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Biological Membranes. Biological membranes Biological membranes Complex, dynamic structures made of lipid and protein molecules Complex, dynamic structures.

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Presentation on theme: "Biological Membranes. Biological membranes Biological membranes Complex, dynamic structures made of lipid and protein molecules Complex, dynamic structures."— Presentation transcript:

1 Biological Membranes

2 Biological membranes Biological membranes Complex, dynamic structures made of lipid and protein molecules Complex, dynamic structures made of lipid and protein molecules Perform many functions Perform many functions Define cell as a compartment Define cell as a compartment Regulate passage of materials Regulate passage of materials Participate in chemical reactions Participate in chemical reactions Transmit signals between cell interior and the environment Transmit signals between cell interior and the environment Act as part of energy transfer and storage Act as part of energy transfer and storage

3 Biological membranes Biological membranes Physically separate cell interior from extracellular environment Physically separate cell interior from extracellular environment Form compartments within eukaryotic cells Form compartments within eukaryotic cells Plasma membrane Plasma membrane Regulates passage of materials Regulates passage of materials Participates in biochemical reactions Participates in biochemical reactions Receives information about environment Receives information about environment Communicates with other cells Communicates with other cells

4 Fluid mosaic model Fluid mosaic model Membranes consist of fluid phospholipid bilayer with a mosaic pattern of associated proteins Membranes consist of fluid phospholipid bilayer with a mosaic pattern of associated proteins Phospholipid molecules are amphipathic and contain Phospholipid molecules are amphipathic and contain Hydrophobic regions which are repelled by water Hydrophobic regions which are repelled by water Hydrophilic regions which are attracted to water Hydrophilic regions which are attracted to water

5 Phospholipid molecules

6 Since the cell is a very watery environment, the heads of the phospholipid molecules face toward the cell. Since the cell is a very watery environment, the heads of the phospholipid molecules face toward the cell. The fatty acid “tails” of the molecules face inward toward the center of the bilayer. The fatty acid “tails” of the molecules face inward toward the center of the bilayer.

7 Phospholipids form bilayers in water Phospholipids in waterDetergent in water

8 Plasma membrane of mammalian red blood cell

9 Membrane properties Membrane properties Orderly arrangement of phospholipid molecules make the cell membrane a liquid crystal Orderly arrangement of phospholipid molecules make the cell membrane a liquid crystal Allow molecules to move rapidly Allow molecules to move rapidly Proteins move within membrane Proteins move within membrane Lipid bilayers are Lipid bilayers are Flexible Flexible Self-sealing Self-sealing Can fuse with other membranes Can fuse with other membranes

10 Detailed structure of the plasma membrane

11 Proteins are embedded in the bilayer Integral membrane proteins Integral membrane proteins Embedded in the bilayer Embedded in the bilayer Transmembrane proteins Transmembrane proteins Integral proteins that extend completely through the membrane Integral proteins that extend completely through the membrane Peripheral member proteins Peripheral member proteins Associated with the surface of the bilayer Associated with the surface of the bilayer

12 Membrane proteins, lipids, and carbohydrates Membrane proteins, lipids, and carbohydrates Asymmetrically positioned to bilayer Asymmetrically positioned to bilayer Sides have different composition and structure Sides have different composition and structure Function of member proteins Function of member proteins Transport of materials Transport of materials Acting as enzymes or receptors Acting as enzymes or receptors Cell recognition Cell recognition Structurally linking cells Structurally linking cells

13 Asymmetry of the plasma membrane

14 Functions of membrane proteins

15 Membranes are selectively permeable (only some materials are allowed in and out) Membranes are selectively permeable (only some materials are allowed in and out) Physical processes Physical processes Osmosis Osmosis Diffusion Diffusion Carrier-mediated processes Carrier-mediated processes Channel proteins Channel proteins Carrier proteins Carrier proteins

16 Diffusion: the movement of molecules from a region of higher concentration to one of lower concentration.

17 Rate of diffusion depends on: Temperature (higher temperature, more movement of molecules) Temperature (higher temperature, more movement of molecules) Size of molecules (smaller molecules tend to diffuse faster) Size of molecules (smaller molecules tend to diffuse faster) Electrical charge (like charges repel and opposites attract) Electrical charge (like charges repel and opposites attract) Difference in concentration (concentration gradient) Difference in concentration (concentration gradient)

18 Some molecules easily diffuse through the membrane Water Water Gases Gases Small polar molecules Small polar molecules Large, lipid soluble molecules Large, lipid soluble molecules

19 Osmosis The diffusion of water across a selectively permeable membrane from a region where there is a greater concentration of water to a region where there is less water. The diffusion of water across a selectively permeable membrane from a region where there is a greater concentration of water to a region where there is less water. Osmotic pressure: the tendency of water to move into a solution. Osmotic pressure: the tendency of water to move into a solution.

