cell Wall of the bac
44
which cycle does the specialized transduction include?
lysogenic and lytic cycle via temperate phages
45
what happens after the first cycle of specialized transduction?
a restricted set of bacterial genes is transferred to another bacterium (incl. new virulence factors)
46
describe the process of specialized transduction
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
what activates viral DNA replication in specialized transduction
heat or radiation
48
the genes for which toxins are transferred from one bacterium to another by specialized?
``` erythrogenic toxin (streptococcus pyogenes) cholera toxin diphteria toxin (corynebacterium diphtheria) and shiga toxin (shigella spp.) ```
49
explain conjugation
transfer of DNA from a donor bacterial cell to a recipient bacterial cell in the conjugational process involving cell to cell contact
50
What is F?
fetility factor which enables bacterial plasmid to transfer genetic material between bacteria
51
F+ means?
bacteria with a plasmid that contain genes for sex pilus ( to attach to recipient cell) and F factor → acts as donors
52
F- means?
bacteria without F factor and sex pilus -> act as recipients
53
How do F+ and F- bacteria connect?
via the sex pilus
54
How is a single strand of plasmid DNA transferred?
from the F+ bacteria to the F- bacteria (mating bridge) -> result F+ bacteria
55
what are Hfr cells?
high frequency recombination cells which are bacteria with a conjugative plasmid (e.g. F factor) integrated into their chromosomal DNA
56
With whom do they connect?
with F- bacteria via sex pilus
57
What happens if Hfr cells and F- bacteria connect?
transfer and replication of DNA material on recipient F- bacteria (only the leading part of the plasmid and some adjacent genes are transferred) → F- bacteria have new genes
58
result of Hfr bacteria and F- cell connection
F- cell has new genetic material
59
what are mutations in microorganisms?
any changes in base sequence of DNA
60
Describe transition
single base change -> one purine is replaced by another purine or pyrimidine replaced by another pyrimidine
61
describe transversion
purine is replaced by a pyrimidine and vice versa
62
describe silent mutation
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
missense mutation is...
different AA being inserted in the protein but may be a conservative mutation if the new AA has similar properties
64
describe nonsense mutation
changes codon encoding an AA to a stop codon -> ribosome will fall off the mRNA and end the synthesis of protein prematurely
65
conditional mutations are
temperature sensitive mutations that change the structure or function of an important protein at elevated temperatures
66
conditional mutations may result from
conservative mutation
67
small deletion or insertion produces
a frameshift mutation
68
small deletion or insertion results in
a change in the reading frame and useless peptide and premature truncation of protein
69
null mutations arise when
there is an extensive insertion, deletion or gross rearrangement of chromosome structure
70
null mutations lead to
the complete destroying of the gene function
71
what could cause null mutations?
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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