cells and cell signaling

• Diffusion is the net movement of molecules from high to low concentration and creates a concentration gradient.
• Osmosis is the diffusion of water from high to low concentration.
• A hypertonic solution is one where solution is more concentrated than within the cell and water moves out. A hypotonic solution is one where solution is less concentrated and water moves in. An isotonic solution is equal in concentration.
• As an object gets larger, the ratio of surface area to volume gets smaller, which makes diffusion more difficult.
• Facilitated diffusion is the movement of ions using a transport protein.
• Active transport is movement of an ion against the concentration gradient and requires energy.
• Transport proteins can be channel proteins, which are unchanging, or carrier proteins, which change shape to squeeze molecules through.
• An electrochemical gradient is a gradient of charges.
• A cell is the smallest unit of life.
• Cells have membrane-bound compartments called organelles.
• Cells are divided into eukaryotes, that have a nucleus and are very compartmentalized, and prokaryotes, that have a nucleoid and few organelles.
• Prokaryotes are divided into bacteria and archaea.
• The plasma membrane surrounds the cell and acts as a selectively permeable barrier. It contains proteins on the surface as well as glycolipids and glycoproteins for cell-cell recognition.
• The nucleus contains most DNA in eukaryotic cells and has a dense area called the nucleolus where RNA is transcribed.
• Ribosomes translate mRNA into proteins and can be free-floating or attached to an organelle. All living things have ribosomes.
• The endomembrane system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, transport vesicles, lysosomes/peroxisomes, and vacuoles. It functions in protein secretion and cellular digestion.
• The endoplasmic reticulum creates macromolecules; the rough ER has ribosomes and creates proteins, and the smooth ER has no ribosomes but makes lipids and detoxifies drugs.
• Vesicles are small, membrane-bound shipping containers that leave the endoplasmic reticulum and travel to the Golgi apparatus.
• The Golgi apparatus processes the products of the ER, modifies them, and ships them to their final destination.
• Lysosomes are specialized vesicles that dissolve waste. Peroxisomes break down toxic chemicals.
• Mitochondria convert stored energy into ATP and contain mitochondrial DNA.
• Chloroplasts are found in plants and are the site of photosynthesis.
• The cell well is found in plants and keeps a firm shape.
• Different types of cells have different organelle proportions - red blood cells have almost none because they need space to carry oxygen.
• The nuclear envelope is a protective double membrane surrounding the nucleus. The nuclear pores are tiny holes that allow entry/exit of the nucleus.
• Nuclear pore complexes regulate traffic in and out of the nucleus using nuclear localization signals that act like zip codes for import.
• Exocytosis is the vesicle merging with the plasma membrane and releasing proteins or other molecules out of the cell. Endocytosis is the pinching off of the plasma membrane to bring in molecules.
• The cytoskeleton is a network of fibers that provides structural support to maintain the cell shape, but is not static.
• The extracellular matrix is the fiber composite on the outside of animal cells.
• Cell junctions allow neighboring cells to interact. In animal cells, there are tight junctions that form strong barriers, desmosomes that anchor adjacent cells, and gap junctions which connect cytoplasm of cells. In plants, there are plasmodesmata, very similar to gap junctions.
• Hormones are a method of distant cell-cell communication and are part of the endocrine system.
• Target cells have receptors that fit the specific hormone/signaling molecule and receive the signal.
• Steroid hormones are lipids that diffuse through a membrane, and nonsteroid hormones are proteins that bind to receptors.
• The three steps of cell signaling are reception, a signaling molecule binding to a receptor and changing its shape; transduction, the path of interaction converting a signal into a change; and cellular response, the end result causing a physical/chemical change.
• Second messengers are small ions/molecules that elicit intracellular responses
• Signal amplification is when a molecule binds to a receptor and creates a larger cellular response, activating many molecules.
• Protein kinases are enzymes that activate proteins by adding a phosphate group (phosphorylation).
• Phosphatases are enzymes that remove phosphate groups.
• Quorum sensing is cell-cell signaling in unicellular organisms, which signals population density.