▪️🔹1.1 Proteins -chemical Elements

Question 1

What 4 elements to proteins contain?

Answer 1

Oxygen, carbon, hydrogen and Nitrogen (some also contain sulphur and phosphorus)

Question 2

What factors make up proteins?

Answer 2

Proteins are polymers made up of monomers called amino acids

Question 3

What is the chain of amino acids in a protein called?

Answer 3

Polypeptide chain

Question 4

How many different amino acids are used to make up Proteins?

Answer 4

20

Question 5

What happens to a basic amino acid at pH7?

Answer 5

At pH7 an amino acid gains a H and becomes positively charged, the carboxyl group which is acidic at pH7 looses a H and becomes negatively charged
:: at pH 7 an amino acid has both a positive and negative charge

Question 6

How is a peptide bond created?

Answer 6

When the amino group of one amino acid reacts with the carboxyl group of another with the elimination of water (condensation reaction) a peptide bond is formed
This creates a dipeptide

Question 7

Name the different levels of organisation of protein structure

Answer 7

Primary structure
Secondary structure
Tertiary structure
Quaternary structure

Question 8

Describe the main features of a primary structure

Answer 8

Order of amino acids in the polypeptide chain, determined by the base sequence in one strand of the DNA molecule

Question 9

Describe the main features of a secondary structure

Answer 9

The shape that the polypeptide chain forms as a result of the hydrogen bonding between (=O on -CO) groups and the (-H on -NH) groups in the twisted peptide bonds along the chain

Question 10

Name the two types of structure present in the secondary structure

Answer 10

An alpha helix (spiral shape, abundant in collagen)

A beta pleated sheet (abundant in fibroin, a silk)

Question 11

Describe the main features of a tertiary structure

Name the bonds maintaining this structure

Answer 11

Alpha helix’s are folded and twisted to give a more complex 3D shape that is maintained by:
Hydrogen bonds
Ionic bonds
Disulphide bonds
That are vital in giving globular proteins e.g enzymes their shape

Question 12

Describe the main features of a quaternary structure

Answer 12

A combination of polypeptide chains,

• Insulin molecule has 2 polypeptide chains
• Associated with non protein groups to form large complex molecules such as haemoglobin

Question 13

What are fibrous proteins?

Answer 13

• Long, thin insoluble molecules.
• Structural functions e.g in bone
• strong and tough

Question 14

Give an example of a fibrous protein

Answer 14

Collagen
Provides strength and toughness needed in tendons
A single collagen fibre consists of 3 identical polypeptide chains linked by hydrogen bond twisted like a plait making the molecule stable

Question 15

What are globular proteins?

Name many examples

Answer 15

-Compact and folded into spherical molecules
-soluble in water
Main many examples of globular proteins: enzymes, antibodies, plasma proteins and hormones

Question 16

Describe the globular protein haemoglobin in detail

Answer 16

Consists of 4 folded polypeptide chains, at the centre of each being the iron-containing group, haem

Question 17

Name a test to identify protein

Name the positive result

Answer 17

The biuret test
Biuret reagent is added to a solution, sodium hydroxide and copper sulphate react to make blue copper hydroxide which interacts with the peptide bonds in the protein to make biuret which it purple
Pale blue —> purple (violet)

Question 18

Lost the four bonds present in the tertiary structure of a protein in order of weakest to strongest

Answer 18

Weakest: 
Hydrogen bonds 
Ionic bonds 
Disulphide bonds 
Peptide bonds
\:Strongest

Question 19

Classify the following proteins
A) enzyme
B) collagen
C) insulin

Answer 19

Enzyme = globular protein 
Collagen = Fibrous protein
Insulin = globular protein