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Cellular membranes. Overview of the body 2/16 The cell 3/16.

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Presentation on theme: "Cellular membranes. Overview of the body 2/16 The cell 3/16."— Presentation transcript:

1 Cellular membranes

2 Overview of the body 2/16

3 The cell 3/16

4 Biological membranes the surface of the cells and the organelles are covered with membranes – compartmentalization Karl Wilhelm von Nägeli middle of the XIX. century – there is a barrier against movement of pigments on the surface of cells – swelling and shrinking - plasma membrane direct proof only with EM Singer and Nicholson (1972): fluid mosaic hypothesis   6-8 nm lipid bilayer + proteins mosaic, because proteins tend to group fluid, because they can easily move laterally lipid/protein ratio depends on function: myelin and mitochondrion 10 6 lipid molecules/μ 2 4/16 Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig. 4-2.

5 Lipid components I. phospholipids –usually more then half of total lipid content –phosphoglycerides phosphatidylcholine (lecithin) phosphatidylserine phosphatidylethanolamine   other, e.g. phosphatidylinositol (PI, PIP, PIP 2 )   role of the cis-, and trans conformation   –sphingomyelins serine + fatty acid = sphingosine (condensation of COOH groups) sphingosine + fatty acid = ceramide (on the amino group of serine) ceramide + phosphate + choline = sphingomyelin (on the OH group of serine)   5/16 Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig. 6-9.

6 Lipid components II. glycolipids –on the outer surface only   –cell to cell recognition, antigens (e.g. blood types)   –plants and bacteria: based on glycerol –animals: based on ceramide –neutral: e.g. galactocerebroside (serine OH in ceramide binds galactose   builds up 40% of myelin outer membrane –gangliosides (serine OH in ceramide binds oligosaccharide containing one or more charged sialic acid (N-acetylneuraminic acid - NANA)   5-10% f total lipids in nerve cells steroids –cholesterol mainly   –more than 18% –decreases fluidity, inhibits crystallization   6/16 Darnell et al., Scientific American Books, N.Y., 1986, Fig Darnell et al., Scientific American Books, N.Y., 1986, Fig Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig. 4-7.

7 Protein components integral or intrinsic proteins: embedded in the membrane, reaching from one side to the other transmembrane part usually forms  -helix, with hydrophobic side chains on the outside transmembrane parts can be predicted by the sequence of amino acids (hydrophobicity)   often multiple transmembrane parts: e.g. 7TM receptors helices are connected by loops functions: ion channel, receptor, enzyme, transporter, etc. peripheral or extrinsic proteins: associated with the membrane on one side only they can be enzymes, proteins serving signalization (G-proteins), etc. 7/16

8 Membrane as a barrier the membrane prevents free exchange of materials - compartmentalization classification by substances: hydrophobic (non-polar) substances - diffusion hydrophilic (polar) substances –uncharged: small molecular weight – diffusion higher molecular weight – by carrier molecules –ions – through ion channels   classification by use of energy: –passive: along the gradient – energy is not needed (diffusion, facilitated diffusion, channel) –active: against the gradient – direct or indirect use of energy – transport molecules special: endocytosis, exocytosis 8/16 Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig

9 Diffusion I. difference between convection (bulk flow) and diffusion water molecules travel 2000 km in one hour, but in random directions glucose only (?) 700 km/h time changes by the square of time example: glucose in capillary: 10  - 90% - 3,5 s 10 cm - 90% - 11 years size limit for cells (30-50  ), plasma flow, axonal transport systems Fick’s first law: J = -D*A*dc/dx flow and concentration is considered from a given point into x-direction 9/16

10 Diffusion II. for spherical molecules (Stokes-Einstein relation): D = kT / (6  r  ) diffusion through a lipid layer depends on concentration at the edges of the lipid layer it depends on the partition coefficient as concentration in the water phase is constant thus the gradient is given by: K(c o - c i ) / x consequently J = - D m KA (c o - c i ) / x partition and diffusion coefficients as well as membrane width are constant for any given substance – permeability coefficient is defined J = - PA (c o - c i ) related parameter: conductance 10/16

11 Osmosis I. in fact it is the diffusion of water penetrates easily, water compartments are in equilibrium Abbé Jean Antoine Nollet (1748) described it first experimenting with a bladder to reach equilibrium, hydrostatic pressure is needed on the side of the solution – osmotic pressure osmos (Greek) = to push linear relationship with temperature (T) and osmolarity (particles per liter of solvent) van’t Hoff: molecules in solution behave thermodynamically like gas molecules volume of 1 mol gas at room temperature is 24 liters osmotic pressure of a solution of 1 osmole is 24 atm at room temperature 11/16

