Table of contents

1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart3h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

3. Energy & Cell Processes

Steps of Transcription

Anatomy & Physiology

3. Energy & Cell Processes

Steps of Transcription

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0:31 minutes

Problem 9

Textbook Question

The nucleotide shown here is called cordycepin triphosphate. It is a natural product of a fungus that is used in traditional medicines. If cordycepin triphosphate is added to a cell-free transcription reaction, the nucleotide is added onto the growing RNA chain but then no more nucleotides can be added. Examine the structure of cordycepin and explain why it ends transcription.

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Examine the structure of cordycepin triphosphate and identify the key components: the triphosphate group, the ribose sugar, and the nitrogenous base.

Compare the structure of cordycepin triphosphate to a typical nucleotide used in RNA synthesis, noting any differences.

Focus on the ribose sugar of cordycepin triphosphate. Identify the functional groups attached to the 2', 3', and 5' carbons of the ribose.

Note that cordycepin triphosphate lacks a hydroxyl group (-OH) at the 3' position of the ribose sugar, which is crucial for forming the phosphodiester bond with the next nucleotide.

Explain that the absence of the 3'-OH group prevents the addition of further nucleotides, thereby terminating the RNA chain elongation and ending transcription.

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Key Concepts

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

Cordycepin Structure

Cordycepin is a modified nucleoside derived from adenosine, where the 3' hydroxyl group is replaced by a hydrogen atom. This structural modification is crucial because it prevents the addition of further nucleotides during RNA synthesis. In a typical nucleotide, the 3' hydroxyl group is essential for forming phosphodiester bonds with incoming nucleotides, thus allowing the RNA chain to elongate.

Transcription Process

Transcription is the process by which RNA is synthesized from a DNA template. During this process, RNA polymerase adds nucleotides to the growing RNA strand, utilizing the 3' hydroxyl group of the last nucleotide to form a bond with the 5' phosphate of the incoming nucleotide. The presence of cordycepin, which lacks a 3' hydroxyl group, halts this process, leading to premature termination of RNA synthesis.

Nucleotide Triphosphate Function

Nucleotide triphosphates, such as cordycepin triphosphate, serve as the building blocks for RNA synthesis. They consist of a nitrogenous base, a ribose sugar, and three phosphate groups. The energy released from the cleavage of the high-energy phosphate bonds during incorporation into RNA provides the necessary energy for the transcription process. However, the lack of a 3' hydroxyl group in cordycepin triphosphate means that it cannot participate in further elongation, effectively terminating transcription.