9. Which of the following molecules are found in substantial quantities in both the cell membrane and DNA?
Answer: A
Phosphate groups are found in substantial quantities in both the cell membrane and DNA.
Phosphate groups play a crucial role in both the structure of cell membranes and the backbone of DNA, making them a common component in both contexts.
A) Phosphate groups
Phosphate groups are integral to the structure of nucleotides, which make up DNA and RNA. Additionally, they are key components of phospholipids, which form the cell membrane's bilayer. This dual presence in both cellular membranes and nucleic acids establishes phosphate groups as the correct answer.
B) Steroids
Steroids are a class of lipids that serve various functions in cell membranes, such as maintaining fluidity, but they do not play a role in the structure of DNA. Therefore, while steroids are present in cell membranes, they are not found in DNA.
C) Lipids
Lipids, while abundant in cell membranes, do not include any specific molecules that are also components of DNA. Lipids encompass a broad category that includes fats, oils, and phospholipids, but they do not directly participate in the formation of genetic material.
D) Nitrogenous bases
Nitrogenous bases are specific to nucleic acids like DNA and RNA, where they pair with phosphate groups and sugars to form the structure of nucleotides. However, they are not found in cell membranes, disqualifying them as a common component of both.
Conclusion
Phosphate groups are the only option that is significantly present in both cell membranes and DNA, fulfilling the requirements of the question. Other options, such as steroids, lipids, and nitrogenous bases, either lack presence in one of the two structures or do not meet the criteria of being found in both. Thus, phosphate groups are definitively the correct answer.