The Plasma Membrane – Gateway to the Cell. The Plasma Membrane is Semipermeable Small molecules...
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Transcript of The Plasma Membrane – Gateway to the Cell. The Plasma Membrane is Semipermeable Small molecules...
The Plasma Membrane is Semipermeable
Small molecules and larger hydrophobic molecules move through.
Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own.
The physical properties of phospholipids account for membrane assembly and many of its properties.
Plasma Membrane Functions
Maintain a high concentration of materials in the cell.
Keep harmful materials out.
Control the movement of materials into and out of the cell.
Let the cell sense its environment.
Transport Processes - Diffusion
Solutes move down a concentration gradient until they are evenly distributed. This is diffusion.
Another way of saying this is that solutes move from a region of higher concentration to a region of lower concentration until there is no difference in concentration.
Three Forms of Transport Across the Membrane
Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out.
Three Forms of Transport Across the Membrane
Examples: Glucose or amino acids moving from blood into a cell.
An nerve electrical impulse results from opening protein channels for ions that move by facilitated diffusion.
Three Forms of Transport Across the Membrane
Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients.
Pinocytosis
This is the most common form of endocytosis.
Pinocytosis takes up most proteins and other large molecules.
Pinocytosis
pinocytic vesicles forming mature transport vesicle
Transport into a capillary cell (blue).
Receptor-Mediated Endocytosis
Receptor proteins make this a highly specific form of transport.
Cholesterol is taken-up this way.
Cholesterol Delivered to Cells is Carried to Cells in a Low-Density Lipoprotein (LDL) Particle
The LDL particle is taken-up by receptor-mediated endocytosis.
The Threshold of Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)
Moving the “Big Stuff”
Molecules are moved out of the cell by vesicles that fuse with the plasma membrane.
Exocytosis: moving things out.
This is how many hormones are secreted and how nerve cells communicate with one another.
Exocytosis and Nervous System Function
A nerve cell communicates to another cell by releasing chemicals via exocytosis at the synaptic terminal.
Exocytosis and Chemical Communication at the Synapse
The synapse is the region where a nerve cell and its target cell are closely apposed.
Black Widow Spider Venom and Exocytosis
Black widow spider venom causes massive exocytosis of neurotransmitter into the synapse.
Botulism and Exocytosis
Botulism is caused by botulinim toxin – a protein produced by a bacterium that sometimes contaminates foods.
Botulinim toxin blocks exocytosis at the synapse and causes paralysis.
Mechanism of botulinum toxin.
Mechanism of botulinum toxin web site.