Proteins

Question 2

Functions of protein

Answer 2

Hair
Skin
Nails
Enzymes
Haemoglobin
Muscles

Question 3

Structure of aminoacid

Answer 3

The amino (-NH2) group & acid (-COOH) groups are involved in the formation of peptide bonds which hold the amino acids together to form a polypeptide chain
Residual (R) groups are involved in hydrogen bond, ionic bond & covalent bond formation which cause the polypeptide chain to fold

Question 4

Protein

Answer 4

Polypeptides & protein are chains of amino acids linked to each other by peptide bonds

Question 6

Heirarachies of protein structure

Answer 6

1. Primary structure
2. Secondary structure
3. Tertiary structure
4. Quaternary structure

Question 7

Primary structure of protein

Answer 7

It is the sequence of amino acids in a polypeptide chain held together by peptide bonds

Question 9

Secondary structure of protein

Answer 9

The secondary structure refers to the folding of the polypeptide chain (primary structure) into helices & pleated sheets. It is held together by H-bonds in the polypeptide backbone

Question 10

Alpha helix

Answer 10

The polypeptide chain is wound to form a helix.
It is held together by hydrogen bonds running parallel with the long helical axis.
There are many H-bonds making this a very stable & strong structure.

Question 11

Beta pleated sheet

Answer 11

The polypeptide chain zig-zags back & forwards forming a sheet. It is also held together by H-bonds

Question 12

Tertiary structure of protein

Answer 12

The tertiary structure of a protein is the complex 3D globular shape the polypeptide chain takes when the polypeptide chain twists & folds around itself

Question 13

The tertiary structure is maintained by:

Answer 13

1. Hydrophobic interactions
2. Hydrogen bond
3. Disulphide bridge
4. Ionic bond

Question 14

Hydrogen bond

Answer 14

The bond forms between some H-atoms [S+] & O atoms [S-]
When these charged groups are close to each other, opposite charges attract, forming H-bond
Bonds are weak the large number of bonds provide a considerable force to maintain the 3D shape

Question 15

Ionic bond

Answer 15

Formed between some of the strongly positive & negative amino acid chains which are sometimes found deep inside the protein molecule. They are stronger than H-bonds but can be broken by changes in pH & high temperatures

Question 16

Disulphide bond

Answer 16

An oxidation reaction occurs between two sulphuric containing groups resulting in a strong covalent bond known as disulphide bond.
These disulphide bonds are much stronger than H-bonds but they appear much less often. They are important for holding the folded polypeptide chains in place

Question 17

Hydrophilic & hydrophobic interactions

Answer 17

The hydrophobic regions of the polypeptide chain face away from water by folding inwards. The hydrophilic regions of the chain remain on the surface of the globular structure

Question 18

Quaternary structure of proteins

Answer 18

Quaternary structure is the linking together of two or more polypeptide chains.
It describes the way these polypeptide chains first together in three dimensions

Question 19

Denaturation

Answer 19

Changes in conditions such as temperature or pH affects the bonds that keep the 3D shapes of protein in place.
Even small changes can cause the bonds to break resulting in the loss of 3D shape of the protein. This is called denaturation

Question 20

Types of proteins

Answer 20

Proteins can be divided into two groups according to their structure
Fibrous
Globular