Protein Structure Levels

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Questions and Answers

What is the primary structure of a protein?

The three-dimensional structure of a polypeptide

The local spatial arrangement of a polypeptide's backbone atoms

The association of subunits in the tertiary structure

The sequence of amino acids linked by a peptide bond (correct)

What is required to break peptide bonds nonenzymatically?

Enzymatic reaction

Heating and high concentrations of urea

Prolonged exposure to a strong acid or base at elevated temperatures (correct)

Cooling and low concentrations of urea

How many possible unique polypeptide chains of 100 residues are there?

20^100 ≈1.27 ×10^130 (correct)

20^10 ≈1.27 ×10^13

20^50 ≈1.27 ×10^65

20^20 ≈1.27 ×10^26

What determines the 3D structure of a protein?

The sequence of amino acids Signup and view all the answers

What is the minimum number of residues a protein typically contains?

40 residues Signup and view all the answers

What is the function of oxytocin?

Uterine contraction during labor and promoting milk release during lactation Signup and view all the answers

What is the number of amino acids in oxytocin and vasopressin?

9 AAs Signup and view all the answers

What is the definition of a peptide?

A polypeptide chain of less than 40 residues Signup and view all the answers

What is the primary function of vasopressin in the kidney?

Increase water reabsorption Signup and view all the answers

What is the role of glutathione in biological systems?

Antioxidant activity Signup and view all the answers

What is the characteristic of the peptide bond?

It is shorter than a single bond and is rigid and planar Signup and view all the answers

What is the consequence of the peptide bond's partial double-bond character?

Prevention of free rotation around the bond Signup and view all the answers

Which bond angles are freely rotatable in a polypeptide chain?

Cα-N and Cα-C Signup and view all the answers

What is the significance of the omega angle in a peptide bond?

It is always 0 or 180° for cis and trans, respectively Signup and view all the answers

What is the purpose of the Ramachandran plot?

To indicate the allowed conformations of polypeptides Signup and view all the answers

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 Signup and view all the answers

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

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Description

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.