Cell Structure & Transport

* Flash cards to learn the structure and function of cell parts.

* Determined by surface area to volume ratio * When cell increases in size, the volume increases faster than the surface area (3:2) so it can’t move materials in and out fast enough to support the volume

* Cells can be modified to increase surface area * Overall shape—be long rather than round * Folds (microvilli) in cell membrane

* Eukaryotic Cells are divided into compartments * Due to enfolding of membranes which created membranes such as ER and Golgi Apparatus * Many enzymes on membrane surfaces * Different local environments allow for specific metabolic functions

* Interdependence within the Cell—all the cell parts/organelles form a system * Example: Sunlight passes through cell wall and cell membrane  sunlight is used by the chloroplast during photosynthesis to create sugar  sugar is transported to mitochondria to be used in cellular respiration to produce ATP

* Endomembrane System—different membranes of the cell that regulate protein traffic and perform metabolic function * Includes—nuclear envelope, endoplasmic reticulum, Golgi bodies, lysosomes, vacuoles, and plasma membrane

Endomembrane System

* Serial Endosymbiosis (Margulis)—sequence of endosymbiotic events * Endosymbiosis—some organelles were small prokaryotes living in a larger prokaryotic cells and became specialized to do their jobs (mutualism) * Applies to mitochondria and chloroplasts * Since not all cells have chloroplasts, it must have been a series of events.

* Evidence of Serial Endosymbiosis * Chloroplasts and mitochondria have their own DNA and inner membranes—they can make their own proteins * Are of similar size to prokaryotic cells * Replicate by splitting (similar to binary fission)

* Phospholipids give fluidity * Molecules contain hydrophilic heads & hydrophobic tails * Weak interactions occur between tails, but they are not touching * Phospholipids line up and form a bilayer * Phospholipids can switch with neighbor but usually not across

* Phospholipids bilayer is affected by: * Temperature—colder temps = stiffer * Degree of saturation of the phospholipids * Unsaturated has more kinks, which means… * Cholesterol—generally decreases fluidity

* Proteins are the mosaic. * Integral Proteins—proteins that are embedded in the membrane * Hydrophilic/hydrophobic portions to keep them in place * Peripheral Proteins—proteins that are on the inner or outer surface * See 1 Page Diagram for Functions!!!!

* Semi-permeable—some molecules can go through membrane and others cannot. * Size determines their ability to move through * Selective Permeability—some molecules can go through membrane and others cannot. * Chemical properties of the molecule determines its ability to go through.

* Phospholipid Bilayer * Hydrophobic molecules are allowed to cross * i.e. hydrocarbons, oxygen, carbon dioxide * Polar and ionic molecules cannot cross easily, so they need a protein to help them through * i.e. water, sugar, sodium ions…

* Does not require cell’s energy * Molecules move down (or with) the concentration gradient * Molecules move down electrochemical gradient * Causes more random distribution * Moves smaller molecules

* Diffusion—movement of molecules from high to low concentration until equilibrium * Generally how small, non-polar molecules (O 2, CO 2,…) go through phospholipid bilayer

* Facilitated Diffusion * Movement of molecules from high to low concentration until equilibrium through transport proteins * Channel proteins might be open or gated

* Osmosis—diffusion of water across a selectively permeable membrane * Osmosis occurs from a hypotonic solution to a hypertonic solution * Hypertonic—more concentrated/more solutes * Hypotonic—more watery/less concentrated/less solutes * Isotonic—2 solutions of equal concentrations

* Osmosis continued…

* Osmoregulation—how cells maintain water balance * Be isotonic * Pump out excess water * Paramecium have contractile vacuole * Cell wall (for plants) * Turgid—full * Flaccid—wilt * Plasmolysis—shrivel and die

* Uses cell energy * Moves molecules against the concentration gradient * May not stop at equilibrium * Moves larger/charged/polar molecules

* Use Transport Proteins (Carrier) * Example—Sodium-potassium pump uses an electrogenic pump to generate voltage across the membrane

* Endocytosis—cell takes in a molecule by forming new vesicles from the plasma membrane * Phagocytosis—”eat”, engulfs a particle * Pinocytosis—”drink”, extracellular fluid is brought into cell

* Exocytosis—cell secretes a molecule by fusing a vesicle with the membrane and spilling contents of the vesicle to outside * Get rid of wastes / secrete hormones / etc