T3 : Amino acids - proteins

First peptide hormone discovered

(a)  

Answer explanation

Frederick Banting and Charles Best were the first to isolate insulin from dog pancreas in 1921.

Insulin is derived from a 84 amino acid prohormone molecule called proinsulin.

It became known that insulin was a two-chain heterodimer consisting of a 21-residue A-chain linked to a 30-residue B-chain by two disulfide bonds derived from cysteine residues (A7-B7 and A20-B19). An intrachain disulfide bond also exists within the A-chain (A6- A11)

• which true about -COOH grp in aa?

• acidic

• basic

• donate proton to solution

• accept proton

• which true about -NH2 grp in aa?

• acidic

• basic

• donate proton to solution

• accept proton

Only (a)   of aa used in building blocks for proteins

What are the special features of aa?

• capacity to polymerize

• novel acid-base properties

• varied structure & chemical functionality in aa side chain

• chirality - mlcl that has a non superimposable mirror image

Answer explanation

Complete mirror image - non superimposable

(a)  

Answer explanation

L-aa are the naturally occuring enantiomers found in all proteins

(a)  

Small condensation products of aa

(a)  

Answer explanation

2 aa linked together to form DIPEPTIDE.

Naming peptides start at the ?

• N-terminus

• C-terminus

Answer explanation

Choose correct statements.

• pure form of 20 α-aa are white, crystalline & high melting solids

• aa soluble in water but insoluble in organic solvents (acetone, chloroform & ether)

• aa exists as dipolar ionic sp.

  • - zwitterions

  • - aa (aq) conduct electric current

• 2 additional aa (incorporated by overriding stop codons)

  • - Selenocysteine (Sec,U)

  • - Pyrrolysine (Pyl, O)

Answer explanation