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DNA Structure and Histone Modifications: Exploring the Molecular Architecture of Genomes

This article explores the intricate structure of DNA, including the double helix, antiparallel strands, major and minor grooves. It also delves into histone-like proteins and their modifications that regulate gene expression and chromatin packaging.

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DNA Structure and Histone Modifications: Exploring the Molecular Architecture of Genomes

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  1. 1- B DNA -- Genome 2- Double helix -- Relaxed form 3- Antiparallel -- Super coil 4- Major groove -- Histone like proteins 5- Minor groove -- Nucleosome 6- Sugar puckering -- Nucleosome core 7- C2 endo --Chromatin 8- C3 Exo -- Linker 9- Syn, Anti -- Sscaffold --Right handed -- Solenoid 10- A DNA, C3 endo position --Melting point 11- Z DNA -- Left handed, G and A in syn position -- G and (A) in C3 endo position -- Base stacking --Hydrogen bond -- Phosphate position -- Hoogsteen Base pair -- Triple stranded helix

  2. Major- and Minor-Groove Sides. Because the two glycosidic bonds are not diametrically opposite each other, each base pair has a larger side that defines the major groove and a smaller side that defines the minor groove. The grooves are lined by potential hydrogen-bond donors (blue) and acceptors (red).

  3. Propeller Twist. The bases of a DNA base pair are often not precisely coplanar. They are twisted with respect to each other, like the blades of a propeller.

  4. Axial View of DNA. Base pairs are stacked nearly one on top of another in the double helix

  5. Structure of Histone Acetyltransferase.    The amino-terminal tail of histone H3 extends into a pocket in which a lysine side chain can accept an acetyl group from acetyl CoA bound in an adjacent site

  6. Histone modifications Histone proteins can undergo various types of modification, the best studied of these beinghistone acetylation. – the attachment of acetyl groups to lysine amino acids in the N-terminal regions of each of the core molecules. These N termini form tails that protrude from the nucleosome core octamer and their acetylation reduces the affinity of the histones for DNA and possibly also reduces the interaction between individual nucleosomes that leads to formation of the 30 nm chromatin fiber Histone acetyltransferases (HATs) – the enzymes that add acetyl groups to histones. Histone acetylation plays a prominent role in regulating genome expression. The tails of the core histones also have attachment sites for methyl and phosphate groups and for the common (‘ubiquitous') protein called ubiquitin. Ubiquitination of histone H2B is part of the general role that ubiquitin plays in control of the cell cycle. Phosphorylation of histone H3 and of the linker histone has been associated with formation of metaphase chromosomes Methylation of a pair of lysine amino acids at the fourth and ninth positions from the N-terminus of histone H3. Methylation of lysine-9 forms a binding site for the HP1 protein which induces chromatin packaging and silences gene expression

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