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THE BIOLOGY OF CELLS: Over its brief 30-year history, cell biology has matured into a vigorous and rapidly expanding discipline. Today, it forms an essential bridge between important basic fields such as biochemistry, developmental biology, physiology, neurobiology, molecular genetics, immunobiology and microbiology. Since cell biology focuses on the functions of cells in diverse contexts, it also provides a natural connection between basic biological research and medicine.

CONTENTS
The Cell / Cellular Chemistry / Nucleus and Chromosomes / Nucleic Acid and Protein Synthesis / Cell Membranes / Protein and Vesicular Traffic / Receptors and Second Messengers / Energy, Mitochondria, and Chloroplasts / Cytoskeleton and Cell Movement / Extracellular Matrix and Cell-Cell Interactions / The Cell Cycle / Cancer and Cell Death / Development and Differentiation / Gene Expression in Eukaryotes and Prokaryotes / Techniques in Cell Biology / Answers to Self-Testing Questions / Glossary

about Organelles

Cell Biology - Topics by organelle system, as part of the interactive learning program at the University of Arkansas for Medical Sciences, Little Rock, AR.

Golgi Apparatus - Introduction to the intracelullar post office, and it's functions, with electron micrograph, from school student in UK.

Golgi Bodies - Electron micrographs, cartoons and explanations of endoplasmic reticulum, the apparatus and their function, from The Natural Toxins Reaseach Center, Texas A&M University, Kingsville.

Malhotra Lab - Studies vesicular transport and Golgi apparatus at the cellular and molecular level. Includes biochemistry, histology and micrographs performed in La Jolla, CA.

Neurohistology Lab - Nucleus, cytoplasm, neuroglia, neuronal processes and fiber terminations of nerves, with flash-dependent electron micrographs, and explanation of their function from the Computer Assisted Teaching System of the University of Vermont, Burlington.

Peroxins - Introduction to the function, phylogenetics and association with human peroxisome biogenesis disorders, and access to an annotated database of Peroxins, and link to cv of author in Nottingham, UK.

The Cell - The structural components and their cellular functions; centrosome, ribosomes, mitochondria, golgi complex, lisosomes, endoplasmic reticulum, chloroplast, vacuoles, cilium andflagellum, with illustrations of the cytoskeleton and cytoplasmic membrane, from

The Peroxisome Website - Information about the peroxisome and associated disorders for people of all scientific backgrounds, from patients to scientists.

Links about Cell Membrane and Adhesion:

CEA The Carcinoembryonic Antigen Family - Comprehensive structural and immunological information on membrane-bound proteins involved in adhesion. Includes molecule cartoons of human, mouse, rat and other species. Details of conference in Frauenchiemsee, Germany.

Cell Junctions - Adhesion and desmosomes research at New York University School of Medicine.

Green, Kathleen J. - Overview of research on adhesion, its role in embryogenesis, differentiation and wound healing. Includes research opportunities, training at Northwestern University Medical School, Chicago, IL.

Integrin - Family of transmembrane proteins involved in the extracellular matrix. Includes classification, ligands, structure images, realted links, discussion forum and guest book.

Thorkild's Lectin Page - Resources introducing the lectins, and research devoted their functions, maintained at University of Copenhagen, Denmark.

dictyBase - Dictyostelium discoideum as a model for cellular development, chemotaxis, motility, cytokinesis defects, phagocytosis and functional genomics, at the Northwestern University Medical School, Chicago, IL.

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Topic 5
Cell Membranes: ��
Plasma (cell) membrane
Each eukaryotic cell has as its boundary to the outside a cell membrane (7.5 to 10 nm in thickness) that envelopes the cytoplasmic matrix containing specialized membrane-bound components called organelles. The cell or plasma membrane is a lipid bilayer containing proteins, cholesterol, and oligosaccharides that functions as a selective barrier for entry and exit of substances. The plasma membrane, by limiting the transport of some things and facilitating the movement of others helps to maintain the internal environment of the cell, which is different from the extracellular fluid. Under an electron microscope membranes appear to have a trilaminar structure. This is because the lipid bilayers are arranged such that hydrophilic phospholipid groups are oriented toward the outside of the membrane while the more hydrophobic lipid fatty acid chains form the middle of the trilaminar structure. The molecular make up of each half of the membrane is different in that different lipids and proteins are more abundant in one side over the other.
Proteins are a very important part of the cell membrane. Basically they can be classified into two groups based on physical distribution. Integral proteins are embedded within the cell membrane and may in fact pass multiple times through the membrane. Peripheral proteins are loosely associated with membrane surfaces. Carbohydrate portions of glycoproteins and glycolipids are found on the external surface of the cell membrane where they are important parts of receptor molecules.
Receptors are necessary to cellular signalling, adhesion, and recognition. Most proteins are fixed in place within the cell membrane by interactions with the cytoskeleton . However, some integral proteins can move about and sometimes will accumulate on one region of the membrane in a process called capping.
The cell membrane is not static. It is remodeled by the addition of new membrane vesicles from the Golgi while removal takes place in the form of endocytotic, phagocytotic and pinocytotic vesicles being formed and then fused with lysozomes for processing. Membrane receptors and membrane are often conserved and recycled to the plasma membrane. This membrane trafficking is important in the cell economy.

Jin Seok Jeon
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jsj291@kmu.ac.kr

Biosciences Web Site: www.nvo.com/jin
Copyright.Jeon 1998-2009. For questions or comments, write to jsj291@kmu.ac.kr