Module 2: Biological Molecules - Proteins

Question 1

What are Proteins?

Answer 1

Proteins are polymers of amino acids joined together by peptide bonds.

Question 2

How many Amino acids does our body need to stay healthy?

Answer 2

20 different amino acids.

Question 3

What is a Dipeptide?

Answer 3

A dipeptide is formed when two amino acids join together.

Question 4

What is a Polypeptide?

Answer 4

A polypeptide is formed when more than to amino acids join together.

Question 5

What elements do Proteins contain?

Answer 5

Carbon.

Oxygen.

Hydrogen.

Nitrogen.

Sulphur.

Question 6

What is the general structure of amino acids?

Answer 6

They consist of a central carbon atom attached to four different groups:

an amine group,

a hydrogen atom,

a carboxyl group and an ‘R’ group which is different in each amino acid.

Question 7

Explain the ‘R’ group.

Answer 7

The identity of the R group will influence how the amino acid interacts with other amino acids, therefore influencing protein folding.

Question 8

Describe the formation of Dipeptides/Polypeptides.

Answer 8

Amino acids join together by peptide bonds to form Dipeptides and Polypeptides. When they join the OH from the carboxyl group on the first amino acid joins with the hydrogen atom on the second amino acid.

This allows a molecule of water to be released therefore it can be called a condensation reaction.

Question 9

Describe the breakdown of dipeptides/polypeptides.

Answer 9

A molecule of water is added to a dipeptide/polypeptide to break peptide bonds. Two amino acids will be formed therefore it can be called a hydrolysis reaction.

Question 10

What are the 4 stages of folding a protein undergoes?

Answer 10

Primary.

Secondary.

Tertiary.

Quaternary.

Question 11

Explain the Primary structure of proteins.

Answer 11

Primary structure of a protein is the order and number of amino acids in a protein.

Peptide bonds have formed between amino acids to form a long, straight chain (polypeptide).

The Primary structure of a polypeptide is determined by the DNA sequence of the gene which encodes that polypeptide.

Question 12

Explain the Secondary structure of a protein.

Answer 12

Along the polypeptide chain they are -NH and -OH groups which have a slightly negative (OH) and positive (NH) charge.

This causes the groups to attract resulting in hydrogen bonds forming between amino acids.

The hydrogen bonds cause the polypeptide chains to twist and fold into shapes- Alpha Helix or Beta pleated sheets.

Question 13

Explain the Tertiary structure of a protein.

Answer 13

More bonds form between the different R groups to give the protein a 3D structure. R-group interactions involve hydrogen bonds, disulfide bonds, ionic bonds and polar interactions.

It is the 3D shape of the protein. It can be globular or fibrous

Question 14

Describe the bonds present in the Tertiary structure of proteins.

-ionic bonds.

-disulfide bridges.

Answer 14

Ionic bonds =
these are attractions between negatively/positively charged R groups on different parts of the molecule.

Disulfide bridges =
when two amino acids of Cysteine join together, disulfides bonds are formed. (strong covalent S-S bonds)

Question 15

Describe the bonds present in the Tertiary structure of proteins

-hydrophobic/hydrophilic interactions.

-hydrogen bonds

Answer 15

Hydrophilic/Hydrophobic interactions =
When hydrophobic R groups are close together in a protein, the clump together.
This means that the hydrophilic R groups are likely to be pushed on the outside, which affects the protein structure.

Hydrogen bonds =
Weak bonds that form slightly positively charged hydrogen atoms in some R groups and slightly negatively charged atoms in other R groups on the polypeptide chain.

Question 16

Explain the Quaternary structure of a protein.

Answer 16

This is the structure formed from the interaction of multiple polypeptide chains held together by bonds.

The Quaternary structure is the way these polypeptide chains are assembled together. It shows how the individual subunits are arranged to form a larger three dimensional structure.

Question 17

What are the 2 types of proteins?

Answer 17

Globular and Fibrous.

Question 18

Describe the structure and function of Globular proteins.

Answer 18

They have a spherical shape: are round and compact.

Hydrophilic R groups are pushed outwards whereas the Hydrophobic R group are pushed inwards due to hydrophilic/hydrophobic interactions in the tertiary structure.

This makes Globular proteins soluble, which makes them easily transported in fluids.

Globular proteins unravel and denature when the temperature or pH deviates from optimum levels.

Question 19

What is a Conjugated protein?

Answer 19

It is a protein with a non- protein group attached. The non protein part is called the prosthetic group.

Globular proteins with prosthetic groups attached (such as haemoglobin) are referred to as conjugated proteins.

Question 20

What are the 3 examples of Globular proteins?

Answer 20

Haemoglobin.

Insulin.

Amylase.

Question 21

Describe the structure and function of Haemoglobin.

Answer 21

It is a globular protein that carries oxygen around the body in red blood cells.

It is a Conjugated protein as each of the four polypeptide chains has a prosthetic group called haem. A haem group contains iron, which oxygen binds to.

Contains 2 alpha chains, 2 beta chains and 4 prosthetic haem groups.

Water soluble so it dissolves in the plasma.

Question 22

Describe the structure and function of Insulin.

Answer 22

It is a hormone secreted by the pancreas. It helps to regulate the blood glucose level.
It is soluble therefore it can be transported in the blood to the tissues where it acts .

An insulin molecule consists of 2 polypeptide chains, which are held together by disulfide bonds.

When they are in pancreas, 6 of these molecules bind together to form a large, globular structure.

Question 23

Describe the function and Structure of Amylase.

Answer 23

Amylase is an enzyme that catalysts the breakdown of starch in the digestive system.

It is made of a single chain of amino acids. Its secondary structure contains both alpha helix and beta pleated sheets. It is a globular protein.

Question 24

Describe the structure and function of Fibrous proteins.

Answer 24

Are long and thin and their primary structure consists of a repetitive sequence of amino acids.

They perform structural roles so they are strong and insoluble.

They are fairly unreactive (unlike many globular proteins)

Fibrous proteins tend to be less sensitive than globular proteins to changes in temperature and pH.

Question 25

What are the 3 examples of Fibrous proteins?

Answer 25

Collagen.

Keratin.

Elastin.

Question 26

Describe Collagen

Answer 26

Collagen consists of three polypeptide chains wrapped tightly around each other to form a stable quaternary structure held together by numerous hydrogen bonds.

Collagen is found in connective tissue, such as skin, muscle and bone.

It is a very strong molecule. Minerals can bind to the protein to increase its rigidity, e.g. in bone.

Question 27

Describe Keratin.

Answer 27

It is found in many external structures of animals, such as skin, hair, nails, feathers and horns. It is extremely strong and insoluble in water.
It can either be flexible (skin) or had and tough (nails).

It consists of long stranded molecules and contains a high proportion of cysteine therefore keratin contains a large number of disulfide bonds.

Question 28

Describe Elastin.

Answer 28

It is found in elastic connective tissue, such as skin, large blood vessels and some ligaments.

They are long strands, containing hydrophobic regions. The strands are also cross linked to each other. It is elastic, so it allows tissues to return to their original shape after they have been stretched.