Cell Structure
The cell is the basic structural, functional and biological unit of all known living organisms. Cells are the smallest unit of life that is classified as a living thing, and are often called the "building blocks of life".
Cells consist of a protoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids. Organisms can be classified as unicellular (consisting of a single cell; including most bacteria) or multicellular (including plants and animals). While the number of cells in plants and animals varies from species to species, humans contain about 100trillion cells. Most plant and animal cells are visible only under the microscope, with dimensions between 1 and 100 micrometres.
The cell membrane (also known as the plasma membrane or cytoplasmic membrane) is a biological membranethat separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. The basic function of the cell membrane is to protect the cell from its surroundings. It consists of the phospholipid bilayer with embedded proteins. Cell membranes are involved in a variety of cellular processes such as cell adhesion, ion conductivity and cell signalingand serve as the attachment surface for several extracellular structures, including the cell wall, glycocalyx, and intracellular cytoskeleton. Cell membranes can be artificially reassembled.
Transport
Diffusion: Diffusion is the movement of a substance from an area of higher concentration to one of lower concentration (down a gradient). It occurs on its own without the input of energy. Many waste materials exit the cell through diffusion because that is their natural direction of movement as they build up within the cell.
Active transport: Sometimes, much-needed nutrients or harmful substances must be transported across the membrane against a concentration gradient. In these cases, the cell must provide energy in order to move the material against the direction of diffusion. This kind of energy-requiring transport is called active transport and, like facilitated diffusion, uses membrane proteins. Often, these proteins cleave ATP in order to obtain the needed energy. Other proteins use the energy released from the diffusion of one substance to power the active transport of another substance.
Exocytosis: Membrane proteins are fine for channeling the movement of ions and small molecules, but for transporting large molecules, a different strategy is required. When cells need to send large molecules (like proteins) outside their plasma membrane borders, they turn to exocytosis. Sizable cargo is loaded into spherical membrane vesicles. These vesicles move toward the plasma membrane and fuse with it, exposing the vesicle interior to the outside of the cell and releasing its contents.
Endocytosis: Sometimes cells have cause to import large molecules. For this challenging task, the solution is endocytosis, which is essentially exocytosis in reverse. Molecules to be imported contact the exterior surface of the plasma membrane, triggering the membrane to fold inward, enveloping them. The infolded membrane pinches off into a vesicle containing the imported molecules, which can be further transported to their eventual destination within the cell.
Facilitated diffusion: Most kinds of materials can't easily diffuse across the plasma membrane unless an opening is provided for them. Cells can support and control the diffusion of these materials by means of membrane proteins. Specific membrane proteins allow passage across the membrane to specific ions or molecules, but not to others. As long as the appropriate membrane protein is present and open, a given ion or molecule can diffuse through the protein, across the membrane, along its concentration gradient. Although facilitated diffusion requires a protein tunnel through the membrane, it is still diffusion, and requires no added energy.
Active & Passive
Transport
Active Transport
Use of ATP (a form of energy) to pump molecules against the concentration gradient i.e., from low solute to high solute concentration.
Passive
Transport
Movement of molecules with the concentration gradient i.e., from high to low concentration, in order to maintain equilibrium in the cells.
How do Cells work?
BY
Lucas Guglielmone, Ivan Stankiewich,
Juan Pando & Alejo Zubizarreta
Sources of information:
www.Wikipedia.org
www.Youtube.com
www.Khanacademy.org
Creatine
Creatinine phosphate was shown to be no substrate of purified creatine kinase from skeletal muscle or of creatine kinase in heart muscle homogenate. It was found to be a competitive inhibitor with respect to creatine phosphate and a noncompetitive inhibitor with respect to ADP.
Abstract
The kinetics of creatine kinase (CK) and adenylate kinase (AK) activities were monitored in intact diaphragm muscle by 18O phosphoryl oxygen exchange to assess whether these two phosphotransferases provide an interrelated function integral to high energy phosphoryl metabolism. This possibility was examined by quantitating the net rates of CK- and AK-catalyzed phosphoryl transfer in comparison to the total cellular ATP metabolic rate when CK activity in the intact diaphragm muscle was progressively inhibited by 2,4-dinitrofluorobenzene. In noncontracting muscle from untreated rats, net rates of CK- and AK-catalyzed phosphotransfer were equivalent to 88 and 7%, respectively, of the total ATP metabolic rate. These results were compared with reported 31P NMR analyses of total creatine phosphate flux to estimate that each creatine phosphate molecule produced undergoes about 50 unidirectional CK-catalyzed phosphotransfers in transit to an ATP consumption site in the intact muscles. Graded inhibition by 2,4-dinitrofluorobenzene of intracellular CK activity by up to 98% resulted in a progressive shift in phosphotransferase catalysis from the CK to the AK system; the sum of the net rates of phosphoryl transfer by combining the increasing AK and decreasing CK activities continued to approximate the total cellular ATP metabolic rate. These results indicate that in diaphragm muscle CK and AK operate as interrelated cellular high energy phosphoryl transfer systems through which the majority of newly generated ATP is processed prior to its utilization.
http://www.jbc.org/content/271/22/12847.short
Source 2
http://www.sciencedirect.com/science/article/pii/S0022282885800675
http://www.diffen.com/difference/Active_Transport_vs_Passive_Transport
Osmosis: Osmosis is simply the diffusion of water; it has its own name because water is so important to life. Solutions with higher amounts of dissolved substances have lower concentrations of water, and water will diffuse across membranes in order to minimize the difference in concentration.
Source 1