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General - Microbiology 🦠 > L4: Microbial Genetics and Drug Resistance > Flashcards

L4: Microbial Genetics and Drug Resistance Flashcards

1
Q

What is the definition of the genome?

A

It is the total genetic information in an organism.

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2
Q

What are the characters of the prokaryotic genome?

A

 Consists of a single copy (Haploid) circular DNA molecule.

 Range from 580-4600 Kbp

 Many bacteria contain extrachromosomal DNA materials as a part of the genome called plasmids and transposons.

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3
Q

What is the definition of bacterial extrachromosomal elements?

A
  • These are the DNA material present in a cell other than chromosomal DNA
  • The most famous extrachromosomal DNA are:
    A. Plasmid.
    B. Transposons.
    C. Bacteriophage (virus infecting bacteria)
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4
Q

What is the definition of plasmids?

A

Plasmids are pieces of DNA that exist separate from the chromosome, they contain an origin of replication so they replicate independently.

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5
Q

What are plasmids classified according to?

A 
1- According to the size of the plasmid 
2- According to copy number
3- Shape of plasmid
4- Moving plasmid from cell to cell 
5- Artificial and natural plasmids
6- according to host range
7- according to compatibility
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6
Q

What are plasmids classified according to size?

A

Starting from a few hundred base pairs up to 3000 Kbp.

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7
Q

What are plasmids classified into according to copy number per cell?

A

1- Stringent plasmids

 1-2 copies / cell
 like F- plasmid and phage – plasmid
hybrid (P1)

2- Low copy number plasmids

 10-15/copies/cell
 such as pSC 101

3- High copy number plasmid
 up to 50 copies/cell
 like ColE, plasmid

4- Extremely high copy number plasmid
 these are specifically engineered to be up to 100-200 copies/cell

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8
Q

What are plasmids classified into according to the compatibility of plasmids?

A

Compatible plasmids:
➢ a cell can maintain more than one plasmid in the same cell (if they carry
different origins of replication).

Incompatible plasmids:
➢ The inability of two plasmids to be maintained in the same cell (if they carry the same origin of replication

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9
Q

What are plasmids classified into according to the shape?

A

The shape of plasmids can be classified into 3 groups

1- Covalently closed circular (CCC) form:
 The most common form
 Present as ds completely closed circular forms (as in E.coli).

2- Semicircular form:
 Transient form
 Present as one strand is completely closed, the other strand is opened.

3- Linear:
 unstable because it is attacked by exonucleases.

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10
Q

What are plasmids classified into according to host range?

A

1- Broad host range plasmids:
➢ Can replicate in a wide range of bacteria.
2- Narrow host range plasmids:
➢ only replicate in one or a few closely related bacteria.

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11
Q

What are plasmids classified into according to moving from one cell to another?

A

Conjugative plasmids: which have the tra genes that can mobilize the plasmid from one cell to another by conjugation

Shuttle vectors: plasmids that propagate in 2 diff. Hosts species (yeast and bacteria)

Non–conjugative plasmids: Cannot be mobilized under any known conditions

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12
Q

What are plasmids classified into according to naturallity or artificiality?

A

1- natural plasmids:
➢ All the above plasmids are present naturally in bacterial and some yeast cells.

2- Artificial plasmids :
➢ are naturally present plasmid but designed artificially
➢ to be used in genetic cloning as vectors
➢ by adding antibiotic-resistant markers or DNA sequences to be the target of
restriction endonucleases.

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13
Q

What is the importance of plasmids?

A
  1. Resistance:
     Antibiotic resistance.
     Heavy metals (metal reductase).
     U/V (DNA repair enzymes).
  2. Conjugation.
  3. Production: Toxins & enzymes and bacteriocin.
  4. Biochemical reactions: Sugar fermentation.
  5. Molecular biology: As a vector.
     Cloning vectors
     Gene therapy: These are plasmids used for the insertion of therapeutic genes to express the protein that is lacking in the cells
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14
Q

What are transposons?

A

Extra-chromosomal small pieces of DNA those are capable of moving themselves from one location in DNA to another, (movable elements or jumping genes).

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15
Q

What are the 3 forms of transposons?

A

(a) Insertion sequence (IS)
(b) Composite transposons (Tn)
(C) Non – composite transposons

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16
Q

What are the characters of the insertion sequence?

A

 The simplest form.

 They encode only proteins needed for their own transposition

 Carry repeated nucleotides at their ends (direct repeats or inverted repeats ~ (15-25).

 Examples: IS 1, 3, and 10.

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17
Q

What are the characters of composite transposons?

A

Contain 2 IS at both ends and central piece of DNA which encode for antibiotic resistance, virulence factors.

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18
Q

What are examples of composite transposons?

A
  • Tn5: encodes for kanamycin resistance.

- Tn10: encodes for tetracycline resistance.

