Eukaryotes: most of the DNA is stored in the nucleus (bounded by a double membrane) |
Prokaryotes: the DNA is concentrated in the nucleoid (not membrane enclosed) |
- Larger organisms do not necessarily have larger cells, just more of them |
- Lipids and proteins are the staple ingredients of membranes, though carbohydrates are also important |
- Phospholipids are the most abundant lipids in cell membranes |
Amphipathic: has both a hydrophyllic and a hydrophobic region |
- The phospholipid bilayer can exist as a stable boundary between two aqueous compartments |
Fluid mosaic model: proposes that the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids |
- Membranes are held together primarily by hydrophobic interactions which are weaker than covalent bonds, allowing for flexibility |
- The temperature at which a membrane solidifies depends on its comprising lipids |
- Kinks in the tails where double bonds are located prevent unsaturated tails from packing as closely together as saturated tails, making the membrane more fluid |
Cholestrol: helps membranes resist changes in fluidity when the temperature changes |
Steroid lipids: resist temperature changes in plant cells |
- Cells recognize other cells by binding to molecules on the extracellular surface of the plasma membrane |
- The diversity of molecules and their location on the cell's surface enable membrane carbohydrates to function as markers distinguishing cells apart |
Selective permeability: substances do not cross the cell membrane indiscriminately |
- Nonpolar hydrophobic molecules can dissolve in the lipid bilayer and can cross it easily without the aid of membrane proteins |
- The hydrophobic interior of the membrane impedes the direct passage of ions and polar (hydrophyllic) molecules through the membrane |
Transport (channel) proteins: span the membrane and have hydrophyllic channels which certain molecules and atomic ions ise as tunnels through the membrane |
Carrier proteins: hold onto their "passengers" and change shape in a way which shuttles them across the membrane |
- Diffusion occurs from a region of higher concentration to a region of lower concentration |
- Molecules diffuse randomly, but populations may diffuse directionally |
- Each substance diffuses along its own concentration gradient, unaffected by those of other substances |
- The behavior of a cell in a solution relies on both solute concentration and membrane permeability |
Tonicity: the ability of a surrounding solution to cause a cell to gain or lose water |
- Higher concentration of non-penetrating solutes: water leaves the cell |
- Lower concentration of non-penetrating solutes: water enters the cell |
Isotonic: no net movement of water (equillibrium) |
Hypertonic: more NPS; the cell loses water, shrivels, and dies |
Hypotonic: less NPS; the cell swells and lyses |
Turgor pressure: the pressure exacted back on a cell which opposes further water intake (in plant cells due to their cell walls) |
Plasmolysis: occurs when a plant is submerged in a hypertonic environment; the cell membrane pulls away from the cell wall at multiple locations |
Sodium-Potassium pump: exchanges sodium for potassium across the cell membranes of animal cells |
- Ions diffuse down their electrochemical gradients |
3 stages of cell signaling: reception, transduction, and response |
Reception: the target cell's detection of a signaling molecule outside the cell |
Transduction: converts the signal to a form which can bring about a specific cellular response |
Response: the transduced signal triggers a specific cellular response |
- Proteins relay signals from receptor to response |
- A signaling pathway may regulate the activity of proteins rather than causing their synthesis by activating gene expression |
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Nuclear envelope: encloses the nucleus and seperated its contents from the cytoplasm |
