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Microbial World > Week 10 > Flashcards

Week 10 Flashcards

1
Q

What are the advantages of making adaptations to the bacterial genome?

A

Microbial diversity

Habitat adaptation

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2
Q

In what ways can changes in the bacterial genome occur?

A

Mutations.
Exchange of genetic material between bacterial cells.
Better adaptation of bacteria to specific environments.

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3
Q

What is a wild-type strain of bacteria?

A

An organism isolated from the environment which has a natural and unchanged genome.

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4
Q

Define mutation.

A

A permanent change in the nucleotide base sequence of a genome.

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5
Q

Define mutant.

A

A cell derived from the wild type that carries a change in the nucleotide sequence.

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6
Q

What are the possible effects of a mutation on a gene?

A

Alter the product of a gene.
Prevent the gene working correctly.
Entirely prevent gene function.
Have no effect on gene function.

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7
Q

What are the 3 main categories of mutation?

A

Point mutations (base substitutions).

Framshifts

Deletions

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8
Q

How does the DNA and polypeptide sequence in a base substitution silent mutation?

A

The DNA sequence changes but the polypeptide sequence remains the same.

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9
Q

How do silent base mutations occur?

A

Although one base changes, the new codon can still code for the same amino acid and therefore the polypeptide sequence remains the same.

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10
Q

What is a Missense mutation base substitution ?

A

There is a single base pair substituted which causes the DNA and polypeptide sequence to be altered.

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11
Q

What happens to the protein when a missense base substitution mutation occurs?

A

Protein may become inactive or have reduced activity.

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12
Q

What is a nonsense base substitution mutation?

A

A single base pair substitution results in the premature formation of a stop codon and therefore causes premature termination of translation.

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13
Q

What is the result of a missense mutation on a protein?

A

Truncated proteins

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14
Q

What are truncated proteins ?

A

Elimination of the N- or C- terminal portion of a protein.

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15
Q

What are the 2 types of frameshift mutation?

A

Insertion and deletion.

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16
Q

What is an insertion frameshift mutation?

A

Insertion of bases (1-100) which leads to a shift in the reading frame. This often has serious effects on the polypeptide sequence.

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17
Q

What is a deletion frameshift mutation?

A

Deletion of bases (1-100) that leads to a shift in the reading frame. Often has serious consequences as the polypeptide sequence can be changed.

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18
Q

What effect do frameshift mutations have on transcription and translation?

A

Change the reading frame and cause a different polypeptide sequence to be formed.

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19
Q

Define transposons.

A

Small pieces of DNA that ‘jump’ around the chromosome or transfer from bacterium to bacterium.

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20
Q

What is horizontal gene transfer?

A

Movement of DNA between cells that are not directly related.

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21
Q

By what process is some of the host’s DNA incorporated into the recipient cell during horizontal gene transfer?

A

Genetic recombination.

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22
Q

What are the possible mechanisms of horizontal gene transfer?

A

Transformation
Transduction
Conjugation

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23
Q

Outline what transformation is

A

The transfer of naked DNA

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24
Q

Outline what transduction is

A

DNA transfer mediated by bacteriophages

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25
Q

Outline what conjugation is

A

Requires the attachment of two related species and formation of a bridge that can transport DNA.

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26
Q

What can cells that take up DNA by transformation be known as?

A

Competent or transformable cells

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27
Q

Outline the full mechanism of bacterial transformation.

A

1) Competent bacteria reversibly bind DNA to their surface using DNA binding protein This soon becomes irreversible.
2) The DNA binding protein drags the DNA through the gram-negative outer membrane or gram-positive wall.
3) Either dsDNA or ssDNA enters the cell.
4) Competence specific proteins bind to the donor DNA and protect against degrading nucleases.
5) DNA integrates into the recipient chromosome by recombination.

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28
Q

What type of recombination is used in bacterial transformation?

A

Homologous

29
Q

What happens if homologous recombination isn’t successful in transformation?

A

The DNA will be degraded.

30
Q

How can bacteria be artificially treated to become competent?

A

By using chemicals or temperature.

31
Q

What is artificial competence?

A

Forcing bacteria to uptake free/ naked DNA to become recombinant.

32
Q

What are the 2 types of transduction ?

A

Generalised

Specialised

33
Q

What is generalised transduction?

A

Virtually any gene from the donor chromosome can be transferred to a recipient bacterial cel.

34
Q

What is specialised transduction?

A

Selective transfer of small, specific sections of the chromosome from the host cell to the recipient cell.

35
Q

What causes transduction to be either generalised or specialised ?

