Dna packaging

DNA is tightly packed in the nucleus of every cell. DNA wraps around special proteins called histones, which form loops of DNA called nucleosomes. These nucleosomes coil and stack together to form fibers called chromatin. Chromatin in turn forms larger loops and coils to form chromosomes.

DNA packaging is crucial because it makes sure that those excessive DNA are able to fit nicely in a cell that is many times smaller.

The DNA in bacterial cells are either circular or linear. To accommodate the size of bacterial cell, supercoiled DNA are folded into loops with each loop resembles shape of bead-like packets containing small basic proteins that is analogous to histone found in Eukaryotes.

1. SHRI SHANKARACHARYA MAHAVIDAYALAYA jUNWANI,BHILAI SEMINAR ON dna packaging Dr.Rachana choudhary Astt.Professor -

2. SYNOPSIS INTRODUCTION NEED FOR PACKAGING PACKAGING OF DNA INTO NUCLEUS ORDER OF PACKAGING 1 ST ORDER- NUCLEOSOME proteins involved in packaging components of nucleosome 2 ND ORDER-SOLENOID FIBER 3 RD ORDER-CHROMATIDS 4 TH ORDER- CHROMOSOME CONCLUSION REFERENCE

3. I NTRODUCTION DNA is the only components of chromosome which acts as a heredity materials. The most important property of DNA is super coiling . DNA is condensed in to a complex structure with Histone & Non-histone proteins . DNA is wrapped around a core of histone molecule and non-histone are some how associated with that complex.

4. NEED FOR PACKAGING Packaging here refers to the condensing of DNA to fit easily into the nucleus. Process of packaging differs in prokaryotes and eukaryotes. In prokaryotes the chromosomes are present freely in the cytoplasm hence packaging is not required. in eukaryotes DNA is packaged as follows:-

5. PACKAGING OF DNA INTO NUCLEUS The length of DNA in the nucleus is far greater than the size of the compartment in which it is contained Condensation of DNA is necessary to fit into the nuclear compartment.

6. ORDERS OF PACKAGING There are various order of packaging: 1 ST order of packaging- Nucleosome 2 ND order of packaging-Solenoid fiber 3 RD order of packaging- Chromatid 4 TH order of packaging-Chromosome

7. NUCLEOSOME It is the fundamental repeating subunit of Eukaryotic chromatin. Made up of chromosomal proteins, histones & non histones

8. CHROMOSOMAL PROTIENS

9. COMPONENTS OF NUCLEOSOME CORE PARTICALS –It is consist of 146 base pair of DNA wrapped 1.8 times in left handed helix . CHROMATOSOME- The core particle interact with one molecule of histone H1 to from a particle containing approx 166 base pair of DNA called chromatosome. NUCLEOSOME- links with the linker DNA forming a nucleosome containing approx 200 base pair of DNA.

10. SOLENOID FIBER The coiling of beads in helical structure is called 30 nm fiber. found in inter phase chromatin & mitotic chromosome. Inter phase chromosome have a diameter of 300 nm coiled metaphase chromosome have diameter of 700 nm.

11. CHROMATID The condensed piece of chromatin has a characteristic scaffolding structure that can be detected in metaphase chromosome. Chromatid forms as a result of extensive looping of the DNA in the chromosome.

12. CHROMOSOME Final packaging of chromosomes occurs by looping & scaffolding. Chromatid fibers condensed & gets packaged & forms chromosome. Final packaging ratio is 1000 nm in inter phase & 10000 nm in mitotic chromosome.

13. ROLE OF SMC PROTIENS Condensin helps in condensation of DNA in metaphase when DNA enters metaphase.

14. CONCLUSION Packaging is a characterstic feature of Eukaryotic chromosomal organization.it involves various orders like formation of nucleosome, solenoid fiber & then chromosomes.

15. REFERENCE PRINCIPLES OF BIOCHEMISTRY BY-NELSON and COX. MOLECUCLAR BIOLOGY BY – KARP. MOLECULAR BIOLOGY BY-B.D.SINGH.

16. THANKS