1.6 proteins

Question 1

What is the size, shape and frequency of proteins?

Answer 1

• Proteins are very large molecules
• Each organism has numerous proteins which are unique to their species
• the shape of any one protein molecules differs from every other type of protein, and is very specific to its function.

Question 2

What are amino acids?

Answer 2

the basic monomer that make up the polypeptide polymer, which make up proteins.

Question 3

What is the structure of an amino acid?

Answer 3

Each amino acid has a central carbon atom with four different chemical groups attached:
1) AMINO GROUP: (-NH2)- a basic group
2) CARBOXYL GROUP: (-COOH)- an acidic group
3) HYDROGEN
4) R GROUP: a variety of different chemical groups.
each amino acid has a different R group

Question 4

Describe the formation of a dipeptide.

Answer 4

Two amino acids undergo a conensation reaction which causes the formation of a peptide bond between the carbon of one AA and the nitrogen atom of the other.

• the water molecule is made from combining the -OH of the carboxyl group and the -H from the amino group of another amino acid.
• likewise, the molecule can be broken up by the adition of water (hydrolysis)

Question 5

What is a polypeptide and how is it formed?

Answer 5

A chain of hundreds of amino acids formed by a series of condensation reactions.

Question 6

What is the primary structure of a protein?

Answer 6

The sequence of amino acids in a polypeptide.

• sequence is determined by DNA
• Determines protein’s ultimate shape and therefore function.
• a change in a single amino acid will change or stop the function.
• Simple proteins may only ave one, but most proteins have multiple polypeptide chains.

Question 7

Describe the secondary structure of a protein.

Answer 7

• The amino acid chains which make up a polypeptide possess -NH and -C=O groups on either side of the peptide bond.
• The -NH group has a + charge and the O of the -C=O group has a - charge.
• this means they readily form weak hydrogen bonds this causes the polypeptide chain to be folded into a 3D shape such as an alpha helix coil.

Question 8

Describe the tertiary structure of a protein.

Answer 8

• The secondary structures of a protein can be twisted and folded further into a complex and specific 3D shape, known as the tertiary structure.
• these are maintained by a number of different bonds
• the tertiary structure makes each protein distinctive and makes it recognizable.

Question 9

What are the bonds which make up the tertiary structure of a protein?

Answer 9

DISULFIDE BRIDGES: fairly strong, not easily broken
IONIC BONDS: formed between a carboxyl and amino groups not involved in forming peptide bonds. weaker and easily broken by changes in PH
HYDROGEN BONDS: numerous but easily broken.

Question 10

describe the quaternary structure of a protein.

Answer 10

Large proteins form complex molecules containing a number of polypeptide chains linked in various ways.
- may also include non-protein groups, eg: iron in the haem group if haemoglobin

Question 11

What is the test for protiens?

Answer 11

Biuret test to detect peptide bonds:

1) Place sample in a test tube and add an equal volume of sodium hydroxide at room temp.
2) Add a few drops of very dilute copper (II) sulfate solution and mix gently
3) A purple colouration indicates the presence of of peptide bonds. if solution stays blue, no protein is present.