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Microbiology PMY 3 > Week 2- Microbial Genetics 2 > Flashcards

Week 2- Microbial Genetics 2 Flashcards

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1
Q

What is gene transfer?

A

Naturally occurring mechanisms for the exchange of genetic information

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2
Q

What are the types of gene transfer?

A
  • Vertical gene transfer

- horizontal/lateral transfer

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3
Q

When people have sex and have a child, what sort of gene transfer is that?

A

Vertical gene transfer

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4
Q

What is vertical gene transfer?

A

Genomic material transferred from a non-parent organism to another organism

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5
Q

What kind of gene transfer is mitosis/meiosis?

A

Vertical gene transfer

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6
Q

What is horizontal gene transfer?

A

Genomic material transferrred between non-parent organisms

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7
Q

List and describe the 3 main mechanisms of horizontal gene transfer

A

Conjugation- prokaryotes (bacteria and Archea)

Transduction-prokaryotes(bacteria and Archea)

Transformation- both prokaryotes and eukaryotes

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8
Q

What methods of gene transfer do bacteria and Archea?

A

Conjugation and transduction

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9
Q

What methods of gene transfer are employed by prokaryotes and eukaryotes?

A

Transformation

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10
Q

What is conjugation?

A

Genetic material transferred from one cell to another using a physical link known as the “sex “pili

-observed only in prokaryotes

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11
Q

What is transformation?

A

When DNA is taken up from the environment and incorporated into the genome of the recipient

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12
Q

What is transduction?

A

A bacteriophage is used to transfer information from one organism to another

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13
Q

What are the limitations of horizontal gene transfer?

A

Fragments must be short, 10,000 base pairs max and only certain cells are competent enough for transformation

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14
Q

How can transformation trigger recombination in the recipient cell?

A

If there are similarities in regions between host and foreign DNA, recombination might occur

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15
Q

Explain transformation in detail

A
  • dead bacteria release their fragmented genome which may be picked up by other bacteria in the environment
  • these fragments must be short for it to be picked up by the host cell (approx. 10,000 bp)
  • direct uptake of naked dsDNA (ssDNA) fragments which are converts to ssDNA before they recombine with the host’s genome
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16
Q

What are the requirements of recombination ?

A
  • Bacterial recombination genes (recA, B and C)

- homology between the DNA involved

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17
Q

How was transformation first observed in experimentation ?

A

Experiment by Frederick Griffith in 1928( Streptococcus pnuemoniae)

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18
Q

What were the findings of Frederick Griffith?

A
  • proved that information transfer occurred of some kind between Streptococcus pneumonia cells
  • suggested proteins being responsible for this “transformation “
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19
Q

Summarize the details of Frederick Griffith

A
  • In 1928, experiment by Frederick Griffith
    • Killed pathogenic strains release Nucleic acid
    • This DNA can be taken up live non-pathogenic strains
    • As a result they will convert the non-pathogenic strains into pathogenic strains that are capable of infecting mice
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20
Q

What does natural competence for transformation entail?

A

Natural competence: bacteria that can naturally take up exogenous DNA

-contains permeable membrane/transport membrane protein

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21
Q

What is induced incompetence?

A

-Not naturally transformable species can be manipulated to become “competent” and able to accept foreign DNA

E.g. E. Coli could be made competent after Ca+

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22
Q

Give a summation about how transformation occurs

A
  1. Competent receptor site binds to extracellular DNA
  2. DNA enters the cell, and the strands separate
  3. DNA separates into single strands and one strand recombined to the host chromosome and transforms the cell

4 the other strand becomes degraded

  1. Heteroduplex is formed as it contains host DNA and transforming DNA
  2. After one replication and it is incorporated into the host and it forms one cell that is transformed and one cell that is transformed
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23
Q

In a heteroduplex, which is the transformed DNA?

A

The outer edge has the transformed DNA

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24
Q

What are the 2 types of pili?

A

Fimbria- attachment pili

Sex pili

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25
Q

What is the function of the sex pili?

A

Involved in genetic transfer between bacterial cells(conjugation)

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26
Q

Describe the sex pili

A

Relatively long and few in numbers(1-6 per cell)

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27
Q

How was conjugation first observed?

A

By Joshua Ledeberg and Edward Tatum in 1946

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28
Q

What are auxotrophs?

A

Organisms that need nutrients to grow

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29
Q

What are protitrophs?

