1) Type II DNA topoisomerases play an important role in DNA transactions by allowing the passage of one DNA strand through another, but these passages can sometimes lead to the formation of knots that impede processes like transcription and replication.
2) Previous studies showed that type IIA DNA topoisomerases can reduce knot formation on relaxed DNA in vitro, but this ability decreases with increasing DNA length.
3) The authors propose that on supercoiled DNA, knots adopt a tighter form that increases their curvature compared to other DNA regions. This allows type IIA topoisomerases to preferentially bind and act on knotted regions due to their affinity for bent DNA, providing an efficient means of recognizing and
This Presentation will be helpful to undergraduate and postgraduate students of biology and biotechnology in understanding the significance of COT curves in determination of gene and genome complexity amoug various organisms
This Presentation will be helpful to undergraduate and postgraduate students of biology and biotechnology in understanding the significance of COT curves in determination of gene and genome complexity amoug various organisms
These slides give you detailed information about Recombinant DNA Technology in simple words. Do read it, these points will help you while studying this topic.
Study of cloning vectors and recombinant dna technologySteffi Thomas
Study of cloning vectors, restriction endonuclease and DNA ligase, Recombinant DNA technology, Application of genetic engineering in medicine, Application of rDNA technology and genetic engineering in the production of interferons, Vaccines-hepatitis-B, Hormones-Insulin, Brief introduction to PCR
DNA replication is the most important process central dogma in the molecular genetics. So i hope this power point presentation useful to the students of B.Sc Agriculture and M.Sc Genetics and Plant Breeding.
These slides give you detailed information about Recombinant DNA Technology in simple words. Do read it, these points will help you while studying this topic.
Study of cloning vectors and recombinant dna technologySteffi Thomas
Study of cloning vectors, restriction endonuclease and DNA ligase, Recombinant DNA technology, Application of genetic engineering in medicine, Application of rDNA technology and genetic engineering in the production of interferons, Vaccines-hepatitis-B, Hormones-Insulin, Brief introduction to PCR
DNA replication is the most important process central dogma in the molecular genetics. So i hope this power point presentation useful to the students of B.Sc Agriculture and M.Sc Genetics and Plant Breeding.
this file includes the packaging of DNA in Prokaryotic and Eukaryotic cell, the difference between DNA and RNA, Semi-conservative mode of DNA replication, and the mechanism of DNA replication.
Dna supercoiling and role of topoisomerasesYashwanth B S
supercoiling is one of the important process to condenses the huge amount of DNA to fit inside the histone and its also plays a role during the replication ,transcription etc..,these activities is carried out by an enzyme called topoisomerases.
1) Phosphodiester bonds in DNA are advantageous because they are m.pdfanujmkt
1)
Phosphodiester bonds in DNA are advantageous because they are more stable chemically when
compared with ester bonds. This stability is rendered because of the negative charge present on a
phosphodiester bond. This charge repels similarly charged ions like OH- ions which have the
ability to carry out a nucleophilic hydrolysis reaction and hence break the bond. Hence such
hydrolysis cannot occur in a phosphodiester bond and it is more stable.
2)
The semi-conservative nature of DNA replication means that during DNA replication, each
daughter DNA has one strand inherited from the parent as it is and the other strand of the double
helix is newly synthesised. This was initially proved by Meselson and Stahl in 1958.
The experiment can be described in the following steps:
These results confirmed the hypothesis made by the 2 scientists as the initial band of heavy DNA
indicated all the DNA of same kind. The intermediate band in second generation indicated that
half the DNA was original (with heavy isotope) and the other half was with normal N. And then
the increase in band-width of normal N containing cells indicated that all new cells now
manufactured their DNA from medium having normal N source.
3)
Topoisomers are DNA molecules with same chemical structure but different topology i.e. they
have different geometrical properties and spatial relations. There are two major Topoisomers of
DNA:
Solution
1)
Phosphodiester bonds in DNA are advantageous because they are more stable chemically when
compared with ester bonds. This stability is rendered because of the negative charge present on a
phosphodiester bond. This charge repels similarly charged ions like OH- ions which have the
ability to carry out a nucleophilic hydrolysis reaction and hence break the bond. Hence such
hydrolysis cannot occur in a phosphodiester bond and it is more stable.
