Cellular clock. Conceptual artwork of a clock and the internal structures (organelles) of an animal cell. This could represent the rate of metabolic cell reactions, the natural ageing and death of a cell, or measuring evolutionary timescales using mitochondrial DNA. The structures seen include the cell nucleus (purple sphere with nuclear pores for genetic information transfer), the ER (endoplasmic reticulum, purple folds), ribosomes (red chains where protein synthesis takes place), the Golgi complex (yellow-green folds, bottom, where protein storage and transport takes place) and several mitochondria (green, the sites of energy synthesis within the cell).