Question

"A residue in the middle of a polypeptide has −CH3 as its side chain or R group. How many atoms does the residue contain?

A. 7
B. 9
C. 10
D. 12
E. 13"

Answer 1

Step-by-step explanation:

A residue in the middle of a polypeptide with −CH3 as its side chain or R group contains 7 atoms.

To determine the number of atoms in the residue, we need to consider the structure of the −CH3 group. It consists of one carbon (C) atom bonded to three hydrogen (H) atoms.

Here's a breakdown of the atoms in the −CH3 group:

1. Carbon (C): 1 atom

2. Hydrogen (H): 3 atoms

Adding these together, we have a total of 4 atoms in the −CH3 group. However, the question specifically asks about the residue in the middle of a polypeptide, which means that the carbon in the −CH3 group is already bonded to the rest of the polypeptide chain.

Since the carbon atom is already counted as part of the polypeptide structure, we only need to consider the three hydrogen atoms in the −CH3 group. Therefore, the residue contains a total of 3 hydrogen atoms.

In conclusion, the residue with a −CH3 side chain or R group in the middle of a polypeptide contains 7 atoms: 1 carbon atom from the polypeptide chain and 3 hydrogen atoms from the −CH3 group. Hence, the correct answer is A. 7.

Answer 2

A polypeptide residue with −CH3 as its side chain contains four atoms.

Step-by-step explanation:

Amino Acid Structure and Side Chains

A polypeptide residue is a single unit within a polypeptide chain. Each residue has a specific side chain or R group. In this case, the side chain is -CH3, which represents a methyl group. A methyl group consists of one carbon atom bonded to three hydrogen atoms.

Counting Atoms in a -CH3 Residue

A methyl group contains a total of four atoms: one carbon atom and three hydrogen atoms.

Answer

The residue with −CH3 as its side chain contains four atoms.