Proteins

Question 1

What is the monomer of proteins?

Answer 1

Amino acids.

Question 2

What polymer do amino acids form?

Answer 2

Polypeptides.

Question 3

How many amino acids occur naturally in proteins?

Answer 3

20/ about 100 identified- this is indirect evidence for evolution.

Question 4

What is the amino group?

Answer 4

(-NH2) - The basic group from which the ‘amino’ part of the name is derived.

Question 5

What is the carboxyl group?

Answer 5

(-COOH) - An acidic group which gives the ‘acid’ part of the name.

Question 6

What is the R group?

Answer 6

A variety of different chemical groups. Each amino acid has a different R group. This is where amino acids differ from each other.

Question 7

How do amino acids form dipeptides?

Answer 7

Condensation reactions. - The water is made by combining the -OH from the carboxyl group and then -H from the amino group of another amino acid.

Question 8

What bond holds two amino acids together?

Answer 8

Peptide bond. (Between the carbon atom of one amino acid and the nitrogen atom of the other.)

Question 9

How can a peptide bond be broken?

Answer 9

Hydrolysis - this gives two constituent amino acids.

Question 10

What does a sequence of amino acids in a polypeptide chain dictate?

Answer 10

The primary structure of a protein.

Question 11

What is the sequence of amino acids in a polypeptide chain determined by?

Answer 11

DNA.

Question 12

What does the primary structure determine?

Answer 12

Shape and hence function of protein.

Question 13

What charge does the hydrogen of the -NH group have?

Answer 13

Overall positive.

Question 14

What charge does the O of the -C=O group have?

Answer 14

Overall negative.

Question 15

What are the bonds between the -NH and the -C=O called? Are they weak or strong?

Answer 15

Hydrogen bonds, weak.

Question 16

What do hydrogen bonds cause?

Answer 16

The polypeptide chain to be twisted into a 3-D shape, such as the coil known as an α-helix.

Question 17

What is the tertiary structure maintained by?

Answer 17

A number of different bonds.

Question 18

Which bonds are formed in the tertiary structure?

Answer 18

disulfide bridges, ionic bonds, hydrogen bonds.

Question 19

How strong are disulfide bridges?

Answer 19

Fairly strong and not easily broken.

Question 20

Where are the ionic bonds formed in a protein?

Answer 20

Between any carboxyl and amino groups that are not involved in forming peptide bonds. These are weaker than disulphide bonds and are easily broken by changes in pH.

Question 21

What is important when it comes to the function of a protein?

Answer 21

The 3-D structure as it makes each protein distinctive and allows them to recognise, and be recognised, by other molecules. It can then interact with them in a specific way.

Question 22

Describe the primary structure of a protein. What does it do?

Answer 22

Primary structure is a sequence of amino acids found in its polypeptide chains. This sequence determines properties and shape.

Question 23

Describe the secondary structure of a protein. What does it do?

Answer 23

The secondary structure is the shape which the polypeptide chain forms as a result of hydrogen bonding. This is most often a spiral known as the α-helix, although other configurations occur.

Question 24

Describe the tertiary structure of a protein. What does it do?

Answer 24

The tertiary structure is due to the bending and twisting of the polypeptide helix into a compact structure. All three types of bond contribute to the maintenance of the tertiary structure.

Question 25

Describe the quaternary structure of a protein. What does it do?

Answer 25

The quaternary structure arises from the combination of a number of different polypeptide chains and associated nonprotein (prosthetic) groups into large, complex protein molecule, e.g., haemoglobin.

Question 26

Which protein test is used?

Answer 26

The Biuret test.

Question 27

Explain how to carry out the biuret test.

Answer 27

1) sample + hydroxide solution at room temp in test tube
2) Add a few drops of copper (II) sulfate solution
3) A purple colour indicates the presence of protein. Otherwise remains blue.

Question 28

What determines the 3-D shape of a protein?

Answer 28

The primary structure.