Ch. 8 Membrane StructureCh. 8 Membrane Structure

Know:Know:– Structure of plasma membraneStructure of plasma membrane– PhospholipidsPhospholipids– Integral proteinsIntegral proteins– Peripheral proteinsPeripheral proteins– CholesterolCholesterol– GlycoproteinsGlycoproteins– GlycolipidsGlycolipids– OligosaccharidesOligosaccharides– Functions of membrane proteinsFunctions of membrane proteins

Phospholipid StructurePhospholipid Structure

Phospholipid Bilayer – held together Phospholipid Bilayer – held together by hydrophobic interactionsby hydrophobic interactions

Membranes are fluid – they are not Membranes are fluid – they are not staticstatic

Factors that affect membrane Factors that affect membrane fluidityfluidity

1.1. Unsaturated fatty acid chains – increase Unsaturated fatty acid chains – increase fluidity due to the chains not packing wellfluidity due to the chains not packing well

2.2. Temperature – low temperatures can decrease Temperature – low temperatures can decrease fluidity when phospholipids settle into a tightly fluidity when phospholipids settle into a tightly packed arrangementpacked arrangement

3.3. Cholesterol – packed in between phosholipidsCholesterol – packed in between phosholipids• High temp. – disrupts movement of phospholipids, High temp. – disrupts movement of phospholipids,

decreases fluiditydecreases fluidity• Low temp. – does not allow phospholipids to pack Low temp. – does not allow phospholipids to pack

together, increases fluiditytogether, increases fluidity

CholesterolCholesterol

Fluid Mosaic ModelFluid Mosaic Model

Membrane structure videoMembrane structure video

Have distinct inside and outside faces Have distinct inside and outside faces (amphipathic)(amphipathic)Proteins dispersed and embedded throughout Proteins dispersed and embedded throughout phospholipids bi-layer (membrane)phospholipids bi-layer (membrane)

2 types of proteins present in membrane:

-Integral proteins-Peripheral proteins

Membrane ProteinsMembrane Proteins

Integral ProteinsIntegral Proteins

Can be:Can be:– Transmembrane- has Transmembrane- has

hydrophobic midsections hydrophobic midsections between hydrophilic ends between hydrophilic ends exposed on each side of exposed on each side of membranemembrane

– Unilateral- reaching only Unilateral- reaching only partway across the membranepartway across the membrane

•Definition-inserted into the membrane, hydrophobic regions are surrounded by hydrocarbon portions of phospholipids

Peripheral ProteinsPeripheral Proteins

Definition: Not embedded but Definition: Not embedded but attached to membrane’s attached to membrane’s surface, can be attached to surface, can be attached to integral proteins of filaments integral proteins of filaments of cytoskeletonof cytoskeleton

Inside and Outside facesInside and Outside faces

Synthesis and modification of the plasma Synthesis and modification of the plasma membrane by the ER and the golgi membrane by the ER and the golgi apparatus determines the asymmetric apparatus determines the asymmetric distribution of lipids, proteins and distribution of lipids, proteins and carbohydratescarbohydrates

Carbs are restricted to the exterior of the Carbs are restricted to the exterior of the membranemembrane

Sidedness of the plasma membrane Sidedness of the plasma membrane – look at Fig. 8.8 in book– look at Fig. 8.8 in book

Proteins on the inside Proteins on the inside of the vesicle become of the vesicle become proteins on the proteins on the outside face of the outside face of the cell membranecell membrane

TransportTransport

Serves as a passage way for certain moleculesServes as a passage way for certain molecules

Enzymatic ActivityEnzymatic Activity

Active sites on interior Active sites on interior surface which surface which catalyze reactions catalyze reactions inside cellsinside cells

Signal TransductionSignal Transduction

Docking sites for Docking sites for chemical chemical messengers that messengers that will cause a change will cause a change in protein shape in protein shape and relays a and relays a message to the cellmessage to the cell

Intercellular joiningIntercellular joining

Proteins on adjacent cells can hook togetherProteins on adjacent cells can hook together

Cell-to-Cell RecognitionCell-to-Cell Recognition

Glycoproteins serve Glycoproteins serve as identification tags as identification tags which are recognized which are recognized by other cellsby other cells

Attachment to CytoskeletonAttachment to Cytoskeletonand ECM and ECM

ECM- extracellular ECM- extracellular matrixmatrix

Helps maintain cell Helps maintain cell shape and fixes shape and fixes location of membrane location of membrane proteinsproteins

Membrane 2 videoMembrane 2 video

Helpful Video?Helpful Video?

http://www.5min.com/Video/Proteins-as-http://www.5min.com/Video/Proteins-as-the-Mosaic-of-the-Cell-Membrane-the-Mosaic-of-the-Cell-Membrane-150624158150624158