Lesson 10 - Protein - amino acid structure & peptide bond formation

Question 1

What are some examples of different proteins

Answer 1

• Enzymes - biological catalysts for reactions
• In the cell membrane (channels and transporters) - to allow things to cross the membrane that usually can’t
• Structural proteins eg. Collagen
• Hormones
• Antibodies - involved in the immune response
• Transport e.g. Haemoglobin - a protein that transports O2 round the body in the blood
• Muscle contraction e.g. Actin and Myosin proteins in muscle cells

Question 2

What are the monomers from which proteins are made?

Answer 2

Amino acids

Question 3

What’s the general structure of an amino acid?

Answer 3

R
|
H2N —- C —- COOH
|
H

Question 4

What do the NH2, COOH and R represent in an amino acid?

Answer 4

NH2 - amine group
COOH - carboxyl group
R - a side chain

Question 5

What’s meant by a functional protein?

Answer 5

Contains 1 or more polypeptides

Question 6

Which elements do proteins contain?

Answer 6

They contain carbon, hydrogen and oxygen – but unlike carbohydrates & lipids, they always contain Nitrogen.
Many proteins also contain sulphur and some contain phosphorus.

Question 7

General formula diagram of an amino acid

Answer 7

H R O
| | ||
N – C – C
| | |
H H OH

Question 8

Polymerisation meaning

Answer 8

• The resulting chain of many amino acids is called a polypeptide
• The sequence/order of amino acids in the polypeptide chain is called the primary structure of a protein
• The primary structure of proteins is determined by our DNA base sequence - instructions for the order of amino acids in proteins
• The primary sequence determines the shape of a protein and therefore its function
• Remember, shape = function
• A protein can be made up of 1 polypeptide chain (simple) or more commonly many

Question 9

Whats the test for protein?

Answer 9

• Add a few drops of biuret reagent (sodium hydroxide & copper (II) sulphate) to the sample you want to test (they can also be added separately)
• The sodium hydroxide and copper sulphate together (biuret reagent) is blue. When added to the test solution, if a purple colour develops this indicates the presence of peptide bonds and therefore protein (The Nitrogen in a peptide bond forms a purple complex with the Copper II ions (Cu2+).
• If no protein is present the solution remains blue.