Plasma Membrane Structure and Function

Topic - MembranesCell Membranes are made ofPHOSPHOLIPIDS & PROTEINS

Amphipathic Molecules with both hydrophilic and hydrophobic regions

phosphatelipidhydrophilichydrophobic

2FLUID MOSAIC MODEL 1972- S.J. Singer and G. Nicolson propose membrane is a mosaic of proteins and phospholipids that are constantly moving and changing

Click here to See Fluidity Animation from: http://www.sp.uconn.edu/~terry/images/anim/fluidmem.gifClick here to SeeFLUIDITYMore than just a barrierExpanding our view of cell membrane beyond just a phospholipid bilayer barrierphospholipids plus

42.4.2Cell Membrane Micrograph

2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.

5A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer

6The carbohydrates are not inserted into the membrane -- they are too hydrophilic for that. They are attached to embedded proteins -- glycoproteins.

2.4.1Structures in Cell Membrane (animation)2.4.1 Draw and label a diagram to show the structure of membranes.

http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP11017Membrane ProteinsProteins determine most of membranes specific functions enzymes, receptors and transportMembrane proteins:peripheral proteins = loosely bound to surface of membraneintegral proteins = penetrate into lipid bilayer, often completely spanning the membrane = transmembrane protein

8Membrane Carbohydrates Attached to proteins (glycoproteins) or lipids (glycolipids)

Play a key role in cell-cell recognitionability of a cell to distinguish neighboring cells from anotherimportant in organ & tissue developmentbasis for rejection of foreign cells by immune system

http://faculty.southwest.tn.edu/rburkett/GB1-osmosis.htm9The four human blood groups (A, B, AB, and O) differ in the external carbohydrates on red blood cells.

HYDROPHILIC/HYDROPHOBIC areas determine positions of molecules in cell membranes

hydrophobic amino acidsstick in the lipid membraneanchors the protein in membrane

hydrophilic amino acidsstick out in the watery fluid in or out of cell10GlycocalyxFuzzy, sticky carbohydrate rich substance at the cell surface.

aid in cell communicationgives support to cell

Cell JunctionsMost cells live in tight knit communities(but some are Footloose)

3 factors act to bind cells togetherGlycoproteins in glycocalyxContours fit together in tongue-and-groove fashionSpecial cell junctions

Tight JunctionsSeries of proteins in cellular membrane which fuse together

Impermeable junctions nothing can pass between the cells

DesmosomesAnchoring junction connections between cells that prevent cells from separating.

Gap JunctionsCommunicating junction between cells.

Adjacent plasma membranes are very close and the cells are connected by hollow cylinders

Membranes provide a variety of cell functions

17Signal transduction - transmitting a signal from outside the cell to the cell nucleus, like receiving a hormone which triggers a receptor on the inside of the cell that then signals to the nucleus that a protein must be made.Semi-permeable membraneNeed to allow passage through the membrane But need to control what gets in or outmembrane needs to be semi-permeableaaH2OsugarlipidsaltNH3So what makes a membrane semi permeable?See a movie18PHOBIC TAILS in center determine what can pass through

19Molecules need to move across membranes in cellsImage modiified from: http://www.accessexcellence.org/AB/GG/importProt.htmlINfoodcarbohydratessugars, proteinsamino acidslipidssalts, O2, H2OOUTwasteammoniasaltsCO2H2O products

What molecules can get through directly?

inside celloutside cellSmall non-polar molar molecules (O2 & CO2) and hydrophobic molecules (fats & other lipids)can slip directly through the phospholipid cell membrane, butlipidsaltaaH2OsugarNH3O2What about other stuff?212.4.4DiffusionDiffusion is the passive movement of particles form a region of high concentration to a region of low concentration

Molecules of dyeMembrane (cross section)Net diffusionNet diffusionEquilibrium

Net diffusionNet diffusionNet diffusionNet diffusionEquilibriumEquilibrium

2.4.4 Define diffusion and osmosis.

Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration.

Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.22http://www.le.ac.uk/pa/teach/va/anatomy/case2/2_2.htmlExample: DIFFUSION IN CELLS

O2 automatically moves from HIGHER concentration (in lungs) to LOWER concentration (in blood)

CO2 automatically moves from HIGHER concentration (in blood) to LOWER concentration (in lungs) http://facstaff.bloomu.edu/gdavis/links%20100.htm

2.4.4Osmosis is the passive movement of water molecules across a permeable membrane from lower solute to higher solute concentration

Hypotonic = lower [solute]Hypertonic = higher [solute]Isotonic = equal [solute]

Hypo -> Hypertonic

Osmosis2.4.4 Define diffusion and osmosis.

Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration.

Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.24

Lowerconcentrationof solute (sugar)Higherconcentrationof sugarSame concentrationof sugarSelectivelypermeable mem-brane: sugar mole-cules cannot passthrough pores, butwater molecules canMore free watermolecules (higherconcentration)Water moleculescluster around sugar moleculesFewer free watermolecules (lowerconcentration)Water moves from an area of higher free water concentration to an area of lower free water concentrationOsmosis2.4.42.4.4 Define diffusion and osmosis.

Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration.

Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.252.4.4

2.4.4 Define diffusion and osmosis.

Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration.

Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.26

Animal cellshttp://www.stchs.org/science/courses/sbioa/metenergy/bloodcells.gif= CYTOLYSIS= CRENATION2.4.5Simple diffusion is the tendency of molecules of a substance to spread out evenly in an available space. Substances diffuse down their gradient (high to low concentration).

