3.1.4.1 Proteins

Question 1

What are amino acids?

Answer 1

Proteins are polymers made up of monomers which are called amino acids

Question 2

What do amino acids determine?

Answer 2

The sequence, type and number of the amino acids within a protein determine its structure and therefore its function

Question 3

What does the R group determine?

Answer 3

Each amino acid has a different R group, so therefore it determines how each amino acid differs, and also how their properties differ.

Question 3

How many different amino acids are there in organisms?

Answer 3

There are 20 different naturally occurring amino acids in living organisms

Question 4

What are the 3 groups which all amino acids contain?

Answer 4

-Amino group (NH2)
-Carboxyl group (COOH)
-R group (differs)

Question 5

What is the bond formed between 2 amino acids called?

Answer 5

A peptide bond

Question 6

What are the elements that amino acids contain?

Answer 6

-Carbon, hydrogen, oxygen, nitrogen
-some contain sulfur in their R group also

Question 7

Describe the primary structure of proteins

Answer 7

-the sequence of amino acids bonded together by peptide bonds
-unique sequence is specific for each protein so determines its structure and function
-amino acids are held together by peptide bonds

Question 7

Describe how a peptide bond is formed?

Answer 7

-peptide bonds are formed when two amino acids undergo a condensation reaction
-this reaction forms a dipeptide and a water molecule
-the dipeptide is held together by a peptide bond
-many amino acids bonded together via condensation reactions is known as a polypeptide

Question 8

What is produced by the hydrolysis of a dipeptide or polypeptide?

Answer 8

The addition of a water molecule breaks peptide bonds which results in the production of amino acids.

Question 9

Describe the secondary structure of a protein?

Answer 9

-hydrogen bonds are formed between the C=O group and H atoms
-this can form either an alpha-helix shape or Beta-pleated sheet
-the shape formed depends on the amino acid sequence

Question 10

Describe the tertiary structure of a protein

Answer 10

-the further folding of the secondary structure to form a unique shape
-this is held in place by bonds between R groups (the bond formed is determined by the R group)
-the bonds can be hydrogen bonds, ionic bonds or disulphide bonds

Question 10

Describe the quaternary structure of a protein?

Answer 10

-occurs in proteins that have more than one polypeptide chain
-the polypeptide chains are held together by hydrogen and ionic bonds

Question 11

Give the functions of proteins in the human body?

Answer 11

-enzymes that catalyse reactions
-red blood cells contain the protein haemoglobin which transports oxygen around the body
-proteins in muscle fibres allow movement of the body
-antigens for cell recognition
-carrier proteins for transport across cell surface membranes
-keratin and collagen for formation of connective tissue and structural components
-antibodies for protection gains invasion of foreign bodies (pathogens).
-insulin and glucagon for hormone control

Question 12

Describe the biochemical test for proteins

Answer 12

-add biurets reagent to the sample
-if protein is present, the colour will change from blue to lilac
-NOTE: this is a qualitative test so does not give a quantitative result for the amount of protein in a sample.

Question 13

How does polarity affect the function of a protein?

Answer 13

Polar amino acids will come into contact with water as they are hydrophilic eg. In cell membranes
Whereas, non-polar amino acids are hydrophobic so will remain inside cells

Question 14

Describe what a globular protein is

Answer 14

Proteins which have an and spherical shape when folded their tertiary structure, making them soluble in water.
-they are soluble as the non-polar hydrophobic r groups orientate themselves inwards, but the polar hydrophilic r groups orientate themselves outwards. This allows water molecules to surround them.
-they are useful in metabolic reactions and can be transported around organisms

Question 15

Describe what a fibrous protein is

Answer 15

A fibrous protein is long strands of polypeptide chains, which have cross-linkages due to hydrogen bonds
-they have little to no tertiary structure, and are insoluble in water.
-fibrous proteins are useful as structural proteins as they are strong and organised (due to repetitive amino acid sequence).