Study guides › B/B › Biochemistry
Protein Structure & Function
A protein's function comes from its folded shape. You will learn the four levels of structure, the forces that hold a fold together and the ways it is lost, hemoglobin and myoglobin binding, structural proteins, and how proteins are separated in the lab.
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What this chapter covers
- Levels of Protein Structure. Each level of structure has its own bonds. Knowing which bond belongs to which level answers half of the structure questions.
- Stabilizing Forces, Denaturation & Chaperones. Folding is driven by entropy of water, and any agent that disturbs the weak forces will unfold a protein.
- Hemoglobin, Myoglobin & Cooperativity. Hemoglobin's sigmoidal curve versus myoglobin's hyperbola is the standard example of cooperative binding on the MCAT.
- Structural Proteins & Functional Classes. The MCAT likes to ask why collagen, keratin, and actin are built as they are, and which vitamin or bond each depends on.
- Separating & Analyzing Proteins. Electrophoresis and chromatography questions ask which property (size, charge, or specific binding) is being exploited.
Key points to know
- Alpha helix: 3.6 residues per turn, H-bond i to i+4, right-handed
- Beta sheet: H-bonds between strands; parallel or antiparallel
- Hydrophobic effect (entropy of water) drives folding
- Denaturation breaks noncovalent bonds, not peptide bonds
- Mb: monomer, hyperbolic, stores O₂; Hb: α₂β₂ tetramer, sigmoidal
- Cooperativity: T state (low affinity) to R state (high affinity)
- Collagen: Gly every third residue; needs vitamin C for proline hydroxylation
- Keratin is an alpha-helical coiled coil with disulfides
Try a practice question
Which pair forms the hydrogen bond that stabilizes an alpha helix?
- C=O of residue i and N–H of residue i+4
- Side chain of residue i and side chain of i+3
- C=O of residue i and N–H of a residue on a neighboring strand
- N–H of residue i and N–H of residue i+4
Show the answer
A. In an alpha helix the backbone carbonyl of residue i bonds to the amide N–H four residues later. Option C describes a beta sheet, and side chains are not involved in the helix backbone bonding.
Common questions
What does this chapter cover?
Protein Structure & Function covers Levels of Protein Structure, Stabilizing Forces, Denaturation & Chaperones, Hemoglobin, Myoglobin & Cooperativity, Structural Proteins & Functional Classes, Separating & Analyzing Proteins.
What should I know first?
Alpha helix: 3.6 residues per turn, H-bond i to i+4, right-handed Beta sheet: H-bonds between strands; parallel or antiparallel Hydrophobic effect (entropy of water) drives folding
24 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.