Biological molecules: Proteins

Question 1

What is the general structure of a protein?

Answer 1

Check biology album in photos

Question 2

What is the monomer of a polypeptide?

Answer 2

amino acids

Question 3

What do polypeptides combine to form?

Answer 3

Proteins

Question 4

How many amino acids can occur in proteins?

Answer 4

20

Question 5

How many different R groups can be used to make an amino acid?

Answer 5

20

Question 6

What do 2 amino acid monomers combine to form?

What reaction is this?

Answer 6

Form a dipeptide in a condensation reaction

Question 7

Describe how the condensation reaction occurs when two amino acids form a dipeptide

Answer 7

The carboxyl group (COOH) of one amino acid joins to an H from another and forms water. The two amino acids then become linked by a new peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other

Question 8

What is polymerisation?

Answer 8

The process that joins many amino acid monomers through a series of condensation reactions

Question 9

What is the primary structure of a protein?

Answer 9

The sequence of amino acids in a polypeptide chain

Question 10

What does the primary structure of a protein determine?

Answer 10

It’s shape and hence its function

Question 11

What is the secondary structure of a protein?

Answer 11

The folding of the polypeptide chain due to hydrogen bonding

Question 12

What are the 2 types of secondary structure?

Answer 12

Alpha helix and beta pleated sheet

Question 13

How is a polypeptide chain able to fold into an alpha helix structure?

Answer 13

As the H of the NH group has an overall positive charge and while the O of the -C=O group has an overall negative charge and so the two groups readily form hydrogen bonds (these are weak), allowing the chain to be folded into the alpha helix shape

Question 14

What is the tertiary structure of a protein?

Answer 14

Where the alpha helixes of the secondary structure twist and fold even more to give the more complex 3D structure of each protein

Question 15

What are the bonds that maintain the tertiary structure and comment on their strength and how they form

Answer 15

• disulfide bridges = fairly strong bonds and so not easily broken, form between the R groups that contain sulphur
• ionic bonds = These are weaker than disulfide bonds and are easily broken by changes in pH. Form between positive and negatively charged R groups
• hydrogen bonds = numerous but easily broken, form between polar R groups through any delta minus or delta plus between hydrogen and oxygen

Question 16

Why is the 3D shape of a protein important?

Answer 16

As it makes each protein distinctive and allows it to recognise and be recognised by other molecules and it can then interact with them in a very specific way

Question 17

What is the quaternary structure of proteins?

Answer 17

Where more than one polypeptide chain is associated together, which are held by the same bonds as those in the tertiary structure.

Question 18

What could a quaternary structure protein associate with that the structures do not? Give an example.

Answer 18

Prosthetic groups ( not protein groups) like the iron containing haem group in haemoglobin

Question 19

How do you test for proteins? Describe how you carry it out

Answer 19

The biuret test as it detects peptide bonds:

1. Place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature
2. Add a few drops of very dilute (0.05%) copper (II) sulfate solution and mix gently
3. A purple coloration indicates the presence of peptide bonds and hence a protein. The solution remains blue is no protein is present

Question 20

What is a fibrous protein?

Answer 20

A protein that is made up of long chains that run parallel to each other and are linked by strong and stable cross bridges. Fiborous proteins are insoluble and have structural functions

Question 21

What is a globular protein?

Answer 21

A spherical, ball shaped protein that has a compact structure, is soluble and carries out metabolic functions

Question 22

Give an example of a fiborous protein

Answer 22

Collagen found in the skin cartilage and bones

Question 23

Give an example of a globular protein

Answer 23

Haemoglobin which transports oxygen in the red blood cells

Question 24

Give 4 features of collagen’s structure

Answer 24

• it’s a tightly wound wound polypeptide chain that forms a secondary structure
• each chain is further linked to a second helix
• it consists of three chains wound together like a rope giving it a quaternary structure
• the cross links between adjacent chains stabilise and give strength