Membrane structure and function
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Membrane Structure and Function. Chapter 7. Plasma membrane of cell selectively permeable ( allows some substances to cross more easily than others) Made mostly of proteins and lipids (phospholipids). Phospholipids and proteins create unique physical environment (fluid mosaic model).

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Membrane Structure and Function

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Membrane structure and function

Membrane Structure and Function

Chapter 7


Membrane structure and function

  • Plasma membrane of cell selectivelypermeable (allows some substances to cross more easily than others)

  • Made mostly of proteins and lipids (phospholipids).

  • Phospholipids and proteins create unique physical environment (fluid mosaic model)


Membrane structure and function

Phospholipid


Membrane structure and function

  • Membrane - bilayer - hydrophilic (water loving) heads pointing outwards, hydrophobic (water fearing) tails pointing inwards.

  • Proteins help membrane to stick to water.


Membrane structure and function

  • Fluid because lipids and proteins can move laterally.

  • As temperatures drop, liquid membrane can solidify.


Membrane structure and function

  • Cholesterol found in membrane helps with fluidity of membrane.

  • Membranes need to be fluid to work properly.


Membrane structure and function

  • Two different types of proteins are found in membrane.

  • 1Peripheral proteins not in membrane, bound to surface of protein.

  • 2Integral proteins in membrane often spanning entire membrane.


Membrane structure and function

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/MembraneProteins.gif


Membrane structure and function

  • Also aids in cell-to-cell recognition (ability of a cell to distinguish one type of neighboring cell from another)


Pass through membrane easily

Pass through Membrane Easily

  • Some substances move steadily across membrane (sugars, ions, and wastes like CO2)

  • Hydrophobic molecules (i.e. hydrocarbons, CO2, and O2) can dissolve in lipid bilayer and cross easily.


Membrane structure and function

  • Charged particles and polar molecules have more difficulty passing.


Membrane structure and function

  • Diffusion - tendency for substance to spread out in open area.

  • Move from an area of Most concentrated to Least concentrated.


Membrane structure and function

  • No force acting upon it - substance will tend to move down it’s concentration gradient (passive transport).


Membrane structure and function

  • Diffusion of molecules with limited permeability through lipid bilayer may be assisted by transport proteins.


Membrane structure and function

http://library.thinkquest.org/27819/media/protein_channel.gif


Membrane structure and function

  • Difference in concentration - ions move from one area to other.

  • Solution with higher [ ] solutes - hypertonic. (water moves out)

  • Solution with lower [ ] solutes -hypotonic. (water moves in)

  • [ ] equal - isotonic.


Membrane structure and function

http://www.biologycorner.com/resources/hypertonic.gif


Membrane structure and function

http://www.biologycorner.com/resources/hypotonic.gif


Membrane structure and function

  • Movement of H2O across selectively permeable membrane - osmosis.


Membrane structure and function

  • Organism does not have rigid walls must have ability to osmoregulate and maintain internal environment.

  • Allows plant to stand up against gravity (turgid cell); not watered, plant will begin to wilt (flaccid cell).


Membrane structure and function

  • Plant loses enough water, plasma membrane will pull away from cell (plasmolysis).


Membrane structure and function

http://faculty.southwest.tn.edu/jiwilliams/plasmolysis.gif


Membrane structure and function

  • facilitated diffusion - diffusion of substance down it’s [ ] gradient with help of transport protein.

  • Some channel proteins (gated channels) open/close depending on presence/absence of physical or chemical stimulus.


Membrane structure and function

In this case, the protein actually rotates

to dump the materials to the inside

of the cell.


Membrane structure and function

  • Active transport- materials need to be moved against [ ] gradient

  • Requires energy of cell to move substances from an area of low [ ] to an area of high [ ] (i.e. sodium-potassium pump in animal cells)


Membrane structure and function

http://www.sp.uconn.edu/~terry/images/anim/antiport.gif


Membrane structure and function

  • Sodium-potassium pump actively maintains gradient of sodium (Na+) and potassium ions (K+) across membrane.

  • Sodium-potassium pump uses energy of 1 ATP to pump 3 Na+ ions out and 2 K+ ions in.


Membrane structure and function

http://bioweb.wku.edu/courses/Biol131/images/neuronions.GIF


Membrane structure and function

  • Some organisms have proton pumps that actively pump H+ out of cell (i.e. plants, bacteria, and fungi)


More active transport

More Active Transport

  • Exocytosis - When membranes meet - fuse - material is let out to outside of cell.

  • Endocytosis - Membrane is inwardly pinched off and vesicle carries material to inside of cell.


Membrane structure and function

http://www.kscience.co.uk/as/module1/pictures/endoexo.jpg


Membrane structure and function

  • 1Phagocytosis (“cell eating”) - cell engulfs particle by extending pseudopodia around it, packaging it in a large vacuole.

  • Contents of vacuole are digested when vacuole fuses with lysosome.


Membrane structure and function

  • 2Pinocytosis (cell drinking) - cell creates vesicle around droplet of extracellular fluid.


Membrane structure and function

  • 3Receptor-mediated endocytosis - specific in transported substances.

  • Extracellular materials bind ligands (receptors) - causes vesicle to form.

  • Allows materials to be engulfed in bulk (i.e. cholesterol in humans)


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