Viruses and Bacteria

1
Viruses and Bacteria
2
VIRUSES

• Virus- very small, acellular, consist of a capsid
  (a protein coat), and nucleic acid, either DNA or
  RNA. They are obligate intercellular parasites
  because they only reproduce when in a host cell.
  
• A virus that infects bacteria is called a
  bacteriophage

3
How Viruses Reproduce

• A virus has specific hosts. It recognizes the
  host with proteins on the capsid that bond
  receptor proteins on the host cell membrane.
• The virus inserts its DNA or RNA into the host.
  The virus then goes into 1 of 2 reproductive
  cycles.
• Lytic cycle- A virus that only reproduces this
  way is called virulent (disease causing). The
  virus uses the hosts enzymes to begin producing
  new virus DNA/RNA and proteins. One of the first
  proteins made are used to shut down the hosts
  own metabolic activities. Late proteins make new
  capsids the new viruses assemble and lytic
  proteins are used to lyse the cell releasing many
  new viruses.
• Lysogenic cycle- viruses that are in the
  lysogenic cycle are called temperate viruses.
  The virus DNA/RNA is incorporated into the host
  cells DNA and copied in the process of the host
  cells cycle. When conditions are favorable for
  the virus the virus will enter the lytic cycle

4
The Lytic Cycle
5
The Lysogenic Cycle
6
Viral Envelopes
7
RetroViruses

• Retroviruses like HIV have RNA instead of DNA.
• They use an enzyme called reverse transcriptase
  to make a copy of DNA to insert into the host
  cells genome.

8
More About Viruses
Vectors- animals infected with a virus, but not
harmed by it and will transmit it to those it
will harm. EX. West Nile Virus. Vaccines- some
animal viruses have been prevented with the use
of a vaccine. This is when dead or weakened
virus in injected so the body mounts an immune
response producing antibodies. Ex. Polio,
rubella, small pox. Viruses and cancer- some
viruses have been associated with cancer.
Oncagenes are inserted with the viral genome
altering the host genome. EX. Human paploma
virus (HPV). Viral medications- repress a
viruses ability to reproduce, but do not get rid
of the virus. EX. Protease inhibitors are given
to HIV patients. Protease is an enzyme that
cuts polypeptide chains, and HIV proteins cant
fold properly unless they are cut, so if protease
is inhibited HIV is inhibited.
9
Bacteria

• Bacteria- usually reproduce asexually, but do
  have ways to recombine their DNA to allow for
  genetic diversity. Most of a bacteria genome is
  on one large piece of circular DNA, but they also
  have smaller circular pieces of DNA called
  plasmids. Plasmids are responsible for
  antibiotic resistance, conjugation, and some
  metabolic factors.

10
Sex and Bacteria

• Conjugation- 2 bacteria cells are connected by
  thin tubes called pili. DNA is cut and made
  linear, and is passed from the donor bacteria to
  the recipient bacteria. Contact if very brief,
  so very little DNA is passed and it is usually a
  plasmid.

11
Changed Bacteria

• Transformation- A living bacterial cell picks up
  and incorporates DNA from a lysed bacteria.

12

• Transduction- pieces of viral DNA is incorporated
  with bacterial DNA and that DNA can be carried to
  the next bacteria infected

13
How Bacteria Regulate Protein Production

• The Lac-Operon
• Operator-repressor control- seen in the lac
  operon in e-coli. E-coli prefers to use glucose
  as a fuel source. In the absence of glucose
  e-coli will use carbohydrates such as lactose,
  but it needs an enzyme to digest it. When there
  is abundant glucose, the bacteria wont make the
  enzymes necessary to digest lactose.
• Right before the code for the enzyme is an
  operator that can bind tightly to a repressor
  protein. The whole unit of operator and code for
  the enzyme is called an operon

14
(No Transcript)
15
The Repressor Protein

• The repressor protein has 2 binding sites. When
  glucose is abundant the repressor protein binds
  to the operator region inhibiting the lactose
  enzymes from being made by inhibiting mRNA
  synthesis. When lactose is abundant the
  repressor binds to the lactose allowing mRNA to
  be made for the enzymes necessary to digest.

16
(No Transcript)
17
cAMP

• Increasing promoter efficiency- a protein
  called CRP (cAMP receptor protein) binds the
  compound, adenosine 3?5?-cyclic monophosphate or
  cAMP, and this complex binds to the DNA just
  ahead of the promoter. This increases the
  efficiency of RNA polymerase in the production of
  mRNA.