Practice question

Eukaryotes are defined by compartmentalization: nuclear envelope with nuclear pore complexes regulating RNA export and protein import via importins, linear chromosomes packaged with histone octamers H2A, H2B, H3, H4 into nucleosomes acetylated and methylated for epigenetic control, membrane-bound organelles including ER continuous with nucleus for secretory protein folding, Golgi for glycosylation, lysosomes for degradation, mitochondria for energy, and in plants chloroplasts for photosynthesis. Ribosomes are 80S in cytosol composed of 40S small subunit with 18S rRNA and 60S large with 28S, 5.8S, 5S rRNA. Division involves regulated G1, S where DNA replicates once per cycle under geminin-Cdt1 control, G2, and M phase mitosis with spindle assembly checkpoint Mad2, BubR1 ensuring chromosome alignment, followed by cytokinesis. Binary fission involving FtsZ contractile ring that constricts single circular chromosome segregation is prokaryotic strategy lacking mitotic spindle, CDK control, and nuclear envelope breakdown. Therefore binary fission as primary mode is not characteristic of eukaryotic cells which rely on mitosis-meiosis.