Table of contents

1. Introduction to Biochemistry4h 34m
2. Water3h 23m
3. Amino Acids8h 10m
4. Protein Structure10h 4m
5. Protein Techniques14h 5m
6. Enzymes and Enzyme Kinetics13h 38m
7. Enzyme Inhibition and Regulation 8h 42m
8. Protein Function 9h 41m
9. Carbohydrates7h 49m
10. Lipids5h 49m
11. Biological Membranes and Transport 6h 37m
12. Biosignaling9h 45m
Review 1: Nucleic Acids, Lipids, & Membranes2h 47m
Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway3h 12m
Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism2h 26m
Review 4: Amino Acid Oxidation, Oxidative Phosphorylation, & Photophosphorylation1h 48m

4. Protein Structure

Alpha Helix Disruption

Biochemistry

4. Protein Structure

Alpha Helix Disruption

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Multiple Choice

Why does proline often 'break' an alpha helix?

Its amino group has no free hydrogen to bond with a carbonyl because of the imino ring.

It is impossible for it to adopt the psi and phi angles required to form an alpha helix.

Its peptide bond often adopts the trans conformation, unlike other amino acids.

Its peptide bond flips frequently between the cis and trans conformations.

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Verified step by step guidance

Understand the structure of proline: Proline is unique among the amino acids because its side chain forms a cyclic structure by bonding to the nitrogen of the amino group, creating an imino group.

Recognize the impact of the imino group: The cyclic structure of proline means that its nitrogen atom is part of a rigid ring, which restricts the rotation around the N-Cα bond, affecting the psi (ψ) and phi (φ) angles.

Consider the hydrogen bonding requirement: In an alpha helix, the backbone amide hydrogen forms a hydrogen bond with the carbonyl oxygen four residues earlier. Proline lacks a free hydrogen on its nitrogen, disrupting this pattern.

Examine the peptide bond conformation: Proline's peptide bond is more likely to adopt a cis conformation compared to other amino acids, which typically favor the trans conformation. This can introduce kinks in the helix.

Analyze the effect on helix stability: Due to these structural constraints, proline is often found at the ends of alpha helices or in turns, where it can introduce a bend or break in the helical structure.