19
Q

What are the characters of non-composite transposons?

A

 Have no IS at their ends but encode for transposition proteins.
 They carry genes for antibiotic resistance, virulence
factors, and catabolic enzymes.

20
Q

What are the examples of non-composite transposons?

A

o Tn 3: carry Ampicillin resistance gene.

o Tn 7: carry streptomycin and trimethoprim resistance

21
Q

What is the definition of gene transfer?

A

It is the process of moving apiece of DNA (Either chromosomal or plasmid) from one cell to another using different means.

22
Q

What are the types of gene transfer?

A

Vertical Gene Transfer: The Transfer of genetic material from parental organism to progeny

Horizontal Gene Transfer:

  • known as lateral gene transfer,
  • organism transfers genetic material to another organism that is not its offspring
23
Q

What are the types of lateral gene transfer?

A

a) Conjugation.
b) Transduction.
c) Transformation.

24
Q

What is the definition of conjugation?

A

It is a form of gene transfer in which two cells come in direct contact and DNA is transferred from one cell (donor) to the other (recipient).

25
Q

What are the requirements for conjugation?

A

 Donor cells should contain F plasmid, which encodes for F pili needed for conjugation.

 The donor plasmid should contain tra gene(conjugative type) to mobilize the plasmid.

26
Q

What are the steps of conjugation?

A

1- Donor Gram-negative bacilli containing F plasmid come in contact with other F-Gram negative bacilli.

2- The F pili of the donor cell (F +) attach to a specific receptor on the recipient cell (F -).

3- The F pili contract the recipient cell to be in close contact and then canalization occurs through the F pili between the two cells.

4- Once the canal is formed, the F plasmid starts to mobilize one strand of its ds DNA to the recipient cell.

5- New ds DNA is formed from the single strand in both donor and recipient cells so the recipient now contains F plasmid and changed to F+ cell which will act as a donor cell.

27
Q

What is the method of conjugation in gram-positive organisms?

A

mediated by signaling molecules called pheromones.

28
Q

Equation of conjugation

A

F+ + F- = 2F+

29
Q

What is the HFr and what are its characteristics?

A
  • If the F plasmid integrates into loci in the chromosome, this integrated F factor creates a high frequency of recombination cell (Hfrcell).
  • If this integrated plasmid is transferred to another cell by conjugation, it can transfer a segment (locus) of the chromosome during excision and can transfer this locus (gene or genes) from the donor cell (Hfr) to a recipient chromosomal cell
30
Q

Where does conjugation mostly occur?

A

Conjugation most frequently occurs in Gram-negative bacilli (only gram-negative have pili) but Gram-positive organisms can make conjugation.

31
Q

What is the definition of transduction?

A

It is a form of gene transfer in which bacteriophage (a virus that infects a bacterial cell) mediate the DNA transfer.

32
Q

What are the types of transduction?

A
  1. Generalized transduction

2. Specialized transduction

33
Q

What are the bacteriophage types in transduction?

A

1- Virulent phage (Lytic cycle)

2- Tempratephage (lysogenic cycle)

34
Q

Which type of cycle happens in generalized transduction?

A

This occurs with the lytic cycle of Bacteriophage (virulent phage).

35
Q

How does generalized transduction take place?

A
  • The phage infects a bacterial cell and replicates, any piece of bacterial DNA can be packaged inside the phage head.
  • By cell lysis and release of phages, it can infect another bacterial cell transferring the chromosomal DNA to the recipient cell.
36
Q

Which type of cycle happens in specialized transduction?

A

This occurs with the temperate or lysogenic bacteriophage

37
Q

How does specialized transduction take place? And why is it called “specialized”?

A

the phage DNA become integrated inside the bacterial DNA at a specific region, When the integrated phage is excised with a piece of bacterial chromosome and infect another bacterial cell transferring this DNA into the recipient cell.

(so it is called specialized)

38
Q

What is the definition of transformation?

A

It is a method of gene transfer in which direct uptake of DNA by recipient cell either naturally or artificially in the laboratory

39
Q

What are the methods of transformation?

A
  • Natural transformation
  • Laboratory induced competence
  • Transformation by electroporation
40
Q

Is natural transformation rare or common and give an example for an organism that works with it?

A

rare occasion e.g., Streptococcus pneumoniae

41
Q

What are the methods of laboratory-induced competence?

A

(increasing the permeability of the cell envelopes) by:
 Electroporation (exposing a mixture of recipient cells and plasmids to the electrical field to form pores in the cell envelopes)

 Adding calcium chloride solution and chilled on ice then heat-shocked

42
Q

What is the definition of transformation by electroporation?

A

(by exposing a mixture of recipient cells and plasmids to an electrical field to form pores in the cell envelopes).

43
Q

Equation of HFr cells

A

HFr cell + F- = HFr cell + F-

General - Microbiology 🦠 (6 decks)

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