The Cell Membrane

1. The Cell Membrane *Very thin (7.5-10 nm) *Elastic *Semipermeable * Dynamic *lipid bilayer *Made of phospholipids, proteins, CHO& otherlipids *amphipathic

2. Phospholipids Flexibility & selective permeability • Fatty acid tails • hydrophobic • Phosphate group head • hydrophilic • Arranged as a bilayer Phosphate Fatty acid

3. Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads

4. Protein: *Hydrophilic & hydrophobic *Integral & peripheral • Cholesterol: permeability & toughness • CHO: recognition sites & attach cells together Glycoprotein Glycolipid Cholesterol Peripheral protein

5. Functions of membrane proteins • 1- structural ptns • 2- passive channels: ungated & gated(voltage / ligand) • 3- carriers for facilitated diffusion • 4- carriers for active transport (uniport /symport/ antiport) • 5- receptors: number & sensitivity change • 6- enzymes • 7- identity ptns • 8-intercellular connections: a. binding j: tight & desmosomes b. gap j • 9- cell adhesion molecules • 10- fixation of cytoskeleton

6. Many Functions of Membrane Proteins Outside Plasma membrane Inside Transporter Enzymeactivity Cell surfacereceptor Cell adhesion Cell surface identity marker Attachment to thecytoskeleton

7. Membrane carbohydrates • Play a key role in cell-cell recognition • ability of a cell to distinguish one cell from another • antigens • important in organ & tissue development • basis for rejection of foreign cells by immune system

8. Movement across the Cell Membrane

9. Diffusion • All molecules are in constant motion • Diffusion • movement from highlow concentration

11. high low Facilitated Diffusion • Diffusion through protein channels • channels move specific molecules across cell membrane • no energy needed facilitated = with help open channel = fast transport

12. Facilitated Diffusion

13. low high Active Transport • Against concentration gradient • Needs carrier protein • Energy is needed conformationalchange ATP “The Doorman”

14. Active transport • Many models & mechanisms ATP ATP antiport symport

15. Active transport • 1ry active: *eg Na+/K+ pump *α &β subunits *α subunit contains 2 binding sites for K+ on the outside & 3 binding sites for Na+ on the inside & an ATP binding site *β subunit has ATPase activity. • 2ry active: *eg Glucose transport 2ry to active transport of Na 1st Na pumped out ….creates concentration gradient… Na & glucose bind a carrier…transports them to inside

16. Getting through cell membrane • Passive Transport • Simple diffusion • diffusion of nonpolar, hydrophobic molecules • lipids • high  low concentration gradient • Facilitated transport • diffusion of polar, hydrophilic molecules • through a protein channel • high  low concentration gradient • Active transport • diffusion against concentration gradient • low  high • uses a protein pump • requires ATP • Vesicular transport ATP

17. Transport summary simplediffusion facilitateddiffusion ATP activetransport

18. How about large molecules? • Moving large molecules into & out of cell • through vesicles & vacuoles • endocytosis • phagocytosis = “cellular eating” • pinocytosis = “cellular drinking” • exocytosis exocytosis

19. Endocytosis fuse with lysosome for digestion phagocytosis non-specificprocess pinocytosis triggered bymolecular signal receptor-mediated endocytosis

20. Osmosis is diffusion of water • Diffusion of water from high concentration of water to low concentration of water • across a semi-permeable membrane • The pressure necessary to stop solvent mol movements= osmotic pressure • The numbers of particles per unit volume of fluid • Measured in mmHg • Osmole osmolarity osmolality

21. The osmolarity of ICF=that ECF=300 mosmol • 280 mosmol is due to Na, Cl & HCO3 • 20 mosmol is due to protein • Tonicity: is the osmolality of a solution relative to the plasma • Plasma proteins of blood is called oncotic pressure. It is important for capillary circulation &regulation of ECF

22. hypotonic hypertonic Concentration of water • Direction of osmosis is determined by comparing total solute concentrations • Hypertonic - more solute, less water • Hypotonic - less solute, more water • Isotonic - equal solute, equal water water net movement of water

23. Donnan effect • The protein anions inside the cells are non diffusible hinder the diffusion of diffusible cations • More osmotically active particles inside the cell • The cell tends to swell • But the Na+/ K+ pump prevents cell rupture

24. Any Questions??