s: (1) nucleolus (2) nucleus (3) Ribosomes (little dots) (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth endoplasmic reticulum (ER) (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles within centrosome]] The nucleolus (also called nucleole) is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus. Ribosomal RNA is transcribed and assembled within the nucleolus. The nucleolus ultrastr… (More on Nucleolus)