Harvard Human Anatomy Chapter 1: Tissues and Organization

The cell membrane forms a selective barrier between the inside and outside of the cell.

Cytoplasm has a network of tubules and filaments (cytoskeleton). The cytoskeleton is suspended in a gel-like material called cytosol.

Organelles are functional components. All are surrounded by a membrane. This membrane segregates them and their functions from the rest of the organelles in the cell.

The nuclear membrane surrounds the nucleus. Largest of organelles. Contains the genetic material of the cell. Serves as control centre. Instruction for constructing all cell components is known as DNA, arranged on chromosomes.

The nucleolus is the site of ribosomal RNA synthesis and ribosome assembly.

Ribosomes leave the nucleus and direct protein synthesis within the cytoplasm.

The endoplasmic reticulum is a system of membrane-bound tubules and cisterna. 

Smooth ER is found in cells specializing in hormone synthesis or detoxification

Rough ER synthesizes proteins and enzymes. Rough because covered with ribosomes clinging to the membrane surface.

Golgi Apparatus is a stack of membranous sacs and cisternae that sort, process and package proteins produced in the rough ER into vesicles. Proteins may be used within the cell or secreted at the cell surface.

Two types of vesicles are lysosomes: small membrane-bound packets of enzymes [acid hydrolases] that can digest microorganisms, cell debris or excess organelles. and peroxisomes: which are smaller membrane-bound packets of enzymes (oxidases) that can oxidize organic substances and form hydrogen peroxide

Mitochondria are the energy sources of the cells, functioning as sites of oxidative phosphorylation and ATP formation. Number of mitochondria in a cell reflects the energy requirements of that cell. Mitochondria are numerous in cells that actively synthesize and secrete protein, such as liver cells.