Proteins

Question 1

How many naturally occurring amino acids are there?

Answer 1

20

Question 2

Name the monomer that makes up protein polymers

Answer 2

Amino acid

Question 3

List the four groups that make up an amino acid

Answer 3

Amino group (-NH2)
Carboxyl group (-COOH)
Hydrogen atom (-H)
R (side) group- this group is variable and can be a variety of different chemical groups. Each amino acid has its own R group and the 20 naturally occurring amino acids differ only in their R (side) group.

Question 4

Describe how a peptide bond is formed between two amino acid monomers

Answer 4

Amino acids join in a condensation reaction. The water molecule is formed from combining an (-OH) from the carboxyl group of one amino acid with a (-H) from the other amino acids. The two amino acids are now joined by a peptide bond between the carbon atom of one amino acid and the nitrogen of another.

Question 5

Describe the primary structure of proteins

Answer 5

Proteins are polymers made up of many amino acid chains.
There are many combinations possible due to the 20 naturally occurring amino acids.
The primary structure of a protein determines its shape and hence its function.
The primary structure of a protein describes its structure on a molecular level.

Question 6

What is the secondary structure of a protein

Answer 6

Polypeptide chains can be twisted into a 3D shape due to hydrogen bonds between chains. This 3D shape could be an alpha-helix or a beta pleated sheet.

Question 7

Describe how hydrogen bonds form to create the secondary structure of proteins

Answer 7

The amino acids that make up a polypeptide chain posses both (-NH) and (-C=O) groups on either side of every peptide bond.
The hydrogen from the (-NH) group has a positive overall charge and the Oxygen from the (-C=O) group has a negative charge and this allows hydrogen bonds to form due to the difference in electro-negativities.

Question 8

Describe the tertiary structure of proteins

Answer 8

The a-helices or beta pleated sheets can be twisted/folded to form a tertiary structure.
This is maintained by a number of different bonds and which bonds are formed where depends on primary structure.
It is the 3D tertiary structure that is important in relation to its function.

Question 9

List and describe the bonds which maintain the tertiary structure of a protein

Answer 9

Disulfide bridges= these are fairly strong so hold the chains together well and are not easily broken
Ionic bonds= formed between the carboxyl and amino groups that are not involved in making peptide bonds. They are weaker than the disulfide bridges and are easily broken by changes in PH
Hydrogen bonds= numerous but easily broken. They add collective strength.

Question 10

What is the quarternary structure of proteins

Answer 10

When two or more large protein molecules that have formed different/individual tertiary structures join together to form complex molecules, this is known as quarternary structure. There can also be non-protein (prosthetic) groups associated with a protein in its quarternary structure such as the haem (iron-containing) group in haemoglobin.

Question 11

Which are the key protein structures to remember

Answer 11

Primary structure= the sequence of amino acids determines the 3D shape of a protein
Tertiary structure= this 3D structure determines the proteins function.