Q3. How is a dipeptide formed?

Background

Topic: Peptide Bond Formation (Protein Structure)

This question tests your understanding of how amino acids link together to form peptides, specifically the chemical process and functional groups involved in forming a dipeptide.

Key Terms and Concepts:

• Amino Acid: Organic molecules with both an amino group (–NH3+) and a carboxylate group (–COO–).

• Peptide Bond (Amide Bond): The covalent bond formed between the carboxyl group of one amino acid and the amino group of another, releasing water (H2O).

• Dipeptide: A molecule consisting of two amino acids joined by a single peptide bond.

Key Reaction:

The general reaction for peptide bond formation is:

Step-by-Step Guidance

1. Identify the functional groups involved: Each amino acid has a carboxylate group (–COO–) and an amino group (–NH3+).

2. Determine which groups react: The carboxylate group of one amino acid reacts with the amino group of another amino acid.

3. Recognize the type of bond formed: The reaction forms an amide (peptide) bond between the carbon of the carboxylate and the nitrogen of the amino group.

4. Consider the byproduct: Water (H2O) is released during this condensation reaction.

5. Set up the reaction equation, but do not combine the molecules yet. Think about which atoms are removed to form water.

Try solving on your own before revealing the answer!

Q4. What is the charge on a zwitterion?

Background

Topic: Amino Acid Structure and Ionization

This question tests your understanding of the concept of zwitterions, which are important in the chemistry of amino acids, especially at physiological pH.

Key Terms:

• Zwitterion: A molecule with both positive and negative charges, but overall electrically neutral.

• Amino Acid at Neutral pH: The amino group is protonated (–NH3+), and the carboxyl group is deprotonated (–COO–).

Key Concept:

At physiological pH, amino acids exist as zwitterions:

The positive and negative charges balance, resulting in a net charge of zero.

Step-by-Step Guidance

1. Recall the structure of an amino acid at neutral pH: it has both a positively charged amino group and a negatively charged carboxylate group.

2. Consider the definition of a zwitterion: a molecule with both positive and negative charges, but no overall charge.

3. Add up the charges: +1 (amino group) and –1 (carboxylate group).

4. Think about what the net charge would be when these charges are combined.

Try solving on your own before revealing the answer!