3.7 : Types Of Proteins

Question 1

What are the properties of globular proteins ?

Answer 1

• compact
• water soluble
• roughly spherical in shape

Question 2

Why are globular proteins soluble ?

Answer 2

The hydrophobic R - groups on the amino acid are kept away from the aqueous environment. The hydrophilic R - groups are on the outside, which means they are soluble.

Question 3

Is insulin globular or fibrous ? Describe its function.

Answer 3

• It is globular
• hormone involved in the regulation of blood glucose concentration
• transported in the bloodstream , so soluble

Question 4

Why do hormones like insulin need to have precise shapes?

Answer 4

Have to be able to fit into specific receptors on cell - surface membranes to have their effect

Question 5

What are conjugated proteins ?

Answer 5

Globular proteins that contain a non - protein component called a prosthetic group

Question 6

Describe the structure of haemoglobin. What is it’s function and how does it do it ?

Answer 6

Quaternary protein made from four polypeptides -> two alpha and two beta subunits

Each subunit contains a prosthetic haem group

The iron ii ions present in the haem groups are each able to combine reversibly with an oxygen molecule

Question 7

Describe the structure of catalase. What is it’s function ?

Answer 7

Quaternary protein containing four haem prosthetic groups

Iron ii ions in the prosthetic groups allow catalase to interact with hydrogen peroxide and speed up its breakdown

Hydrogen peroxide is a common byproduct of metabolism but is damaging to cells and cell components if allowed to accumulate

Catalase makes sure this doesn’t happen

Question 8

Describe the structure and properties of fibrous proteins

Answer 8

Long , insoluble molecules

This is due to the presence of a high promotion of amino acids with hydrophobic R - groups in their primary structures

Limited range of amino acids, usually with small R - groups

Amino acid sequence in primary structure is quite repetitive

This leads to very organised structures

Question 9

What is the main difference between fibrous and globular proteins ?

Answer 9

Fibrous proteins tend to make strong, long molecules which are not folded into complex 3D shapes like globular proteins

Question 10

Is keratin globular or fibrous? What bonds does it have and how does it affect it ?

Answer 10

Fibrous

Large proportion of cysteine

This results in many strong disulfide bonds forming strong, inflexible and insoluble materials

The degree of disulfide bonds determines the flexibility - hair contains fewer bonds making it more flexible than nails, which contain more bonds

Question 11

Is elastin fibrous or globular ? What is the structure and function ?

Answer 11

Fibrous

Present in the walls of blood vessels and in the alveoli of the lungs

They give these structures the flexibility to expand when needed, but also to return to their normal size

Quaternary protein made from molecules called tropoelastin

Question 12

Is collagen fibrous or globular ? What is it’s function and structure ?

Answer 12

Fibrous

Connective tissue found in skin, tendons , ligaments and the nervous system

Number of different form but all are made up of three polypeptides wound together in a long and strong rope - like structure

Collagen has flexibility