Organization of DNA and chromatin structure | Molecular biology |Biochemistry|First Aid Lecture|Lec4
Channel: Dr. Jamil Lectures
Date: 2022-05-10

In this lecture we will discuss about chromatin structure,chromosomes,nucleosome,chromatin types,Heterochromatin,Euchromatin,Organization of DNA ,DNA methylation,Histone Methylation,Histone acetylation,histone acetylation.

https://youtu.be/u6TNlvY72VQ
https://youtu.be/2OX34XAKGYQ
https://youtu.be/aP06bUvyqCA



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Chromatin structure DNA exists in the condensed, chromatin form to 
fit into the nucleus. DNA loops twice around a 
histone octamer to form a nucleosome (“beads 
on a string”). H1 binds to the nucleosome 
and to “linker DNA,” thereby stabilizing the 
chromatin fiber.
Phosphate groups give DNA a ⊝ charge. Lysine 
and arginine give histones a ⊕ charge.
In mitosis, DNA condenses to form 
chromosomes. DNA and histone synthesis 
occurs during S phase.
Mitochondria have their own DNA, which is 
circular and does not utilize histones.
Heterochromatin
Condensed, appears darker on EM (labeled H 
in A ; Nu, nucleolus). Sterically inaccessible, 
thus transcriptionally inactive.  methylation, 
 acetylation.
HeteroChromatin = Highly Condensed.
Barr bodies (inactive X chromosomes) may be 
visible on the periphery of nucleus.
Euchromatin
 Less condensed, appears lighter on EM (labeled 
E in A ). Transcriptionally active, sterically 
accessible.
Eu = true, “truly transcribed.”
Euchromatin is Expressed.
DNA methylation 
Changes the expression of a DNA segment 
without changing the sequence. Involved with 
aging, carcinogenesis, genomic imprinting, 
transposable element repression, and 
inactivation of the X chromosome. 
DNA is methylated in imprinting.
Methylation within gene promoter (CpG islands) 
typically represses (silences) gene transcription
Histone methylation 
Usually causes reversible transcriptional 
suppression, but can also cause activation 
Histone acetylation 
Removal of histone’s ⊕ charge  relaxed DNA 
coiling   transcription.
Histone Acetylation makes DNA Active.
Histone deacetylation 
Removal of acetyl groups  tightened DNA 
coiling   transcription
depending on location of methyl groups.



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