Table of contents

1. Introduction to Biochemistry4h 34m
2. Water3h 23m
3. Amino Acids8h 10m
4. Protein Structure10h 4m
5. Protein Techniques14h 5m
6. Enzymes and Enzyme Kinetics13h 38m
7. Enzyme Inhibition and Regulation 8h 42m
8. Protein Function 9h 41m
9. Carbohydrates7h 49m
10. Lipids5h 49m
11. Biological Membranes and Transport 6h 37m
12. Biosignaling9h 45m
Review 1: Nucleic Acids, Lipids, & Membranes2h 47m
Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway3h 12m
Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism2h 26m
Review 4: Amino Acid Oxidation, Oxidative Phosphorylation, & Photophosphorylation1h 48m

3. Amino Acids

Zwitterion

Biochemistry

3. Amino Acids

Zwitterion

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Multiple Choice

Which of the following structures represents a zwitterion?

H$_3$N$^+$–CH$_2$–COO$^-$

H$_2$N–CH$_2$–COOH

H$_2$N–CH$_2$–COO$^-$

H$_3$N$^+$–CH$_2$–COOH

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Verified step by step guidance

Step 1: Understand the concept of a zwitterion. A zwitterion is a molecule that contains both a positive and a negative charge, but is overall electrically neutral. This typically occurs in amino acids at a specific pH (isoelectric point).

Step 2: Analyze the given structures. Look for the presence of both a positively charged group (e.g., H$_3$N$^+$) and a negatively charged group (e.g., COO$^-$) within the same molecule.

Step 3: Evaluate the first structure, H$_3$N$^+$–CH$_2$–COO$^-$. This structure contains a positively charged amino group (H$_3$N$^+$) and a negatively charged carboxylate group (COO$^-$), making it a zwitterion.

Step 4: Evaluate the second structure, H$_2$N–CH$_2$–COOH. This structure has a neutral amino group (H$_2$N) and a neutral carboxylic acid group (COOH), so it is not a zwitterion.

Step 5: Evaluate the remaining structures. H$_2$N–CH$_2$–COO$^-$ has a neutral amino group and a negatively charged carboxylate group, while H$_3$N$^+$–CH$_2$–COOH has a positively charged amino group and a neutral carboxylic acid group. Neither of these are zwitterions because they lack both charges simultaneously.