2: Protein Structure and Function

Question 1

What is the conformation of a protein? What is the usual conformation of a protein? What determines the conformation of a protein? What does this mean for polypeptides with a particular sequence of amino acids?

Answer 1

• its 3-dimensional structure
• a globular shape

the folding of polypeptides in that protein:

• sequence of amino acids in a polypeptides determines how the folding is done
• and so determines the conformation of a protein

conformation will tend to be precisely the same

Question 2

How is the structure of a protein stabilised?

Answer 2

by intramolecular bonds between amino acids in the polypeptides that are brought together by the folding process

Question 3

What is ‘denaturation’?

Answer 3

a process that damages the conformation of protiens

Question 4

Give 2 causes of denaturation of proteins.

Answer 4

• heat

- pH

Question 5

How does heat denature proteins?

Answer 5

• causes vibrations within protein molecules = break intramolecular bonds = cause conformation change
• heat denaturation = almost always irreversible

Question 6

Give example of heat denaturing proteins.

Answer 6

• demonstrated by heating egg white (contains dissolved albumin proteins)
• proteins denatured and turn insoluble

Question 7

How does pH denature proteins?

Answer 7

• every protein has ideal pH at which its conformation is normal
• if pH = increased (adding alkali) or decreased (adding acid) = conformation may initially stay the same but denaturation will eventually occur when pH has deviated too far from ideal
• this is because pH change causes intramolecular bonds to break within protein molecule

Question 8

Give 6 examples of proteins synthesized by living organisms and say what type of protein they are e.g. hormone.

Answer 8

1. rubisco (enzyme)
2. insulin (hormone)
3. immunoglobulins (antibodies)
4. rhodopsin (pigment)
5. collagen (structural protein)
6. spider silk (structural protein)

Question 9

Function of protein: rubisco.

Answer 9

• is an enzyme
• active site catalyses the photosynthesis reaction that fixes carbon dioxide from the atmosphere
• provides all carbon needed by living organisms o make sugars and other carbon compounds

Question 10

Function of protein: insulin.

Answer 10

• is a hormone
• carried dissolved in the blood and binds specifically and reversibly to insulin receptors in the membranes of body cells, causing cells to absorb glucose and lower the blood glucose concentration

Question 11

Function of protein: immunoglobulins.

Answer 11

• is an antibody
• binds to pathogens
• immune system can produce a huge range of immunoglobulins, each with a different type of binding site, allowing specific immunity against many diseases

Question 12

Function of protein: rhodopsin.

Answer 12

• is a pigment
• that makes the rod cells of the retina light-sensitive
• has non-amino acid part called retinal that absorbs a photon of light -> rod cell sends a nerve impulse to the brain

Question 13

Function of protein: collagen.

Answer 13

• is a structural protein
• 3 polypeptides wound together to form a rope-like conformation
• used in skin to prevent tearing, in bones to prevent fractures and in tendons and ligaments to give tensile strength

Question 14

Function of protein: spider silk.

Answer 14

• structural protein
• used to make webs for catching prey and lifelines on which spiders suspend themselves
• very high tensile strength and becomes stronger when stretched, so resisting breakage