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L2-PlasmaMembrane.pdf

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The plasma membrane forms the outer boundary of the cell and is selectively permeable. It regulates communication between the cell's interior and exterior environments. The cytoplasm contains the cytosol and various organelles. The cytosol is the intracellular fluid that contains dissolved nutrients, waste products, and cytoskeletal elements. It is the site of many cellular chemical reactions. The nucleus houses the cell's DNA within chromosomes and controls most cellular functions. Nutrients and waste diffuse across the membrane, while the cell maintains concentrations using membrane transport proteins and cellular energy.

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Nutritional Physiology Unit 1 Unit of Life The cell-Structure & Function Dr. Sweta Patel
Sectional View of the Cell
Plasma Membrane forms the cells flexible outer surface, separating the cells internal environment (inside the cell) from the external environment (outside the cell). Selective barrier communication among cells and between cells and their external environment. Cytoplasm consists of all the cellular contents between the plasma membrane and the nucleus Cytosol: The fluid portion: contains water, dissolved solutes, and suspended particles Nucleus houses most of a cells DNA. Chromosome: a single molecule of DNA associated with several proteins, contains thousands of hereditary units called genes that control most aspects of cellular structure and function.
Plasma Membrane: structure Lipid bilayer 3 types of lipid: 75% Phospholipid, 20% cholesterol, 5% glycolipids Amphipathic molecules: dual nature Lipid Integral Protein [Transmembrane Protein] Peripheral Protein Modification of Protein 1. Glycoprotein 2. Lipoprotein Protein
Glycocalyx The carbohydrate portions of glycolipids and glycoproteins form an extensive sugary coat. Cell to cell pattern varies The glycocalyx acts like a molecular signature that enables cells to recognize one another. One of the basis of the immune response that helps us destroy invading organisms. enables cells to adhere to one another in some tissues and protects cells from being digested by enzymes in the extracellular fluid. The hydrophilic properties of the glycocalyx attract a film of fluid to the surface of many cells.
Function of Membrane Protein Act as, Ion Channels Carriers Receptor Enzyme Linker Cell identity marker
1. Membrane Fluidity lipid molecules readily exchange places with their neighbors within a monolayer (~107 times a second). This gives rise to a rapid lateral diffusion, 10million times per second It depends on number of cholesterol and double- bond [kink] present in fatty acids "flip-flop" : occurs less than once a month for any individual molecule. Membrane Physiology
Importance of membrane Fluidity Rigid membrane would lack mobility A completely fluid membrane would lack the structural organization and mechanical support required by the cell Allows interactions to occur within the plasma membrane enables the movement of the membrane components responsible for cellular processes such as cell movement, growth, division, and secretion. self-seal if torn or punctured.
2. Membrane Permeability Selectively permeable permeable to nonpolar, uncharged molecules, such as oxygen, carbon dioxide, and steroids Impermeable to ions and large, uncharged polar molecules such as glucose Slightly permeable to small, uncharged polar molecules such as water and urea, a waste product from the breakdown of amino acids. Importance: allows a living cell to maintain different concentrations of certain substances on either side of the plasma membrane.
3. Electrochemical Gradient The selective permeability of the plasma membrane allows a living cell to maintain different concentrations of certain substances on either side of the plasma membrane. A concentration gradient is a difference in the concentration of a chemical from the inside to the outside of the plasma membrane. Typically, the inner surface of the plasma membrane is more negatively charged and the outer surface is more positively charged. A difference in electrical charges between two regions constitutes an electrical gradient. Because it occurs across the plasma membrane, this charge difference is termed the membrane potential Oxygen molecules and sodium ions (Na) are more concentrated in the extracellular fluid than in the cytosol; the opposite is true of carbon dioxide molecules and potassium ions (K). The combined influence of the concentration gradient and the electrical gradient on movement of a particular ion is referred to as its electrochemical gradient.
