13.1 Proteins

Introduction

Proteins are found in our muscles, bones, skin, hair, and almost every part of the body. Proteins are also known as the building blocks of life because they are the most abundant molecules present in the body.

Proteins are called natural polyamides because they are naturally occurring polymers. Proteins are large, complex molecules made up of long chains of monomers which are all amino acids. Amino acids are the basic structural unit of protein.

This section explains what proteins are, their basic unit (amino acids), and their structure.

Definition

Proteins: Proteins are large, complex molecules made up of long chains of monomers called amino acids.

Amino Acids: An amino acid is a simple organic compound consisting of two functional groups:

• A basic group (amine group, -NH₂)
• An acidic group (carboxylic group, -COOH)

with a variable alkyl group (R) that is unique to each amino acid.

In simple words: Proteins are natural polymers made of amino acids. Amino acids are the building blocks of proteins.

Main Idea

• Proteins are found in our muscles, bones, skin, hair, and almost every part of the body.
• Proteins are also known as the building blocks of life because they are the most abundant molecules present in the body.
• Proteins are called natural polyamides because they are naturally occurring polymers.
• Proteins are large, complex molecules made up of long chains of monomers which are all amino acids.
• Amino acids are the basic structural unit of protein.
• An amino acid is a simple organic compound consisting of:
• Protein synthesis requires adequate amounts of amino acids.
• Molecules of amino acids join together through the amino group (-NH₂) of one molecule and the carboxyl group (-COOH) of another molecule by eliminating a water molecule.
• The bond that joins two amino acid units is called a peptide bond.
• When two amino acids join, the molecule is called a dipeptide.
• In thousands of amino acid units joined together, the result is a protein molecule. This sequence of amino acid linkages is called the primary structure of the protein.

Core Concept

Key point: Proteins are natural polyamides made of amino acids. Amino acids are the building blocks of proteins.

Detailed Explanation

What are Proteins?

Proteins are found in our muscles, bones, skin, hair, and almost every part of the body.

• Proteins are also known as the building blocks of life because they are the most abundant molecules present in the body.
• Proteins are called natural polyamides because they are naturally occurring polymers.
• Proteins are large, complex molecules made up of long chains of monomers which are all amino acids.

Key point: Proteins are natural polyamides made of amino acids.

Amino Acids: The Basic Unit of Protein

Amino acids are the basic structural unit of protein.

An amino acid is a simple organic compound consisting of:

• A basic group (amine group, -NH₂)
• An acidic group (carboxylic group, -COOH)
• A variable alkyl group (R) that is unique to each amino acid.

Key point: Amino acids are the basic structural unit of proteins. They contain an amine group, a carboxylic group, and a variable R group.

Protein Synthesis

The body makes proteins through a process called protein synthesis. Protein synthesis requires adequate amounts of amino acids.

Molecules of amino acids join together through the amino group (-NH₂) of one molecule and the carboxyl group (-COOH) of another molecule by eliminating a water molecule.

Key point: Protein synthesis requires amino acids. Amino acids join together by eliminating a water molecule.

The Peptide Bond

The bond that joins two amino acid units is called a peptide bond.

The bond is:

-C - NH- (with a double bond to O on the C)

When two amino acids join, the molecule is called a dipeptide.

In thousands of amino acid units joined together, the result is a protein molecule. This sequence of amino acid linkages is called the primary structure of the protein.

Key point: The peptide bond joins amino acids together. Two amino acids joined together form a dipeptide. Many amino acids joined together form a protein.

Structure of Proteins

The source describes four levels of protein structure:

• Primary structure: Primary protein structure is a sequence of amino acids in a chain.
• Secondary structure: Secondary protein structure is formed by folding and twisting of the amino acid chain.
• Tertiary structure: Tertiary protein structure is formed when the twists and folds of the secondary structure fold again to form a larger three-dimensional structure.
• Quaternary structure: Quaternary protein structure is a protein consisting of more than one folded amino acid chain.

Key point: Proteins have four levels of structure: primary, secondary, tertiary, and quaternary.

