Table of contents

1. Matter and Measurements4h 31m
2. Atoms and the Periodic Table5h 23m
3. Ionic Compounds2h 18m
4. Molecular Compounds2h 18m
5. Classification & Balancing of Chemical Reactions3h 17m
6. Chemical Reactions & Quantities2h 27m
7. Energy, Rate and Equilibrium3h 46m
8. Gases, Liquids and Solids3h 25m
9. Solutions4h 10m
10. Acids and Bases3h 29m
11. Nuclear Chemistry56m
BONUS: Lab Techniques and Procedures1h 38m
BONUS: Mathematical Operations and Functions47m
12. Introduction to Organic Chemistry1h 34m
13. Alkenes, Alkynes, and Aromatic Compounds2h 12m
14. Compounds with Oxygen or Sulfur1h 6m
15. Aldehydes and Ketones1h 1m
16. Carboxylic Acids and Their Derivatives1h 11m
17. Amines39m
18. Amino Acids and Proteins1h 51m
19. Enzymes1h 37m
20. Carbohydrates1h 41m
21. The Generation of Biochemical Energy2h 8m
22. Carbohydrate Metabolism2h 22m
23. Lipids2h 26m
24. Lipid Metabolism1h 45m
25. Protein and Amino Acid Metabolism1h 37m
26. Nucleic Acids and Protein Synthesis2h 54m

17. Amines

Classifying Amines

GOB Chemistry

17. Amines

Classifying Amines

Previous problemNext problem

Problem 34e

Textbook Question

Draw the structure of the following amino acids, dipeptides, and tripeptides at low pH (pH 1) and high pH (pH 14). At each pH, assume that all functional groups that might do so are ionized.
e. Gln-Ala-Asn

Verified step by step guidance

Step 1: Understand the problem. You are tasked with drawing the structure of the tripeptide Gln-Ala-Asn (Glutamine-Alanine-Asparagine) at two different pH levels: low pH (pH 1) and high pH (pH 14). At each pH, you need to account for the ionization states of the functional groups in the amino acids.

Step 2: Recall the ionizable groups in amino acids. Amino acids have an amino group (-NH2), a carboxyl group (-COOH), and sometimes ionizable side chains. At low pH, the amino group is protonated (-NH3⁺), and the carboxyl group is not ionized (-COOH). At high pH, the amino group is deprotonated (-NH2), and the carboxyl group is ionized (-COO⁻).

Step 3: Analyze the specific amino acids in the tripeptide. Glutamine (Gln) and Asparagine (Asn) have side chains that are not ionizable under physiological pH ranges, so their side chains remain neutral. Alanine (Ala) also has a non-ionizable side chain (a methyl group). Focus on the terminal amino and carboxyl groups of the peptide and their ionization states at the given pH levels.

Step 4: Draw the structure at low pH (pH 1). At this pH, the N-terminal amino group of Gln will be protonated (-NH3⁺), the C-terminal carboxyl group of Asn will be in its non-ionized form (-COOH), and the peptide bonds between the amino acids will remain neutral. Ensure that the side chains of Gln, Ala, and Asn are drawn in their neutral forms.

Step 5: Draw the structure at high pH (pH 14). At this pH, the N-terminal amino group of Gln will be deprotonated (-NH2), the C-terminal carboxyl group of Asn will be ionized (-COO⁻), and the peptide bonds will remain neutral. Again, ensure that the side chains of Gln, Ala, and Asn are drawn in their neutral forms, as they are not ionizable under these conditions.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Play a video:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Amino Acid Structure

Amino acids are organic compounds composed of a central carbon atom, an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain (R group). The structure of amino acids can change based on pH, affecting the ionization of the amino and carboxyl groups, which is crucial for understanding their behavior in different environments.

Peptide Bonds

Peptide bonds are covalent bonds formed between the carboxyl group of one amino acid and the amino group of another, releasing a molecule of water in a condensation reaction. This bond links amino acids together to form dipeptides and tripeptides, which are essential for building proteins and understanding their structure at varying pH levels.

Ionization at Different pH Levels

The ionization state of amino acids and peptides is influenced by the pH of the environment. At low pH (acidic), amino groups are protonated, while carboxyl groups are mostly in their non-ionized form. Conversely, at high pH (basic), carboxyl groups are deprotonated, and amino groups may lose a proton, affecting the overall charge and structure of the molecules.

Watch next

Master Amine Classification Concept 1 with a bite sized video explanation from Jules

Start learning