HISTONES
Histones
- Most abundant chromatin Protein.
- Histones are divided into-
- Core Histone
- Linker Histone
- 5 classes- H1, H2A, H2B (Lysine), H3 and H4 (arginine).
- Linker histone- is loosely bound to nucleosome.
- Modifications-
- Acetylation of H3 & H4
- Acetylation of histones associated with chromosomal assembly during DNA replication.
- Phosphorylation of H1 is associated with condensation of chromosome during replication.
- 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-
- Constitutive- seen in centromere and chromosomal ends of the telomere.
- 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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