are polysomes formed in nucleoplasm?
Answers
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Understanding:
• Translation can occur immediately after transcription in prokaryotes due to the absence of a nuclear membrane
In eukaryotes, the ribosomes are separated from the genetic material (DNA and RNA) by the nucleus
After transcription, the mRNA must be transported from the nucleus (via nuclear pores) prior to translation by the ribosome
This transport requires modification to the RNA construct (e.g. 5’-methyl capping and 3’-polyadenylation)
Prokaryotes lack compartmentalised structures (like the nucleus) and so transcription and translation need not be separated
Ribosomes may begin translating the mRNA molecule while it is still being transcribed from the DNA template
This is possible because both transcription and translation occur in a 5’ → 3’ direction
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Skill:
• Identification of polysomes in electron micrographs of prokaryotes and eukaryotes
A polysome (or a polyribosome) is a group of two or more ribosomes translating an mRNA sequence simultaneously
The polysomes will appear as beads on a string (each 'bead' represents a ribosome ; the ‘string’ is the mRNA strand)
In prokaryotes, the polysomes may form while the mRNA is still being transcribed from the DNA template
Ribosomes located at the 3’-end of the polysome cluster will have longer polypeptide chains that those at the 5’-end
Polysomes
polysome