Cell Transport Cell Membrane Review What is the function of the cell membrane? To control what enters and leaves the cell
Components of the Cell Membrane Phospholipids - composed of: A hydrophilic head Two hydrophobic tails Bilayer What can pass through the phospholipids? Small, hydrophobic, & uncharged
molecules Ex: O2, CO2 Components continued What molecules cant pass through the phospholipids?
Large, hydrophilic, & charged Ex: amino acids, water, , How does the cell move these? Transport proteins Other parts of cell membrane Glycoproteins Used for signaling other cells
Blood type Cholesterol Embedded within the membrane Helps to keep membrane fluid (in lower temperatures), but not too fluid (warmer temperatures)
Fluid Mosaic Model What does it mean for the cell membrane to be a fluid mosaic model? Fluid: shifting of the phospholipids Mosaic: interspersion of proteins How do we know this is the correct model? Freeze fracture Recap
1 What types of molecules can pass through just the phospholipids? 2 How do the others enter/exit the cell? Why is it important for
molecules to be able to move in and out of cells? Cells need things they dont make Eliminate waste Maintain regular internal conditions aka
Homeostasis Cell Transport The movement of molecules in and out of a cell is known as cell transport.
There are two types of transport Passive Active Molecules move from an area of high concentration to an area of low concentration Direction of flow is the
concentration gradient Does not require energy Passive Transport An example is diffusion Over time, the concentration of particles becomes
evenly dispersed and reaches equilibrium Examples: dye, perfume, smell of food Simple diffusion in a cell Molecules move down their
concentration gradient through the cell membrane For molecules that can pass between the phospholipids Small, uncharged, hydrophobic Simple
e l p Sim Example: Gas exchange What about molecules that
cant pass through the phospholipids? Some large, charged, hydrophilic molecules can diffuse through a transport protein Facilitated Diffusion Transport proteins help
molecules move across the membrane Still from high to low concentration Still requires no energy Two types of proteins: channel & carrier Carrier Proteins
Grabs the molecule, changes shape, and flips to the other side Example: glucose Channel Proteins Protein acts like a tunnel for molecules to pass through
Example: Ion channels allows charged ions to move past hydrophobic region of membrane Channel Proteins Aquaporins channel protein that allows water to move past the hydrophobic region
of the membrane Osmosis movement of water across a cell membrane Recap Passive transport No energy required Down concentration gradient Two types:
Simple diffusion Facilitated diffusion Carrier protein Channel protein Vocabulary Solution a liquid homogenous mixture of two or more substances Two components: Solute substance that gets
dissolved in a solution Solvent substance doing the dissolving in a solution More Vocabulary Concentration mass of solute in a volume of solution The more solute in
a given volume, the greater the concentration Scenario: What if there is a difference in concentration, but the solute is too big to pass through the membrane?
Semipermeable membrane https://youtu.be/GbudKs-49jo Water will move until equilibrium is reached Mass of solutes did not change, but the
volume of solution did change This brings the two concentrations closer together New concept: Tonicity Tonicity ability of a surrounding solution to cause a cell to gain or lose water Isotonic
The concentration is the same inside and outside of the cell Results in no net movement of water Preferred by animal cells. Why? Stable internal conditions are maintained: HOMEOSTASIS What if there is a difference in concentration? Hypotonic
Concentration outside the cell is less than inside the cell More water enters the cell than leaves the cell Hypertonic Concentration outside the cell is greater than inside the cell More water leaves the cell than enters the cell
If the cell cant maintain homeostasis Cytolysis Crenation Tonicity in Plant Cells Cell wall prevents bursting
Plasmolysis Elodea Left: Elodea in tap water, 400x Right: Elodea in 10% NaCl, 400x
Osmotic Pressure pressure exerted by the movement of water during osmosis Vacuole stores water Recap What is tonicity?
Practice: Active Transport 1 Moves molecules from low concentration to high concentration
2 Against concentration gradient 3 Requires ATP ATP 4
Occurs via pumps or vesicles Sodium Potassium Pump Uses membrane protein to move sodium and potassium ions against their
concentration gradients Requires ATP (energy) Ex: nerve cells Proton Pump Moves protons (H+) across the membrane Ex: Lysosomes need
acidic conditions for digestion pH = power of hydrogen Photosynthesis & Respiration Active Transport by Vesicle Endocytosis
Importing large particles or whole cells Ex: White blood cell engulfing bacteria Exocytosis Exporting substances outside the cell Ex: Golgi
Types of Endocytosis Pinocytosis Phagocytosis Taking in fluid or small molecules nonspecific Taking in large molecules or
whole cells Can be specific Recap Active Transport Low to high concentration (against gradient) Requires energy (ATP) Pumps (membrane proteins) Sodium-Potassium pump Proton pump
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