BioNinja

The Nucleus

One of the key distinguishing features of a eukaryotic cell is the presence of a nucleus (prokaryotic cells do not have nuclei)

• The nucleus is a double membrane structure with pores that stores the genetic material of the cell

The presence of a nucleus allows eukaryotes to separate the processes of transcription (nucleus) and translation (cytoplasm)

• Transcription is the process by which specific DNA instructions (genes) are converted into RNA transcripts (mRNA)

• Translation involves the synthesis of polypeptide chains (proteins) from the RNA transcripts by ribosomes

Separating the processes of transcription and translation allows for the post-transcriptional modification of mRNA before it is translated by ribosomes

• These modifications help to stabilise the mRNA transcript (via capping and polyadenylation) and remove non-coding sequences (introns) via splicing

• This greatly improves the efficiency of protein synthesis and allows for tighter control of gene expression than is possible in prokaryotic cells

Compartments

Another defining feature of eukaryotic cells is the presence of membrane-bound organelles in the cytoplasm (prokaryotic organelles are not membrane-bound)

• This enables the organelles to maintain an internal chemistry that is different to the cytoplasm (and suitable to its specific function)
  

• It also allows for the concentration of key enzymes and metabolites needed to optimise the function of the organelle
  

Lysosomes and phagocytic vacuoles provide evidence for the advantage of compartmentalising the cytoplasm into discrete sections

• These organelles contain hydrolytic enzymes that are responsible for digesting cellular debris or engulfed pathogenic materials

• If these enzymes were not contained within a specific compartment, they would freely digest the contents of the cell (autophagy)