What can diffuse through membrane Protein - free Lipid Bilayers Are Highly Impermeable to Ions The smaller the molecule and the more soluble it is in oil can pass easily Small nonpolar molecules, such as O2 (32 daltons) and CO2 (44 daltons), readily dissolve in lipid bilayers and therefore rapidly diffuse across them Uncharged polar molecules also diffuse rapidly across a bilayer if they are small enough. Water (18 daltons), ethanol (46 daltons), and urea (60 daltons), glycerol (92 daltons) diffuses less rapidly; glucose (180 daltons), can not lipid bilayers are highly impermeable to charged molecules (ions) Transportation Across the membrane
Types Transportation carrier proteins channel proteins carriers, permeases, or transporters bind the specific solute to be transported and undergo a series of conformational changes in order to transfer the bound solute across the membrane need not bind the solute they form hydrophilic pores that extend across the lipid bilayer concentration gradient Against concentration gradient passive Diffusion Active Diffusion
Passive Diffusion Is a passive process in which the random mixing of particles in a solution occurs because of the particles kinetic energy. They move down their concentration gradient.
Several factors influence the diffusion rate of substances across plasma membranes Steepness of the concentration gradient : The greater the difference in concentration between the two sides of the membrane, the higher the rate of diffusion. charged particles Temperature: The higher the temperature, the faster the rate of diffusion diffusion processes occur more rapidly in a person with a fever Mass of the diffusing substance: The larger the mass - the slower its diffusion rate. Smaller molecules diffuse more rapidly than larger ones. Surface area: The larger the membrane surface area -the faster the diffusion rate. the air sacs of the lungs have a large surface area Diffusion distance: The greater the distance -the longer it takes. Diffusion across a plasma membrane takes only a fraction of a second because it is so thin.
Simple Diffusion is a passive process in which substances move freely through the lipid bilayer of the plasma membranes of cells without the help of membrane transport proteins Nonpolar, hydrophobic molecules including oxygen, carbon dioxide, and nitrogen gases; fatty acids; steroids; and fat-soluble vitamins (A, D, E, and K). Small, uncharged polar molecules such as water, urea, and small alcohols also pass through the lipid bilayer by simple diffusion.
Facilitated Diffusion Solutes that are too polar or highly charged to move through the lipid bilayer by simple diffusion can cross the plasma membrane by a passive process called facilitated diffusion. CHANNEL-MEDIATED FACILITATED DIFFUSION Through a membrane channel [ion channels] - integral transmembrane proteins that allow passage of small, inorganic ions that are too hydrophilic to penetrate the nonpolar interior of the lipid bilayer. Eg. For Na, K, Ca ions CARRIER-MEDIATED FACILITATED DIFFUSION a carrier (also called a transporter) is used to move a solute down its concentration gradient across the plasma membrane. The solute binds to a specific carrier on one side of the membrane and is released on the other side after the carrier undergoes a change in shape. E.g Glucose transporter
Osmosis Type of passive diffusion is a type of diffusion in which there is net movement of a solvent through a selectively permeable membrane the solvent is water, which moves by osmosis across plasma membranes from an area of higher water concentration to an area of lower water concentration. During osmosis, water molecules pass through a plasma membrane in two ways: (1) by moving through the lipid bilayer via simple diffusion, as previously described, and (2) by moving through aquaporins- integral membrane proteins that function as water channels. the solution with the impermeable solute also exerts a force, called the osmotic pressure.
Tonicity Isotonic solution: The concentrations of solutes that cannot cross the plasma membrane are the same on both sides of the membrane in this solution. E.g NaCl: 0.9% hypotonic solution: a solution that has a lower concentration of solutes than the cytosol. hypertonic solution: higher concentration of solutes than does the cytosol
Active Diffusion Uphill [against concentration gradient] Some polar or charged solutesTwo sources of cellular energy can be used to drive active transport: (1) Energy obtained from hydrolysis of adenosine triphosphate (ATP) is the source in primary active transport; (2) energy stored in an ionic concentration gradient is the source in secondary active transport..
