Question

Which of the following is NOT a way in which gene expression differs in prokaryotes and eukaryotes?

One mRNA transcript may code for several enzymes in prokaryotes

Introns are found within eukaryotic coding genes

Ribosomes are larger in prokaryotes than eukaryotes

Transcription and translation can occur simultaneously in prokaryotes

Eukaryotic mRNAs are modified prior to translation

Answer 1

Ans: B

Eukaryotic ribosomes are larger. They consist of a 60S large subunit and a 40S small subunit, which come together to form an 80S particle having a mass of 4200 kd, compared with 2700 kd for the prokaryotic 70S ribosome.

Like prokaryotes, eukaryotes can control gene expression at the levels of transcription, translation, and post-translation.The basic mechanics of transcription and translation are similar in eukaryotes and prokaryotes.

Because bacteria lack nuclei, transcription and translation are coupled.

In a eukaryotic cell, almost all transcription occurs in the nucleus and translation occurs mainly at ribosomes in the cytoplasm.

Eukaryote gene structure and function differ from prokaryote gene structure and function in several important ways. Eukaryotes generally have many more genes and these genes are spread across multiple chromosomes. Prokaryotes have fewer genes and these genes are all located on one chromosome. Groups of genes producing proteins with related functions are often organized into operons in prokaryotes but not in eukaryotes. Eukaryotes also have mRNA that must have its introns excised and the mRNA transported out of the nucleus to the ribosomes. The greater complexity of the eukaryote genome means that a greater variety and complexity of control mechanisms is necessary. There are also more steps in the transcription and translation process at which control of expression can occur in eukaryotes.