ICAR AIEEA PG 2024 - Animal Biotechnology

Histone tails undergo diverse reversible post-translational modifications, prominently including acetylation (of lysines), methylation (of lysines and arginines), phosphorylation (of serines, threonines, and tyrosines), and ADP-ribosylation (of glutamates), forming the 'histone code' that regulates chromatin architecture and DNA access.

Functions of DNA replication enzymes:
DNA polymerase: Catalyzes 5' to 3' deoxynucleotide polymerization (I)
Helicases: Unwinds parental duplex DNA at the replication fork (II)
Topoisomerases: Relieves positive supercoiling and torsional strain ahead of replication fork (III)
DNA primase: Synthesizes short RNA primers required for initiation (IV).

Eukaryotic/mammalian DNA polymerases:
Pol $\alpha$: Contains primase activity, initiates synthesis and lagging strand primer elongation / gap filling (I)
Pol $\beta$: Involved in nuclear base excision repair (BER) (II)
Pol $\gamma$: Replicates and repairs mitochondrial DNA (III)
Pol $\delta$: Highly processive synthesis of the leading (and lagging) strand with proofreading (IV).

Standard physiological ion concentrations in mammalian extracellular fluid (plasma/interstitial fluid):
$\text{Na}^+$: $\sim 135-145\text{ mmol/L}$ (140 mmol/L)
$\text{K}^+$: $\sim 3.5-5.0\text{ mmol/L}$ (4 mmol/L)
$\text{Cl}^-$: $\sim 95-105\text{ mmol/L}$ (100 mmol/L)
$\text{Mg}^{2+}$: $\sim 1.5\text{ mmol/L}$.

Tissue distribution of collagen types:
Type I: Most abundant, present in bone, tendons, skin, and most connective tissues (I)
Type II: Primary collagen of hyaline and elastic cartilage, vitreous humor (II)
Type III: Reticular fibers found in distensible organs like blood vessels, skin, lungs (III)
Type IV: Meshwork-forming collagen of the basement membrane (IV).