A

Organisms that have materials needed to grow

30
Q

What were the conclusions of the experiment of Joshua Lederberg and Edward Tatum in 1946?

A

Conclusions:

  • Some type of gene exchange between both strains
  • Such conversion to wild type cannot b a result of spontaneous mutation
31
Q

Describe the experiment of Joseph Lederberg and Edward Tatum in 1946

A

-Lederberg and Tatum demonstratedthe conjugation process between two K12 strains of E. Coli which were autotroph for different nutrients

Strain A: needs methionine and thi-

Strain B needs leucine threonine

-the resultant strain after conjugation was prototrophic for all 5 nutrients

32
Q

Describe the best study example of conjugation

A

The F+ factor in E. Coli

F+ is a plasmid (replicons) which can exist in 2 forms :

- independent replicons, F+ as a plasmid
- integrated in the chromosome that is known as a Hfr, high frequency recombination strains

This can be donated

33
Q

Describe the donation of the F plasmid

A

Donor: F positive(fertility factor, F+)

Recipient : is deficient for F factor ( F negative, F-)

34
Q

DNA transfer in conjugation requires a…

A

Sex pili

35
Q

Summarize the process of conjugation

A
  1. Conjugation occurs between F+ and F - cell
  2. One strand of the F factor is nicked by an endonuclease and moves across the conjugation tube
  3. The DNA complement is synthesized on both single strands
  4. Movement across conjugation tube is completed; DNA synthesis is completed
  5. Ligases closes circles; conjugants separate
36
Q

What are high frequency recombinant strains?

A

Bacteria with integrated F+ are called Hfr(not F+)

37
Q

F factor can be randomly….

A

Integrated in the chromosome although some places have higher frequency of integration

38
Q

How are F factor genes integrated into the chromosomes?

A

By homologous recombination

39
Q

What happens to chromosomal genes during F factor transfer in conjugation?

A

F factor mobilizes chromosomal genes during transfer

-but mating usually stops before transfer of entire chromosome

The recipient becomes diploid for certain genes- merozygous state

40
Q

What is a merozygous state?

A

When a cell is partially diploid

41
Q

What is gene mapping?

A

Maps can be created by comparing the order of the entry of chromosomes DNA into a recipient cell

42
Q

Why is the F insertion sites for the same strain possibly different?

A

This is due to the delicate nature of the conjugation tubes, they break prior to the passage of an entire chromosome, despite having same gene and gene loci

43
Q

How is conjugation of the Hfr strains for gene mapping?

A

Using Hfr strains allows for complete mapping of bacterial chromosomes

The gene closest to the F factor is the first to enter the recipient cell

Other genes enter in the order in which they appear on chromosomal DNA

The rate of entry is constant for each gene

44
Q

Describe the structure of the bacteriophage

A

Structure-

Head- nucleic acid and protein

  • Tail and contractive sheath
  • tail fibers and pins
  • Base/end plate
45
Q

What are the 2 mechanisms for viral replication?

A

Lytic viral cycle

Lysogenic viral cycle

46
Q

What is the lytic viral cycle?

A

When virus replicates, produces lysozyme and lyses the host cell

47
Q

What is the lysogenic viral cycle?

A

Viral DNA becomes part of the host DNA

48
Q

Discuss in details the steps of the lytic viral cycle

A
  1. Phage is absorbed to bacterial host cell
  2. Phage DNA is injected; host DNA is degraded
  3. Phage DNA is replicated; phage protein components are synthesized
  4. Mature pages are assembled
  5. host cell is lysed
49
Q

What is a virulent virus?

A

Virus that causes severe diseases

50
Q

What are the temperate/ nom-virulent viruses?

A

Viruses that only cause the symptoms of a disease

51
Q

How is the viral particle released?

A

By host cell lysis or new viruses budding off the host cell

52
Q

What are virulent viruses responsible for?

A

Host cell infection and viral particle synthesis

53
Q

What are temperate viruses?

A

Viruses that have the ability to induce lysogenic state with prolonged survival without causing cell lysis

54
Q

Discuss the events of the lysogenic viral cycle

A
  • Once the host is infected the viral genome integrates into the host genome or will survive as cytoplasmic episome
    • proohage (provirus)
  • when the host cell multiplies, each daughter cell will contain the prophage(copy of the viral genome)
  • once the prophage is activated (when host is under stress it will become a rellicon )and create its own viral DNA. it will continue the lytic viral cycle and form viral particles to be released by either:
  1. Host cell lysis
  2. Exocytosis by budding
55
Q

How may a prophage be activated?

