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01 cell membrane(fluid mosaic model).pptx
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- 2. Structure of cellmembrane • Trilayer (7-10 nm) which separate living cell from nonliving surroundings • Two electron dense layer separated by electron lucent layer • Composition: – Lipids 40% – Proteins 55% – Carbohydrates 05%
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- 4. Fluid mosaic model •Singer and Nicolson 1972 • Membrane is an aggregation of proteins & other molecules embedded in the fluid matrix of the lipid bilayer • Phospholipid bilayer :- – Continuous structure – Fluid in nature • Change in shape without disruption – barrier to entry or exit of polar substances • Proteins :- – Mosaic of globular proteins inserted into the Phospholipid bilayer. – “iceberg of proteins in the ocean of lipid” – Gatekeepers -- regulate traffic • 50 lipid molecules for each protein molecule
- 5. Lipid bilayer • Thebasic framework of the plasma membrane • Phospholipids 75% – Phosphotidyl choline & Sphyngomyelins – Phosphotidyl ethanolamine & Phosphotidyl serine • Cholesterol 20% • Glycolipids 05%
- 6. Phospholipid • Phosphate grouphead – Hydrophilic • Fatty acid tail – Hydrophobic • Arranged as bilayer
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- 8. Fluidity of cell membrane •Has a consistency of olive oil • Lipid molecule exchange places about 10 million times per second (flip flop ) • % of unsaturated fatty acids in phospholipids – Double bound – kink in the tail • Cholesterol – More stronger at normal temperature – Increased fluidity at low temperature • Invitro fertilization is possible
- 9. Proteins in thecell membrane • Proteins determine membrane’s specific functions • Classification of membrane proteins: 1. Depending upon their location • Integral proteins • Peripheral proteins – Extrinsic proteins – Intrinsic proteins 2. Depending upon their composition • Lipoprotein • glycoprotein
- 10. Integral proteins • Extendacross the entire lipid bilayer • Not easily removable (without disrupting the membrane) • Proteins are amphipathic in nature – Hydrophilic amino acids • Serine, threonine,cycteine,tyrosine, asparagines etc – Hydrophobic amino acids • Glycine, alanine, valine, leucine, isoleucine, methionine etc • Hydrophilic amino acid faces ECF and ICF • Hydrophobic amino acids interact with the fatty acid tail • Single pass or multiple pass
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- 12. Peripheral proteins • Peripheralproteins are found at the inner or outer surface of the membrane • Can be stripped away from the membrane without disturbing membrane integrity • Types: – Intrinsic proteins- enzymes – Extrinsic proteins- Glycoproteins • Cell surface identity marker & Cell adhesion molecules
- 13. Functions of membraneproteins 1. Formation of Channel – Passageway to allow specific substance to pass through 2. Transporter Proteins – Bind a specific substance, change their shape & move it across membrane 3. Act as Enzyme – speed up reactions 4. Receptor Proteins – Cellular recognition site – Bind to substance—hormones 5. Cell Identity Marker – Allow cell to recognize other similar cells 6. Linker – Anchor proteins in cell membrane or to other cells – Allow cell movement – cell shape & structure
- 14. Functions of cellmembrane proteins Outside Plasma membrane Inside Transporter Cell surface receptor Enzyme activity Cell surface identity marker Attachment to the cytoskeleton Cell adhesion
- 15. Carbohydrate in cellmembrane • Two forms – Glycoproteins – Glycolipids • Glycocalyx layer covers the entire cell membrane • Functions: – Do not allow the negatively charged molecules to pass – Tight fixation of the cells with one another – Also serve as receptor – Make the cell surface slippery
- 17. Intercellular junctions • Junctionspresent between two cells. • Cell adhesion molecules: – Integrins-heterodimers, binds to receptors – IgG subfamily -binding with antigens – Cadherins- • Ca 2+ dependent and homophilic – Selectins- binds to carbohydrates • Mechanism of adhesions: – Anchorage with cytoskeleton – Homophilic binding – Heterophilic binding – Binding to laminins present in the ECF
- 18. Types of junctions Tightjunctions / Zona occludens Adherens junctions / Zona adherens Desmosomes Hemidesmosomes Gap junctions
- 19. Tight junctions – Zonaoccludens – Cell membrane of the cells fuse with each other – No space in between the cells – Act like barrier for the movement of substances – Examples: • Apical margins of epithelial cells • Renal tubular epithelial cells • Blood brain barrier • Blood aqueous barrier, blood testes barrier etc
- 20. Adherens junctions • Cellmembranes of adjacent cells are separated by a 15-20 nm wide space • Focal obliteration by dense accumulation of proteins • Radiation of intermediate filaments into the cell from the site of junction • Types : – Desmosomes –focal thickening on both the cells surfaces – Hemidesmosomes- focal thickening on one cell surface • Examples : – Epidermis – Cells attachment to basal lamina and actin filament
- 21. Gap junctions • Channelson the lateral surfaces of the cells • Exchange of molecules between the cells • Channel have six (6) sub units- connexin • Intercellular space 2-3 nm • Example : – Heart – Basal part of the epithelial cells of intestinal mucosa • Functions: – Intercellular exchange of substances with a molecular weight < 1000 – Rapid propagation of electrical impulse – Exchange of chemical messengers between cells