Clinical Biochemistry Lecture 3: Protein Structure

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Questions and Answers

Which of the following bonds helps to stabilize the quaternary structure of a protein?

Covalent bond

Peptide bond

Hydrogen bond (correct)

Disulfide bond

What type of forces are involved in the stabilization of the quaternary structure of a protein?

Hydrophobic and van der Waals forces (correct)

Electrostatic and gravitational forces

Mechanical and thermal forces

Covalent and ionic forces

Which of the following proteins does not have a quaternary structure?

Hemoglobin

Lactate dehydrogenase

Insulin

Myoglobin (correct)

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

Quaternary structure Signup and view all the answers

Which of the following is not a characteristic of a protein with quaternary structure?

Has a single polypeptide chain Signup and view all the answers

Which of the following interactions is involved in the stabilization of the tertiary structure of a protein?

Hydrophobic interaction 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 elimination of a water molecule in peptide bonds?

Formation of a covalent bond Signup and view all the answers

What is the clinical importance of primary structure?

It is used to diagnose or study genetic diseases Signup and view all the answers

What is the result of the conversion of pro-insulin to active insulin?

Loss of C-peptide Signup and view all the answers

What is the secondary structure of proteins formed by?

Hydrogen bonding between the hydrogen of NH and oxygen of C=O groups Signup and view all the answers

How many amino acids are involved in the formation of secondary structure?

3-4 amino acids Signup and view all the answers

What is the result of the folding or twisting of the primary structure?

Formation of secondary structure Signup and view all the answers

What is the disease that occurs due to an abnormal amino acid sequence?

Sickle cell disease Signup and view all the answers

What is the primary way that α-helix structures are stabilized?

Hydrogen bonds between NH and CO groups of the same polypeptide chain Signup and view all the answers

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

2.8 Å Signup and view all the answers

How do the polypeptide chains in β-pleated sheets interact with each other?

Through hydrogen bonds between NH and C=O groups of different polypeptide chains Signup and view all the answers

What is the shape of the polypeptide chain in a β-pleated sheet?

Almost fully extended Signup and view all the answers

What is the direction of the hydrogen bonds in β-pleated sheets relative to the polypeptide backbone?

Perpendicular Signup and view all the answers

How can the arrangement of polypeptide chains in β-pleated sheets occur?

In both parallel and anti-parallel pleated sheets Signup and view all the answers

What is an example of a protein that exhibits tertiary structure?

Myoglobin Signup and view all the answers

What is the result of the folding and twisting of the polypeptide chain in tertiary structure?

A three-dimensional arrangement of the polypeptide chain 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, part of the Clinical Biochemistry lecture series at Al-Ayen University's College of Medicine.