The nucleus contains the genetic information, encoded in DNA maintained as extremely long molecules making up chromosomes . Most of the time chromosomes cannot be directly seen without specialized microscopes, but the DNA stains well with various dyes, so even in light microscopy can be seen as a general blur, and is hence called chromatin . The nucleus is bounded by a double membrane with large nuclear pores to facilitate biochemical traffic across it. A particularly darkly staining or dense region is the nucleolus where ribosomes are formed. They are also bounded by a double membrane and this time the inner membrane is highly convoluted and it is here that their crucial biochemistry takes place.
Mitochondria also have their own DNA , remnants of a bacterial chromosome.
There is a cytomembrane system of endoplasmic reticulum , Golgi complex , and secretory vesicles that processes and secretes proteins beyond the cell membrane. Ribosomes attached to the endoplasmic reticulum give it a rough appearance, and proteins destined to be secreted are directed into the endoplasmic reticulum by a signal sequence of 15 hydrophobic non-polar amino acids at their amino end. Cilia and flagella provide motility for cells via their internal structure of microtubules based from the centriole or basal body . Your textbook has several sections on plant cell structures, such as figures 4.9 and 4.17, mastery of which is not required for this course. Click here to return to the Biology 104 home page.