A

Under some conditions like:

UV radiation

Changes in the environment

56
Q

Describe transferred DNA via transduction

A

Transferred DNA is relatively small size (few kB) and rarely includes multiple genes

57
Q

How was transduction first described?

A

In 1952 by Joshua Lederberg and Norton Zinderas the ability to convert Salmonella typhimurium from autotroph to prototroph

They used the David U-tube method with filters separating both strains by varying the size of pores
58
Q

Can pathogenicity be transduced?

A

In some case pathogenic islands can be transducer by phages

-from benign to pathogenic from Vibro cholerae

59
Q

What are the 2 types of transduction mechanisms?

A
  • Generalized transduction

- specialized transduction

60
Q

State what is generalized transduction

A

Bacterial chromosome is randomly spliced by bacteriophage enzymes into DNA fragments of various size

61
Q

What kind of organisms carry out generalized transduction?

A

Virulent(lytic) as well as temperate phages

62
Q

What level frequency transduction is generalized transduction?

A

Low frequency

63
Q

Summarize the events of Generalized transduction

A

Bacterial DNA fragments can be packed and carried by bacteriophage particles into infected host cells

  • these are defective bacteriophage only injected bacterial DNA instead of viral genome
  • Any locus of the bacterial chromosome can be carried over
  • The transferred bacterial DNA can recombine with the homologous chromosomal region of the adjacent
  • the donor and recipient are closely related
64
Q

Give in detail, the steps of generalized transduction

A
  1. Phage infects cell A(the donor cell) by normal means
  2. During replication and assembly, a phage particle incorporates a segment of bacterial DNA by mistake
  3. Cell A then lyses and releases the mature phases, including the genetically altered one
  4. The altered phage penetrates another host cell (cell B), injecting the DNA from cell A rather than viral nucleic acid
  5. Cell B receives this donated DNA which recombined with its own DNA because the virus is defective( biologically inactive as a virus )it is unable to complete a lytic cycle. The transduced cell survives and can use this new genetic material
65
Q

When does specialized transduction occur?

A

Only occurs with temperate phases during lysogenic cycle

66
Q

What level frequency is specialized transduction?

A

High frequency

67
Q

Give a synopsis or specialized transduction

A
  • When prophage is activated during the excision process it grabs parts of the surrounding host DNA due to an error
  • the bacterial DNA together with the viral counterpart will be introduced into a new recipient host cell(limited number of genes are transferred due to integration)
  • non-pathogenic strains may be converted to a pathogens due to transfer of virulence factors
    - diphtheria toxins, cholera toxins
68
Q

Give in detail, the steps of a Specialized transduction

A
  1. Lysogenized cell: integrated viral DNA (prophage) in host chromosome
  2. Prophage excuses from the host chromosome
  3. Incorrect excision introduces adjacent bacterial DNA into the excised viral DNA
  4. Replication and synthesis of phage DNA and phage protein components are assembled
  5. Viral head is packed with viral DNA containing the adjacent portion of bacterial DNA. Mature phages are assembled and released
  6. Phage infection and phage+bacterial DNA injection
  7. Viral+ Bacterial DNA integrates into host chromosome

8 recipient bacteria gains from any new beneficial genes

69
Q

Give an outline of steps in specialized transduction

A
  1. Prophage is within the bacterial chromosome
  2. Excised phage DNA contains some bacterial DNA
  3. New viral particles are synthesized. Some contain bacterial DNA in addition to phage DNA
  4. Cell A lyses and releases all new bacteriophages
  5. In cell B, infection of recipient cell transfers bacterial DNA to a new cell
  6. Recombination results in two possible outcomes: either bacterial DNA or a combination of viral and bacterial DNA being incorporated into the bacterial chromosome
70
Q

Differentiate generalized and specialized transduction

A
  1. Phage infects bacterium is generalized but in specialized, bacterial cell has prophage integrated between genes A and B
  2. Host DNA is hydrolyzed into pieces and phage DNA and proteins are made in generalized while in specialized prophage DNA sometimes exits incorrectly, taking adjoining bacteria with it
  3. In generalized, occasionally a bacterial DNA fragment is packaged in a phage capsid while in specialized phage particles carry bacterial DNA along with phage DNA

4 both have recombination/ crossing over

Recombinants have genotypes (A+B-) different from either donor ( A+B+) or recipient(A-B-)

Microbiology PMY 3 (24 decks)

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