Plasma Membranes are Intelligently Designed Lesson 5 by Owen Borville August 13, 2024 Biology
The plasma membrane of the cell was discovered in the late 19th century, and its chemical composition in the early 20th century, mainly lipids, proteins, and carbohydrates.
The Fluid Mosaic Model describes the plasma membrane's structure as a mosaic of components including phospholipids, cholesterol, proteins, glycoproteins, and glycolipids (sugar chains attached to proteins or lipids, respectively) resulting in a fluid character (fluidity).
glycoproteins are a combination of carbohydrates and proteins on the plasma membrane's exterior surface
glycolipids are a combination of carbohydrates and lipids on the plasma membrane's exterior surface
Phospholipids are molecules of the plasma membrane's main fabric
Hydrophilic means water-loving areas of molecules, polar
Hydrophobic means water-hating molecules, non-polar
Phospholipid molecule has a 3-carbon glycerol backbone with two fatty acid molecules attached to carbons 1 and 2, and a phosphate group attached to the third carbon
Amphiphilic (dual-loving) molecule possesses a polar or charged area and a non-polar or uncharged area capable of interacting with both hydrophilic and hydrophobic environments (as in a phospholipid molecule)
Proteins are the plasma membrane's second component.
Integral proteins, or integrins, integrate completely into the membrane structure and interacts extensively with the membrane lipids' hydrocarbon chains and often spans the membrane
Peripheral proteins are proteins at the plasma membrane's surface either on its exterior or interior side; not imbedded in phospholipids
Carbohydrates are the third major plasma membrane component. They are always on the cell's exterior surface and are bound to either proteins (glycoproteins) or to lipids (glycolipids). Carbohydrates help cells recognize other cells.
Glycocalyx are the carbohydrates on the cell's exterior surface and is highly hydrophilic (water loving) polar
Membrane Fluidity explained by its mosaic in part. Also, the nature of phospholipids help maintain fluidity.
Also, cholesterol is a cell membrane component attached between phospholipids and between the two phospholipid layers and tends to dampen temperature effects on the membrane
Plasma membranes are selectively permeable (semi-permeable) in that certain substances are allowed to enter and leave the cell, but some harmful substances are prevented from entering and essential substances are kept from leaving. This selectivity allows the cell to survive and without this selectivity, the cell could not survive.
Passive transport is naturally occurring phenomenon as substances move from higher concentration areas to lower concentration areas. A c0ncentration gradient is a physical space where there is a single substance concentration range.
Selective Permeability: plasma membranes are asymmetric as the membrane's interior is not identical to its exterior, and adds to the selective nature of the membrane.
Plasma membranes are amphiphilic (hydrophilic and hydrophobic regions), which helps move some materials through and prevent other materials from leaving. Polar substances have difficulty passing through the membrane.
Diffusion is a passive process of transport as a substance of low weight moves from higher concentration areas to lower concentration areas; concentration gradient.
Factors that affect diffusion: extent of concentration gradient; greater concentration difference will make substances move faster.
Mass of molecules diffusing as heavier molecules move slowly and light molecules move quickly.
Temperature increase also increases the energy of movement and diffusion rate.
Solvent density increase reduces the diffusion rate.
Solubility increases for non-polar or lipid-soluble molecules than polar molecules.
Surface area increases the diffusion rate while a thicker membrane reduces diffusion rate
Greater distance travelled slows the diffusion rate
Filtration process is a variation of diffusion
Solutes are dissolved substances that form a solution
Sometimes pressure enhances the diffusion rate
Facilitated transport or facilitated diffusion is the process which material moves down a concentration gradient (high to low) using integral membrane proteins and materials diffuse across the plasma membrane with the help of membrane proteins.
Transport proteins are the integral membrane proteins involved in facilitated transport of a substance by binding it. Transport proteins function as either channels for the material or carriers for the material and are transmembrane proteins.
Channel proteins have hydrophilic domains exposed to the intracellular and extracellular fluids; in addition, they have hydrophilic channel through their core that provides a hydrated opening through the membrane layers to allow polar compounds to pass through. Some ions can control the opening entrance to the channel.
Aquaporins are channel proteins that allow water to pass through the membrane at a very high rate.
Carrier proteins in the plasma membrane moves a substance across the plasma membrane by changing its own shape and binding the substance as it carries it inside the cell.
Osmosis is the transport of water through a semipermeable membrane according to the water's concentration gradient across the membrane that results from the presence of solute that cannot pass through the membrane; the water concentration gradient is inversely proportional to the solute's concentrate. The water will move to less concentrated areas according to the gradient.
Tonicity is how an extracellular solution can change a cell's volume by affecting osmosis or the capability of a solution to modify the volume of cells by altering their water content.
