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Questions from microbiology

1. Describe how DNA serves as genetic information.
2. Describe the process of DNA replication.
3. Describe protein synthesis, including transcription, RNA processing, and translation.
4. Explain the regulation of gene expression in bacteria by induction, repression, feedback inhibition, and catabolic
repression, using the lac operon as an example.
5. Compare the mechanisms of genetic recombination in bacteria.
6. Define transduction, transformation, conjugation, competence
7. Describe the functions of plasmids and transposons.
8. Discuss how genetic mutation and recombination provide material for natural selection to act on.
9. Define gene, RNA polymerase
10. Compare selection and mutation.

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1.Describe how DNA serves as genetic information.

Genetic material is used to store the genetic information of an organic life form. For all currently known living organisms, the genetic material is almost exclusively Deoxyribonucleic Acid (DNA).

DNA serves as genetic information for all the prokaryotes as well as eukaryotes sparing some of the RNA viruses and prions. DNA is made of bases A, T, G, and C which make up a particular base sequence. Genes are located on DNA and these genes code for polypeptides, rRNA and tRNA. Genes on DNA are first transcribed to mRNA which are further translated into proteins. The nucleotide sequence of DNA guides the synthesis of RNA and protein. Thus, it is the DNA level that carries the genetic information from generation to generation, not the proteins.
F. Crick proposed that all biological information is encoded in DNA, transmitted by DNA replication, transcribed into RNA, and translated into protein. This role for DNA is called the Central dogma of molecular biology.
Earlier it was thought that proteins carry the genetic information. DNA as a genetic material was studied by earlier scientists. In 1928, Griffith experimented with virulence in Pneumococcus. He determined that nonvirulent strains (rough-strain) could be transformed (genetically changed) to virulent (smooth) strains if the remains of dead virulent bacteria were made available to the living nonvirulent bacteria. Griffith called the genetic information which could be passed from one bacteria to another the "transforming principle."
In 1944, Avery et. al. showed that the transforming material was pure DNA not protein, lipid or carbohydrate. How is it possible for the rough-strain pneumococcus bacteria to transform itself into a virulent form?
Finally, in 1952, Alfred Hershey and Martha Chase performed the definitive experiment that showed that DNA was, in fact, the genetic material. This was done by bacteriophage infection by radiolabelling sulfur for detecting proteins and phosphorus for tracing DNA. By radiolabelling sulphur in one culture, they could tag the path of proteins and not DNA, because there is no sulphur in DNA and there is sulphur in the amino acids methionine and cysteine. By radiolabelling phosphorous, the opposite effect could be achieved. DNA could be traced and not protein, because there is phosphorous in the phosphate backbone of DNA and none in any of the amino acids.

2.Describe the process of DNA replication.

The replication of DNA is an important and complex process, one upon which life depends.

Replication is the preparation of DNA copies prior to reproduction of the cell or organism. DNA is replicated by semiconservative (half conserved) mode of replication where each strand serves as a template for DNA synthesis.

Enzymes and proteins involved in DNA replication:
1.DNA helicase: unwinds DNA in front of opening replication fork (otherwise DNA would quickly tangle). Uses ATP, makes single-stranded cut, allows one strand to swivel freely around the other.
2.Single-stranded DNA binding proteins: bind to separated DNA strands, prevent from base-pairing back together
3.RNA primase: DNA polymerase III cannot start a growing chain from scratch; needs a short primer (a few nucleotides) to add to. This is carried out by DNA-dependent RNA primase, makes very short piece of RNA by base-pairing RNA nucleotides with template DNA.
4.DNA polymerase : adds new nucleotides at free 3'ends of growing chain, uses base-pairing rules to insert complementary nucleotides (A opposite T, G opposite C, etc.) Can keep on adding indefinitely for millions of nucleotides if not blockage. Also removes RNA primers, fills in gaps by base pairing, inserts new DNA nucleotides to replace RNA primer. (several types of this enzyme)
5.DNA ligase: seals any gaps where adjacent nucleotides on one strand have not been covalently joined.
6.Telomerase: adds specific DNA sequence repeats ("TTAGGG" in all vertebrates) to the 3' ("three prime") end of DNA strands in the telomere regions present in eukaryotic DNA.
DNA replication begins with a partial unwinding of the double helix at an area known as the replication fork. An enzyme known as DNA helicase accomplishes this unwinding. This unwound section appears under electron microscopes as a "bubble" and is thus known as a replication bubble.
As the two DNA strands separate ("unzips") and the bases are exposed, the enzyme DNA Polymerase moves into position at the point where synthesis will begin.
The start point for DNA polymerase is a short segment of RNA known as an RNA primer. The very term "primer" is indicative of its role that is to "prime" or start DNA synthesis at certain points. The primer is "laid down" complementary to the DNA template by an enzyme known as RNA Polymerase or Primase.
The DNA polymerase (once it has reached its starting point as indicated ...

Solution Summary

Genetic material is used to store the genetic information of an organic life form. For all currently known living organisms, the genetic material is almost exclusively Deoxyribonucleic Acid (DNA). F. Crick proposed that all biological information is encoded in DNA, transmitted by DNA replication, transcribed into RNA, and translated into protein. Natural selection acts upon two major sources of genetic variation: mutations and recombination of genes through sexual reproduction.

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