Question

What determines the shape of a protein? ...

Which of the following is not a function of protein molecules? ...

Which type of substance are enzymes made of? ...

What is the name of a substance that speeds up the rate of a chemical reaction, but is unchanged by the proce

ss?

Answer 1

 Proteins are the most abundant biomolecules of the living system.

 Chief sources of proteins are milk, cheese, pulses, peanuts, fish, meat, etc.

 They occur in every part of the body and form the fundamental basis of structure and

functions of life.

 They are also required for growth and maintenance of body.

 The word protein is derived from Greek word, “proteios” which means primary or of

prime importance.

 Proteins are polypeptides.

[Peptide == a compound consisting of two or more amino acids linked in a chain].

 Proteins are linear chains of amino acids linked by peptide bonds.

 Each protein is a polymer of amino acids.

[Monomer == a molecule that can be bonded to other identical molecules to form a

polymer].

 Dietary proteins are the source of essential amino acids.

 Therefore, amino acids can be essential or non-essential.

[Non-Essential Amino Acids == Amino Acids that our body can make].

[Essential Amino Acids == We get them through our diet/food].

 Collagen is the most abundant protein in animal world.

 Ribulose bisphosphate Carboxylase-Oxygenase (RuBisCO) is the most abundant protein in the whole of the biosphere.Structure of Proteins

 You have already read that proteins are the polymers of α-amino acids and they are

connected to each other by peptide bond or peptide linkage.

 Chemically, peptide linkage is an amide [an organic compound containing the group -

C(O)NH2] formed between –COOH group and –NH2 group.

 The reaction between two molecules of similar or different amino acids, proceeds

through the combination of the amino group of one molecule with the carboxyl

group of the other.

 This results in the elimination of a water molecule and formation of a peptide bond –

CO–NH–. The product of the reaction is called a dipeptide because it is made up of

two amino acids.

 If a third amino acid combines to a dipeptide, the product is called a tripeptide.

 A tripeptide contains three amino acids linked by two peptide linkages.

 Similarly when four, five or six amino acids are linked, the respective products are

known as tetrapeptide, pentapeptide or hexapeptide, respectively.

 When the number of such amino acids is more than ten, then the products are called

polypeptides.

 A polypeptide with more than hundred amino acid residues, having molecular mass

higher than 10,000u is called a protein.

 However, the distinction between a polypeptide and a protein is not very sharp. Polypeptides with fewer amino acids are likely to be called proteins if they ordinarily

have a well-defined conformation of a protein such as insulin which contains 51

amino acids.

 Proteins can be classified into two types on the basis of their molecular shape:

Fibrous Proteins and Globular proteins.

Fibrous proteins

 When the polypeptide chains run parallel and are held together by hydrogen and

disulphide bonds, then fibre– like structure is formed.

 Such proteins are generally insoluble in water. Some common examples are keratin

(present in hair, wool, silk) and myosin (present in muscles), etc.

Globular proteins

 This structure results when the chains of polypeptides coil around to give a spherical

shape.

 These are usually soluble in water. Insulin and albumins are the common examples

of globular proteins.

Primary structure of proteins

 Proteins may have one or more polypeptide chains. Each polypeptide in a protein has

amino acids linked with each other in a specific sequence and it is this sequence of

amino acids that is said to be the primary structure of that protein.

 Any change in this primary structure i.e., the sequence of amino acids creates a

different protein.

Secondary structure of proteins

 The secondary structure of protein refers to the shape in which a long polypeptide Protein found in a biological system with a unique three-dimensional structure and

biological activity is called a native protein.

 When a protein in its native form, is subjected to physical change like change in

temperature or chemical change like change in pH, the hydrogen bonds are

disturbed. Due to this, globules unfold and helix get uncoiled and protein loses its

biological activity. This is called denaturation of protein.

 During denaturation 2° and 3° structures are destroyed but 1º structure remains

intact. The coagulation of egg white on boiling is a common example of

denaturation. Another example is curdling of milk which is caused due to the

formation of lactic acid by the bacteria present in milk.

Role of Proteins

1. Some transport nutrients across cell membrane,

2.