Microbial Genetics Flashcards

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1
Q

In E. coli, the DNA is twisted by what enzyme?

A

Topoisomerase II or DNA gyrase

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2
Q

Define the process of DNA replication

A
  1. Two strands of parental DNA are unwound and separated from each other in one small DNA segment after another
  2. Free nucleotides are matched up to the exposed bases of the single-stranded parental DNA
  3. Then the parental DNA is unwound a bit further to allow the addition of the next nucleotides
  4. The original strand and the newly synthesized daughter strand rewind
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3
Q

What is the point at which replication occurs called?

A

Replication fork

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4
Q

Why is DNA replication called semiconservative replication?

A

Because each new double-stranded DNA molecule contains one original, conserved strand and one new strand

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5
Q

What enzyme is involved in the process of adding new nucleotide to the growing DNA strand?

A

DNA polymerase, which can add new nucleotides to the 3’ end only (5’ –> 3’ direction)

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6
Q

Function of RNA Primer

A

RNA primer is needed to start synthesis. DNA polymerase can then add nucleotides to the 3’ end of the RNA.

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7
Q

What is leading strand? What is lagging strand?

A
  1. Leading strand: the DNA stand that is continuously synthesized
  2. Lagging strand: since DNA polymerase can only add nucleotides to the 3’ end, one new DNA must be synthesized in pieces consisting Okazaki fragments.
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8
Q

What is transcription?

A

The synthesis of a complementary strand of RNA from a DNA template

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9
Q

Explain the transcription process

A
  1. RNA polymerase binds to the DNA promoter
  2. RNA ploymerase assembles free nucleotides into a new chain
  3. RNA synthesis continues until RNA polymerase reaches DNA terminator
  4. Single-stranded mRNA are released from the DNA
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10
Q

Explain the transcription process

A
  1. RNA polymerase binds to the DNA promoter
  2. RNA ploymerase assembles free nucleotides into a new chain
  3. RNA synthesis continues until RNA polymerase reaches DNA terminator
  4. Single-stranded mRNA are released from the DNA (and transported to ribosomal RNA)
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11
Q

There are 64 possible codons but only 20 AAs, what is this situation called? Why is it important?

A
  1. It’s called degeneracy of the code
  2. Degeneracy allows for a certain amount of change, or mutation in the DNA w/o affecting the protein ultimately produced
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12
Q

List the 3 nonsense or stop codons

A

UAA
UAG
UGA

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13
Q

List the start codon. What AA does it code for?

A

AUG

Methionine – the initiating methionine is often removed later, so not all proteins begin with Met.

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14
Q

Explain the translation process

A
  1. mRNA is transported to the Ribosome; a tRNA carrying the first AA is paired w/ the start codon on mRNA
    - - The place on the ribosome where the first tRNA sits is called the P site
  2. A tRNA carrying the 2nd AA approaches (at A site of the Ribosome)
  3. The ribosome moves along the mRNA until the wnd tRNA is in the P site, and the process continues
  4. When the ribosome reaches a Stop codon, the polypeptide is released
  5. Finally, the last tRNA is released, and the ribosome comes apart
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15
Q

Why can’t the RNA transcrip by used for translation in Euk. cells?

A
  1. Euk. genes are composed of Exons and Introns, which are transcribed to RNA by RNA polymerase
    - - Exons: The regions of DNA which can be expressed
    - - Introns: The intervening regions of DNA that do not encode protein
  2. The long RNA transcript must be processed by ribozymes to remove the intron-derived RNA and splice together the exon-derived RNA, producing an mRNA
  3. The mature mRNA then travels to the cytoplasm, where it is used by rRNA to direct protein synthesis
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16
Q

Simply describe the transcription and translation process

A
  1. DNA is transcribed into mRNA
  2. mRNA attaches to ribosomes
  3. rRNA delivers the AAs to the ribosome
  4. The ribosome assembles the AAs into polypeptide chains
17
Q

What is a repressor?

A
  1. A repressor is a regulatory protein which mediates regulatory mechanism that inhibits gene expression so to decrease the synthesis of enzymes
  2. Repressors block the ability of RNA polymerase to initiate transcription from the repressed genes
    - - Repressors locate after the Promoter
18
Q

How is the repressedn gene induced to start transcription?

A
  1. An inducer binds to the repressor protein and alters it so it can’t bind to the operator site
  2. In the absence of an operator-bound repressor protein, RNA polymerase can transcribe the structural genes into mRNA, which is then translated into proteins
19
Q

Base substituation mutation: missense mutation, nonsense mutatuon
Frameshift mutation:

A
  1. Base substituation: a single base at one point in the DNA sequence is replaced w/ a dif. base
  2. Frameshift mutation: one or a few nucleotide pairs are deleted or inserted in the DNA
20
Q

Base substituation mutation: missense mutation, nonsense mutation
Frameshift mutation:

A
  1. Base substituation: a single base at one point in the DNA sequence is replaced w/ a dif. base
    a. Missense mutation: incorrect AA is inserted to the protein
    b. Nonsense mutation: a stop codon is created in the middle os an mRNA molecule, preventing synthesis of a complete functional protein
  2. Frameshift mutation: one or a few nucleotide pairs are deleted or inserted in the DNA
21
Q

UV induced DNA mutation

A

Adjacent Thymines in a DNA strand can cross-link to form thymine dimers.
– Such dimers unless repaired, may cause serious damage or death to the cell b/c it can’t properly transcribe or replicate such DNA

22
Q

Genetic transduction

A
  1. In the proces of infection, the phage attaches to the donor bacterial cell wall and injects ins DNA into the bacterium
  2. The phage DNA acts as a template for the synthesis of new phage DNA and also directs the synthesis of phage protein cots. During phage development inside the infected cell, the bacterial chromosome is broken apart by phage enzymes and,
  3. At least some pieces of bacterial DNA are mistakenly packaged inside phage protein coats. The resulting phage particles then carry bacterial DNA instead of phage DNA
  4. When the released phage particles later infect a new population of bacteria, bacterial genes will be transferred to the newly infected recipient cells at low frequency
  5. Transduction of cellular DNA by a virus can lead to recombination b/w the DNA of the donor host cell and the DNA of the recipient host cell.