http://www.bing.com/videos/watch/video/fluid-mosaic-model-of-the-cell-http://www.bing.com/videos/watch/video/fluid-mosaic-model-of-the-cell-membrane/e1ed8109107c1c4617f5e1ed8109107c1c4617f5-1290926227736?membrane/e1ed8109107c1c4617f5e1ed8109107c1c4617f5-1290926227736?

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Note the kinks in the phospholipid tails.Note the kinks in the phospholipid tails.Recall this is due to double bonds (unsaturated) and Recall this is due to double bonds (unsaturated) and

increases fluidityincreases fluidity

Note the cell membrane is a bilayre, due to Note the cell membrane is a bilayre, due to spontaneous positioning of the polar and non-polar spontaneous positioning of the polar and non-polar ends of the phospholipids which form it.ends of the phospholipids which form it.

Note structural support of the protein filaments acting like scaffolding – Note structural support of the protein filaments acting like scaffolding – giving the cell a shapegiving the cell a shapeNote also the cholesterol studded here and there on either side of the Note also the cholesterol studded here and there on either side of the bilayre; it maintains fluidity, preventing the cell from ‘melting’ in heat and bilayre; it maintains fluidity, preventing the cell from ‘melting’ in heat and from becoming too rigid in the cold from becoming too rigid in the cold

In the freeze fracture technique cells are flash frozen in liquid nitrogen, In the freeze fracture technique cells are flash frozen in liquid nitrogen, dropped from a height, or split with a knife, and gold is evaporated onto dropped from a height, or split with a knife, and gold is evaporated onto their exposed surfaces; with the hope that something interesting might their exposed surfaces; with the hope that something interesting might be visualized on the screen of the scanning electron microscopebe visualized on the screen of the scanning electron microscope

How does a SEM work?How does a SEM work? The SEM is an instrument that The SEM is an instrument that produces a largely magnified image produces a largely magnified image by using electrons instead of light to by using electrons instead of light to form an image. A beam of electrons form an image. A beam of electrons is produced at the top of the is produced at the top of the microscope by an electron gun. The microscope by an electron gun. The electron beam follows a vertical path electron beam follows a vertical path through the microscope, which is through the microscope, which is held within a vacuum. The beam held within a vacuum. The beam travels through electromagnetic travels through electromagnetic fields and lenses, which focus the fields and lenses, which focus the beam down toward the sample. Once beam down toward the sample. Once the beam hits the sample, electrons the beam hits the sample, electrons and X-rays are ejected from the and X-rays are ejected from the sample.sample. Detectors collect these X-rays, Detectors collect these X-rays, backscattered electrons, and backscattered electrons, and secondary electrons and convert secondary electrons and convert them into a signal that is sent to a them into a signal that is sent to a screen similar to a television screen. screen similar to a television screen. This produces the final image.This produces the final image.

FUNCTIONS OF THE CELL MEMBRANE FUNCTIONS OF THE CELL MEMBRANE PROTEINS PROTEINS

Some form "channels" through which Some form "channels" through which various substances enter and depart from various substances enter and depart from the cell. Enzymes help speed up chemical the cell. Enzymes help speed up chemical

reactions. Some proteins, when attached to reactions. Some proteins, when attached to special chemicals, serve as receptors, special chemicals, serve as receptors,

setting functions such as hormone synthesis setting functions such as hormone synthesis into operation. This attachment launches into operation. This attachment launches

the beginning of a certain function such as the beginning of a certain function such as the synthesis of hormone in the cell. The the synthesis of hormone in the cell. The

identifiers of the cell are the proteins identifiers of the cell are the proteins receiving information regarding whether receiving information regarding whether

other cells in the body are foreign invaders. other cells in the body are foreign invaders. Some proteins assume structural functions; Some proteins assume structural functions; others serve as attachment points for cells others serve as attachment points for cells

to adhere to one another. Other proteins are to adhere to one another. Other proteins are important in anchoring the cell skeleton. important in anchoring the cell skeleton.

                                                                                                  

Cell-cell recognition is critically important for any kind of Cell-cell recognition is critically important for any kind of organism to function.  This job is mainly undertaken by organism to function.  This job is mainly undertaken by membrane carbohydrates.  In order for cells to recognize each membrane carbohydrates.  In order for cells to recognize each other, they bind to molecules found on the cell’s surface, which other, they bind to molecules found on the cell’s surface, which happen to mostly be carbohydrates.  Membrane carbohydrates happen to mostly be carbohydrates.  Membrane carbohydrates sometimes bind covalently to lipids, forming what is to be called sometimes bind covalently to lipids, forming what is to be called a glycolipid, while the majority of membrane carbohydrates are a glycolipid, while the majority of membrane carbohydrates are covalently bound to proteins, making the two together covalently bound to proteins, making the two together glycoproteins.  Carbohydrate markers found on red blood cells, glycoproteins.  Carbohydrate markers found on red blood cells, for example, dictate what blood type you are.for example, dictate what blood type you are.

Passive transport: diffusionPassive transport: diffusion

Net Diffusion to EquilibriumNet Diffusion to Equilibrium

Only small and hydrophobic molecules can diffuse Only small and hydrophobic molecules can diffuse through the cell membrane!through the cell membrane!

Recap = Facilitated diffusion is when an assisting protein Recap = Facilitated diffusion is when an assisting protein remains in place and “helps” a molecule across by remains in place and “helps” a molecule across by

undergoing a change in shape that moves the binding site undergoing a change in shape that moves the binding site from one side of the membrane to the other. It is still from one side of the membrane to the other. It is still passive since the molecule is still moving down their passive since the molecule is still moving down their

concentration gradient.concentration gradient.

Passive transport: Passive transport: Osmosis = the movement of water through a semi-Osmosis = the movement of water through a semi-

permeable membrane from high to low permeable membrane from high to low concentrationconcentration

Tonicity Tonicity

Tonicity IITonicity II

Active TransportActive TransportCertain molecules need to be kept in the cell at a concentration that is Certain molecules need to be kept in the cell at a concentration that is

greater than the surrounding environment.greater than the surrounding environment.This requires the expenditure of energy, usually in the form of ATPThis requires the expenditure of energy, usually in the form of ATP

http://www.bing.com/videos/watch/video/membrane-potential/http://www.bing.com/videos/watch/video/membrane-potential/15fba088859d7cfdfe3915fba088859d7cfdfe39-1233195565344?15fba088859d7cfdfe3915fba088859d7cfdfe39-1233195565344?cpkey=6cb98a2ebaadbf1c6c6a6cb98a2ebaadbf1c6c6a-1078418866799%7c%7c%7c%7ccpkey=6cb98a2ebaadbf1c6c6a6cb98a2ebaadbf1c6c6a-1078418866799%7c%7c%7c%7c

Proton Pump Proton Pump (active)(active) PProton pump.roton pump. By pumping H+ By pumping H+ outout of the cell with the of the cell with the hydrolysishydrolysis of ATP, of ATP, proton pumpsproton pumps produce an produce an H+ H+ gradientgradient and a charge separation called a and a charge separation called a membrane membrane potentialpotential. These two forms of potential energy can be . These two forms of potential energy can be

used to drive active transport of used to drive active transport of solutessolutes..

Coupled Channel Coupled Channel (active) (active)

(Sucrose/Glucose – H+ Symport)(Sucrose/Glucose – H+ Symport)