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Archive for October, 2007

The Saint Louis University School of Medicine researchers have announced a major finding that could lead to development of better therapies for one of the most common neurological disorders, Parkinson’s disease.

Dopamine is required for smooth and coordinated function of the body’s muscles and movements. Parkinson’s disease occurs when dopamine producing nerve cells of substantia nigra region of the brain die or become impaired. The symptoms of the disease develop after more than 80% of these dopamine-producing cells die or are damaged.

The breakthrough came when the scientists found that during Parkinson’s disease development process dopamine is converted into a highly toxic chemical called DOPAL. This chemical, DOPAL, causes the clumping of alpha-synuclein protein in the brain. This triggers the death of dopamine-producing cells, ultimately leading to Parkinson’s. Read the full story here.

via: ScienceDaily


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As mentioned earlier, DNA pol III is the enzyme which carries out the replication of large E. coli chromosome. DNA pol I, because of the following properties, does not qualify as the enzyme for E. coli chromosome replication:

1) The polymerization rate (nucleotides added/sec) of this enzyme is 16-20 nucleotides/sec or approximately 600 nucleotides/min, which is too slow. It is slow by a factor of 100 or more to account for the rate at which the replication fork moves during bacterial chromosome replication.

2) DNA pol I has a very low processivity, 3-200 nucleotides added before polymerase dissociates.

3) A bacterial strain, isolated in 1969 by John Cairns, had a mutant DNA pol I gene, which produced the inactive enzyme. But, surprisingly this bacterial strain was viable. This clearly shows that even in the absence of active DNA pol I, E. coli can survive and replicate its chromosome. It means there is another DNA polymerase present to perform the function of DNA replication.


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The Toyota RIN was unveiled at the Tokyo Motor Show with the motto of providing the healthy driving. The car is truly an amazing piece of engineering with ergonomic seats, oxygen-level conditioner, a humidifier, color-changing steering wheel controls, and as the full story here says “it’s compact and green! Literally and figuratively…”.

via: Inhabitat


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A recent finding published in the journal Nature Chemical Biology reports the synthesis of a carbohydrate-based vaccine for cancer. The study carried out in mice demonstrated that the vaccine triggers a strong immune response to cancer cells. The vaccine has been created synthetically and has shown promising results in creating an antibody response that can kill cultured epithelial cells derived from mice. The results are highly encouraging and “astounding”. However, Geert-Jan Boons, Franklin professor of chemistry and the lead author cautions, “There’s a very big step going from mice to humans,”. Read the full story here.

via: Physorg


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DNA pol I: It is a single subunit enzyme with a mol wt of 103,000. It has 3’→5′ exonuclease proofreading activity. The polymerization rate, i.e. nucleotides added per second to a growing DNA molecule, is 16-20. The processivity of DNA pol I is 3-200. Processivity is the number of nucleotides before polymerase dissociates from the nucleic acid. DNA pol I has 5’→3′ exonuclease activity, not found in DNA pol II or DNA pol III.

DNA pol II: The enzyme is composed of more than 4 subunits. It has 3’→5′ exonuclease proofreading activity. The polymerization rate is 40 and processivity is 1500.

DNA pol III: The enzyme is composed of more than 10 subunits. It has 3’→5′ exonuclease proofreading activity. The polymerization rate is 25-1000 and processivity is more than 500,000.


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DNA Polymerases

The enzyme required for DNA replication is DNA polymerase. All living organisms which have DNA as their genetic material require DNA polymerase enzyme.

We will begin our discussion of DNA polymerases with the E. coli enzymes. This prokaryote has 5 different kinds of DNA polymerase: DNA pol I, DNA pol II, DNA pol III, DNA pol IV and DNA pol V. It is DNA pol I, which was discovered by A. Kornberg and also named Kornberg Enzyme. However, DNA pol I is not suited for replication of large E. coli chromosome. The reasons for this would be discussed in a later post. In the early 1970s, DNA pol II and DNA pol III were discovered. DNA pol IV and DNA pol V were discovered much later, in 1999. DNA pol III is the principal replication enzyme in E. coli. DNA pol II is involved in DNA repair. DNA polymerases IV and V are also involved in a special form of DNA repair. “DNA pol I performs a host of clean-up functions during replication, repair and recombination” (Lehninger Principles of Biochemistry, Nelson and Cox, 3rd edition). It is not the primary enzyme of replication in the prokaryote.


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This post is a tribute to Arthur Kornberg. He died of respiratory failure on Friday in Stanford, California at the age of 89. He discovered the enzyme DNA polymerase, which replicates the DNA molecule. The search for an enzyme that could synthesize DNA started in 1955, which finally culminated in 1959 with a Nobel Prize to Arthur Kornberg in medicine. He and his co-workers purified and characterized DNA polymerase from E. coli. The enzyme they purified is named DNA polymerase I. Four other DNA ploymerases are found in E. coli. The enzyme has also been named Kornberg Enzyme in honour of the scientist. The enzyme is made of a single polypeptide and has a mol wt of 103,000. Read the full story here.


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