Viruses and DNA Technology

Viruses and Bacteria are the simplest biological systems.
They are the microbial models where scientists find life's fundamental molecular mechanisms in their most basic state.
Microbiologists have provided evidence that the henes are made of DNA and have worked out most of the major steps in DNA replication, transcription, and translation.
Viruses and Bacteria have unique genetic features that help us understand the diseases that they cause.


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Viruses are small and simple cells.
Most are a little more than aggregates of the nucleic acids and protein genes in a protein coat.
Viruses are not cells.
They are infection particles that are made up of nucleic acid and are enclosed in a protein coat, and sometimes they are surrounded by a membranous coat.
They range in size from 20nm in diameter, to just barely being resolvable with a light microscope.
Their genome includes double-stranded DNA, single-stranded DNA, double-stranded RNA, or single strand RNA, depending on the type of virus.
Capsid- A protein shell that encloses the viral genome. They are built up of protein subunits called capsomeres.
Viral Envelopes- Contained by some viruses; membranes that cloak their capsids. They are derivied from the membrane of the host cell.
Viruses are obligate intracellular parasites.
They are able to reproduce within a host cell.
They lack the enzymes needed for metabolism, and the ribosomes required for protein synthesis.
Host Range- The limited number of host that a virus can infect and paratize.
Although some viruses have a wide enough to infect multiple species, while others can only infect a single species.
The viral infection begins when the virus is able to enter the host cell. After it gets inside, the virus begins to reprogram the cell to copy the viral nucleic acid and manufacture proteins from the viral genome.


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Bacteria are prokaryotic organisms.
They have cells that are muchc smaller and more simply organized than eukaryotes.
Bacteria are very adaptable.
The major component of thebacterial genome is one double-stranded, circular DNA molecule.
They are able to divide due to binary fission.
This is protectedby replication of the bacterial chromosome from a single origin of repication.

Lytic Cycle- The phage reproductive cycle that culminates the death of the host cell.external image lytic%20vs%20lysogenic.gif
The bacterium lyses breaks open and releases the phages produced in the cell to infect others in the last stage of the cycle.
Lysogenic Cycle- The phage genome is able to replicate without destroying the host cell.
Everytime the host cell divides, the viral DNA is copied and is passed on to the daughter cells.
Occasionally the viral genome exits the bacterial chromosome and initiates the lytic cycle. This switch can be initiated by an environmental trigger.
Vaccines can help to prevent the viral infection, but are not insured to cure the infection once it occurs.
Antibiotics that can kill the bacteria by inhibiting enzymes or processes are powerless against the viruses.
Some of the recently developed drugs can combat some viruses, mainly by the interference of the viral nucleic acid synthesis.
The emergance of these new viral diseases is due to three processes:
  1. Mutation: a major source of new viral diseases. The RNA viruses tend to have high mutation rates because thre replication of their nucleic acid lacks proofreading. This is the case in Flu epidemics.
  2. Spread of exiting viruses from one species to another: Estimated that 3/4 of the new human diseases have oringinated in other animals.
  3. Disease spread from small, isolated population: AIDS disease was unknown to the world for decades before being spread around the world.

Along with mutations, genetic recombination makes more diversity within the bateria population.
Recombination- The combining of DNA from two individuals into a single genome.

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Occurs in three processes:
  1. Transformation: the alteration of a bacterial cell's genotype by the uptake of foreign DNA from surrounding environment.
  2. Transduction: Occurs when a faulty page carries bateria genes from one host cell to another.
  3. Conjunction: Transfers genetic material between two bacterial ells that are temporarily joined

When a bateria is exposed to an antibiotic, all individuals with the R plasmid will survive and increase in the overall population.

Gel Electrophoresis

Seperates macromolecules on the bases od their rate of movement through a gel in an electromagnetic field.
The rate of movement depends on size, electrical charge and pther physical properties of the macromolecules.
For the linear molecules, the seperation depends o the size with longer fragments moving less along the gel.

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DNA technology can help solve many violent crimes by using blood, semen, or all other traces that may be left at the scene of the crime.
Although this can help, it only excludes suspects.