DNA polymerase III

DNA pol III is the principal replication enzyme of E. coli. The enzyme is highly complex and has more than 10 types of subunits. These subunits are α, ε, θ, τ, δ, δ’, β, χ, ψ, γ. The α, ε and θ subunits combine to form the core polymerase. The core polymerase has a limited [...]

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Why DNA pol I is not suited to replicate E. coli chromosome?

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 [...]

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DNA polymerases of E. coli

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 [...]

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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 [...]

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H-DNA

Today I would be writing about a very unusual form of DNA, that is, H-DNA.
The H-DNA is a triple helix. This particularly unusual form of DNA is found in vitro or possibly during recombination and DNA repair. It forms by pairing and interwinding of 3 strands of DNA. Two of the three strands contain pyrimidines [...]

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Z-DNA

Z-DNA was discovered in vitro under high salt conditions. It is know to exist in the interband regions of the giant salivary gland chromosomes of Drosophila and in the transcriptionally active macronucleus of the ciliated protozoan Stylonchia mytilus. The properties of Z-form DNA are listed below:
1) It is a left-handed helix and the helical diameter [...]

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A-form DNA

The A-DNA is favoured in many solutions that are relatively of water. The properties of A-DNA are:
1) Right-handed helix
2) Helix rise per base pair is 0.23 nm
3) The number of base pairs per helical turn is 11.
4) A-form DNA is shorter and has a greater helical diameter than the B-DNA. The helical diameter of A-DNA [...]

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DNA forms: A, B, Z, H

One of the properties of the DNA is that it shows confirmational flexibility, and could exist in alternative structural forms. The Watson-Crick structure is the B-form DNA, or B-DNA. The B from is the most stable structure for a random sequence DNA molecule under physiological conditions and is therefore “the standard point of reference in [...]

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DNA structure

The double helical model of DNA structure was given by Watson and Crick.
DNA molecule is helical with two periodicities along its long axis, a primary one of 0.34 nm and a secondary one of 3.4 nm. The most predominant form of DNA present in the cell is B-form. It is a right-handed double helix and [...]

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DNA: Its properties

Some of the properties of the DNA are listed below:
1) Double helical
2) Acidic in nature
3) Shows antiparallelity
4) Shows confirmational flexibility (alternative structures) and bending
5) Binds with basic histone proteins
6) Absorbs UV light at 260 nm (heterocyclic rings of nucleotides absorb in the UV region)
7) Undergoes reversible strand separation; many DNA molecules are circular; local unwinding [...]

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