Primary Active Transport Carrier proteins that mediate primary active transport are often called pumps. hydrolysis of ATP changes the shape of a carrier protein E.g Sodium potassium pump Three Na + in the cytosol bind to the pump protein Binding of Na triggers the hydrolysis of ATP into ADP This chemical reaction changes the shape of the pump protein, expelling the three Na into the extracellular fluid Two K + in the extracellular fluid to the pump protein The binding of K + triggers release of the phosphate group from the pump protein As the pump protein reverts to its original shape, it releases K + into the cytosol.
SECONDARY ACTIVE TRANSPORT Secondary active transport indirectly uses energy obtained from the hydrolysis of ATP. The energy stored in a Na+ or H + concentration gradient is used to drive other substances across the membrane against their own concentration gradients. Some of the stored energy can be converted to kinetic energy (energy of motion) and used to transport other substances against their concentration gradients. If these transporters move two substances in the same direction they are called symporters Na + /glucose and Na/amino acid symporters If these transporters move two substances in the opposite direction they are called antiporters Na+ /H + and Na+/Ca+ antiporters
Transport in Vesicles small, spherical sac. Vesicles also import materials from and release materials into extracellular fluid Endocytosis: materials move into a cell in a vesicle formed from the plasma membrane. Receptor mediated Phagocytosis Bulk phase endocytosis Exocytosis: materials move out of a cell by the fusion with the plasma membrane of vesicles formed inside the cell.
Endocytosis 1. Receptor-mediated endocytosis highly selective type- cells take up specific ligands. A vesicle forms after a receptor protein in the plasma membrane recognizes and binds to a particular particle in the extracellular fluid. E.g. For cells take up cholesterol containing low-density lipoproteins (LDLs), transferrin (an iron-transporting protein in the blood), some vitamins, antibodies, and certain hormones by receptor-mediated endocytosis.
Phagocytosis The cell engulfs large solid particles E.g worn-out cells, whole bacteria, or viruse Phagocytes, those cells, that are able to carry out phagocytosis [Macrophage, neutrophiles] Phagocytosis begins when the particle binds to a plasma membrane receptor on the phagocyte, causing it to extend pseudopods Pseudopods surround the particle outside the cell, and the membranes fuse to form a vesicle called a phagosome Phagocytosis is a vital defense mechanism that helps protect the body from disease
bulk-phase endocytosis [Pinocytosis] tiny droplets of extracellular fluid are taken up. No receptor proteins are involved; all solutes. Dissolved in the extracellular fluid are brought into the cell the plasma membrane folds inward and forms a vesicle containing a droplet of extracellular fluid. The vesicle detaches or pinches off from the plasma membrane and enters the cytosol.
EXOCYTOSIS exocytosis releases materials from a cell. All cells carry out exocytosis, but it is especially important in two types of cells: (1) secretory cells that liberate digestive enzymes, hormones, mucus, or other secretions; (2) nerve cells that release substances called neurotransmitters In some cases, wastes are also released by exocytosis. During exocytosis, membrane-enclosed vesicles called secretory vesicles Segments of the plasma membrane lost through endocytosis are recovered or recycled by exocytosis. The balance between endocytosis and exocytosis keeps the surface area of a cells plasma membrane relatively constant.
TRANSCYTOSIS Transport in vesicles may also be used to successively move a substance into, across, and out of a cell. In this active process, called transcytosis. vesicles undergo endocytosis on one side of a cell, move across the cell, and then undergo exocytosis on the opposite side. E.g. Transcytosis occurs most often across the endothelial cells that line blood vessels and is a means for materials to move between blood plasma and interstitial fluid. For instance, when a woman is pregnant, some of her antibodies cross the placenta into the fetal circulation via transcytosis
Cytoplasm Cytosol(intracellular fluid) + organelles Cytosol: 7590% water Various dissolved and suspended components: different types of ions, glucose, amino acids, fatty acids, proteins, lipids, ATP, and waste products. Function: The cytosol is the site of many chemical reactions required for a cells existence. For example, enzymes in cytosol catalyze glycolysis.

