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

Amino Acid Classifications

GOB Chemistry

18. Amino Acids and Proteins

Amino Acid Classifications

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1:56 minutes

Problem 6a

Textbook Question

Draw the structure for each of the following amino acids at physiological pH:
a. lysine

Verified step by step guidance

Understand that at physiological pH (approximately 7.4), amino acids exist in their zwitterionic form. This means the amino group (-NH2) is protonated to form -NH3⁺, and the carboxylic acid group (-COOH) is deprotonated to form -COO⁻.

Identify the structure of lysine. Lysine is an amino acid with a side chain containing a primary amine group (-NH2) attached to a four-carbon chain. Its general structure includes an alpha carbon bonded to an amino group, a carboxyl group, a hydrogen atom, and the side chain.

Modify the structure of lysine to reflect its zwitterionic form at physiological pH. The alpha amino group (-NH2) becomes -NH3⁺, and the alpha carboxyl group (-COOH) becomes -COO⁻.

Add the side chain of lysine to the structure. The side chain contains a terminal amino group (-NH2) that remains protonated as -NH3⁺ at physiological pH because it is a basic group.

Combine all components to draw the complete structure of lysine at physiological pH. Ensure the alpha carbon is central, with the amino group (-NH3⁺), carboxylate group (-COO⁻), hydrogen atom, and the side chain (with its terminal -NH3⁺ group) correctly attached.

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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 (the alpha carbon) bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain (R group) that determines the specific properties of the amino acid.

Physiological pH

Physiological pH refers to the pH level of human blood and other bodily fluids, which is typically around 7.4. At this pH, amino acids can exist in their zwitterionic form, where the amino group is protonated (-NH3+) and the carboxyl group is deprotonated (-COO-), affecting their overall charge and solubility.

Lysine Properties

Lysine is a basic amino acid characterized by its positively charged side chain at physiological pH. Its side chain contains an additional amino group, which contributes to its basicity and makes lysine essential for protein synthesis, enzyme function, and various metabolic processes in the body.

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Related Practice

Textbook Question

Which of the following amino acids is most likely to be found on the outside of a soluble protein, and which of them is more likely to be found on the inside? Explain each answer. (Hint: Consider the effect of the amino acid side chain in each case and that the protein is folded up into its globular form.)

a. Valine

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Textbook Question

List the amino acids with side chains that are capable of hydrogen bonding. Draw an example of two of these amino acids hydrogen bonding to one another. For each one, draw a hydrogen bond to water in a separate sketch. Refer to Section 8.2 for help with drawing hydrogen bonds.

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Textbook Question

What are some differences between each of the following pairs?

c. polar and nonpolar amino acids

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Textbook Question

How does the polarity of the R group in leucine compare to the R group in serine?

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Textbook Question

Classify each of the amino acids in problem 16.5 as polar or nonpolar. If polar, indicate if the R group is neutral, acidic, or basic. Indicate if each is hydrophobic or hydrophilic.

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Textbook Question

Draw the structure for each of the following amino acids and put an asterisk (*) next to any chiral carbon centers in your structure:

b. lysine

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Textbook Question

Classify each of the amino acids in Problem 10.1 as polar (neutral, acidic, or basic) or nonpolar and as hydrophobic or hydrophilic.

a. alanine

b. lysine

c. tryptophan