PROTEINS

Question 1

What are proteins required for?

Answer 1

Proteins are required for life, growth, and maintenance of the body.

Question 2

What is the origin of the word ‘protein’?

Answer 2

The word ‘protein’ is derived from the Greek word ‘proteios,’ meaning primary or of prime importance.

Question 3

What are proteins made of?

Answer 3

All proteins are polymers of α-amino acids.

Question 4

What functional groups do amino acids contain?

Answer 4

Amino acids contain amino (–NH₂) and carboxyl (–COOH) functional groups.

Question 5

How are amino acids classified?

Answer 5

Amino acids are classified as α, β, γ, δ, etc., based on the position of the amino group relative to the carboxyl group.

Question 6

Which type of amino acids are obtained from protein hydrolysis?

Answer 6

Only α-amino acids are obtained on hydrolysis of proteins.

Question 7

Can amino acids contain other functional groups?

Answer 7

Yes, amino acids may contain other functional groups in addition to amino and carboxyl groups.

Question 8

How are α-amino acids named?

Answer 8

α-Amino acids have trivial names that often reflect their properties or sources.

Question 9

Why is glycine named so?

Answer 9

Glycine is named for its sweet taste; ‘glykos’ means sweet in Greek.

Question 10

Why is tyrosine named so?

Answer 10

Tyrosine was first obtained from cheese; ‘tyros’ means cheese in Greek.

Question 11

How are amino acids represented?

Answer 11

Amino acids are generally represented by a three-letter symbol, and sometimes by a one-letter symbol.

Question 12

How are amino acids classified based on their chemical nature?

Answer 12

Amino acids are classified as acidic, basic, or neutral depending on the number of amino and carboxyl groups.

Question 13

What makes an amino acid neutral?

Answer 13

An amino acid is neutral if it has an equal number of amino and carboxyl groups.

Question 14

What makes an amino acid basic?

Answer 14

An amino acid is basic if it has more amino groups than carboxyl groups.

Question 15

What makes an amino acid acidic?

Answer 15

An amino acid is acidic if it has more carboxyl groups than amino groups.

Question 16

What are nonessential amino acids?

Answer 16

Nonessential amino acids are those that can be synthesized by the body.

Question 17

What are essential amino acids?

Answer 17

Essential amino acids are those that cannot be synthesized by the body and must be obtained through diet.

Question 18

What are the physical properties of amino acids?

Answer 18

Amino acids are usually colorless, crystalline solids that are water-soluble and have high melting points.

Question 19

How do amino acids behave in comparison to simple amines or carboxylic acids?

Answer 19

Amino acids behave like salts rather than simple amines or carboxylic acids due to the presence of both acidic (–COOH) and basic (–NH₂) groups.

Question 20

What is a zwitterion?

Answer 20

A zwitterion is a dipolar ion formed in aqueous solution when the carboxyl group loses a proton and the amino group accepts a proton.

Question 21

What is the charge of a zwitterion?

Answer 21

A zwitterion is neutral but contains both positive and negative charges.

Question 22

Why do amino acids show amphoteric behavior?

Answer 22

Amino acids show amphoteric behavior in their zwitterionic form because they can react with both acids and bases.

Question 23

Which amino acid is not optically active?

Answer 23

Glycine is the only naturally occurring α-amino acid that is not optically active.

Question 24

Why are most α-amino acids optically active?

Answer 24

Most α-amino acids are optically active because their α-carbon atom is asymmetric.

Question 25

In which configurations do amino acids exist?

Answer 25

Amino acids exist in both ‘D’ and ‘L’ forms, but most naturally occurring amino acids have the L-configuration.

Question 26

What are proteins made of?

Answer 26

Proteins are polymers of α-amino acids.

Question 27

How are amino acids connected in proteins?

Answer 27

Amino acids are connected by peptide bonds or peptide linkages.

Question 28

What is a peptide linkage chemically?

Answer 28

A peptide linkage is an amide bond formed between a –COOH group and an –NH₂ group.

Question 29

How is a peptide bond formed?

Answer 29

A peptide bond forms when the amino group of one amino acid reacts with the carboxyl group of another, eliminating a water molecule.

Question 30

What is the product of a reaction between two amino acids?

Answer 30

The product is called a dipeptide because it consists of two amino acids.

Question 31

What happens when glycine reacts with alanine?

Answer 31

The carboxyl group of glycine reacts with the amino group of alanine, forming a dipeptide called glycylalanine.

Question 32

What is formed when a third amino acid joins a dipeptide?

Answer 32

A tripeptide is formed, containing three amino acids linked by two peptide bonds.

Question 33

What are peptides with four, five, or six amino acids called?

Answer 33

Tetrapeptide (four amino acids), Pentapeptide (five amino acids), Hexapeptide (six amino acids).

Question 34

What is a polypeptide?

Answer 34

A polypeptide is a chain of more than ten amino acids linked by peptide bonds.

Question 35

When is a polypeptide considered a protein?

Answer 35

A polypeptide with more than 100 amino acids and a molecular mass over 10,000u is typically called a protein.

Question 36

Is the distinction between polypeptides and proteins clear?

Answer 36

No, the distinction is not sharp. Some polypeptides, like insulin (51 amino acids), are considered proteins due to their defined structure.

Question 37

Proteins are classfied into 2

Answer 37

Fibrous and globular

Question 38

How are proteins classified based on molecular shape?

Answer 38

Proteins are classified into two types based on their molecular shape.