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L2-PlasmaMembrane.pdf

  • 1. Nutritional Physiology Unit 1 Unit of Life The cell-Structure & Function Dr. Sweta Patel
  • 2. Sectional View of the Cell
  • 3. Plasma Membrane forms the cells flexible outer surface, separating the cells internal environment (inside the cell) from the external environment (outside the cell). Selective barrier communication among cells and between cells and their external environment. Cytoplasm consists of all the cellular contents between the plasma membrane and the nucleus Cytosol: The fluid portion: contains water, dissolved solutes, and suspended particles Nucleus houses most of a cells DNA. Chromosome: a single molecule of DNA associated with several proteins, contains thousands of hereditary units called genes that control most aspects of cellular structure and function.
  • 4. Plasma Membrane: structure Lipid bilayer 3 types of lipid: 75% Phospholipid, 20% cholesterol, 5% glycolipids Amphipathic molecules: dual nature Lipid Integral Protein [Transmembrane Protein] Peripheral Protein Modification of Protein 1. Glycoprotein 2. Lipoprotein Protein
  • 5. Glycocalyx The carbohydrate portions of glycolipids and glycoproteins form an extensive sugary coat. Cell to cell pattern varies The glycocalyx acts like a molecular signature that enables cells to recognize one another. One of the basis of the immune response that helps us destroy invading organisms. enables cells to adhere to one another in some tissues and protects cells from being digested by enzymes in the extracellular fluid. The hydrophilic properties of the glycocalyx attract a film of fluid to the surface of many cells.
  • 6. Function of Membrane Protein Act as, Ion Channels Carriers Receptor Enzyme Linker Cell identity marker
  • 7. 1. Membrane Fluidity lipid molecules readily exchange places with their neighbors within a monolayer (~107 times a second). This gives rise to a rapid lateral diffusion, 10million times per second It depends on number of cholesterol and double- bond [kink] present in fatty acids "flip-flop" : occurs less than once a month for any individual molecule. Membrane Physiology
  • 8. Importance of membrane Fluidity Rigid membrane would lack mobility A completely fluid membrane would lack the structural organization and mechanical support required by the cell Allows interactions to occur within the plasma membrane enables the movement of the membrane components responsible for cellular processes such as cell movement, growth, division, and secretion. self-seal if torn or punctured.
  • 9. 2. Membrane Permeability Selectively permeable permeable to nonpolar, uncharged molecules, such as oxygen, carbon dioxide, and steroids Impermeable to ions and large, uncharged polar molecules such as glucose Slightly permeable to small, uncharged polar molecules such as water and urea, a waste product from the breakdown of amino acids. Importance: allows a living cell to maintain different concentrations of certain substances on either side of the plasma membrane.
  • 10. 3. Electrochemical Gradient The selective permeability of the plasma membrane allows a living cell to maintain different concentrations of certain substances on either side of the plasma membrane. A concentration gradient is a difference in the concentration of a chemical from the inside to the outside of the plasma membrane. Typically, the inner surface of the plasma membrane is more negatively charged and the outer surface is more positively charged. A difference in electrical charges between two regions constitutes an electrical gradient. Because it occurs across the plasma membrane, this charge difference is termed the membrane potential Oxygen molecules and sodium ions (Na) are more concentrated in the extracellular fluid than in the cytosol; the opposite is true of carbon dioxide molecules and potassium ions (K). The combined influence of the concentration gradient and the electrical gradient on movement of a particular ion is referred to as its electrochemical gradient.
