B2.1 (proteins, from SME, 2.3.2, AI)

Question 1

What can a protein consist of?

p

Answer 1

A protein may consist of a single polypeptide or more than one polypeptide linked together.

Question 2

What are single polypeptide chain proteins?

Answer 2

Single polypeptide chain proteins include lysozyme, an enzyme present in mucus secretions and tears, that kills bacteria as part of our primary defences against pathogens.

Question 3

What are proteins made up of two polypeptide chains?

Answer 3

Proteins with two polypeptide chains include insulin, a hormone responsible for regulating blood glucose levels, and integrins, a group of membrane proteins that span a phospholipid bilayer and act as a receptor.

Question 4

What is the structure of integrins?

Answer 4

Integrins’ two polypeptide chains each have a hydrophobic section that sits in the membrane bilayer.

Question 5

What are proteins with three polypeptide chains?

Answer 5

Proteins with three polypeptide chains include collagen, the main structural protein in skin, tendons, ligaments and the walls of blood vessels.

Question 6

What are proteins with four polypeptide chains?

Answer 6

Proteins with four polypeptide chains include haemoglobin, which binds oxygen in red blood cells and delivers it from the lungs to respiring tissues.

Question 7

What is a subunit in a multi-polypeptide protein?

Answer 7

Each polypeptide chain in a multi-polypeptide protein is referred to as a subunit of the protein.

Question 8

What determines the 3D structure of proteins?

Answer 8

The amino acid sequence determines the three-dimensional conformation of a protein.

Question 9

What is the significance of a protein’s conformation?

Answer 9

Proteins perform their diverse roles because of their 3-D shape and structure, known as the protein’s conformation.

Question 10

How does the amino acid sequence affect protein folding?

Answer 10

The precise sequence of amino acids determines how the protein folds and aligns itself as the individual amino acids are being added at the ribosome.

Question 11

What happens to amino acids during protein formation?

Answer 11

Amino acids are always added in the same sequence so a protein can start to form its shape even before it is fully formed.

Question 12

What structures can form due to bonds between amino acids?

Answer 12

Bonds form between parts of amino acids that can cause a bridge to form between one part of the chain and another, creating loops, sheets, helices, and folds.

Question 13

What can alter a protein’s 3-D shape?

Answer 13

If an amino acid is not present in its usual place in the chain due to mutation, this can drastically alter the protein’s 3-D shape and affect its function.

Question 14

What type of protein is haemoglobin?

Answer 14

Haemoglobin is a globular protein that forms a globe-shaped structure.

Question 15

What is the structure of collagen?

Answer 15

Collagen is a fibrous protein that has a repeating sequence of amino acids to create a helical structure.

Question 16

What is denaturation in proteins?

Answer 16

Denaturation is the irreversible change of protein conformation caused by temperature and pH extremes.

Question 17

What causes denaturation?

Answer 17

Heat and extremes of pH are the most common causes of denaturation.

Question 18

What happens to the protein’s shape during denaturation?

Answer 18

The altered protein shape may affect its function, physical state, and general usefulness in its original role.

Question 19

Can denaturation be reversed?

Answer 19

Denaturation is almost always irreversible; the protein cannot be re-formed in its original conformation by reversing the change in conditions.

Question 20

How can small denaturations and renaturations occur?

Answer 20

Small denaturations and renaturations are possible in certain proteins to respond to small fluctuations in pH, e.g., haemoglobin.

Question 21

What is an example of denaturation in cooking?

Answer 21

Denaturation can be seen most easily by looking at the changes in an egg white as the egg is fried or poached.

Question 22

What happens to albumin during cooking?

Answer 22

Heating causes the hydrophobic amino acids in albumin to appear at the edges, causing the protein to become insoluble.

Question 23

What is the optimum pH for pepsin?

Answer 23

The stomach enzyme pepsin, a protein-digesting enzyme, has an optimum pH of 2.

Question 24

What are extremophiles?

Answer 24

Certain extremophiles have evolved to have proteins that are stable even at extreme pH or temperature, e.g., Thermus aquaticus, a bacteria that lives in hot springs at 80°C.

Question 25

Why can’t many drugs be taken orally?

Answer 25

Many drugs are proteins that cannot be taken by mouth because the protein will be denatured by stomach acid.

Question 26

What is an important tip regarding protein bonds?

Answer 26

Remember to avoid confusing the bonds that hold a protein’s shape together with the peptide bonds that attach each amino acid in sequence.