Topic 11 Amides and peptide bonds Flashcards
The basic structure of an amide
RCONH2
Why are amides less basic than amines?
- Amides are stabilized by resonance
2. Nitrogen lone pair is delocalized to the carbonyl oxygen
Draw hydrolysis under both acidic and basic conditions
Peptide bonds: A. can be hydrolysed with either strong acid or strong base. B. have a delocalised sp3 hybridized structure. C. are formed by a condensation reaction in which a water is added. D. have limited rotation around the junction formed by the C- N to N-C axes. E. predominantly adopt cis rather than trans conformations.
A. can be hydrolysed with either
strong acid or strong base.
The planarity of an amide bond arises as a consequence of: A. Van der Waals interactions B. Solvation C. Hydrogen bonding interactions D. Resonance between the nitrogen and carbonyl group E. The presence of a thiol functional group
D. Resonance between the
nitrogen and carbonyl group
Insulin is a small protein comprising two polypeptide chains, each with the following amino acid compositions (you may need to look up the various amino acid codes):
A-chain: Gly-Ile-Val-Glu-Gln-Cys-Cys-Thr-Ser-Ile-Cys-Ser-Leu-Tyr-Gln-Leu-Glu-Asn-Tyr-Cys-Asn
B-chain: Phe-Val-Asn-Gln-His-Leu-Cys-Gly-Ser-His-Leu-Val-Glu-Ala-Leu-Tyr-Leu-Val-Cys-Gly-Glu-Arg-Gly-Phe-Phe-Tyr-Thr-Pro-Lys-Ala
How many (1) peptide bonds and (2) amide bonds are present in insulin?
1) 49
2) 54
The amide group comprises which two functional groups? A. Amino and hydroxyl B. Amino and alkoxy C. Amino and carbonyl D. Carbonyl and hydroxyl E. Amino and thiol
C. Amino and carbonyl
Which of the following amino acid residues act as helix disrupters? Select all that apply.
A. Serine B. Threonine C. Glycine D. Proline E. Phenylalanine
C. Glycine
D. Proline
Which of the following statements about amides is TRUE?
A. Amides are formed spontaneously from carboxylic acids and nitriles.
B. Tertiary amides are not water soluble.
C. Tertiary amides can act as hydrogen bond donors but not acceptors.
D. Primary amides can act as hydrogen bond donors but not acceptors.
E. Secondary amides can act as both hydrogen bond donors and acceptors.
E. Secondary amides can act as both hydrogen bond donors and acceptors.
In an amide bond:
A. The carbonyl group is sp3 hybridized, and the amine is sp2 hybridized.
B. The amine group is sp3 hybridized, and the carbonyl is sp2 hybridized.
C. Both the carbonyl and amine groups are sp3 hybridized.
D. Both the carbonyl and amine groups are sp2 hybridized.
E. Electrons form a delocalised structure but the bonds are not hybridized.
D. Both the carbonyl and amine groups are sp2 hybridized.
Peptide bonds:
A. predominantly adopt trans rather than cis conformations.
B. have limited rotation around the junction formed by the Cα-N to N-C axes.
C. have a delocalised sp3-hybridised structure.
D. are formed by a condensation reaction in which a water is added.
E. can be hydrolysed with strong acid but not strong base.
A. predominantly adopt trans rather than cis conformations.
2 ways to solve the unfavourable reaction of amide synthesis:
- add a base to catalyse reaction
2. couple with a favoured reaction
How are peptides synthesised?
Add a reversible protection group to the amino acid, to make sure that the correct sides react together
How does UV/Vis spectroscopy work?
The EM radiation has the energy to shift electrons between orbitals. The functional groups absorb at different wavelengths, so they can be identified. Absorbance usually arises from pi-pi interactions.
Draw a reaction scheme for the acid-catalysed hydrolysis of a peptide bond. Your scheme should include curly arrows to show the movement of electrons. Using annotations, provide a brief explanation of each step.
