16 Questions
What is the primary structure of a protein?
The sequence of amino acids linked by a peptide bond
What is required to break peptide bonds nonenzymatically?
Prolonged exposure to a strong acid or base at elevated temperatures
How many possible unique polypeptide chains of 100 residues are there?
20^100 ≈1.27 ×10^130
What determines the 3D structure of a protein?
The sequence of amino acids
What is the minimum number of residues a protein typically contains?
40 residues
What is the function of oxytocin?
Uterine contraction during labor and promoting milk release during lactation
What is the number of amino acids in oxytocin and vasopressin?
9 AAs
What is the definition of a peptide?
A polypeptide chain of less than 40 residues
What is the primary function of vasopressin in the kidney?
Increase water reabsorption
What is the role of glutathione in biological systems?
Antioxidant activity
What is the characteristic of the peptide bond?
It is shorter than a single bond and is rigid and planar
What is the consequence of the peptide bond's partial double-bond character?
Prevention of free rotation around the bond
Which bond angles are freely rotatable in a polypeptide chain?
Cα-N and Cα-C
What is the significance of the omega angle in a peptide bond?
It is always 0 or 180° for cis and trans, respectively
What is the purpose of the Ramachandran plot?
To indicate the allowed conformations of polypeptides
What are the sterically forbidden conformations in a polypeptide chain?
Those with ϕ and ψ values that bring atoms closer than the van der Waals distance
Study Notes
Protein Structure Levels
- Primary structure: the sequence of amino acids linked by a peptide bond
- Secondary structure: local spatial arrangement of a polypeptide's backbone atoms without regard to the conformations of its side chains
- Tertiary structure: three-dimensional structure of an entire polypeptide, including its side chains
- Quaternary structure: association of subunits in the tertiary structure to form multimeric protein
Primary Structure
- Sequence of amino acids in a protein is called the primary structure of the protein
- Peptide bonds are resistant to heating and high concentrations of urea
- Prolonged exposure to a strong acid or base at elevated temperatures is required to break these bonds nonenzymatically
- Theoretical possibilities for polypeptides are unlimited (20n possible sequences for a protein of n residues)
- Amino acid sequence determines the 3D structure of a protein
Biologically Active Peptides
- Oxytocin and vasopressin are biologically active peptides (hormones) composed of 9 amino acids
- Oxytocin: uterine contraction during labor & promoting milk release during lactation
- Vasopressin: antidiuretic hormone; increases water reabsorption in the kidney & promotes the constriction of blood vessels, thereby increasing blood pressure
- Glutathione: a tripeptide with antioxidant activity, maintaining sulfhydryl groups of proteins in the reduced state and the iron of heme in the ferrous (Fe2+) state
Peptide Bond Characteristics
- Peptide bond has a partial double-bond character, making it rigid and planar, preventing free rotation around the bond
- Bonds between the α-carbons and the α-amino group (Cɑ-N) or between the α-carbons and α-carboxyl groups (Cɑ-C) can be freely rotated
Ramachandran Plot
- The Ramachandran Diagram indicates allowed conformations of polypeptides based on sterically allowed values of φ and ψ
- Sterically forbidden conformations have φ and ψ values that would bring atoms closer than the corresponding van der Waals distance
This quiz covers the four levels of protein structure, including primary, secondary, tertiary, and quaternary structures. Learn about the sequence of amino acids, spatial arrangements, and associations of subunits.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