2)
The semi-conservative nature of DNA replication means that during DNA replication, each
daughter DNA has one strand inherited from the parent as it is and the other strand of the double
helix is newly synthesised. This was initially proved by Meselson and Stahl in 1958.
The experiment can be described in the following steps:
These results confirmed the hypothesis made by the 2 scientists as the initial band of heavy DNA
indicated all the DNA of same kind. The intermediate band in second generation indicated that
half the DNA was original (with heavy isotope) and the other half was with normal N. And then
the increase in band-width of normal N containing cells indicated that all new cells now
manufactured their DNA from medium having normal N source.
3)
Topoisomers are DNA molecules with same chemical structure but different topology i.e. they
have different geometrical properties and spatial relations. There are two major Topoisomers of
DNA:.
In this slideshare, we know about the DNA supercoiling. How does it forms, size of DNA in a human body. How the chromosomes are formed. Useful enzymes that regulate the coiling of DNA. Relaxing stage of DNA which is circular form the left handed and right handed DNA coiling. Mostly in our body left handed coiling DNA are found. Importance of coiling their function and little bit of the structure of Supercoiling.
B-DNA, Z-DNA, A-DNA, stability of dsDNA helix, DNA denaturation, factors affecting Tm ,GC content, ionic strength, DNA as a genetic material, Griffith’s experiment, Hershey-chase experiment
2. Figure 1. Recognition and elimination of knots on crammed, long DNA molecules become easy when the DNA is supercoiled. (A) Schematic presenta-
tion of torsionally relaxed, knotted DNA molecule that forms a trefoil knot and is confined to a small volume. Specific unknotting of such a molecule
requires topoisomerase IIA action on these crossings where a passage would lead to unknotting. However, these crossings are hardly different from
accidental overlaps and topoisomerases IIA action on those crossings would rather introduce new knots than unknot the existing one. (B) In super-
coiled DNA molecules, the knotted portion becomes tightened as this decreases their free energy.12 Tightened knots have a higher curvature than the
rest of the DNA, allowing type IIA DNA topoisomerases to specifically bind and act on them as these enzymes have high affinity to bent DNA.9
tightening by DNA supercoiling provides models6,7 since tightened knots can be References
1. Schoeffler AJ, et al. Q Rev Biophys 2008; 41:41-101.
an efficient way to differentiate knotted seen as composed of hairpins or of hooked
2. Portugal J, et al. Nucleic Acids Res 1996; 24:4890-4.
portions from the rest of the molecules. juxtapositions. In addition, our proposal 3. Deibler RW, et al. BMC Mol Biol 2007; 8:44.
Finding the needle in the haystack is easy if would explain why the unknotting ability 4. Rybenkov VV, et al. Science 1997; 277:690-3.
one has a strong magnet. Similarly type II of type IIA DNA topoisomerases sharply 5. Vologodskii AV, et al. Proc Natl Acad Sci USA 2001;
98:3045-9.
DNA topoisomerases could use their affin- decreases with the size of relaxed DNA 6. Buck GR, et al. J Mol Biol 2004; 340:933-9.
ity to bent DNA as a knot magnet, pro- molecules. Indeed, studies of the size of 7. Burnier Y, et al. Nucl Acids Res 2007; 35:5223-31.
vided that the DNA is supercoiled. The the knotted domains in torsionally relaxed 8. Liu Z, et al. Phys Rev E Stat Nonlin Soft Matter Phys
2010; 81:31902.
proposal that type IIA DNA topoisomer- polymers revealed that the size of the knot-
9. Dong KC, et al. Nature 2007; 450:1201-5.
ases preferentially recognize knots due to ted domain increases with the size of the 10. Travers A, et al. EMBO Rep 2007; 8:147-51.
their increased curvature is consistent with molecules,13 and therefore the curvature in 11. Bates AD, et al. Oxford, UK: Oxford University
the hairpin5 and hooked juxtaposition the knotted regions decreases. Press, 2005.
12. Witz G, et al. Proc Natl Acad Sci USA 2011;
108:3608-11.
13. Marcone B, et al. J Phys A Math Gen 2005; 38:15.
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