Every cell typically contains hundreds of different kinds of macromolecules that function together to generate the behavior of the cell. Each type of protein is usually sent to a particular part of the cell. An important part of cell biology is the investigation of molecular mechanisms by which proteins are moved to different places inside cells or secreted from cells.
Most proteins are synthesized by ribosomes in the cytoplasm. This process is also known as protein biosynthesis or simply protein translation. Some proteins, such as those to be incorporated in membranes membrane proteins, are transported into the ER or endoplasmic reticulum during synthesis and further processed in the Golgi apparatus. From the Golgi, membrane proteins can move to the plasma membrane, to other subcellular compartments or they can be secreted from the cell. The ER and Golgi can be thought of as the "membrane protein synthesis compartment" and the "membrane protein processing compartment", respectively. There is a semi-constant flux of proteins through these compartments. ER and Golgi-resident proteins associate with other proteins but remain in their respective compartments. Other proteins "flow" through the ER and Golgi to the plasma membrane. Motor proteins transport membrane protein-containing vesicles along cytoskeletal tracks to distant parts of cells such as axon terminals.
Some proteins that are made in the cytoplasm contain structural features that target them for transport into mitochondria or the nucleus. Some mitochondrial proteins are made inside mitochondria and are coded for by mitochondrial DNA. In plants, chloroplasts also make some cell proteins.
Extracellular and cell surface proteins destined to be degraded can move back into intracellular compartments upon being incorporated into endocytosed vesicles. Some of these vesicles fuse with lysosomes where the proteins are broken down to their individual amino acids. The degradation of some membrane proteins begins while still at the cell surface when they are cleaved by secretases. Proteins that function in the cytoplasm are often degraded by proteasomes.
Movement of proteins
Cell division - The origin of new cells.
Cell signaling - Regulation of cell behavior by signals from outside.
Active transport and Passive transport - Movement of molecules into and out of cells.
Adhesion - Holding together cells and tissues.
Transcription and mRNA splicing - gene expression.
Cell movement: Chemotaxis, Contraction, cilia and flagella
DNA repair and Cell death
Metabolism: Glycolysis, respiration, Photosynthesis
Autophagy - The process whereby cells "eat" their own internal components or microbial invaders. Other cellular processes
Microscopy and Immunostaining
Gene knockdown and Transfection
Cell culture and Radioactive tracers
PCR and In situ hybridization
DNA microarray screens of gene expression
Computational genomics approaches are used to find patterns in genomic information Techniques
Purification of cells and their parts is achieved in the following ways:
- Release of cellular organelles by disruption of cells.
Separation of different organelles by centrifugation.
Proteins extracted from cell membranes by detergents and salts or other kinds of chemicals.
Immunoprecipitation Purification of cells and their parts
Organelle - term used for major subcellular structures
Chloroplast - key organelle for photosynthesis
Cilia - motile microtubule-containing structures of eukaryotes
Cytoplasm - contents of the main fluid-filled space inside cells
Cytoskeleton - protein filaments inside cells
Ribosome - RNA and protein complex required for protein synthesis in cells
Endoplasmic reticulum - major site of membrane protein synthesis
Flagella - motile structures of bacteria, archaea and eukaryotes
Golgi apparatus - site of protein glycosylation in the endomembrane system
Membrane lipid and protein barrier
Lipid bilayer - fundamental organizational structure of cell membranes
Vesicle - small membrane-bounded spheres inside cells
Mitochondrion - major energy-producing organelle
Nucleus - holds most of the DNA of eukaryotic cells See also
Anton van Leeuwenhoek
Keith R. Porter
H. Robert Horvitz
Christian de Duve
Edmund Beecher Wilson
Peter D. Mitchell
George Emil Palade
Geoffrey M. Cooper