Cell Membrane Structure & Cell Transport Notes

Cell Membrane Fluid mosaic model Mosaic  mixed composition primarily of phospholipids and proteins. Fluid  it is not a solid layer; it is selectively permeable. Phospholipids are arranged in a bilayer Proteins on the surface (act as markers) Proteins embedded in the bilayer (transport)

Structure of Phospholipids Hydrophilic, Water-Loving, & Polar Phospholipids contain……. hydrophilic phosphate head & 2 hydrophobic fatty acid tails Hydrophobic, Water-Fearing, & Non-Polar

Phospholipid Bilayer Forms due to the polarity (opposite ends) of the phospholipids Phosphate heads (polar) Close to the water of the cytoplasm and/or water inside the cell Face outward Fatty acid tails Face inward to avoid being near water Creates a barrier b/w inside and outside of the cell

Phospholipid Bilayer Phosphate heads one layer of phospholipids Fatty acid Tails Phosphate heads

Transport Proteins Span the phospholipid bilayer Interior is able to open to both sides May change shape when they interact with solute Move water-soluble substances across a membrane May be passive or active

Cell Membrane Structure

Cell Membrane Structure

Cell Membrane Function Creates a barrier b/w inside & outside of cell Proteins that pass through the entire bilayer act a channel to transport large substances OR transport substances against their gradients

Cell Membrane: Selectively Permeability CAN PASS THRU MEMBRANE ------------------------------------- O2 and CO2 H2O and glucose (sugar) CANNOT PASS THRU MEMBRANE ------------------------------------- Ions (charged)-like salt Large molecules

Cell Transport Passive Transport Active Transport Uses no ATP (energy) High  Low Concentration Down the concentration gradient Ex. Simple diffusion Osmosis Facilitated Diffusion Active Transport Uses ATP (energy) Low  High Concentration Against the concentration gradient Ex. Transport/Carrier Protein Endocytosis Exocytosis

Types of Passive Transport Simple Diffusion  HL; no E; CO2 and O2 Osmosis  HL; no E; H2O Facilitated Diffusion  HL; no E; glucose thru a transport protein

Simple Diffusion: A drop of dye inters a bowl of water. Gradually, the dye molecules become evenly dispersed through the molecules of water.

Factors Affecting Diffusion Rate Steepness of concentration gradient Steeper gradient  faster diffusion Molecular size Smaller molecules faster diffusion Temperature Higher temperature  faster diffusion

Concentration Gradients Molecules ALWAYS move down their concentration gradient in passive transport From high  low

Osmosis – A Type of Passive Transport Net movement of water from high  low Between two regions separated by a selectively permeable membrane Red dot = H20 Blue Dot = Solute

How will Water Move? Water will always move from where there is more water to where there is less water

Tonicity -Iso=same -Hypo=HippO -Hyper=out H2O in cells swells H2O moves out and out with H2O (go OUTside and play if you are hyper)!

2% sucrose solution 10% sucrose solution 2% sucrose solution distilled water Hypotonic Conditions Hypertonic Conditions Isotonic Conditions

Turgor Pressure & Plasmolysis Occurs in plants b/c of the cell wall Turgor Pressure Occurs when water moves from hypotonic environment into the hypertonic plant cell Cell membrane expands and pushes against the cell wall creating pressure Plasmolysis Occurs when water moves from hypotonic plant cell to a hypertonic environment Cell membrane shrivels (plants wilts & may die)

Turgor Pressure & Plasmolysis

Facilitated Diffusion – A Type of Passive Transport Using a protein to move a substance from where it is in a high concentration to where it is in a low concentration

Active Transport Uses energy (ATP) Moves from low to high concentration Against concentration gradient Several types: Transport Protein Endocytosis & Phagocytosis Exocytosis

Transport Protein – A Type of Active Transport Na+/K+ Pump

Endocytosis – A Type of Active Transport Moves bulk items that are larger

Endocytosis A patch of cell membrane forms a vesicle that sinks into the cytoplasm. Cell takes “in” molecules A special type is called “phagocytosis”

Phagocytosis or Cell Eating Active (requires ATP) Changes in microfilaments change cell shape to form a bulging lobe that surrounds target and forms a vesicle edible bacterium amoeba

Exocytosis – A Type of Active Transport A cytoplasmic vesicle fuses with the cell membrane and its contents are released outside. Cell membrane cytoplasm