Levels of protein structure

Question 1

What level of structure is the sequence of amino acids that forms the protein?

Answer 1

Primary

Question 2

What level of structure is formed when the chain of amino acids coils to form an alpha helix or a beta pleated sheet?

Answer 2

Secondary

Question 3

What kind of bonds hold the secondary structure in place?

Answer 3

Hydrogen. These are weak bonds, but many are formed, so overall they give great stability to parts of the protein molecule.

Question 4

What level of structure is formed when the coils and pleats of the secondary structure themselves coil or fold?

Answer 4

Tertiary. Lots of bonds are involved in this (e.g. hydrophobic/hydrophilic interactions, ionic bonds [as R groups on amino acids are sometimes charged] , disulphide bonds [cysteine has sulfur in its R group], hydrogen bonds)

Question 5

Maintaining the same tertiary structure is vital to the function of enzymes. Why?

Answer 5

Because if it were changed, then the enzymes active site structure may be changed so that is would no longer be complementary to its substrate so would no longer be able to catalyse the reaction that its supposed to catalyse.

Question 6

What are the two big groups of protein?

Answer 6

Globular and fibrous

Question 7

Describe globular proteins.

Answer 7

Usually roll up to form balls.
Usually soluble.
Include enzymes (e.g. protease and amylase) and antibodies.

Question 8

Are fibrous proteins usually soluble or insoluble?

Answer 8

Insoluble - they usually have structural roles

Question 9

What kind of protein is haemoglobin?

Answer 9

• Globular (so soluble).
• Function: carry oxygen from lungs to tissues.
• It consist of 4 polypeptide chains - 2 alpha chains and 2 beta chains (therefore has a quaternary structure), and each polypeptide has a haem group which contains an iron ion.
• The haem group is known as a prosthetic group because it isn’t made of amino acids so it is non protein.
• Oxygen molecule binds to iron in haem group (so one haemoglobin can carry 4 oxygen molecules as has 4 haem groups)

Question 10

What kind of protein is collagen, and what is its function?

Answer 10

• Fibrous (so insoluble).
• Function: provide mechanical strength in many areas such as walls of arteries, tendons, bones, and connective tissues
• No prosthetic group