12 Osmosis II. osmotic pressure depends on the number of particles:  = i * m * RT it is usually calculated from molarity using a correction factor taken from precalculated tables it is measured by changes in freezing and boiling points hyposmotic, hyperosmotic, isosmotic hypotonic, hypertonic, isotonic –similar but not equivalent notions! –first is calculated, second is observed as the effect on living cells, e.g. glycerol and NaCl –isosmotic NaCl solution: saline (0,9%), physiological solution 12/16

13 Ion channels built up by intrinsic (integral) proteins  -helices, connected by loops ions (Na +, K +, Ca ++, Cl -, etc.) can only pass through channels or by transport molecules analysis using patch clamp method   selectivity for ions – size, charge, dehydration energy (K + > Na + )   large families: grouped by ion specificity and opening mode leakage, voltage-, ligand-dependent, mechanosensitive voltage-dependent: best known: 4 motifs, 6 helices each - Na +, Ca ++ 1 protein molecule, K + 4 molecules, with 1-1 motif  ; three states   ligand-dependent: 5 motifs (pentamer) in general, 5 molecules, each with 4 helices   13/16 Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig. 6-60, Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig

14 Transport by carriers I. conformation change upon binding of the transported molecule do not travel between the two sides of the membranes grouped by the use of energy: –facilitated diffusion –active transport grouped by the number of carried substances –uniporter – 1 substance –symporter - 2 substances in the same direction –antiporter - 2 substances in opposite directions   characteristics: –saturation –selectivity –competition 14/16 Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig

15 Transport by carriers II. facilitated diffusion –along the gradient –no use of energy –large, polar molecules, e.g. glucose    active transport –direct use of energy, hydrolysis of ATP –in the case of ions, it is called a pump –Na + /K + pump, in neuronal and muscle cells - antiporter - exact mechanism is not known   –H + - mitochondrion - ATP synthesis by the passage of 3 H + –indirect use of energy, usually on the expense of the Na + gradient –e.g. uptake of glucose and amino acids in the kidney and gut - gradient is small –water uptake in the kidney   15/16 Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig

16 Endocytosis and exocytosis transport of macromolecules endocytosis – uptake of substances –mechanism: vesicle budding off from the membrane –pinocytosis – “drinking” – small vesicles – constitutive, continuous in all cells – e.g. membrane recycling   –phagocytosis – “eating” – larger vesicles stimulus- induced, in special cells   receptor-mediated endocytosis –“clathrin coated pits” - receptors accumulate   –units with lysosome after budding off –entrance of proteins, hormones, viruses, toxins, etc. exocytosis – release of substances –mechanism: fusion of vesicle with the membrane signal-induced exocytosis – nerve and endocrine cells – role of Ca ++   constitutive exocytosis – going on continuously 16/16 Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig

17 End of text

18 Fluid mosaic membrane Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig. 4-2.

19 Types of phospholipids Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig. 6-9.

20 Inositol phosphates Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig

21 Phosphoglycerides Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig. 4-3.

22 Glycocalyx Darnell et al., Scientific American Books, N.Y., 1986, Fig

23 AB0 blood types Darnell et al., Scientific American Books, N.Y., 1986, Fig. 3-79

24 Cerebrosides Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig

25 Gangliosides Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig

26 Structure of cholesterol Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig. 4-4.

27 Cholesterol in the membrane Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig. 4-7.

28 Hydrophobicity

29 Passing through the membrane Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig

30 Examination of ion channels Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig. 6-60, 6-61.

31 Selectivity of channels Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig

32 Voltage-dependent channels Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig

33 Activation - inactivation Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig

34 Nicotinic Ach receptor Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig

35 Transport types Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig

36 Facilitated diffusion Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig

37 Facilitated diffusion mechanism

38 Na + - K + pump

39 Indirect active transport Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig

40 Pinocytosis

41 Endocytosis

42 Receptor-mediated endocytosis Eckert: Animal Physiology, W.H.Freeman and Co., N.Y.,2000, Fig

43 Exocytosis in the synapse Alberts et al.: Molecular biology of the cell, Garland Inc., N.Y., London 1989, Fig


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