In mature insulin,chain $A$ and chain $B$ are interlinked by which bond?

$ELISA$ is used to detect viruses where the key reagent is . . .

What is produced by genetically engineered bacteria?

Which protein is used for the treatment of emphysema?

Consider the following statements about insulin.
$I.$ Human insulin is made up of $51$ amino acids arranged in two polypeptide chains.
$II.$ The two polypeptide chains are interconnected by two disulphide bridges.
$III.$ In mammals,including humans,insulin is synthesised as a pro-hormone,which contains an extra stretch called the $C$-peptide.
$IV.$ $C$-peptide is not present in the mature insulin.
Which of the statements given above are correct?

How many polypeptide chains is human insulin composed of?