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BIOL - Chapter 4
Cell Structure and Membranes
| Question | Answer |
|---|---|
| What is the simplest structural unit of a living organism? | The cell |
| Cell theory | 1. Cells are the fundamental units of life 2. All living organisms are composed of cells 3. All cells come from preexisting cells |
| Cell membranes | separate the internal environment from the external environment, giving cells or cell compartments the ability to regulate their internal composition |
| Cytoplasm | everything inside a cell, except for the nucleus |
| Fluid mosaic model | lipids and proteins move laterally through the membrane |
| hydrophilic 'heads' | on the outside (charged) |
| hydrophobic fatty acid 'tails' | on the inside (nonpolar) |
| What is the purpose of the hydrophobic interior? | prevents diffusion of polar molecules and ions through the membrane |
| phospholipids vary in terms of what? | fatty acid chain length, degree of saturation, and polar groups |
| Membrane fluidity is influenced by? | lipid composition and temperature |
| short, unsaturated chains increase what? | fluidity |
| cholesterol alters interactions among what? | fatty acid side chains |
| fluidity decreases in? | cold conditions; some organisms alter lipid composition in cold environments |
| Integral membrane proteins | at least partly embedded in phospholipid bilayer. Hydrophobic regions interact with membrane interior; hydrophilic regions interact with the aqueous environment |
| Anchored membrane proteins | covalently attached to fatty acids or other lipid groups |
| Peripheral membrane proteins | no hydrophobic groups; not embedded in the bilayer - polar or charged regions interact with exposed parts of integral membrane proteins or with charged heads of phospholipids |
| Transmembrane proteins | extend through the bilayer; they may have domains with different functions on the inner and outer sides of the membrane |
| Carbohydrates on the outer cell membrane play roles in? | communication and adhesion |
| Glycolipid | carbohydrate attached to a lipid |
| Glycoprotein | oligosaccharide attached to a protein |
| Proteoglycan | many carbohydrates attached to a protein |
| Selective permeability | biological membranes allow some substances, but not others, to pass |
| Active transport | requires energy and the assistance of specialized membrane proteins |
| Diffusion | random movement of particles toward a state of equilibrium; a net movement from regions of higher concentration to regions of lower concentration |
| Diffusion in water is slow, speed depending on: | diameter of molecules temperature concentration gradient area and distance |
| In a complex solution (with many different solutes), diffusion of each solute depends only on: | its own concentration |
| A higher concentration inside the cell | causes the solute to diffuse out |
| higher concentration outside | causes the solute to diffuse in |
| Simple diffusion | O2, CO2, and small, nonpolar, lipid soluble molecules can cross the membrane unaided. Water and urea can also pass, but permeability is lower. |
| Osmosis | net movement of water from a region of lower solute concentration to a region of higher solute concentration |
| Osmotic pressure | pressure that must be applied to a solution to prevent flow of water across a membrane by osmosis |
| π=cRT | c is the osmolarity (total # of solute particles/liter of water) R is the gas constant T is the absolute temperature |
| osmolarity | Osmotic pressure can be quantified by osmolarity-solute particles per liter of water (solute concentration) |
| Tonicity | relative concentration of solutes on either side of a membrane; determines direction and extent of net water movement. |
| Solutes that can't cross the membrane | determine tonicity of a solution |
| Solutes that can cross will | diffuse to equilibrium, and thus don't affect net water movement |
| Isotonic solution | has equal solute concentrations |
| hypotonic solution | has a lower solute concentration |
| hypertonic solution | has a higher solute concentration |
| When there is a net flow of water, it occurs | from the hypotonic to the hypertonic |
| What determines the direction of osmosis in all animal cells? | Concentration of solutes |
| Cell Walls | limit the volume of water that can be taken up |
| Turgor pressure | the internal pressure against the cell wall - as it builds up, it prevents more water from entering |
| Facilitated diffusion | passive transport of solutes down their concentration gradient with the help of integral transmembrane proteins |
| Channel proteins | form channels across the membrane |
| Aquaporins | channels for movement of water |
| Carrier proteins | bind to a solute to speed up diffusion |
| Ion channels | channel proteins that allow specific ions to pass through; water can "hitchhike" along with some ions |
| gated channels | open when a stimulus causes the protein to change shape |
| ligand-gated | the stimulus is a ligand, a chemical signal |
| Voltage-gated | the stimulus change in electrical charge difference across the membrane |
| Carrier proteins | transport polar molecules such as sugars and amino acids |
| Glucose transporters | glucose is quickly broken down in the cell, so there is always a strong concentration gradient that favors glucose uptake |
| The system can become saturated when | all of the carrier molecules are bound, the rate of diffusion reaches a maximum. |
| Active transport | energy from ATP (adenosine triphosphate) is needed to move substances against their concentration gradients |
| Specific carrier proteins move substances in: | only one direction, either into or out of the cell |
| Primary active transport | involves direct hydrolysis of ATP for energy |
| Sodium-potassium (Na+ - K+) pump (Primary active transport) | moves Na+ out of cell and K+ in. One molecule of ATP moves two K+/- and three Na+/- ions. This maintains K+ at a higher concentration inside the cell, and Na+ at a higher concentration outside the cell |
| Secondary active transport | uses energy stored in ion concentration or electrical gradients, which are established by primary active transport |
| The Na+ - K+ pump (Secondary active transport) | establishes a concentration gradient of Na+, then passive diffusion of Na+ back into the cell provides energy for glucose transport/One protein usually moves both the ion and the transported molecule across the membrane (coupled transport or co-transport) |
| Vesicles | small, membrane-enclosed structures -Macromolecules are too charged to pass through biological membranes of eukaryotes, so instead they cross in vesicles - small, membrane-enclosed structures |
| Exocytosis | moves materials out of cells |
| Secretion | vesicle migrates toward the cell membrane and fuses with it. Vesicle contents empty and vesicle membrane is incorporated into the cell membrane |
Created by:
Alexolotl
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