Fibrous and globular proteins

Question 1

What is a fibrous protein?

Answer 1

Has a relatively long, thin structure, is insoluble in water and metabolically inactive, often having a structural role within an organism.

Question 2

What is a globular protein?

Answer 2

Has molecules of a relatively spherical shape, which are soluble in water, and often have metabolic roles within the organism.

Question 3

What is a prosthetic group?

Answer 3

A non-protein component that forms a permanent part of a functioning protein molecule.

Question 4

Describe a fibrous protein.

Answer 4

They have regular, repetitive sequences of amino acids and are usually insoluble in water.

Question 5

What do fibrous proteins usually do?

Answer 5

They usually form fibres which form a structural role.

Question 6

Globular proteins tend to fold up into what shape?

Answer 6

A sphere

Question 7

How does a globular protein turn itself into a spherical shape?

Answer 7

Any hydrophobic R-groups are turned inwards and the hydrophilic R-groups are turned outwards.

Question 8

Why are globular proteins soluble in water?

Answer 8

Because the hydrophobic R-groups face in to create a spherical shape it means that the hydrophilic R-groups are facing outwards. Water molecules are attracted and can attach to the hydrophilic R-groups. This then makes it soluble in water.

Question 9

What is the purpose of collagen?

Answer 9

To provide mechanical strength.

Question 10

What does collagen do in the artery walls?

Answer 10

It prevents them from bursting and allows them to withstand high pressures.

Question 11

Bones are first made of collagen and then reinforced with ________ .

Answer 11

Calcium phosphate.

Question 12

Where in the body can collagen be found?

Answer 12

Arteries
Bones
Tendons
Cartilage
Connective tissue.

Question 13

What do tendons do?

Answer 13

Connect muscle to bone.

Question 14

Why is keratin very strong?

Answer 14

It contains lots of cysteine (an amino acid) so contains a lot of disulphide bridges making it very strong.

Question 15

What is the function of Keratin?

Answer 15

To provide mechanical protection
An impermeable barrier to infection
Waterproof so that no water born pollutants can enter

Question 16

What is made up of Keratin in the body?

Answer 16

Hair
Fingernails
Claws
Hoofs
Horns
Scales
Fur
Feathers

Question 17

What are the characteristics of Elastin? Why is this?

Answer 17

Strong and extensible.

Cross-linking and coiling of the polypeptide chain

Question 18

Where is elastin found? Describe it’s function at each place.

Answer 18

Skin, allows it to stretch around bones.
Lungs, allows it to inflate and deflate.
Bladder, allows it to expand to hold urine.
Blood vessels, allows them to expand and constrict to assist the maintenance of blood pressure.

Question 19

Describe the structure of haemoglobin.

Answer 19

The quaternary structure is made up of four polypeptide chains.
2 of the chains are alpha globin chains.
2 of the chains are beta globin chains.

Question 20

What is on the outside of each globin chain in a haemoglobin molecule?

Answer 20

A haem group (a prosthetic group)

Question 21

What is contained in each haem group?

Answer 21

An iron ion.

Question 22

What is the function of haemoglobin?

Answer 22

To carry oxygen out of the lungs and to the tissue.

It also carries carbon dioxide form the tissue to the lungs.

Question 23

When something happens to haemoglobin at the lungs the RBC goes from purple to red. What is happening?

Answer 23

The oxygen binds to the iron ion at the lungs which turns the RBC and in turn the blood, red.

Question 24

What is insulin made up of?

Answer 24

Two polypeptide chains.

Question 25

Describe the two polypeptide chains of insulin.

Answer 25

The first chain begins with a section of alpha helix.

The second chain ends with a beta pleated sheet.

Question 26

Because there are hydrophilic R-groups on the outside of insulin what does this allow it to be?

Answer 26

Water soluble.

Question 27

What does insulin do?

Answer 27

It binds to glycoprotein receptors on the outside of muscle and fat cells to increase their uptake of glucose.

Question 28

What is the function of pepsin?

Answer 28

To digest proteins.

Question 29

Pepsin lives in the stomach. How is it able to survive there? Relate to its structure.

Answer 29

It contains 43 acidic R-groups.

Few of the basic groups accept hydrogen ions so that the tertiary structure is unchanged by stomach acid.