The number of chiral carbon(s) present in peptide, Ile-Arg-Pro, is...............

First, we recall the definition: a carbon atom is called chiral when it is attached to four different substituents, so that its mirror image is not super-imposable on the original molecule.

Next, we note that in any naturally occurring L-α-amino acid (except glycine) the α-carbon (the carbon directly attached to the -NH2 group, the -COOH group, the side chain R, and a hydrogen atom) satisfies this condition and is therefore chiral. Hence, each residue of Isoleucine (Ile), Arginine (Arg) and Proline (Pro) automatically supplies one chiral α-carbon.

Now, we must examine whether the side chains contribute any additional chiral centres.

(i) For Isoleucine, the side chain is $$-CH(CH_3)CH_2CH_3$$. The first carbon after the α-carbon (called the β-carbon) is attached to four different groups: $$-CH_3,\ -H,\ -CH_2CH_3,$$ and the rest of the backbone. Thus this β-carbon is also chiral. Therefore, Isoleucine contributes $$1\ (\text{α}) + 1\ (\text{β}) = 2$$ chiral carbons.

(ii) For Arginine, the side chain $$-(CH_2)_3-NH-C(=NH)NH_2$$ contains no carbon that is connected to four different groups; all of them are either methylene (-CH2-) or guanidinium carbons with multiple bonds. Hence Arginine contributes only its single α-chiral carbon, giving $$1$$ chiral centre from Arginine.

(iii) For Proline, although its side chain forms a five-membered ring with the α-nitrogen, the α-carbon still bears four different groups (-NH- in the ring, -CO-, -H, and the rest of the ring), so Proline supplies exactly $$1$$ chiral carbon. There are no other stereogenic carbons in the ring.

Adding all the contributions, we have

$$ \text{Total chiral carbons}=2\ (\text{Ile}) + 1\ (\text{Arg}) + 1\ (\text{Pro}) = 4. $$

So, the answer is $$4$$.