3.7 Types of proteins

Question 1

What are the characteristics of globular proteins?

Answer 1

• Compact
• Water soluble
• Spherical
• Hydrophilic R-groups on the outside - this makes these proteins soluble

Question 2

What roles is a globular protein involved in?

Answer 2

• Chemical reactions
• Immunity
• Muscle contraction

Question 3

What type of protein is insulin?

Answer 3

Globular

Question 4

Explain what insulin is

Elaborate on hormones

Answer 4

1. A hormone involved in regulation of blood glucose concentration
2. Hormones are transported via bloodstream so need to be soluble
   - Hormones need to fit into specific receptors on plasma membranes to have their effect so need to have a precise shape

Question 5

What are conjugated proteins?

Answer 5

Globular proteins containing a non-protein component called a prosthetic group

Question 6

What are simple proteins?

Answer 6

Proteins without prosthetic groups

Question 7

Elaborate on prosthetic groups

Answer 7

• Different types
• Lipids can mix with proteins forming lipoproteins
• Carbohydrates can mix with proteins forming glycoproteins
• Metal ions + molecules from vitamins form prosthetic groups
• These are called cofactors when they’re needed for the protein to carry out its function
• Haem groups (containing an iron II ion) are an example of prosthetic groups

Question 8

Spare

Answer 8

spare

Question 9

spare

Answer 9

spare

Question 10

spare

Answer 10

spare

Question 11

What is haemoglobin?

Answer 11

Red, oxygen-carrying pigment founds in erythrocytes (red blood cells)

Question 12

What type of protein is haemoglobin?

Answer 12

Quaternary protein

Question 13

Describe and elaborate on the structure of haemoglobin

Answer 13

• Made from 4 polypeptides, 2 alpha subunits and 2 beta subunits
• Each subunit contains a prosthetic haem group
• Iron ions in haem group can combine reversibly with an oxygen molecule - this enables haemoglobin to transport oxygen

Question 14

as

Answer 14

as

Question 15

as

Answer 15

as

Question 16

as

Answer 16

as

Question 17

as

Answer 17

as

Question 18

What is catalase? What type of protein is catalase?

Answer 18

1. Enzyme

2. Quaternary protein

Question 19

What is catalase made up of?

Answer 19

4 haem prosthetic groups

Question 20

What does the presence of iron II ions allow catalase to do?

Answer 20

Allows catalase to interact with hydrogen peroxide and speed up its breakdown

Question 21

What is hydrogen peroxide?

Answer 21

A common byproduct of metabolism

Damaging to cells if it accumulates - catalase prevents this from happening

Question 22

What do fibrous proteins tend to make?

Answer 22

Strong, long molecules NOT folded into 3-D shapes like globular proteins

Question 23

What are fibrous proteins made from? Explain why.

Answer 23

Long, insoluble molecules - due to the presence of a high proportion of amino acids with hydrophobic R-groups in their primary structures

Question 24

What do fibrous proteins contain?

Answer 24

Limited range of amino acids with small R-groups

Question 25

Describe the amino acid sequence in the primary structure of fibrous proteins. What does this lead to?

Answer 25

1. Repetitive

2. Leads to very organised structures

Question 26

Give examples of fibrous proteins

Answer 26

1. Keratin
2. Elastin
3. Collagen

Question 27

What is keratin?

Answer 27

Hair
Skin
Nails

Question 28

What does keratin contain? What does this result in?

Answer 28

1. A high proportion of the sulfur-containing amino acid, cysteine
2. Many strong disulfide bridges forming strong, inflexible and insoluble materials