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Eukaryotic chromosome organization

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Eukaryotic chromosome organization

  1. 1. STRUCTURAL ORGANIZATION OF EUKARYOTIC CHROMOSOME.. AKHILESH PANCHAL MSC 2ND SEM DEPARTMENT OF BIOTECHNOLOGY, GUK
  2. 2. CONTENTS • Chromosome • Histones and chromatin • Nucleosomes • Structural hierarchy of chromosome • Reference
  3. 3. CHROMOSOMES • The DNA of all eukaryotes is organized into morphologically distinct units called Chromosomes. Each chromosome contains a single enormous DNA molecule • For example – DNA molecule in a single chromosome of fruit fly Drosophilla DNA has a molecular weight greater than 10^10 and length of 1.2 cm • (In human 23 pairs of chromosome can be found.) • As we know that DNA cannot spontaneously fold to form such compact structure bcoz the molecule would b strained enormously. • Instead, DNA is made compact by hierarchy of different types of foldings, each of which is mediated by one or more protein molecules.
  4. 4. • DNA molecule in a eukaryotic chromosome is bound to very basic proteins called histones.The complex comprising DNA and histones is called Chromatin . • There are five major classes of histones –H1, H2A, H2B, H3, H4. • Histones have an unusual amino acids composition in that they are extremely rich in positively charged amino acids lysine and arginine. • (H1 – lysine rich , H3 and H4 are arginine rich ) • The positive charge of the histones is one of the major features of the molecule enabling them to bind to the negatively charged phosphates of the DNA. HISTONES AND CHROMATIN
  5. 5. NUCLEOSOME • Nucleosome is the basic structural unit of DNA packaging in eukaryotes. The structure of a nucleosome consists of a segment of DNA wound around eight histone proteins and resembles thread wrapped around a spool. The nucleosome is the fundamental subunit of chromatin. • They serve as a scaffold for formation of higher order chromatin structure as well as for a layer of regulatory control of gene expression
  6. 6. STRUCTURAL HIERARCHY OF CHROMOSOME • In the first level of compaction, short stretches of the DNA double helix wrap around a core of eight histone proteins at regular intervals along the entire length of the chromosome • The DNA-histone complex is called chromatin. The individual beadlike, histone DNA complex is called a nucleosome, and DNA connecting the nucleosomes is called linker DNA. • A DNA molecule in this form is about seven times shorter than the double helix without the histones, and the beads are about 10 nm in diameter, in contrast with the 2-nm diameter of a DNA double helix.
  7. 7. • The next level of compaction occurs as the nucleosomes and the linker DNA between them are coiled into a 30-nm chromatin fiber. This coiling further shortens the chromosome so that it is now about 50 times shorter than the extended form. • In the third level of packing, a variety of fibrous proteins is used to pack the chromatin. • These fibrous proteins also ensure that each chromosome in a non- dividing cell occupies a particular area of the nucleus that does not overlap with that of any other chromosome.
  8. 8. REFERENCE • Molecular biology -8th edition, David Freifelder • Cell biology – C. B. Power • https://courses.lumenlearning.com › ... • Chromosome Structure | Biology for Majors I – Lumen Learning
  9. 9. THANK YOU......

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