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Microbial Genetics II
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9
Microbiology
Professional
07/19/2011

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Term

 

 

 

Processes Leading to Mutagenesis

Definition

 

  • Removal of an incorrectly inserted base is prevented.
  • Tautomerization – an inserted base changes its base pairing   properties
  • Base is altered and has a new base pairing property.
  • A base is skipped during replication.
  • MUTAGENS INCREASE THE RATE OF MUTAGENESIS
Term

 

 

 

Classes of Mutagens

Definition
  • Chemicals -
  • Base analogs
  • Intercalating Agents
  • Chemicals that react with DNA like alkylating agents

  • Physical -
  • Radiation including UV usually causing thymine dimers to form
  • Most Carcinogens are mutagenic.  
Term

 

 

 

DNA Repair Mechanisms 

Definition
  • Direct DNA repair is the direct enzymatic removal of dimers.
  • Excision repair is the excision of a DNA segment containing the damaged DNA followed by synthesis of a new strand. Bacteria and people can do this as evidenced by the affect of mutations.
  • Recombination or postreplication repair is the retrieval of missing information by genetic recombination when both strands are damaged.
  • The SOS response is the induction of many genes after DNA damage or interruption of DNA replication.
  • Error-prone repair is the last resort before it dies. 
Term

 

 

 

Plasmids

Definition
Used for cloning specific DNA fragments

Circular independent pieces of dsDNA

Replicate autonomously via origin of replication

Can integrate into chromosome
Term

 

 

 

Classification of Plasmids

Definition
  • Over 1,000 different plasmids
  • Two Main Groups: Large plasmids that are self-transmissible and small plasmids that nonconjugative.
  • Copy number per cell varies
  • Plasmids can produce different sex pili
  • Plasmids can be in the same incompatability group  
Term

 

 

 

Phenotypic Effects of Plasmids

 

Definition
  • Code for bacterial toxins
  • Code for enzymes that metabolize unusual substrates
  • Code for antibiotic resistance (The R plasmids)     
  1.      R plasmids have two parts: resistance transfer  factor (RTF) and the R determinant that encodes resistance to antibiotics
  • The F plasmid can integrate into the bacterial chromosome to form an Hfr strain.
Term

 

 

 

Conjugation 

Definition
  • Most frequent form of gene transfer and occurs between many different bacterial species.
  • Involves cell-cell contact and the presence of a sex pili.
  • F-plasmid is conjugative and encodes the conjugation apparatus that includes pili and tra genes. This plasmid can integrate into the chromosome to form Hfr strains.
  • Some non-conjugative plasmids can be transferred along with the conjugative plasmid
Term

 

 

 

R Plasmids

 

Definition
  • R plasmids can encode resistance to multiple antibiotics. These resistance cassettes can be acquired from the bacterial chromosome by transposition.
  • They can be transferred rapidly by conjugation.
  • Inappropriate use of antibiotics has led to an increase in antibiotic resistant bacteria.
  • R plasmids are unstable and can be rapidly lost if the selection pressure is lessened.
  • R plasmids have a resistance transfer region (RTF) and a resistance determinant (r-determinant).
Term

 

 

 

Why Clone DNA?

Definition
To produce a purified protein

To obtain a fragment of DNA to use as a probe

To obtain DNA for mutagenesis studies

To sequence DNA
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