Proteins

Question 1

How are proteins formed?

Answer 1

Amino acids as basic monomer units combine to make a polymer called polypeptide which then can be combined to make proteins.

Question 2

How do amino acids show evidence of evolution?

Answer 2

The 20 naturally occurring amino acids which can be found in proteins also can be found in all living organism, therefore, it shows indirect evidence for evolution.

Question 3

Draw the structure of amino acid.

Answer 3

Draw on a piece of paper.

Question 4

What are the components in an amino acid?

Answer 4

Every amino acid has a central carbon atom and it’s attached to 4 other chemical groups.

• Amino group - NH2, a basic group which forms the amino part of the amino acid.
• Carboxyl group - COOH, an acidic group which forms the acid part of the amino acid.
• Hydrogen atom - H.
• R (side) group - a variety of different chemical groups, each amino acid has a different R group. The 20 naturally occurring amino acids differ only in their R group.

Question 5

How is a dipeptide formed?

Answer 5

Amino acid monomers combine through a condensation reaction by removing a molecule of water and it forms a dipeptide.

Question 6

How is the water molecule formed?

Answer 6

It’s made from combining an OH from the carboxyl group from one amino acid and an H from the amino acid.

Question 7

What bond is formed between the amino acid?

Answer 7

The two amino acids are linked by a new peptide bond between the carbon atom of one amino acid and the nitrogen atom of another amino acid.

Question 8

How can dipeptide be broken?

Answer 8

Through hydrolysis.

Question 9

Draw the formation of a peptide bond.

Answer 9

Draw on a piece of paper.

Question 10

How is polypeptide formed?

Answer 10

Through a series of condensation reactions, many amino acid monomers can be joined through polymerisation and the chains of amino acids are a polypeptide.

Question 11

Why is the structure of amino acid important?

Answer 11

Amino acid determines the primary structure of a protein which therefore determines its shape and function. A change of a single amino acid in the primary sequence will change the shape of the protein which may stop it carrying out its function.

Question 12

What is the secondary structure of proteins?

Answer 12

The linked amino acid has - NH and -C=O on either side of every peptide bond. The H has an overall positive charge but the O has a negative charge and it causes the 2 groups to form hydrogen bonds.

Question 13

What’re the 2 shapes which a polypeptide can form into?

Answer 13

The hydrogen bonds cause the long chain of the polypeptide chain to be twisted into a 3D shape, as a coil known as an alpha helix.
Or folded into a beta-pleated sheet.

Question 14

What is the tertiary structure?

Answer 14

The alpha helix secondary structure can be twisted and folded to give a more complex and specific 3D tertiary structure, this way it achieves maximum stability or lowest energy state.

Question 15

What are the bonds in the tertiary structure?

Answer 15

1) Ionic bond - formed between any carboxyl and amino group that is not involved in forming a peptide bond. It is weaker than a disulfide bond and can be easily broken due to change in PH.
2) Disulfide bridge - Fairly strong so it’s not easily broken.
3) Hydrogen bonds - easily broken but strong when there’s a lot of them.

Question 16

Describe the unique feature within the quaternary structure.

Answer 16

• It has more than one protein.

- It has a prosthetic (non-protein) group e.g. Fe2+

Question 17

What is the test for proteins and how does it test for the proteins?

Answer 17

Biuret test which detects peptide bonds.

Question 18

How is the test carried out?

Answer 18

• Add sample into a test tube and add an equal volume of NaOH solution at RT.
• Add a few drops of very dilute copper (II) sulfate solution and mix.
• If peptide bonds are present hence a protein, the solution will turn purple, if none present, it will remain blue.

Question 19

What are the 2 basic types of proteins?

Answer 19

• Fibrous proteins e.g. collagen have structural functions.

- Globular proteins e.g. enzymes and hemoglobin, carry out metabolic functions.

Question 20

How does cross-linkages between amino acids of polypeptide chains increase the strength and stability of a collagen fiber?

Answer 20

It has three polypeptide chains wound around each other, the chain coils around each other. Hydrogen bonds form between these coils, which are around 1000 amino acids in length due to its length, it gives structural strength. This strength is increased by the fact that collagen molecules form further chains with other collagen molecules and form Covalent Cross Links with each other, which are staggered along the molecules to further increase stability.

Question 21

What are the functions of collagen?

Answer 21

• Form the structure of bones
• Makes up cartilage and connective tissue
• Prevents blood that is being pumped at high pressure from bursting the walls of arteries
• Is the main component of tendons, which connect skeletal muscles to bones

Question 22

What are the differences between hemoglobin and collagen?

Answer 22

• Shape - H is globular while C is fibrous.
• Solubility - H is soluble in water while C is insoluble.
• Amino Acid constituents - H contains a wide range of amino acids but C only has 35% of its primary structure made up of Glycine.
• Prosthetic group - H contains a haem prosthetic group whereas C doesn’t have one.