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MICRO > Genetic Exchange > Flashcards

Genetic Exchange Flashcards

1
Q

What is Transformation?

A

The uptake of DNA from a medium and its incorporation into a host chromosome!!

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2
Q

In nature, what is the source of transformation? what is it sensitive too?

A

In nature, usually lysed cells provide free floating DNA molecules for transformation
this makes them sensitive to DNase which chews up naked DNA

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3
Q

What does it mean for a cell to need competence for transformation to occur.

A

Cells need to reach a certain level of competence which is based on growth before they are able to perform transformation

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4
Q

If there is enough homologues in the host DNA what occurs to the up taken DNA?

A

Recombination occurs and DNA is incorporated into the genome

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5
Q

What occurs of the host cell does not like the up taken DNA?

A

Degradation

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6
Q

What bacteria is well studied for competence and transformation?

A

Streptococcus Pneumoniae

it is gram positive!!!

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7
Q

Explain how S. Pneumoniae initiates transformation

A

1) during exponential GROWTH the cell secretes competence factor (CF)
2) CF binds to cell surface which signals translation of many new proteins

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8
Q

what is the major protein synthesized after CF binding that is responsible for transformation ?

A

Autolysin

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9
Q

explain how DNA enters the cell and the 2 major proteins involved (start with CF binding) (6)

A
  • CF binds and causes autolysin translation
  • Autolysin chews up some of the Peptidoglycan layer and exposes a DNA binding protein and a nuclease on cell surface.
  • DNA binds to binding protein in double strand form
  • nuclease cuts off (hydrolyzes) one of the strands of DNA
  • other strand is facilitated into the cell
  • may integrate may degrade
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10
Q

what is a transformant?

A

An up taken DNA that enters genome of host thereby altering its genetic makeup

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11
Q

true or false, Any DNA molecule can bind to the DNA binding protein in Competent factor transformation (human, pig, bird, etc)

A

TRUE, transformation allows the binding of any species DNA

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12
Q

What are the 4 proteins associated with transformation in GRAM POSITIVE bacteria?

A

binding protein: a pilus called ComEA

nuclease: called EndA
channel: called ComEC
chaperone: ComFA

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13
Q

What bacteria is well studied for No competence factors and transformation?

A

Gram negative Haemophilus influenzae

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14
Q

How do we know when gram positive cells are competent?

A

they release CF’s

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15
Q

How do we know when gram negatives are competent?

A

we don’t know for sure.

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16
Q

Explain how transformation works in gram negative cells

A
  • gram negative bacteria becomes competent during growth
  • Double stranded DNA enters OM and then enters PM as Single stranded DNA
  • Only binds DNA of close relatives!
17
Q

why do gram negative cells e.g Haemophilus influenzae only bind DNA of close relatives?

A

this ensures the homology of the up taken DNA is similar to the host. This increases the chances of recombination occuring

18
Q

For gram negative bacteria (Haemophilus influenzae) what is one requirement for DNA to be up taken.

A

It must contain a specific 11 base pair sequence

19
Q

What creates the pore in the gram negative transformation? what is its equivalent in the gram positive transformation?

A

PilQ creates pore in negative

ComEC creates pore in positive

20
Q

Explain Artificial transformation

A

Treat non competent cells such as E. Coli with cold CaCl2 to mimic artificial competent

21
Q

True or false, in artificial transformation linear DNA is easier to up take than plasmids

A

false, Plasmids are easier to up take

22
Q

Explain Electroporation (3 steps)

A

1) make cells electrically competent by washing them in cold distilled water
2) now competent cells are mixed with naked DNA and exposed to high voltage pulses
3) pulses open up small, resealable holes for DNA to enter through
Very universal for non-competent DNA

23
Q

What is transduction? what is the general process?

A

Genetic info can be transferred from one bacteria to another via a bacteriophage.
During phage infection bacterial DNA is accidentally packaged into a phage head. This phage infects new bacterium and supplies New DNA of last infected cell

24
Q

What are the two types of bacteriophages? how do each reproduce?

A

Virulent phages: reproduce via the lytic cycle

temperate phages: reproduce via lysogenic cycle

25
Q

Explain the 5 steps of the lytic cycle infection!

A

1) adsorption: bacteriophage binds specific receptors
2) injection of DNA, capsule remains outside
3) new DNA directs synthesis of phage DNA and phage Proteins
4) DNA is packed into phage heads
5) phages lyse the cell and proceed to next host

26
Q

Explain lytic transduction randomness

A
  • mis packaging is completely random
  • therefore any gene can be placed into phage head
  • phage head only contains bacterial genome
  • upon infection of next host, no phage will be made because no phage DNA is in the Head
27
Q

what is the term given to the phage with the bacterial DNA?

A

transducing particle

28
Q

Explain the lysogenic cycle

A
  • some phages can integrate their DNA into the host cells DNA
  • DNA replication and cell replication occur a few times
  • eventually the phage DNA is excited out of the host DNA chromosome
  • then it enters the lytic cycle
29
Q

give an example of a temperate phage

A

lambda

30
Q

what is the newly integrated DNA in the lysogenic cycle called? what is the name of the host cell?

A

prophage is the DNA

the host cell is called a lysogen

31
Q

True or false, the prophage must be integrated at specific sites on host DNA?

A

True, in the case of lambda, it is always between galactin and biotin

32
Q

What is specialized transduction?

A
  • lysogenic transduction to begin with
  • excision of prophage is not precise so some chromosomal DNA pops out with it
  • now transducing particle has both DNA of phage and host
33
Q

Does specialized transduction give rise to new bacteriophages?

A

It can but it normally does not since some phage DNA is missing and therefore cant properly code for new phages. Similar to F’ conjugation.

34
Q

why are the transducing particles considered specialized?

A

because upon excitation of prophage some chromosome DNA pops out with it. This is then replicated many times. The cell lyses and every phage that leaves is defective but carries the ‘specialized excited gene’

MICRO (28 decks)

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