Question

A researcher is looking at a cellular sample using an electron microscope. He observes that while mRNA is being transcribed from the DNA that ribosomes are binding to the mRNA to make proteins. Is this sample from a bacterial or a eukaryotic cell? Explain your answer to receive full credit.

Answer 1

The researcher is looking at the bacterial cell. Gene expression is the process of manufacture of its corresponding protein which is a multilayered process with two steps. First step involves transfer of information from DNA to the messenger RNA (mRNA) by the process of transcription. In this process DNA of a gene provides as a template for the complementary base pairing and the enzyme RNA polymerases II catalyzes the formation of pre-mRNA and is then processed to a matured mRNA. This mRNA is single stranded copy of the gene and is further translated into a protein molecule. The process of translation consists of reading the genetic code on mRNA which is relates DNA sequence to amino acid sequence in proteins. mRNA consists of group of three bases which constitutes a codon and each codon corresponds to a particular amino acid. Thus mRNA sequence is used as a template to assemble the chain of amino acids which forms a protein molecule. Translation process occurs in the machinery which is located within the specialized organelle called ribosomes.

In the prokaryotes the ribosomes get attached to the mRNA while the process of transcription from DNA is still under process. Hence, it can be confirmed that the researcher is looking at the bacterial cell. In this situation, translation begins at the 5' end of mRNA while the 3' end is still attached to DNA.

In the eukaryotic cell the matured mRNA molecules leave the nucleus and travel to the cytoplasm where the ribosomes are present.