The hormones of the adrenal cortex are derivatives of cholesterol.

TLS Online TPP Program

#Id: 8274

#Unit 1. Molecules and their Interaction Relevant to Biology

Two Requirements for Hydrogen Bonding:

First molecules has hydrogen attached to a highly electronegative atom (N, O, F) called as (hydrogen bond donor)

Second molecule has a lone pair of electrons on a small highly electronegative atom (N, O, F) called as (hydrogen bond acceptor)

TLS Online TPP Program

#Id: 8275

#Unit 1. Molecules and their Interaction Relevant to Biology

Since the hydrogen donor (N, O, or F) is strongly electronegative, it pulls the covalently bonded electron pair closer to its nucleus, and away from the hydrogen atom.

The hydrogen atom is then left with a partial positive charge, creating a dipole-dipole attraction between the hydrogen atom bonded to the donor and the lone electron pair of the acceptor. This results in a hydrogen bond.

TLS Online TPP Program

#Id: 8276

#Unit 1. Molecules and their Interaction Relevant to Biology

TLS Online TPP Program

#Id: 8277

#Unit 1. Molecules and their Interaction Relevant to Biology

For maximum stability, the donor pair (AH) and the acceptor (B) are usually colinear (that is, i., AHB = 180°), but deviations of up to 30° are known.

TLS Online TPP Program

#Id: 8278

#Unit 1. Molecules and their Interaction Relevant to Biology

Plot of density versus temperature for liquid water.

The maximum density of water is reached at 4°C.

The density of ice at 0°C is 0.9167 g cm-3•

TLS Online TPP Program

#Id: 8279

#Unit 1. Molecules and their Interaction Relevant to Biology

Charge–charge (ionic) interactions

These interactions occur between the side chains of oppositely charged residues as well as between the NH3+ and COO− groups at the ends of polypeptide.