Understanding the structural and molecular interactions that induce shape and function for a protein has been an obstacle for some of your students. You decide to plan a lesson to introduce them to the basic amino acid structure and then use that concept to introduce the different levels of protein structure. To reinforce your lesson on amino acids, you need to aid the students in understanding that most naturally occurring amino acids have a shared base structure. Each amino acid has an amine group, an alpha-carbon (or central carbon), an R-side group, and a carboxyl group. The R-side group is what gives each amino acid its distinctive characteristics--for example, whether the amino acid will be acidic or basic, hydrophilic or hydrophobic, or charged. Choose the statement that does NOT pertain to amino acids.
a. All amino acids must contain a nitrogen-based molecule and a carboxylic acid.
b. Amino acids always contain a sulfur atom in their R-side group.
c. The groups composing an amino acid are located around a central alpha-carbon.
d. The R-side group will determine the overall chemical properties of an individual amino acid.

b. Amino acids always contain a sulfur atom in their R-side group.

Explanation:

Amino acids are monomeric units of protein molecules. This means that a protein molecule is made up of a chain of amino acids. As stated in this question, an amino acid is structurally made up of a central carbon atom called α carbon, an amine group (-NH2), a carboxylic acid group (-COOH), and a R-group side chain, which distinguishes each amino acid from one another.

Based on this question, all amino acids must possess the following characteristics:

- must contain a nitrogen-based molecule (amine group) and a carboxylic acid.

- The groups i.e amine, carboxylic acid and R chain are located around a central alpha-carbon.

- The R-side group will determine the overall chemical properties of an individual amino acid i.e whether acidic, basic, hydrophilic etc.

However, considering the fact that the R side chain of individual amino acids are different from one another, not all amino acids will contain a sulfur atom in their R-side group. Note that, Methionine and cysteine are the two common sulfur-containing amino acids.

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