3.6 : Structure Of Proteins

Question 1

What are peptides?

Answer 1

Polymers made of amino acid molecules.

Question 2

What are proteins made of?

Answer 2

One or more polypeptides arranged as complex macromolecules.

Contain carbon, hydrogen, oxygen and nitrogen.

Question 3

Describe the twenty different amino acids

Answer 3

5 are non essential as our bodies can make them from other amino acids

9 are essential and can only be obtained from what we eat

6 are conditionally essential as they are only needed by infants and growing children

Question 4

Give the general structure of amino acids

Answer 4

Has an amine group and a carboxylate group with a central carbon atom in the middle. Has an R group joined to the central carbon.

Question 5

How do amino acids join together?

Answer 5

• the hydroxyl in the carboxylic acid group of one amino acid reacts with a hydrogen in the amine group of another amino acid
• a peptide bond is formed between the amino acids and water is produced ( condensation )
• the result is a dipeptide. When this is repeated a lot a polypeptide forms
• it is catalysed by the enzyme peptidyl transferase

Question 6

What happens when different R - groups interact?

Answer 6

They form different types of bonds and these lead to the long chains of amino acids folding into complex structures ( proteins ).

Question 7

Describe the structure and bonding in the primary structure

Answer 7

Structure : sequence in which the amino acids are joined. The amino acids in the sequence influence how it folds into its final shape, and therefore its function.

Bonding : peptide bonds

Question 8

Describe the structure and bonding in the secondary structure

Answer 8

Structure : the oxygen, hydrogen and nitrogen atoms of the amino acids interact. Hydrogen bonds may form, pulling it into a coil shape called an alpha helix. Polypeptide chains can also lie parallel to one another joined by hydrogen bonds, forming sheet - like structures. This is called the beta pleated sheet.

Bonding : hydrogen bonds

Question 9

Describe the structure, interactions and bonding in the tertiary structure

Answer 9

Structure : the folding of a protein into its final shape. Often includes sections of secondary structure.

Interactions : hydrophobic and hydrophilic intersections - weak interactions between polar and non - polar R - groups

Bonding : - hydrogen bonds - the weakest of the bonds formed

• ionic bonds - stronger than H bonds, and form between oppositely charged R - groups
• disulfide bonds - covalent and the strongest of the bonds but only form between R - groups that contain sulfur atoms

Question 10

Describe the structure and bonding in the quaternary structure

Answer 10

Structure : two or more individual proteins called subunits, which can be identical or different

Bonding : same as in tertiary sector, but they are between different proteins rather than within one molecule

Question 11

How do you breakdown peptides?

Answer 11

• water molecule used to break the peptide bond in a hydrolysis reaction
• protease used to catalyse reverse reaction