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21 Osmotic pressure Osmotic pressure Concentration of dissolved substances in a solution Concentration of dissolved substances in a solution Isotonic: equal solute concentration Isotonic: equal solute concentration Hypertonic: solution has a greater concentration of solutes than the cell, loses water in plasmolysis Hypertonic: solution has a greater concentration of solutes than the cell, loses water in plasmolysis Plasmolysis (collapse of a cell due to loss of water. Plasmolysis (collapse of a cell due to loss of water. Hypotonic: solution has a lesser concentration of solutes than the cell, gains water and swells Hypotonic: solution has a lesser concentration of solutes than the cell, gains water and swells

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23 Turgor pressure The internal hydrostatic pressure usually present in walled cells. The internal hydrostatic pressure usually present in walled cells. Turgor pressure provides structural support in plants which do not have wood. Turgor pressure provides structural support in plants which do not have wood.

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25 Movement of particles through proteins If substances cannot pass through the lipid bilayer, they may still move through the membrane via protein channels. If substances cannot pass through the lipid bilayer, they may still move through the membrane via protein channels. This may or may not require energy from the cell. This may or may not require energy from the cell. Passive transport: no energy expenditure Passive transport: no energy expenditure Active transport: energy expended by the cell. Active transport: energy expended by the cell.

26 Facilitated diffusion does not require energy Facilitated diffusion does not require energy Occurs down a concentration gradient Occurs down a concentration gradient Active transport requires energy Active transport requires energy Moves ions or molecules against a concentration gradient Moves ions or molecules against a concentration gradient Cotransport requires energy Cotransport requires energy ATP-powered pump maintains a concentration gradient ATP-powered pump maintains a concentration gradient

27 Sodium-Potassium Pump

28 Sucrose proton cotransport

29 Cells expend metabolic energy to carry on physiological processes Cells expend metabolic energy to carry on physiological processes Exocytosis: large molecules leave the cell through fusion with the membrane Exocytosis: large molecules leave the cell through fusion with the membrane Endocytosis: large molecules enter the cell through fusion with the membrane Endocytosis: large molecules enter the cell through fusion with the membrane Phagocytosis Phagocytosis Pinocytosis Pinocytosis Receptor-mediated endocytosis Receptor-mediated endocytosis

30 Exocytosis

31 Phagocytosis

32 Phagocytosis is used by macrophages to help defend the body from bacteria

33 Amoebae feed using phagocytosis

34 Pinocytosis

35 Receptor-mediated endocytosis

36 Cells communicate by cell signaling Cells communicate by cell signaling Signaling molecules include Signaling molecules include Neurotransmitters Neurotransmitters Hormones Hormones Regulatory molecules Regulatory molecules

37 Cell signaling involves Cell signaling involves Synthesis and release of signaling molecule Synthesis and release of signaling molecule Transport to target cells Transport to target cells Reception by target cells involving special surface receptors where the signaling protein docks. Reception by target cells involving special surface receptors where the signaling protein docks. Signal transduction cells convert an extracellular into an intracellular one. Signal transduction cells convert an extracellular into an intracellular one. Response by the cell: interior of the membrane protein undergoes a change in conformation, which activates proteins in the cytoplasm—often in a chain reaction. Response by the cell: interior of the membrane protein undergoes a change in conformation, which activates proteins in the cytoplasm—often in a chain reaction. Termination of signal Termination of signal

38 Signal transduction

39 Cells in close contact often develop intercellular junctions Cells in close contact often develop intercellular junctions Anchoring junctions connect epithelial cells Anchoring junctions connect epithelial cells Desmosomes composed of filaments which hold cells subject to mechanical stresses together (in animal cells) Desmosomes composed of filaments which hold cells subject to mechanical stresses together (in animal cells) Adhering junctions cement cells together with proteins Adhering junctions cement cells together with proteins Tight junctions seal off intercellular spaces in some animal cells. Seals are protein links. Tight junctions seal off intercellular spaces in some animal cells. Seals are protein links.

40 Gap junctions: permit transfer of small molecules and ions. These contain pores that connect cells. Allow rapid chemical and electrical communication between cells. Plasmodesmata: allow movement of certain molecules and ions between plant cells. Plasmodesmata: allow movement of certain molecules and ions between plant cells. Plasma membranes are continuous though the gaps.

41 Desmosomes

42 Tightjunctions

43 Gap junctions

44 Plasmodesmata


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