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

18. Amino Acids and Proteins

Primary Protein Structure

GOB Chemistry

18. Amino Acids and Proteins

Primary Protein Structure

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Problem 34a

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.
a. Val

Verified step by step guidance

Step 1: Understand the structure of valine (Val). Valine is an amino acid with the following structure: an amino group (-NH₂), a carboxyl group (-COOH), and a side chain (R group) that is isopropyl (-CH(CH₃)₂). At neutral pH, the amino group is protonated (-NH₃⁺), and the carboxyl group is deprotonated (-COO⁻).

Step 2: Analyze the behavior of valine at low pH (pH 1). At low pH, the environment is highly acidic, so all ionizable groups will be protonated. The amino group will remain as -NH₃⁺, and the carboxyl group will be protonated to -COOH. The side chain of valine does not ionize, so it remains unchanged.

Step 3: Draw the structure of valine at low pH. Represent the amino group as -NH₃⁺, the carboxyl group as -COOH, and the side chain as -CH(CH₃)₂. Ensure the correct connectivity of the groups to the central carbon (α-carbon).

Step 4: Analyze the behavior of valine at high pH (pH 14). At high pH, the environment is highly basic, so all ionizable groups will lose protons. The amino group will deprotonate to -NH₂, and the carboxyl group will remain deprotonated as -COO⁻. The side chain of valine does not ionize, so it remains unchanged.

Step 5: Draw the structure of valine at high pH. Represent the amino group as -NH₂, the carboxyl group as -COO⁻, and the side chain as -CH(CH₃)₂. Again, ensure the correct connectivity of the groups to the central carbon (α-carbon).

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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 that serve as the building blocks of proteins. Each amino acid consists of a central carbon atom, an amino group (–NH2), a carboxyl group (–COOH), a hydrogen atom, and a variable R group that determines the specific properties of the amino acid. Understanding the structure of amino acids is crucial for analyzing their behavior at different pH levels.

Ionization at Different pH Levels

The ionization state of amino acids and peptides changes with pH due to the protonation and deprotonation of functional groups. At low pH (acidic conditions), amino groups are typically protonated, while carboxyl groups are also protonated, leading to a positively charged species. Conversely, at high pH (basic conditions), carboxyl groups lose protons and become negatively charged, while amino groups may become neutral, affecting the overall charge and structure of the molecule.

Peptide Bond Formation

Peptide bonds are covalent bonds that link amino acids together to form dipeptides and tripeptides. This bond forms through a condensation reaction, where the carboxyl group of one amino acid reacts with the amino group of another, releasing a molecule of water. Understanding peptide bond formation is essential for drawing the structures of dipeptides and tripeptides, especially when considering their ionization states at varying pH levels.

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How many ways can four different amino acids be arranged in a peptide so that each peptide is unique?

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How many amino acid units do these atoms come from? Why are these units planar?