Osmolarity is the solution's total solute concentration. Tonicity often directly correlates with osmolarity.
Hypotonic situation is when the extracellular fluid has lower osmolarity than the fluid inside the cell, and water enters the cell.
Hypertonic situation is when the extracellular fluid has higher osmolarity than the fluid inside the cell, resulting in water moving out of the cell.
Isotonic situation is when the extracellular fluid has the same osmolarity as the fluid inside the cell, resulting in no net water movement in or out of the cell.
Plasmolysis is the detaching of the cell membrane from the cell wall and constricting the cell membrane when a plant cell is in a hypertonic solution.
Active transport mechanisms require the cell's energy, usually in the form of adenosine triphosphate (ATP).
Electrochemical gradients are electrical and chemical forces that produce a gradient, such as with potassium and sodium ions.
Pumps are active transport mechanisms that works against electrochemical gradients.
Primary active transport moves ions or small molecules across a membrane and may create a difference in charge across that membrane, directly dependent on ATP
Secondary active transport is movement of material that results from primary active transport to the electrochemical gradient (does not directly depend on ATP).
Transporters (protein types)
Uniporter carries one specific ion or molecule.
Symporter carries two different ions or molecules, both in the same direction.
Antiporter carries two different ions or molecules, but in different directions.
Electrogenic pump is a pump that creates a charge imbalance
Endocytosis is a type of active transport that moves particles, such as large molecules, parts of cells, and even whole cells, into a cell.
Phagocytosis (cell eating) is the process by which a cell takes in large or relatively large particles, such as other cells. (such as when white blood cells remove invading particles).
Clathrin is a protein that coats (stabilizes) the plasma membrane's inward facing surface and assists in forming specialized structures, like coated pits, for phagocytosis.
Pinocytosis (cell drinking) is a variation of endocytosis that imports macromolecules that the cell needs from the extracellular fluid.
Potocytosis is a variation of pinocytosis that uses a different coating protein (caveolin) on the plasma membrane's cytoplasmic side
Caevolin is a protein that coats the plasma membrane's cytoplasmic side and participates in the liquid uptake process by potocytosis.
Receptor-mediated endocytosis is a variation of endocytosis that involves using specific binding proteins in the plasma membrane for specific molecules or particles, and clathrin-coated pits that become clathrin-coated vesicles.
Exocytosis is the process of passing bulk material out of a cell.
The plasma membrane of the cell was discovered in the late 19th century, and its chemical composition in the early 20th century, mainly lipids, proteins, and carbohydrates.
The Fluid Mosaic Model describes the plasma membrane's structure as a mosaic of components including phospholipids, cholesterol, proteins, glycoproteins, and glycolipids (sugar chains attached to proteins or lipids, respectively) resulting in a fluid character (fluidity).
glycoproteins are a combination of carbohydrates and proteins on the plasma membrane's exterior surface
glycolipids are a combination of carbohydrates and lipids on the plasma membrane's exterior surface
Phospholipids are molecules of the plasma membrane's main fabric
Hydrophilic means water-loving areas of molecules, polar
Hydrophobic means water-hating molecules, non-polar
Phospholipid molecule has a 3-carbon glycerol backbone with two fatty acid molecules attached to carbons 1 and 2, and a phosphate group attached to the third carbon
Amphiphilic (dual-loving) molecule possesses a polar or charged area and a non-polar or uncharged area capable of interacting with both hydrophilic and hydrophobic environments (as in a phospholipid molecule)
Proteins are the plasma membrane's second component.
Integral proteins, or integrins, integrate completely into the membrane structure and interacts extensively with the membrane lipids' hydrocarbon chains and often spans the membrane
Peripheral proteins are proteins at the plasma membrane's surface either on its exterior or interior side; not imbedded in phospholipids
Carbohydrates are the third major plasma membrane component. They are always on the cell's exterior surface and are bound to either proteins (glycoproteins) or to lipids (glycolipids). Carbohydrates help cells recognize other cells.
Glycocalyx are the carbohydrates on the cell's exterior surface and is highly hydrophilic (water loving) polar
Membrane Fluidity explained by its mosaic in part. Also, the nature of phospholipids help maintain fluidity.
Also, cholesterol is a cell membrane component attached between phospholipids and between the two phospholipid layers and tends to dampen temperature effects on the membrane
Plasma membranes are selectively permeable (semi-permeable) in that certain substances are allowed to enter and leave the cell, but some harmful substances are prevented from entering and essential substances are kept from leaving. This selectivity allows the cell to survive and without this selectivity, the cell could not survive.
Passive transport is naturally occurring phenomenon as substances move from higher concentration areas to lower concentration areas. A c0ncentration gradient is a physical space where there is a single substance concentration range.
