lecture 2 non covalent interactions

What are non-covalent interactions?

Weak interactions between molecules, important in DNA, proteins, and enzyme-substrate binding.

What are electrostatic forces?

Attractions between oppositely charged regions of molecules, helping them orient correctly.

What is a dipole?

A separation of positive and negative charge in a molecule, e.g. H₂O and HCl.

Why are CO₂ and CCl₄ non-polar?

Their symmetrical shapes cause their polar bond dipoles to cancel.

What are van der Waals interactions?

Weak attractive or repulsive forces between molecules that are close together.

What are London dispersion forces?

Weak, short-lived attractions caused by temporary dipoles from moving electrons.

What affects the strength of dispersion forces?

Size and shape. Larger, flatter molecules generally experience stronger forces.

What are dipole-dipole and dipole-induced dipole interactions?

Dipole-dipole: attraction between permanent dipoles. Dipole-induced: a polar molecule induces a temporary dipole in a non-polar molecule.

What are steric forces?

Repulsive forces caused by valence electron shells when molecules get too close.

What is hydrogen bonding?

A relatively strong interaction involving hydrogen bonded to N, O or F and a lone pair on another electronegative atom.

What are hydrogen bond donors and acceptors?

Donor: H bonded to N, O or F. Acceptor: an electronegative atom with a lone pair.

What is the role of hydrogen bonding in DNA?

Holds complementary base pairs together: A–T has 2 hydrogen bonds and G–C has 3.

How does hydrogen bonding stabilise proteins?

Hydrogen bonds form between backbone N–H donors and carbonyl oxygen acceptors.

What are ionic interactions?

Attractions between oppositely charged groups, such as charged carboxyl and amino groups.

What is a salt bridge?

An ionic attraction between oppositely charged amino acid side chains that stabilises protein structure.

What is the difference between hydrophobic and hydrophilic?

Hydrophobic = non-polar and water-repelling. Hydrophilic = polar and water-attracting.

What are hydrophobic interactions?

Non-polar regions group together away from water, helping protein folding and lipid bilayer formation.

What is π stacking?

Attractive or repulsive interactions between the π-electron systems of aromatic rings, occurring in DNA.

Which non-covalent interactions stabilise proteins?

Hydrogen bonding, ionic interactions, hydrophobic interactions, and van der Waals forces.

Which non-covalent interactions stabilise DNA?

Hydrogen bonding between complementary bases and π stacking between neighbouring bases.