Cell Structure & Transport

*Unit 2 Notes

*Cell Parts*Flash cards to learn the

structure and function of cell parts.

*Cell Parts

*Cell Parts

*Cell Parts

*Cell Parts

*Cell Size

*Cell Size

*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

*Cell Size

*Cells can be modified to increase surface area

*Overall shape—be long rather than round

*Folds (microvilli) in cell membrane

*Compartmentalization

*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

*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

*Interdependence

*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

*Interdependence

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*Evolutionary Significance

*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.

*Evolutionary Significance

*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)

*Evolutionary Significance

*Cell Membrane-Fluid Mosaic

Model

*Cell Membrane-Fluid Mosaic Model

*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

*Cell Membrane-Fluid Mosaic

Model

*Cell Membrane-Fluid Mosaic

Model

*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

*Cell Membrane—Fluid Mosaic

Model

*Cell Membrane-Fluid Mosaic

Model

*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!!!!

*Cell Membrane Function

*Cell Membrane Function

*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.

*Cell Membrane Function

*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…

*Cell Membrane Function

*Types of Transport

*Passive Transport Characteristics

*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

*Passive Transport Types

*Diffusion—movement of molecules from high to low concentration until equilibrium

*Generally how small, non-polar molecules (O2, CO2,…) go through phospholipid bilayer

*Passive Transport

Type

*Facilitated Diffusion

*Movement of molecules from high to low concentration until equilibrium through transport proteins

*Channel proteins might be open or gated

*Passive Transport Types

*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

*Passive Transport Types

*Osmosis continued…

*Passive Transport Types

*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

*Active Transport Characteristics

*Uses cell energy

*Moves molecules against the concentration gradient

*May not stop at equilibrium

*Moves larger/charged/polar molecules

Active Transport Types

*Use Transport Proteins (Carrier)

*Example—Sodium-potassium pump uses an electrogenic pump to generate voltage across the membrane

*Active Transport Types

*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

*Active Transport Types

*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