Classification of Protein

The proteins are classified on the basis of the shape, constitution, and nature of the molecule.

Each amino acid is connected to the next amino acid by covalent bonds.

Key point: Proteins are classified based on shape, constitution, and nature. Amino acids are connected by covalent bonds.

Do You Know?

Enzymes:

• Enzymes are proteins that fasten chemical reactions in the body.
• They act like small machines that help break down food, make molecules, and carry out other important functions in cells, all without being used up or changed themselves.

Hemoglobin:

- Hemoglobin is found in red blood cells in our blood and carries oxygen from your lungs to your cells.

Collagen:

- A protein called collagen is a strong and tough material that makes up our skin and fingernails and even helps to hold our internal organs in place.

Insulin:

• Insulin is a protein hormone that is made by specific cells inside the pancreas called beta cells.
• Insulin signals cells to absorb sugar from the bloodstream. Cells can't absorb sugar without insulin.
• Insulin protein is first produced as an immature, inactive chain of amino acids (preproinsulin).

Key point: Proteins have many important functions in the body, including acting as enzymes, transporting oxygen, providing structural support, and regulating blood sugar.

Summary Table

Intermediate Level

Proteins:

• Found in muscles, bones, skin, hair, and almost every part of the body.
• Known as the building blocks of life.
• Natural polyamides — naturally occurring polymers.
• Made of amino acids.

Amino acids:

• Basic structural unit of protein.
• Contains:

Protein synthesis:

• Requires adequate amounts of amino acids.
• Amino acids join together through the amino group of one molecule and the carboxyl group of another, eliminating a water molecule.
• The bond is called a peptide bond.
• Two amino acids joined together form a dipeptide.
• Many amino acids joined together form a protein.
• The sequence of amino acid linkages is called the primary structure of the protein.

Structure of proteins:

• Primary: Sequence of amino acids in a chain.
• Secondary: Folding and twisting of the amino acid chain.
• Tertiary: Twists and folds of the secondary structure fold again to form a larger three-dimensional structure.
• Quaternary: Protein consisting of more than one folded amino acid chain.

Examples:

- Enzymes, hemoglobin, collagen, insulin.

Key point: Proteins are natural polyamides made of amino acids. Amino acids are the building blocks of proteins.

Solved Example

Example: Describe the Structure of an Amino Acid

Question: Describe the structure of an amino acid.

Solution:

An amino acid is a simple organic compound consisting of:

• A basic group (amine group, -NH₂)
• An acidic group (carboxylic group, -COOH)
• A variable alkyl group (R) that is unique to each amino acid.

Final Answer: An amino acid contains an amine group, a carboxylic group, and a variable R group.

Example: What is a Peptide Bond?

Question: What is a peptide bond?

Solution:

The bond that joins two amino acid units is called a peptide bond.

The bond is:

-C - NH- (with a double bond to O on the C)

Final Answer: A peptide bond is the bond that joins two amino acids together. It is formed by the elimination of a water molecule.

Important Points

• - Proteins are found in our muscles, bones, skin, hair, and almost every part of the body.
• - Proteins are also known as the building blocks of life because they are the most abundant molecules present in the body.
• - Proteins are called natural polyamides because they are naturally occurring polymers.
• - Proteins are large, complex molecules made up of long chains of monomers which are all amino acids.
• - Amino acids are the basic structural unit of protein.
• - An amino acid is a simple organic compound consisting of:
• 1. A basic group (amine group, -NH₂)
• 2. An acidic group (carboxylic group, -COOH)
• 3. A variable alkyl group (R) that is unique to each amino acid.
• - The body makes proteins through a process called protein synthesis.
• - Molecules of amino acids join together through the amino group (-NH₂) of one molecule and the carboxyl group (-COOH) of another molecule by eliminating a water molecule.
• - The bond that joins two amino acid units is called a peptide bond.
• - When two amino acids join, the molecule is called a dipeptide.
• - In thousands of amino acid units joined together, the result is a protein molecule.
• - The sequence of amino acid linkages is called the primary structure of the protein.
• - Four levels of protein structure:
• 1. Primary: Sequence of amino acids in a chain.
• 2. Secondary: Folding and twisting of the amino acid chain.
• 3. Tertiary: Twists and folds of the secondary structure fold again to form a larger three-dimensional structure.
• 4. Quaternary: Protein consisting of more than one folded amino acid chain.
• - Examples of proteins: Enzymes, hemoglobin, collagen, insulin.

