Cell Biology

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Cytoplasm
The cytoplasmic matrix is not an unstructured liquid gel as once was thought. The cytosol makes up some 50% of the cell volume. It contains numerous cytoskeletal elements, organelles, vesicles, metabolic enzymes and sometimes pigment deposits. The matrix coordinates the movement of intracellular organelles, and provides a framework for the orga9nization of enzyme pathways such as those within the glycolytic series. All of the necessities of protein synthesis are found within the cytosol and it contains numerous enzymes that build large molecules and break down small molecules. Protein motors are present in the cytosol to help transport things along the cytoskeletal framework.


Mitochondria
These organelles are the power houses of the cell and contain the molecular machinery for the conversion of energy from the breakdown of glucose into adenosine triphosphate (ATP), the energy currency of the cell. Mitochondria are mostly protein, but some lipid, DNA and RNA are present. These generally spherical organelles have an outer membrane surrounding an inner membrane that folds (cristae) into a scaffolding for oxidative phosphorylation and electron transport enzymes. Most mitochondria have flat shelf-like cristae, but those in steroid secreting cells may have tubular cristae. The mitochondiral matrix contains the enzymes of the citric acid cycle, fatty acid oxidation and mitochondrial nucleic acids. The metabolic activity of the cell is related to the number of cristae and the number of mitochondria within a cell. Cells with a lot of metabolic activity, such as heart muscle, have many well-developed mitochondria. New mitochondria are formed from preexisting mitochondria when they grow and divide.


Ribosomes
Ribosomes are small organelles composed of ribosomal RNA (rRNA) and 80 some different proteins. rRNA is synthesized in the nucleolus and the ribosomal sub-units are assembled there from rRNA and imported cytoplasmic made...