Chapter 6 section 4

Question 1

What two key factors drive protein folding?

Answer 1

Hydrophobic effect (burying nonpolar groups) and distribution of polar vs. nonpolar residues.

Question 2

What are the main features of fibrous proteins?

Answer 2

Parallel organization, mechanical strength, insolubility, and structural roles.

Question 3

Name three major fibrous proteins.

Answer 3

α-Keratin, β-Keratin (fibroin), and collagen.

Question 4

What stabilizes α-keratin?

Answer 4

Coiled coils of α-helices with hydrophobic repeats.

Question 5

what gives β-keratin (fibroin) its strength?

Answer 5

Stacked β-sheets tightly packed with Gly, Ala, and Ser.

Question 6

Why does collagen need vitamin C?

Answer 6

For hydroxylation of proline, which stabilizes the triple helix.

Question 6

how do globular proteins differ from fibrous proteins?

Answer 6

Globular proteins are compact, soluble, and functional, not just structural.

Question 6

What is the basic unit of collagen?

Answer 6

Tropocollagen — a triple helix of three polypeptides.

Question 7

Why must every third residue in collagen be glycine?

Answer 7

glycine is small enough to fit into the triple helix core.

Question 8

Where are polar vs. hydrophobic residues found in globular proteins?

Answer 8

Polar residues on the outside, hydrophobic residues in the core.

Question 9

What is a protein domain?

Answer 9

An independently stable, compact unit that functions as a modular building block.

Question 9

Why are α-helices and β-sheets common inside protein cores?

Answer 9

Their internal H-bonding shields polar backbones in the hydrophobic interior.

Question 10

Give a common example of protein denaturation.

Answer 10

Cooking an egg — ovalbumin denatures.

Question 11

What happens during protein denaturation?

Answer 11

Loss of 3D structure and function due to disruption of weak forces.

Question 12

What did Anfinsen’s ribonuclease experiment show?

Answer 12

Amino acid sequence alone determines 3D structure.

Question 13

What is a molten globule?

Answer 13

A folding intermediate with secondary structure but loose tertiary packing.

Question 14

What does Levinthal’s paradox reveal about folding?

Answer 14

Proteins can’t fold by random sampling — they follow guided pathways.

Question 15

What is hydrophobic collapse?

Answer 15

Nonpolar residues cluster in the core, driving initial folding.

Question 16

What does the folding funnel represent?

Answer 16

Folding proceeds downhill toward the lowest-energy native state.

Question 17

What is the main thermodynamic driving force for folding?

Answer 17

Entropy gain of water released when hydrophobic groups are buried.

Question 18

Why are proteins only marginally stable?

Answer 18

Flexibility is needed for function.

Question 19

Name three protein functions that require motion.

Answer 19

Ligand binding, catalysis, and regulation.

Question 19

What are intrinsically unstructured proteins (IUPs)?

Answer 19

Flexible proteins lacking a fixed 3D structure that fold upon binding partners.

Question 19

What are molecular chaperones?

Answer 19

Proteins that assist folding and prevent misfolding.