Remember

• - Proteins = natural polyamides made of amino acids.
• - Amino acids = building blocks of proteins.
• - Amino acid = amine group (-NH₂) + carboxylic group (-COOH) + R group.
• - Amino acids join by eliminating a water molecule.
• - Bond = peptide bond.
• - Two amino acids = dipeptide.
• - Many amino acids = protein.
• - Primary structure = sequence of amino acids.
• - Secondary = folding and twisting.
• - Tertiary = 3D structure.
• - Quaternary = more than one folded chain.
• - Examples: Enzymes, hemoglobin, collagen, insulin.

Common Mistakes

Quick Revision

Proteins:

Proteins are found in our muscles, bones, skin, hair, and almost every part of the body. Proteins are also known as the building blocks of life because they are the most abundant molecules present in the body. Proteins are called natural polyamides because they are naturally occurring polymers. Proteins are large, complex molecules made up of long chain of monomers which are all amino acids. Amino acids are the basic structural unit of protein. An amino acid is a simple organic compound consisting of two functional groups, a basic group (Amine group -NH₂), an acidic group (carboxylic group -COOH) with a variable alkyl group (R) that is unique to each amino acid.

The body makes proteins through a process called protein synthesis. Protein synthesis requires adequate amounts of amino acids.

Molecules of amino acids join together through the amino group (-NH₂) group of one molecule and the carboxyl (-COOH) group of another molecule by eliminating a water molecule.

The bond that joins two amino acid units is called a peptide bond. The molecule is called a dipeptide. There is an amino group on the left and a carboxyl on the right. Each of these groups can further join to join more amino acid units. In thousands of amino acid units join to form a giant molecule of protein. This sequence of amino acid linkages is called the primary structure of the protein.

Classification of Protein:

The proteins are classified on the basis of the shape, constitution, and nature of the molecule. Each amino acid is connected to the next amino acid by covalent bonds.

• Primary structure: Primary protein structure is a sequence of amino acids in a chain.
• Secondary structure: Secondary protein structure is formed by folding and twisting of the amino acid chain.
• Tertiary structure: Tertiary protein structure is formed when the twists and folds of the secondary structure fold again to form a larger three-dimensional structure.
• Quaternary structure: Quaternary protein structure is a protein consisting of more than one folded amino acid chain.

DO YOU KNOW?

Enzymes are proteins that fasten chemical reactions in the body. They act like small machines that help break down food, make molecules, and carry out other important functions in cells, all without being used up or changed themselves. Hemoglobin is found in red blood cells in our blood and carries oxygen from your lungs to your cells. In addition, a protein called collagen is a strong and tough material that makes up our skin and fingernails and even helps to hold our internal organs in place.

Insulin is a protein hormone that is made by specific cells inside the pancreas called beta cells. Insulin signals cells to absorb sugar from the bloodstream. Cells can't absorb sugar without insulin. Insulin protein is first produced as an immature, inactive chain of amino acids (preproinsulin).

60-Second Revision

• Proteins = natural polyamides made of amino acids.
• Amino acids = building blocks of proteins.
• Amino acid = amine group (-NH₂) + carboxylic group (-COOH) + R group.
• Amino acids join by eliminating a water molecule.
• Bond = peptide bond.
• Two amino acids = dipeptide.
• Many amino acids = protein.
• Primary structure = sequence of amino acids.
• Secondary = folding and twisting.
• Tertiary = 3D structure.
• Quaternary = more than one folded chain.
• Examples: Enzymes, hemoglobin, collagen, insulin.
• ⚠️ Warning: proteins are natural polyamides — they are polymers made of amino acids, not simple molecules.