A

The way the bacteriophage interacts with the host chromosome.

36
Q

Outline the mechanism of bacterial transduction.

A

1) Phage injects its DNA.
2) Phage enzymes degrade host DNA. This allow the phage to take over the mechanisms of the host cell and use them for replication.
3) Bacterial cell synthesises new Phages.
4) Transducing phage injects donor DNA into the recipient host cell.
5) Donor DNA is incorported into recipients chromosome by recombination.
6) Transduce cell formed.

37
Q

In what type of bacterial cells does conjugation occurs?

A

Gram +ve and Gram -ve

38
Q

What is required for conjugation occur ?

A

Cell to cell contact known as mating.

39
Q

Which plasmid of E.coli is used in conjugation?

A

F plasmid

40
Q

What is meant by the ‘F’ plasmid of E.coli?

A

The fertility plasmid

41
Q

What is the origin of transfer for conjugation in E.coli?

A

The oriT section.

42
Q

What is used to connect the donor and recipient cells in conjugation?

A

A conjugation pius

43
Q

Outline the mechanism of bacterial conjugation.

A

1) Donor cell attaches to a recipient with its pilus.
2) Pilus draw cells together.
3) One strand of the F plasmid DNA transfers to the recipient.
4) The recipient synthesises a complimentary strand via the rolling circle method of DNA replication, to become a F+ cell with a pilus.
5) The donor cell synthesises a complimentary strand, restoring its complete plasmid.
6) The donor and recipient cells both have a double stranded DNA plasmid and are not both F+.

44
Q

What is the DNA content of the recipient and donor bacterial cells after conjugation?

A

Double stranded DNA plasmid and are not both F+.

45
Q

What are F+ cells ?

A

Contain the fertility plasmids.

46
Q

What are F- cells?

A

Don’t contain the fertility plasmid.

47
Q

Briefly, what are Hfr cells?

A

Cells where the F plasma has integrated into the bacterial chromosome.

48
Q

What type of cells do Hfr cells conjugate with?

A

F- cells.

49
Q

Why are recombinant Hfr cells composed of a portion of the F plasmid and some chromosomal genes?

A

The transfer of the F plasmid begins but the pilus breaks before the transfer is complete.

50
Q

Are the recombinant Hfr cells formed F+ or F- and why?

A

F- because they only contain a portion of the F plasmid.

51
Q

Outline the mechanism of Hfr conjugation.

A

1) F plasmid integrates into chromosome by recombination.
2) Cells join via conjugation pilus.
3) Portion of F plasmid partially moves into recipient cell trailing a strand of the donor’s DNA.
4) Conjugation ends with pieces of F plasmid and donor DNA in recipient cells; cells synthesis complimentary DNA strands
5) Donor DNA and recipient DNA recombine to make recombinant F- cells.

52
Q

By what process do transposons move?

A

Transposition.

53
Q

Where does transposition occur?

A

Between plasmids and chromosomes.
Within chromosomes.
Between bacteria via plasmids.

54
Q

Describe the structure of transposons.

A

They have palindromic sequences at both ends.

55
Q

Describe the structure of a simple transposon.

A

2 transposons and a transposes enzyme.

56
Q

What are jumping transposons?

A

Move around within a DNA molecules

57
Q

What are replicating transposons

A

Replicate whilst moving aroids transposons and can move onto plasmids.

58
Q

What are complex transposons used for?

A

To transport genes which are not connected with transposition.

59
Q

Give an example of a gene transferred by complex transposons.

A

Antibiotic resistance genes.

60
Q

How can the success of conjugation be assessed?

A

By determining how many recombinants are generated.

61
Q

If a cell is sensitive to streptomycin, will it grow in the presence of streptomycin?

A

No

62
Q

If a cell is resistant to streptomycin, will it grow in the presence of streptomycin?

A

Yes

63
Q

What is meant by minimal media or minimal agar?

A

The minimum media needed for colony growth without the presence of amino acids or with very few amino acids.

64
Q

Are Leucine and Tyrosine present in minimal agar?

A

No

65
Q

When doing conjugation experiment calculations, why don’t you count the number recombinant cells.

A

Recipient and donor cells are heavily in excess so the number of recipients is negligable.

66
Q

How is the total cell count (cfu/ml) calculated?

A

(Mean cell count x Inverse dilution) / volume of plate.

67
Q

How is the success of a transformation experiment calculated?

A

Through the number of transformants formed.

68
Q

Describe the sensitivity of competent cells to E.coli antibiotics

A

Sensitive

Microbial World (10 decks)

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