Cells

• cell - the basic unit of life; unicellular or multicellular.
• cell membrane or plasma membrane - separates the cell from its surrounding environment; controls what goes in and out of the cell.
• cytoplasm - gel-like internal substance of cells that includes many organelles suspended in watery intracellular fluid called cytosol; responsible for holding the components of the cell and protects them from damage.
• nucleus - large membranous structure near the center of the cell; contains genetic materials like DNA.
• nuclear pores - gateways into and out of the nucleus, allowing passage of large molecules.
• The cell membrane has a phospholipid bilayer, which is a double layer of phospholipids. The heads are hydrophilic (water loving) and the tails are hydrophobic (water fearing).
• A cell controls what moves through the membrane by means of Integral Membrane Proteins (IMPs) embedded in the phospholipid bilayer.
• endoplasmic reticulum - made of membranous-walled canals and fl at, curving sacs arranged in parallel rows throughout the cytoplasm; proteins move through the canals.
• rough endoplasmic reticulum - has ribosomes attached on its wall; functions in protein synthesis and intracellular transportation.
• smooth endoplasmic reticulum - no ribosomes on its wall; synthesizes certain lipids and carbohydrates and creates membranes for use throughout the cell.
• ribosomes - site of protein synthesis in the cell; made up of rRNA and proteins.
• golgi apparatus - a series of membrane-bound flattened sacs that are involved in the modification and packaging of proteins.
• lysosomes - the cell’s digestive system; enzymes digest the protein structures of defective cell parts, including integral membrane proteins, and particles that have become trapped in the cell.
• mitochondria - the “power plants” of cells; catalyze a series of oxidation reactions that provide nearly most of a cell’s energy supply.
• cytoskeleton - the cell’s internal supporting framework; made up of tiny, flexible fibers.
• microfilaments - smallest cell fibers; serve as "cellular muscles".
• intermediate filaments - twisted protein strands slightly thicker than microfilaments; form much of the supporting framework in many types of cells.
• microtubules - tiny, hollow tubes that are the thickest of the cell fibers; move things around inside the cell.
• centrosome - an area of the cytoplasm near the nucleus that coordinates the building and breaking apart of microtubules in the cell; plays an important role during cell division.
• proteasomes - break down abnormal/misfolded proteins and normal proteins no longer needed by the cell.
• peroxisomes - small membranous sacs containing enzymes that detoxify harmful substances that enter the cells.
• microvilli - found in epithelial cells that line the intestines and other areas where absorption is important; they help increase the surface area manyfold.
• cilia and flagella - cell processes that have cylinders made of microtubules and molecular motors at their core.
• desmosome - fibers on the outer surface of each desmosome interlock with each other; anchored internally by intermediate fi laments of the cytoskeleton.
• spot desmosomes - are like “spot welds” at various points connecting adjacent membranes.
• belt desmosomes - encircle the entire cell.
• gap junctions - membrane channels of adjacent plasma membranes adhere to each other; form gaps or “tunnels” that join the cytoplasm of two cells; fuse two plasma membranes into a single structure.
• tight junctions - occur in cells that are joined by “collars” of tightly fused material; molecules cannot permeate the cracks.
• passive transport process - do not require any energy expenditure of the cell membrane.
• diffusion - molecules move from an area of high concentration to an area of low concentration, down a concentration gradient.
• simple diffusion - molecules cross through the phospholipid bilayer.
• osmosis - diffusion of water through a selectively permeable membrane; limits diffusion of at least some of the solute particles.
• osmotic pressure - water pressure that develops as a result of osmosis.
• potential osmotic pressure - maximum pressure that could develop in a solution when it is separated from pure water by a selectively permeable membrane.
• isotonic - has equal potential osmotic pressure.
• hypertonic - has higher potential osmotic pressure.
• hypotonic - has lower potential osmotic pressure.
• facilitated diffusion (mediated passive transport)- a special kind of diffusion in which the movement of molecules is made more efficient by the action of transporters embedded in a cell membrane.
• channel-mediated passive transport - channels are specific allowing only one type of solute to pass through; channels allow membranes to be selectively permeable.
• carrier-mediated passive transport - carriers attract and bind to the solute, change shape, and release the solute out the other side of the carrier.