Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

14. DNA Synthesis

Chargaff's Rules

General Biology

14. DNA Synthesis

Chargaff's Rules

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0:47 minutes

Problem 3

Textbook Question

In analyzing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules?
a. A=G
b. A+G=C+T
c. A+T=G+C
d. A=C

Verified step by step guidance

Understand the base-pairing rules in DNA: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C). This means the amount of A should equal the amount of T, and the amount of G should equal the amount of C.

Consider the option A=G. This would imply that the amount of Adenine is equal to the amount of Guanine, which contradicts the base-pairing rules since A pairs with T, not G.

Evaluate the option A+G=C+T. This option suggests that the sum of Adenine and Guanine equals the sum of Cytosine and Thymine. This is consistent with the base-pairing rules because A pairs with T and G pairs with C, so the total number of purines (A and G) should equal the total number of pyrimidines (C and T).

Analyze the option A+T=G+C. This implies that the sum of Adenine and Thymine equals the sum of Guanine and Cytosine. While this might seem consistent at first glance, it does not necessarily follow the base-pairing rules directly, as it does not account for the specific pairing of A with T and G with C.

Consider the option A=C. This suggests that the amount of Adenine is equal to the amount of Cytosine, which contradicts the base-pairing rules since A pairs with T, not C.

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Key Concepts

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

Base Pairing Rules

Base pairing rules in DNA refer to the specific pairing between nitrogenous bases: adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). This complementary base pairing is due to hydrogen bonding, where A forms two hydrogen bonds with T, and G forms three hydrogen bonds with C, ensuring the DNA double helix structure is stable and consistent.

Chargaff's Rule

Chargaff's Rule states that in a DNA molecule, the amount of adenine (A) is equal to thymine (T), and the amount of guanine (G) is equal to cytosine (C). This rule is derived from the base pairing rules and implies that the total purines (A+G) equal the total pyrimidines (C+T), maintaining a consistent ratio across different organisms.

DNA Structure

DNA is structured as a double helix, composed of two strands running in opposite directions. Each strand is made up of a sugar-phosphate backbone and nitrogenous bases. The specific pairing of bases (A with T and G with C) across the two strands allows for the replication and transmission of genetic information, as each strand can serve as a template for creating a new complementary strand.

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