Selective Permeability: plasma membranes are asymmetric as the membrane's interior is not identical to its exterior, and adds to the selective nature of the membrane.
Plasma membranes are amphiphilic (hydrophilic and hydrophobic regions), which helps move some materials through and prevent other materials from leaving. Polar substances have difficulty passing through the membrane.
Diffusion is a passive process of transport as a substance of low weight moves from higher concentration areas to lower concentration areas; concentration gradient.
Factors that affect diffusion: extent of concentration gradient; greater concentration difference will make substances move faster.
Mass of molecules diffusing as heavier molecules move slowly and light molecules move quickly.
Temperature increase also increases the energy of movement and diffusion rate.
Solvent density increase reduces the diffusion rate.
Solubility increases for non-polar or lipid-soluble molecules than polar molecules.
Surface area increases the diffusion rate while a thicker membrane reduces diffusion rate
Greater distance travelled slows the diffusion rate
Filtration process is a variation of diffusion
Solutes are dissolved substances that form a solution
Sometimes pressure enhances the diffusion rate
Facilitated transport or facilitated diffusion is the process which material moves down a concentration gradient (high to low) using integral membrane proteins and materials diffuse across the plasma membrane with the help of membrane proteins.
Transport proteins are the integral membrane proteins involved in facilitated transport of a substance by binding it. Transport proteins function as either channels for the material or carriers for the material and are transmembrane proteins.
Channel proteins have hydrophilic domains exposed to the intracellular and extracellular fluids; in addition, they have hydrophilic channel through their core that provides a hydrated opening through the membrane layers to allow polar compounds to pass through. Some ions can control the opening entrance to the channel.
Aquaporins are channel proteins that allow water to pass through the membrane at a very high rate.
Carrier proteins in the plasma membrane moves a substance across the plasma membrane by changing its own shape and binding the substance as it carries it inside the cell.
Osmosis is the transport of water through a semipermeable membrane according to the water's concentration gradient across the membrane that results from the presence of solute that cannot pass through the membrane; the water concentration gradient is inversely proportional to the solute's concentrate. The water will move to less concentrated areas according to the gradient.
Tonicity is how an extracellular solution can change a cell's volume by affecting osmosis or the capability of a solution to modify the volume of cells by altering their water content.
Osmolarity is the solution's total solute concentration. Tonicity often directly correlates with osmolarity.
Hypotonic situation is when the extracellular fluid has lower osmolarity than the fluid inside the cell, and water enters the cell.
Hypertonic situation is when the extracellular fluid has higher osmolarity than the fluid inside the cell, resulting in water moving out of the cell.
Isotonic situation is when the extracellular fluid has the same osmolarity as the fluid inside the cell, resulting in no net water movement in or out of the cell.
Plasmolysis is the detaching of the cell membrane from the cell wall and constricting the cell membrane when a plant cell is in a hypertonic solution.
Active transport mechanisms require the cell's energy, usually in the form of adenosine triphosphate (ATP).
Electrochemical gradients are electrical and chemical forces that produce a gradient, such as with potassium and sodium ions.
Pumps are active transport mechanisms that works against electrochemical gradients.
Primary active transport moves ions or small molecules across a membrane and may create a difference in charge across that membrane, directly dependent on ATP
Secondary active transport is movement of material that results from primary active transport to the electrochemical gradient (does not directly depend on ATP).
Transporters (protein types)
Uniporter carries one specific ion or molecule.
Symporter carries two different ions or molecules, both in the same direction.
Antiporter carries two different ions or molecules, but in different directions.
Electrogenic pump is a pump that creates a charge imbalance
Endocytosis is a type of active transport that moves particles, such as large molecules, parts of cells, and even whole cells, into a cell.
Phagocytosis (cell eating) is the process by which a cell takes in large or relatively large particles, such as other cells. (such as when white blood cells remove invading particles).
Clathrin is a protein that coats (stabilizes) the plasma membrane's inward facing surface and assists in forming specialized structures, like coated pits, for phagocytosis.
Pinocytosis (cell drinking) is a variation of endocytosis that imports macromolecules that the cell needs from the extracellular fluid.
Potocytosis is a variation of pinocytosis that uses a different coating protein (caveolin) on the plasma membrane's cytoplasmic side
Caevolin is a protein that coats the plasma membrane's cytoplasmic side and participates in the liquid uptake process by potocytosis.
Receptor-mediated endocytosis is a variation of endocytosis that involves using specific binding proteins in the plasma membrane for specific molecules or particles, and clathrin-coated pits that become clathrin-coated vesicles.
Exocytosis is the process of passing bulk material out of a cell.