single strand chromosome model by R parihar.pptx

Single strength chromosome models

1. Jai Narain Vyas University jodhpur Department of botany Seminar topic – single strand chromosome models Submitted to -: Dr. Sunita Arora SUBMITTED BY:- RAMESH KUMAR

2. What is ssDNA? The ssDNA definition is as follows: Single-stranded DNA is the single DNA strand that is created during the replication process of DNA. The replication of single-stranded DNA forms two separate single-stranded chromosomes that join together to form double-stranded DNA (dsDNA). Single-stranded DNA genome also exists in class II of viruses known as the Parvoviridae and microviridae .

3. ssDNA compared to that of dsDNA.

4. Single Strand Models Various studies have demonstrated that chromosomes are single stranded. These studies include the stretching of lamp brush chromosomes and action of enzymes on their structure.

5. Tylor’s side chain model or centipede model. Taylor (1957) postulated that the chromosomes consist of a long protein backbone from which DNA coils branch off just like the legs of a centipede.

6. The Freese -Taylor model According to this model there are two protein spines instead of one. The DNA chains stretch between them like the steps of a ladder. In effect the DNA molecules are kept in position by the protein linkers.

7. Coiled coil model. According to Nebel and others the chromosome is made up of only a single fibril. This fibril is tightly coiled and the coil is thrown into secondary coils.

8. Ris’modified model. Ris suggested a modified model according to which the chromosome fibril is folded to form the chromosome. The 20A wide helix is associated with histone (protein) for form a 100A diameter nucleohistone fibril. Folding of the 100A fibril takes place because of calcium bridges to form a 250A diameter basic fibril.

9. Folded fibre model of DuPraw. DuPraw studied whole mounts of human leucocytes under the electron microscope. The essential features of DuPraw’s folded fibre model are that: (1) the DNA supercoil is packed into a 80-100A Type A fibre, and (2) that the fibre is further coiled to form a 200-350A Type B fibre. DuPraw’s model of DNA-histone association is now considered unlikely by the discovery that DNA itself is looped around histone beads to form nucleosomes.

10. Reference... Difference Between ssDNA and dsDNA. ( n.d. ). Compare the Difference Between Similar Terms. Retrieved December 22, 2021, from https://www.differencebetween.com/difference-between-ssdna-and-dsdna/
How long is your DNA? – BBC Science Focus Magazine. ( n.d. ). Retrieved December 22, 2021, from https://www.sciencefocus.com/the-human-body/how-long-is-your-dna/ Liautard , J. P. (1984). Rapid separation of single-stranded DNA from double-stranded DNA by reversed-phase high-performance liquid chromatography. Journal of Chromatography A, 285, 221–225. https://doi.org/10.1016/S0021-9673(01)87756-6

11. Thank you