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Questions and Answers
What is the purpose of the peptide bond in the structure of proteins?
What is the main difference between a peptide and a polypeptide?
What is the role of proline in protein structure?
What is the relationship between proline and hydroxyproline mentioned in the text?
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What is the significance of the trans-configuration of amino acid side-chains in proteins?
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What is the relationship between serine, threonine, and enzymatic catalysis mentioned in the text?
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What is the significance of the N-terminus and C-terminus mentioned in the text?
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Study Notes
Glutathione and Its Forms
- Glutathione is a tripeptide that protects cells from damaging free radicals and reactive oxygen species (ROS).
- It is formed from the side-chain carboxyl group of glutamate, the alpha-amino group of cysteine, and glycine.
- Glutathione has a reduced form (gamma-glutamylcysteinylglycine) and an oxidized form (glutathione disulphide, GSSG), which is formed by two glutathione tripeptides joined by a disulfide bond between the cysteine residues.
Neuropeptides
- Substance P is a neuropeptide containing 11 amino acids, involved in pain perception and vasodilation.
- Vasoactive intestinal peptide (VIP) is a 28-amino acid peptide produced by the intestines, hypothalamus, and other tissues, involved in gut motility and secretion, and circadian rhythms.
Human Peptides
- Enkephalins are pentapeptides (Tyr-Gly-Gly-Phe-Met) with natural opiate (painkilling) activity.
- Enterostatin is a pentapeptide (Ala-Pro-Gly-Pro-Arg) derived from pancreatic procolipase, involved in appetite suppression and increasing satiety.
- Bradykinin is a nonapeptide (nine amino acid residues) that is a powerful vasodilator and anti-inflammatory.
- Angiotensin II is an octapeptide found in lungs and other cells, a powerful vasoconstrictor that raises blood pressure.
- Oxytocin is a nonapeptide that stimulates uterus contraction and milk ejection.
Cyclic Peptides
- Cyclic peptides occur when an amino terminus forms a peptide bond with its carboxy terminus, or an amino terminus covalently bonds with an amino acid side-chain, or a carboxyl terminus covalently bonds with an amino acid side-chain, or two side chains of a peptide covalently bond with each other.
- Examples of natural cyclic peptides include Daptomycin (antibiotic) and Cyclosporine A (immunosuppressant).
Amino Acids and Peptides
- Peptides are short chains of amino acids joined by peptide bonds, with a N-terminus and a C-terminus (except for cyclic peptides).
- A dipeptide contains 2 amino acids linked via a peptide bond, a tripeptide has 3 amino acids, and so on.
- Polypeptides have less than 50 amino acid residues, while proteins have more than 50 amino acid residues.
- The peptide bond is planar and quite rigid, with little rotation allowed, and amino acid residue side-chains (R groups) can be arranged in a cis- or a trans-configuration, with trans-configuration being more common.
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Description
Test your knowledge on the structure and function of glutathione, a tripeptide involved in protecting cells from free radicals and reactive oxygen species. Learn about the formation of glutathione and its reduced and oxidised forms.