  • 11. What can diffuse through membrane Protein - free Lipid Bilayers Are Highly Impermeable to Ions The smaller the molecule and the more soluble it is in oil can pass easily Small nonpolar molecules, such as O2 (32 daltons) and CO2 (44 daltons), readily dissolve in lipid bilayers and therefore rapidly diffuse across them Uncharged polar molecules also diffuse rapidly across a bilayer if they are small enough. Water (18 daltons), ethanol (46 daltons), and urea (60 daltons), glycerol (92 daltons) diffuses less rapidly; glucose (180 daltons), can not lipid bilayers are highly impermeable to charged molecules (ions) Transportation Across the membrane
  • 12. Types Transportation carrier proteins channel proteins carriers, permeases, or transporters bind the specific solute to be transported and undergo a series of conformational changes in order to transfer the bound solute across the membrane need not bind the solute they form hydrophilic pores that extend across the lipid bilayer concentration gradient Against concentration gradient passive Diffusion Active Diffusion
  • 13. Passive Diffusion Is a passive process in which the random mixing of particles in a solution occurs because of the particles kinetic energy. They move down their concentration gradient.
  • 14. Several factors influence the diffusion rate of substances across plasma membranes Steepness of the concentration gradient : The greater the difference in concentration between the two sides of the membrane, the higher the rate of diffusion. charged particles Temperature: The higher the temperature, the faster the rate of diffusion diffusion processes occur more rapidly in a person with a fever Mass of the diffusing substance: The larger the mass - the slower its diffusion rate. Smaller molecules diffuse more rapidly than larger ones. Surface area: The larger the membrane surface area -the faster the diffusion rate. the air sacs of the lungs have a large surface area Diffusion distance: The greater the distance -the longer it takes. Diffusion across a plasma membrane takes only a fraction of a second because it is so thin.
  • 15. Simple Diffusion is a passive process in which substances move freely through the lipid bilayer of the plasma membranes of cells without the help of membrane transport proteins Nonpolar, hydrophobic molecules including oxygen, carbon dioxide, and nitrogen gases; fatty acids; steroids; and fat-soluble vitamins (A, D, E, and K). Small, uncharged polar molecules such as water, urea, and small alcohols also pass through the lipid bilayer by simple diffusion.
  • 16. Facilitated Diffusion Solutes that are too polar or highly charged to move through the lipid bilayer by simple diffusion can cross the plasma membrane by a passive process called facilitated diffusion. CHANNEL-MEDIATED FACILITATED DIFFUSION Through a membrane channel [ion channels] - integral transmembrane proteins that allow passage of small, inorganic ions that are too hydrophilic to penetrate the nonpolar interior of the lipid bilayer. Eg. For Na, K, Ca ions CARRIER-MEDIATED FACILITATED DIFFUSION a carrier (also called a transporter) is used to move a solute down its concentration gradient across the plasma membrane. The solute binds to a specific carrier on one side of the membrane and is released on the other side after the carrier undergoes a change in shape. E.g Glucose transporter
  • 17. Osmosis Type of passive diffusion is a type of diffusion in which there is net movement of a solvent through a selectively permeable membrane the solvent is water, which moves by osmosis across plasma membranes from an area of higher water concentration to an area of lower water concentration. During osmosis, water molecules pass through a plasma membrane in two ways: (1) by moving through the lipid bilayer via simple diffusion, as previously described, and (2) by moving through aquaporins- integral membrane proteins that function as water channels. the solution with the impermeable solute also exerts a force, called the osmotic pressure.
  • 18. Tonicity Isotonic solution: The concentrations of solutes that cannot cross the plasma membrane are the same on both sides of the membrane in this solution. E.g NaCl: 0.9% hypotonic solution: a solution that has a lower concentration of solutes than the cytosol. hypertonic solution: higher concentration of solutes than does the cytosol
  • 19. Active Diffusion Uphill [against concentration gradient] Some polar or charged solutesTwo sources of cellular energy can be used to drive active transport: (1) Energy obtained from hydrolysis of adenosine triphosphate (ATP) is the source in primary active transport; (2) energy stored in an ionic concentration gradient is the source in secondary active transport..
