Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

29. Amino Acids

Proteins and Amino Acids

Organic Chemistry

29. Amino Acids

Proteins and Amino Acids

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1:31 minutes

Problem 3

Textbook Question

The herbicide glyphosate (Roundup®) kills plants by inhibiting an enzyme needed for synthesis of phenylalanine. Deprived of phenylalanine, the plant cannot make the proteins it needs, and it gradually weakens and dies. Although a small amount of glyphosate is deadly to a plant, its human toxicity is quite low. Suggest why this powerful herbicide has little effect on humans.

Verified step by step guidance

Step 1: Understand the mechanism of glyphosate's action. Glyphosate inhibits an enzyme called EPSP synthase, which is involved in the shikimate pathway. This pathway is essential for the synthesis of aromatic amino acids like phenylalanine, tyrosine, and tryptophan in plants.

Step 2: Recognize that humans and animals do not possess the shikimate pathway. Instead, humans obtain aromatic amino acids through their diet, as these are essential amino acids that cannot be synthesized by the human body.

Step 3: Analyze the chemical structure of glyphosate (provided in the image). Glyphosate contains functional groups such as a phosphonate group and an amine group, which are specifically designed to interact with the active site of EPSP synthase in plants. These interactions are highly specific to the plant enzyme and do not affect human enzymes.

Step 4: Consider the biochemical differences between plants and humans. The specificity of glyphosate for the plant enzyme ensures that it does not interfere with human metabolic pathways, making its toxicity to humans very low.

Step 5: Conclude that glyphosate's low human toxicity is due to the absence of the shikimate pathway in humans and the specificity of glyphosate for the plant enzyme EPSP synthase, which humans do not possess.

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Key Concepts

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

Amino Acid Synthesis

Phenylalanine is an essential amino acid that plants synthesize through specific enzymatic pathways. Glyphosate inhibits the enzyme EPSP synthase, which is crucial for the shikimic acid pathway, leading to a deficiency in phenylalanine. This disruption prevents the formation of proteins necessary for plant growth and survival.

Selective Toxicity

Glyphosate exhibits selective toxicity, meaning it targets specific biological pathways in plants that are not present in humans. Humans do not possess the shikimic acid pathway, which makes glyphosate ineffective against human cells, thus explaining its low toxicity in humans despite its potency as a herbicide.

Chemical Structure and Function

The chemical structure of glyphosate, as shown in the image, includes a phosphonate group that plays a key role in its herbicidal activity. This structure allows glyphosate to mimic a substrate in the shikimic acid pathway, effectively blocking the enzyme's function in plants while remaining non-reactive in human metabolic processes.

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Related Practice

Textbook Question

Show how you would synthesize any of the standard amino acids from each starting material. You may use any necessary reagents.

(a)

Textbook Question

Show how the following amino acids might be formed in the laboratory by reductive amination of the appropriate α-ketoacid.

(a) alanine

Textbook Question

Show how you would synthesize any of the standard amino acids from each starting material. You may use any necessary reagents.

(b)

Textbook Question

Show how you would use bromination followed by amination to synthesize the following amino acids.

(b) leucine

Textbook Question

Give equations for the formation and hydrogenolysis of N-benzyloxycarbonyl methionine.

Textbook Question

Three peptides were obtained from a trypsin digestion of two different polypeptides. In each case, indicate the possible sequences from the given data and tell what further experiment should be carried out in order to determine the primary structure of the polypeptide.

a. polypeptide I:

1. Val-Gly-Asp-Lys

2. Leu-Glu-Pro-Ala-Arg

3. Ala-Leu-Gly-Asp

Textbook Question

Show the peptides that would result from cleavage by the indicated reagent:

a. Val-Arg-Gly-Met-Arg-Ala-Ser by carboxypeptidase A

b. Ser-Phe-Lys-Met-Pro-Ser-Ala-Asp by cyanogen bromide

c. Arg-Ser-Pro-Lys-Lys-Ser-Glu-Gly by trypsin

Textbook Question

Show how valine can be prepared by

d. a N-phthalimidomalonic ester synthesis.