If
14
C-labeled uracil is added to the growth medium of cells, what macromolecules will be labeled?
A. DNA (deoxyribonucleic acid) B. RNA (ribonucleic acid) C. Lipids D. Proteins E. Carbohydrates
The Correct Answer and Explanation is :
When (^{14}C)-labeled uracil is added to the growth medium of cells, the primary macromolecule that will be labeled is B. RNA (ribonucleic acid).
Explanation:
Uracil is one of the four nucleobases found in RNA, the others being adenine, guanine, and cytosine. Unlike DNA, which contains thymine instead of uracil, RNA utilizes uracil as one of its building blocks. When cells are provided with (^{14}C)-labeled uracil, they incorporate it into RNA during the process of transcription. This incorporation happens because uracil serves as a template for synthesizing RNA from the DNA template strand.
While DNA does contain uracil in some cases (e.g., through the action of certain enzymes or in certain organisms), it primarily contains thymine. Thus, adding (^{14}C)-labeled uracil directly results in the labeling of RNA and not DNA.
The labeling of RNA can be important for studying gene expression, RNA turnover, and the synthesis of different RNA types, such as messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). These processes are crucial for protein synthesis and cellular function.
As for the other macromolecules listed:
- A. DNA (deoxyribonucleic acid): While it is possible for uracil to be involved in DNA through deamination of cytosine, the incorporation of (^{14}C)-labeled uracil specifically into DNA is not the primary pathway.
- C. Lipids, D. Proteins, and E. Carbohydrates: These macromolecules do not utilize uracil in their structure. Lipids are composed mainly of fatty acids and glycerol, proteins are made up of amino acids, and carbohydrates consist of sugar molecules. Therefore, none of these macromolecules would be labeled by the addition of (^{14}C)-labeled uracil.
In conclusion, the primary macromolecule labeled by the addition of (^{14}C)-labeled uracil to the growth medium is RNA, reflecting its role in cellular processes and gene expression.