Histones

HISTONES


Histones

  • Most abundant chromatin Protein.
  • Histones are divided into-
  1. Core Histone
  2. Linker Histone
  • 5 classes- H1, H2A, H2B (Lysine), H3 and H4 (arginine).
  • Linker histone- is loosely bound to nucleosome.
  • Modifications-
  1. Acetylation of H3 & H4
  2. Acetylation of histones associated with chromosomal assembly during DNA replication.
  3. Phosphorylation of H1 is associated with condensation of chromosome during replication.
  4. Methylation correlated with activation or repression of gene transcription.
  • Chromatins are of two types-
  • Euchromatin- Transcriptionally active chromatin and is uncondensed. Chromatins are less stained.
  • Heterochromatin- Transcriptionally inactive, chromatin stains densely, chromatin densely packed. 2 types-
  1.  Constitutive- seen in centromere and chromosomal ends of the telomere.
  2.  Facultative
  • Chromosomes-
  •  In humans, there are 23 pairs of chromosomes.
  •  The position of centromere is the characteristic mark for specific chromosome.
  •  The centromere is AT rich region.
  • Total number of chromosome in humans is 46 (23 pairs).
  • The number of base pairs in haploid set of chromosome is 3.0 x 1O9 (3 billion bp)
  • Percentage of exons in human genome is approximately 1.14% (1.5-2%)
  • The number of protein coding genes in human genome is 20,687.
  • The genes account for 10-15% of DNA.

Exam Important

  • Total number of chromosome in humans is 46 (23 pairs).
  • The number of base pairs in haploid set of chromosome is 3.0 x 1O9 (3 billion bp)
  • Percentage of exons in human genome is approximately 1.14% (1.5-2%)
  • The number of protein coding genes in human genome is 20,687.
  • The genes account for 10-15% of DNA.
  • Euchromatin is transcriptionally active and heterochromatin is transcriptionally inactive.
  • For euchromatin, chromatin is less densely packed.
  • For heterochromatin, chromatin is densely packed.
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