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Chapter 18 Viruses
part of test 3
20
Biology
Undergraduate 2
03/08/2013

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Term
Genetics of bacteria and viruses
Definition
  • genes of bacteria are ofund in bacterial chromosomes
  • usually a single type of chromosome
  • may have more than 1 copy of that chromosome
  • # of copies depends on the bacterial species and on growth conditions
  • typicall 1-4 identical chromosomes
Term

Bacterial Chromosomes

 

Definition
  • molecules of double-stranded DNA
  • usually circular
  • tend to be shorter
  • contains a few thousand unique genes
  • mostly structual genes
  • single orgin of replication
Term
Compaction
Definition
  • typical bacterial chromosome must be compacted about 1,000-fold
Term
why does bacterial DNA need to be compacted?
Definition
  • bacterial DNA is not wound around histone proteins to form nucleosomes
  • proteins important in forming loop domains (compacts DNA about 10-fold)
  • DNA supercoiling (topoisomerases twist the DNA and control degree of supercoiling)
Term

what are some characteristics Plasmids?

 

Definition
  • small, circular pieces of DNA that exist independently of bacterial chromosome
  • occur naturally in many strains of bacteria and in a types of eukaryoic cells, such as yeast
  • own orgin of replication that allows it to be replicated independently of the bacterial chromosome
  • not usually necessary for survival but can provide growth advantages
Term
what is an episome?
Definition
plasmid that can integrate into bacterial chromosome
Term
what are the 5 types of plasmids?
Definition
  1. Resistance plasmids (R factors)
  2. Degradative plasmids
  3. Col-plasmids
  4. Virulence plasmids
  5. Fertility plasmids (F factors)

 

Term
How would you describe Resistance plasmids (R factors)?
Definition
they contain genes that confer resistance against antibodies and other types of toxins
Term
what are degradative plasmids?
Definition
plasmids that carry genes that enable the bacterium to digest and utilize an unusual substance
Term

what are Virulence plasmids?

 

Definition
plasmids that carry genes tha turn a bacterium into a pathogenic strain
Term
what is the role of fertility plasmids?
Definition
they allow bacteria to mate with each other.
Term
How can reproduction be described?
Definition
  • cells of some species, such as E.coli, can divide every 20-30 minutes
  • single cell can form a bacterial colony in less than a day
  • reproduction by binary fission, execpt when mutation occurs then each daughter cell contains an identical copy of the mother cell's genetic material
  • plasmids may replicate indenpendently of the bacterial chromosome
  • does not involve genetic contributions from 2 different parents
Term
what happens in reproduction what a mutation occurs?
Definition
binary fission does not go through but instead each daughter cell contains an identical copy of the mother cell's genetic material
Term

how can you explain genetic diversity?

 

Definition
mutations that occur that after the bacterial genome and affect the traits of bacterial cells
Term
what is genetic transfer?
Definition
genetic material is transferred from one bacterial cell to another
Term
what is conjugation?
Definition
direct physical interaction transfers genetic material from donor to recipient cell
Term
what happens in conjugation?
Definition
  • transformation
  • DNA released from a dead bacterium into the environment is take up by another bacteria
  • a virus transfers genetic information from one bacterium to another
Term
what did Lederberg and Tatum do?
Definition
  • they demonstrated genetic transfer between bacteria and led to the discovery of conjugation with E.coli
  •  studied strains of E.coli that had different nutritional requirements for growth, which corresponds to alleic differences between the strain
Term
what were conclusions of Lederberg and Tatum working with E.coli?
Definition
  • when 2 strains were mixed, found new genotypes,not mutation.
  • without physical contact, genetic material could not be transferred.

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