Small, non-ionic, non-polar particles are able to pass through the phospholipids is the membrane is permeable to them.

2.4.5 Explain passive transport across membranes by simple diffusion and facilitated diffusion.28Facilitated diffusionMove from HIGH to LOW concentration with aid of membrane transport proteins passive transportno energy neededfacilitated = with help

292.4.5Facilitated diffusion is the movement of molecules across a membrane with the aid of channel proteins.

Channel proteins create a bridge for particles to cross between the membrane. Their size and chemical properties makes them specific to one molecule.

2.4.5 Explain passive transport across membranes by simple diffusion and facilitated diffusion.30

Carriers and Channels are specificinside celloutside cellsugaraaH2OsaltNH3. . . BUT STILL MOVES FROM [HIGHER] to [LOWER]31What if cell needs to move a molecule _________ the CONCENTRATION GRADIENT?_______________Cell example:Want to put MORE glucoseinto mitochondria when there isalready glucose in there(LOWER HIGHER)

Image from: http://www.biologyclass.net/mitochondria.jpg AGAINSTWhat if a cell needs to move _____ or ______ moleculesthat cant getthrough themembrane?

http://www.d.umn.edu/~sdowning/Membranes/membraneImages/jpegimages/diffusionmedium.jpgLARGEPOLARWhat if cell needs to move molecules really _______? (cant wait for it to diffuse)Cell example:Movement of Na + & K+ ions required to send nerve signals

http://www.steve.gb.com/images/science/neuron.pngFASTCells need a ____ to ____ molecules across cell membranes that _______ across by ___________ WAYHELPcant gothemselves2.4.6Active transport involves moving substances AGAINST their concentration gradients (from low to high concentration). This is done by protein pumps embedded in the membrane.

In contrast to passive transport, active transport requires energy in the form of ATP.

2.4.6 Explain the role of protein pumps and ATP in active transport across membranes.362.4.6Active Transport with ATP

2.4.6 Explain the role of protein pumps and ATP in active transport across membranes.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

37Active transportSODIUM-POTASSIUM PUMPSets up difference in charge across membranes

Pumps 3 Na+ outand 2 K+ in

Makes cells more + outside more - inside

Animation from: http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/eustruct/images/sppump.gifSee a movie about Na+ - K+ pump38Plants have nitrate & phosphate pumps in their roots.Why?Nitrate for amino acidsPhosphate for DNA & membranes

Not coincidentally these are the main constituents of fertilizer.

2.4.62.4.6 Explain the role of protein pumps and ATP in active transport across membranes.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

422.4.7Vesicles can be to used to transport materials within the cytoplasm of the cell without mixing their components.

They are small sacs of membrane that can change shape and move in and out of the cell

Made in the rough Endoplasmic Reticulum by pinching off small regions of membrane

ATP supplies energy

2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.432.4.7

TransmembraneglycoproteinsSecretoryproteinGlycolipidGolgiapparatusVesicleTransmembraneglycoproteinMembrane glycolipidPlasma membrane:Cytoplasmic faceExtracellular faceSecretedprotein4123Their membranes are made by the rough Endoplasmic Reticulum, which later merge with the plasma membrane via fusion.

Membrane carbohydrates / lipids that are synthesized in the rER are modified in the Golgi apparatus

2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.44

2.4.7Important Steps for VesiclesMove material around in cell

2. Protein is synthesized by ribosomes on the rER

3. Protein is stored in the cisternae of the rER

4. Vesicles bud off cisternae and carry protein to the golgi apparatus

2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.45

2.4.7Important Steps for Vesicles5. Protein is processed in golgi apparatus

6. Protein is released in more vesicles and moved to the plasma membrane

7. Vesicle fuses with membrane

8. Protein is released

2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.462.4.8Phospholipids in the plasma membrane are able to move within the bilayer, which results in its fluidity.

This fluidity allows proteins embedded in the cell surface to float around and between plasma membranes

Lateral movement(~107 times per second) Flip-flop(~ once per month)2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.47

2.4.8Membrane Fluidity2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.

http://www.youtube.com/watch?v=jM_xePC70Yo

48

2.4.8Bulk transport across the plasma membrane occurs by exocytosis and endocytosis. In exocytosis, transport vesicles migrate to the plasma membrane, fuse with it, and release their contents

In endocytosis, the cell takes in macromolecules by forming new vesicles from the plasma membrane

2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.

http://www.youtube.com/watch?v=jM_xePC70Yo

49

2.4.8Bulk transport across the plasma membrane occurs by exocytosis and endocytosis. In exocytosis, transport vesicles migrate to the plasma membrane, fuse with it, and release their contents

In endocytosis, the cell takes in macromolecules by forming new vesicles from the plasma membrane2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.

http://www.youtube.com/watch?v=jM_xePC70Yo

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2.4.82.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.

http://www.youtube.com/watch?v=jM_xePC70Yo

51Example in cells:WHITE BLOOD CELL ENGULFING BACTERIA using PhagocytosisSEE PHAGOCYTOSIS MOVIE

http://fig.cox.miami.edu/~cmallery/255/255ion/fig14x28.jpgEXOCYTOSISActive transport (requires ATP)Uses vesiclesReleases substances to outside

INSULIN being released by pancreas cells using exocytosis53

http://fig.cox.miami.edu/~cmallery/255/255ion/fig14x26.jpgTransport summary

552.4.8http://programs.northlandcollege.edu/biology/Biology1111/animations/active1.swfhttp://programs.northlandcollege.edu/biology/biology1111/animations/passive1.swf

Passive TransportActive Transport56