Which of the following is not required for transcription?
a. RNA polymerase
b. DNA
c. Uracil nucleotides
d. Ribosomes
The correct answer and explanation is:
Correct Answer: d. Ribosomes
Explanation (300 words):
Transcription is the biological process by which the information in a DNA sequence is copied into a complementary RNA strand. This is the first step in gene expression and occurs in the nucleus of eukaryotic cells or the cytoplasm in prokaryotic cells.
Let’s examine the listed options:
- a. RNA polymerase – This enzyme is essential for transcription. It binds to a promoter region on the DNA and facilitates the synthesis of RNA by adding ribonucleotides complementary to the DNA template strand.
- b. DNA – The template for transcription is a strand of DNA. RNA polymerase reads the DNA sequence and builds an RNA molecule based on its instructions. So, DNA is absolutely necessary for transcription.
- c. Uracil nucleotides – In RNA, uracil (U) replaces thymine (T) found in DNA. Thus, uracil-containing ribonucleotides (specifically, UTP – uridine triphosphate) are needed for building the RNA strand during transcription.
- d. Ribosomes – Ribosomes are not involved in transcription. They are the cellular machinery responsible for translation, which is the second step of gene expression. Translation involves reading the mRNA (produced during transcription) and synthesizing a protein from it. Thus, ribosomes are crucial for protein synthesis, not RNA synthesis.
Summary:
Transcription requires RNA polymerase, DNA, and ribose-based nucleotides (including those with uracil). However, ribosomes are not needed for transcription—they play their role later, during translation.
Hence, the correct answer is:
d. Ribosomes.