Protein structure

Question 1

What is a protein?

Answer 1

Polymers of amino acids, joined together by peptide bonds

Question 2

Describe how amino acids bond to form the primary structure of a protein

Answer 2

Condensation reaction between H (from amine) and OH (from carboxyl). A covalent peptide bond is formed between the two amino acids.

Question 3

Describe how R groups interact to determine the tertiary structure of the protein

Answer 3

• Some R groups repel, some attract
• Disulphide bridges form between specific atoms
• Hydrogen bonds form
• Ionic bonds form between oppositely charged atoms
• Hydrophilic R groups move to the outside of the molecule, in contact with water molecules inside the aqueous cell
• Hydrophobic R groups move to the inside of the molecule, shielded from other water molecules

Question 4

State two properties of collagen that make it suitable for its purpose

Answer 4

• Strong
• Flexible

Question 5

Describe how you would user a biochemical test to show if a solution contained protein

Answer 5

• Add biuret reagent to solution
• Blue to lilac/purple indicates protein is present

Question 6

What is hydroxylating

Answer 6

Introduce a hydroxyl group (OH-) into a molecule or compound

Question 7

Which two substances are formed when amino acid molecules join together?

Answer 7

• Water
• Peptide

Question 8

Explain how a change in the primary structure of a globular protein may result in a different 3D structure

Answer 8

• Different sequence of amino acids
• Tertiary structure changes
• Different bonds in different places

Question 9

Describe how the secondary structure of a polypeptide is produced by bonds between amino acids.

Answer 9

• Hydrogen bonds (between NH group of one amino acid and C=O group
• Forming beta plated sheets or alpha helix’s

Question 10

What is the primary structure of a protein

Answer 10

The specific sequence of amino acids in a polypeptide chain

Question 11

What is the secondary structure of a protein (2 marks)

Answer 11

The sequence of amino acids causes parts of a protein molecule to twist and bend into alpha helix shapes or beta pleated sheets.
Hydrogen bnonds hold the secondary structure

Question 12

What is the tertiary structure of a protein (3 marks)

Answer 12

The further folding of the secondary structure
To form a unique 3D shape
Held in place by ionic, hydrogen and disulphide bonds between R groups

Question 13

What is the quaternary structure of a protein

Answer 13

A protein made up of more than one polypeptide chain

Question 14

Give an example of a protein with a quaternary structure

Answer 14

Haemoglobin is made up of 4 polypeptide chains

Question 15

What happens when a protein denatures

Answer 15

Ionic and hydrogen bonds that hold the tertiary structure together break down. Unique 3D structure collapses back into secondary structure.

Question 16

How are proteins denatured

Answer 16

Too high a temperature (too much kinetic energy)
Too high/low a pH (too many H+ or OH-)

Question 17

Explain the importance of the primary structure

Answer 17

If even one amino acid in the sequence is different then it will cause the ionic/hydrogen/disulphide bonds to form in a different location.
This results in a different 3D shape

Question 18

What is a Globular protein

Answer 18

• Protein that is spherical in shape
• Soluble in water

Question 19

Why are globular proteins soluble in water

Answer 19

They have hydrophilic amino acids on their surface so hydrophilic R groups can react with water molecules in the aqueous cytoplasm of a cell.

Question 20

What is the function of haemoglobin

Answer 20

To bind reversibly to oxygen

Question 21

Give three examples of globular proteins

Answer 21

Enzymes, hormones, haemoglobin

Question 22

What are fibrous proteins

Answer 22

Proteins that play a structural role (they are also insoluble)

Question 23

Give three places where you are likely to find fibrous proteins

Answer 23

Bones, tendons, walls of arteries

Question 24

Why is keratin useful

Answer 24

• Found in outer surface of skin, hair and fingernails
• It is very strong because it contains large volumes of the amino acid cysteine
• Cysteine forms disulphide bridges in the protein structure which are very strong covalent bonds

Question 25

Why are fibrous proteins insoluble in water

Answer 25

Contain high volumes of amino acids with hydrophobic R groups

Question 26

Where do we find collagen

Answer 26

In tendons, which connect muscles to bones. And ligaments, which connect bones to each other

Question 27

What is the structure of collagen

Answer 27

Polypeptide chains in collagen wrap tightly together to form a triple helix

Question 28

Why can collagen polypeptides wrap very tightly around each other

Answer 28

• Every third amino acid is glycine, which has a tiny R group of just a hydrogen atom, allowing for a large number of hydrogen bonds between the polypeptide chains. Which helps stabilise the quaternary structure of the protein

Question 29

What are collagen polypeptides chains joined together by

Answer 29

• Many hydrogen bonds
• Strong crosslinks

Question 30

What are the larger structures of collagen called

Answer 30

Microfibrils and fibrils

Question 31

How do microfibrils and fibrils avoid weak spots

Answer 31

The molecules are staggered so there aren’t gaps running along the structure (weak spots)