chapter 5 section 7

Question 1

What general role do proteins play in biology

Answer 1

Proteins perform almost all biological functions except information storage.

Question 2

What is a ligand in the context of protein function?

Answer 2

A molecule that binds specifically and noncovalently to a protein.

Question 3

Name some classes of proteins based on function.

Answer 3

Transport proteins, scaffold proteins, catalytic proteins (enzymes), regulatory proteins, hormones, switch proteins (e.g., G-proteins), structural proteins, motor proteins.

Question 4

How many protein-encoding genes are in the human genome?

Answer 4

Slightly more than 19,000.

Question 5

Which protein functional categories have the most entries in humans?

Answer 5

Enzymes, nucleic acid-binding proteins, and signal transduction proteins.

Question 6

What percentage of human proteins have unknown function?

Answer 6

Approximately 15%.

Question 7

How do proteins bind ligands?

Answer 7

Through noncovalent interactions, making binding reversible

Question 8

What determines the specificity of a protein for a ligand?

Answer 8

The binding site’s structural complementarity, charge distribution, and H-bonding capacity.

Question 9

What happens to a protein when a ligand binds?

Answer 9

The protein often undergoes a ligand-induced conformational change, stabilizing the interaction

Question 10

Why are most proteins considered “binding proteins”?

Answer 10

Because binding other molecules is central to their function (e.g., enzymes, regulatory proteins, structural proteins, transport proteins).

Question 11

What is protein–protein interaction?

Answer 11

When proteins bind to other proteins to carry out their functions, forming oligomers or complexes

Question 12

Give examples of protein–protein interactions

Answer 12

Hemoglobin subunits forming an oligomer; scaffolding proteins organizing signaling pathways.

Question 13

How do all proteins perform their function?

Answer 13

Through specific recognition and binding of a target molecule.

Question 14

What is structural complementarity?

Answer 14

The principle that a protein’s 3D structure matches the shape, charge, and H-bonding pattern of its ligand.

Question 15

What is a protein–ligand dissociation reaction?

Answer 15

PL⇌P+L — the reversible binding of a ligand to a protein

Question 16

What is the dissociation constant (𝐾𝐷)?

Answer 16

KD=[P][L]/[PL] ; it measures how tightly a ligand binds to a protein. Lower 𝐾𝐷 = stronger binding.

Question 17

Why is the ligand usually in excess in binding experiments?

Answer 17

To ensure that the protein binding sites are the limiting factor for the interaction