Clinical Biochemistry: Structure of Proteins

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Questions and Answers

What type of bonds contribute to the stabilization of the three-dimensional tertiary structure of a protein?

Phosphodiester bonds

Peptide bonds

Hydrogen bonds (correct)

Disulfide bonds

What is the arrangement of polymeric polypeptide subunits in three-dimensional complexes called?

Secondary structure

Quaternary structure (correct)

Primary structure

Tertiary structure

Which of the following proteins is an example of a monomeric protein?

Myoglobin (correct)

Insulin

Hemoglobin

Lactate dehydrogenase

What type of interactions hold subunits of polymeric proteins together?

Noncovalent interactions Signup and view all the answers

Which of the following forces is NOT involved in stabilizing the quaternary structure of proteins?

Peptide bonds Signup and view all the answers

What type of proteins have a quaternary structure?

Polymeric proteins Signup and view all the answers

What type of structure is formed when a polypeptide chain is twisted by equal amounts about each α-carbon?

α-Helix Signup and view all the answers

Which type of protein structure is composed of two or more polypeptide chains?

β-Pleated sheet Signup and view all the answers

What is the distance between nitrogen and oxygen atoms in hydrogen bonds in α-helix?

2.8 Å Signup and view all the answers

In which type of protein structure are hydrogen bonds perpendicular to the polypeptide backbone?

β-Pleated sheet Signup and view all the answers

What is the relationship between the CO group of an amino acid and the NH group in an α-helix?

The CO group is bonded to the NH group of an amino acid 3-4 residues apart Signup and view all the answers

What is the arrangement of polypeptide chains in a parallel pleated sheet?

The chains are parallel to each other Signup and view all the answers

What is the name of the protein that is an example of a tertiary structure?

Myoglobin Signup and view all the answers

What is the significance of the folding of a polypeptide chain in tertiary structure?

It allows distant amino acid residues to interact Signup and view all the answers

What is the primary structure of proteins composed of?

A sequence of amino acids forming the backbone of proteins Signup and view all the answers

What is the result of the peptide bond formation between amino acids?

Elimination of a water molecule Signup and view all the answers

What is the importance of knowing the primary structure of proteins in genetic diseases?

To diagnose or study the disease Signup and view all the answers

What is proinsulin converted to by the loss of C-peptide?

Active insulin Signup and view all the answers

What is the result of hydrogen bonding between the hydrogen of NH and oxygen of C=O groups?

Folding or twisting of the primary structure Signup and view all the answers

Approximately how many amino acids apart in the linear sequence protein are hydrogen bonds formed?

3-4 amino acids Signup and view all the answers

What is the difference between primary and secondary structure of proteins?

Primary structure is the sequence of amino acids, while secondary structure is the folding of the primary structure Signup and view all the answers

What is the objective of learning about the structure and function of proteins?

To understand the structure and function of primary, secondary, tertiary, and quaternary proteins Signup and view all the answers

Study Notes

Primary Structure of Proteins

The sequence of amino acids forming the backbone of proteins are joined covalently by peptide bonds.
Peptide bonds are formed between the α-carboxyl group of one amino acid and the α-amino group of another with the elimination of a water molecule.
Clinical importance: many genetic diseases are due to abnormal amino acid sequences, and knowledge of primary structure can be used to diagnose or study the disease (e.g., Sickle cell disease).
Proinsulin is a single polypeptide chain with 86 amino acid, converted to active insulin by loss of C-peptide.

Secondary Structure of Proteins

Hydrogen bonding between the hydrogen of NH and oxygen of C=O groups of the polypeptide chain occurs, forming secondary structure.
Two important kinds of secondary structure:
- α-Helix (helicoidal structure): stabilized by hydrogen bonds between NH and CO groups of the same chain, with an optimal nitrogen to oxygen (N-O) distance of 2.8 Å.
- β-Pleated sheet structure: composed of two or more polypeptide chains, stabilized by hydrogen bonds between NH and C=O groups in different polypeptide chains.

Tertiary Structure

The peptide chain, with its secondary structure, may be further folded and twisted about itself, forming a three-dimensional arrangement of the polypeptide chain.
Amino acid residues distant from each other in the sequence can be brought near due to folding, forming regions essential for protein function (e.g., active site or catalytic site of enzymes).
Tertiary structure is stabilized by:
- Hydrogen bonds
- Hydrophobic interactions
- Van der Waals forces
- Disulfide bond
- Ionic (electrostatic) bonds or salt bridges.

Quaternary Structure of Protein

Only proteins with more than one polypeptide chain (polymeric) have a quaternary structure.
Not all proteins are polymeric, some are monomeric (e.g., myoglobin).
The arrangement of polymeric polypeptide subunits in three-dimensional complexes is called the quaternary structure of the protein.
Examples of proteins with quaternary structure: Hemoglobin (Hb), Lactate dehydrogenase.
The subunits of polymeric protein are held together or stabilized by:
- Hydrophobic interactions
- Hydrogen bond
- Ionic bonds
- Van der Waals forces.

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Description

This quiz covers the structure and function of proteins, as part of Clinical Biochemistry lecture no. 3.