  • 20. Primary Active Transport Carrier proteins that mediate primary active transport are often called pumps. hydrolysis of ATP changes the shape of a carrier protein E.g Sodium potassium pump Three Na + in the cytosol bind to the pump protein Binding of Na triggers the hydrolysis of ATP into ADP This chemical reaction changes the shape of the pump protein, expelling the three Na into the extracellular fluid Two K + in the extracellular fluid to the pump protein The binding of K + triggers release of the phosphate group from the pump protein As the pump protein reverts to its original shape, it releases K + into the cytosol.
  • 21. SECONDARY ACTIVE TRANSPORT Secondary active transport indirectly uses energy obtained from the hydrolysis of ATP. The energy stored in a Na+ or H + concentration gradient is used to drive other substances across the membrane against their own concentration gradients. Some of the stored energy can be converted to kinetic energy (energy of motion) and used to transport other substances against their concentration gradients. If these transporters move two substances in the same direction they are called symporters Na + /glucose and Na/amino acid symporters If these transporters move two substances in the opposite direction they are called antiporters Na+ /H + and Na+/Ca+ antiporters
  • 22. Transport in Vesicles small, spherical sac. Vesicles also import materials from and release materials into extracellular fluid Endocytosis: materials move into a cell in a vesicle formed from the plasma membrane. Receptor mediated Phagocytosis Bulk phase endocytosis Exocytosis: materials move out of a cell by the fusion with the plasma membrane of vesicles formed inside the cell.
  • 23. Endocytosis 1. Receptor-mediated endocytosis highly selective type- cells take up specific ligands. A vesicle forms after a receptor protein in the plasma membrane recognizes and binds to a particular particle in the extracellular fluid. E.g. For cells take up cholesterol containing low-density lipoproteins (LDLs), transferrin (an iron-transporting protein in the blood), some vitamins, antibodies, and certain hormones by receptor-mediated endocytosis.
  • 24. Phagocytosis The cell engulfs large solid particles E.g worn-out cells, whole bacteria, or viruse Phagocytes, those cells, that are able to carry out phagocytosis [Macrophage, neutrophiles] Phagocytosis begins when the particle binds to a plasma membrane receptor on the phagocyte, causing it to extend pseudopods Pseudopods surround the particle outside the cell, and the membranes fuse to form a vesicle called a phagosome Phagocytosis is a vital defense mechanism that helps protect the body from disease
  • 25. bulk-phase endocytosis [Pinocytosis] tiny droplets of extracellular fluid are taken up. No receptor proteins are involved; all solutes. Dissolved in the extracellular fluid are brought into the cell the plasma membrane folds inward and forms a vesicle containing a droplet of extracellular fluid. The vesicle detaches or pinches off from the plasma membrane and enters the cytosol.
  • 26. EXOCYTOSIS exocytosis releases materials from a cell. All cells carry out exocytosis, but it is especially important in two types of cells: (1) secretory cells that liberate digestive enzymes, hormones, mucus, or other secretions; (2) nerve cells that release substances called neurotransmitters In some cases, wastes are also released by exocytosis. During exocytosis, membrane-enclosed vesicles called secretory vesicles Segments of the plasma membrane lost through endocytosis are recovered or recycled by exocytosis. The balance between endocytosis and exocytosis keeps the surface area of a cells plasma membrane relatively constant.
  • 27. TRANSCYTOSIS Transport in vesicles may also be used to successively move a substance into, across, and out of a cell. In this active process, called transcytosis. vesicles undergo endocytosis on one side of a cell, move across the cell, and then undergo exocytosis on the opposite side. E.g. Transcytosis occurs most often across the endothelial cells that line blood vessels and is a means for materials to move between blood plasma and interstitial fluid. For instance, when a woman is pregnant, some of her antibodies cross the placenta into the fetal circulation via transcytosis
  • 28. Cytoplasm Cytosol(intracellular fluid) + organelles Cytosol: 7590% water Various dissolved and suspended components: different types of ions, glucose, amino acids, fatty acids, proteins, lipids, ATP, and waste products. Function: The cytosol is the site of many chemical reactions required for a cells existence. For example, enzymes in cytosol catalyze glycolysis.