Domains and structure

What is a protein domain?

A distinct structural and potentially functional region within a single polypeptide chain, often connected to other domains by short linkers.

What is the difference between a domain and a subunit?

Domain: a region within one polypeptide (tertiary structure). Subunit: an individual polypeptide chain in a multisubunit protein (quaternary structure).

What are the functions of phenylalanine hydroxylase's three domains?

Catalytic: converts Phe to Tyr. Regulatory: regulates activity. Tetramerization: mediates assembly of subunits.

How do globular and fibrous proteins differ?

Globular: compact and often spherical. Fibrous: elongated and involved in protective, connective, or supportive functions.

Where are hydrophobic and hydrophilic residues generally found in globular proteins?

Hydrophobic residues are generally buried in the core; hydrophilic residues are generally exposed on the surface.

What is a prosthetic group?

A non-amino-acid group required for protein structure or activity.

What is the function of the Rossmann fold?

Creates a binding site for a cofactor such as NAD⁺.

Why can forming multiple subunits be advantageous for proteins?

It reduces the need for one long polypeptide chain and provides a structural basis for regulating protein activity.

What is the quaternary structure of PFK in Lecture 6?

Homotetramer: four identical polypeptide subunits.

What is the quaternary structure of glycogen phosphorylase in Lecture 6?

Homodimer: two identical polypeptide subunits.