3.6 Structure Of Proteins

Question 1

What do all amino acids have in common and what distinguishes them from each other

Answer 1

Amine group (NH2)
R group distinguishes
Carboxyl cooh group

NH2C(R group)(H)COOH

Question 2

How do the synthesis of proteins happen ?

• what enzyme does it?

Answer 2

Peptide bond - H2O is lost and C of carboxyl group and N of amine group will form a covalent bond . Thus condensation reaction , CONH

2) then multiple Amino acids join by peptide bonds , catalysed by enzyme peptidyl transferase present in ribosomes to make polypeptide

Question 3

What is primary structure of a protein?

What is it determined by ?

Answer 3

The primary structure describes the linear sequence of the amino acids in the polypeptide

• determined by DNA( as it has sequence transported by mRNA and determines order etc)

Question 4

What is secondary structure of a protein?

What is it determined by ?

What do they make ?

Answer 4

• Here the first folding of a protein takes place
• due to HYDROGEN bonds between the O on carboxyl acid and And H bonded to N on amino groups
• type of folding determined by the ORDER OF AMINO ACIDS , as then hydrogen bonds either make alpha helix or beta pleated sheet

Question 5

What is tertiary structure ?

What is it determined by ?

Why- why determined by and what does this make?

Answer 5

The FURTHER FOLDING of a protein to make final shape

• determined by interactions of R GROUPS
• also determined by secondary structure

: because alpha helix will become GLOBULAR PROTEINS
: beta pleated sheets will become a FIBROUS PROTEINS

Question 6

What types of R groups interactions are there for tertiary structure ?

Answer 6

1) Hydrogen bonding
2) Hydrophilic and hydrophobic interactions = Weak van def waal forces
3) disulphides bridge - covalent bond between two Sulphur atoms (from cysteine )
4) Ionic bonds - between negatively and positively charged R groups

Question 7

Quaternary structure ?

Answer 7

: reactions between different polypeptide chains known as subunits
- can be the same interactions as tertiary but difference is they between whole subunits now

For example haemoglobin contains 4 chains with two sets of identical units , this is the quaternary structure …

Question 8

How to test for proteins again quick

Answer 8

Biurets test- blue solution based of a copper sulfate ALKALINE solution )

• add it, if it goes purple , then it is positive
• here in the presence of a peptide bond, Cu (II) ions will become reduced to form a violet lilac complex in an alkaline solution

Alternatively mix sample with equal volum of 10% NAoH and 1% copper sulfate , so that it is alkaline then do it normally etc

Question 9

What are some basic functions of proteins ?

Answer 9

• enzymes
• for signalling (glycoproteins act as receptors , but also peptide hormones )
• structural (keratin in hair, collagen between bones)
• contractile (spindle fibres, muscles actin )
• storage (white of an egg as albumin)
• transport (haemoglobin oxygen)
• defensive (antibodies )

Question 10

How does a protein split again?

Answer 10

Protease enzyme and hydrolysis reaction, here add water and peptide bond breaks to reverse to amino acids

Question 11

Amino acid most common snd what can they be

Answer 11

They can be ph buffers and the most common is glycine