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Chapter seven: Membrane structures and functions. - Coggle Diagram
Chapter seven: Membrane structures and functions.
the cellular membrane of the cell is made of phospholipids, which are amphipathic. this means that one section is hydrophobic, and the other is hydrophilic.
the heads are polar, aka hydrophilic. the tails are non-polar, meaning they're hydrophobic.
unsaturated hydrocarbon tails are fluid and enhance membrane fluidity.
saturated tails are packed together and increase membrane viscosity. within animal membranes Cholesterol moderates' fluidity of the membrane based on temperature. at high temperatures it reduces fluidity while at low temperatures it disrupts the packing of the phospholipids.
the Fluid Mosaic Model is the most accepted model of the membrane structure. the Model explains the membrane as a mosaic of proteins within the fluid bilayer of the phospholipid membrane.
within the membrane are many different proteins with various functions. They are found in the fluid matrix of the bilayer. Proteins determine and help the membrane with various functions. with different types of cells come different proteins.
integral proteins: this type of protein has extended into the hydrophobic portion of the membrane.
peripheral proteins: these proteins do not penetrate the lipid bilayer at all, instead they are bound rather loosely to the surface of the cell membrane and often to exposed integral proteins.
transmembrane proteins: technically a part of the integral proteins, these types span all the way through the cell membrane onto the other side.
within the cytoplasmic part of the membrane, some proteins are held in place by via an attachment to the cytoskeleton.
Functions.
Transport proteins: these proteins are either active or passive in their transportation. they span across the membrane and either allow particular solutes into the cell; or they shuttle a substance into the cell by changing shape.
Passive transport: this type of transport requires no energy from the cell.
Active transport: this requires ATP to get substances in or out of the cell.
one type of active transport is a sodium-potassium pump: which pumps those elements across the membrane. this pump is also an electrogenic pump: meaning it generates a voltage across the membrane. it is found in animal cells.
a proton pump is used in plants, fungi, and bacteria. it actively transports protons (H+) out of the cell. with this pumping it transfers the positive charge from the cytoplasm to the extracellular solution.
cotransport: a transport protein couples a downhill diffusion of a solute to an uphill transport of a secondary substance against its own gradient.
Enzyme activity: these proteins work exclusively with enzymes.
signal transduction: the protein has a binding site for a specific shape of a chemical messenger. with that messenger the protein may change shape allowing a relay message into the cell, and binding to a cytoplasmic protein.
cell to cell recognition: glycoproteins (carbs and protein combination) will serve as identification tags so cells can temporarily bind together.
cell to cell recognition allows for cells to recognize each other and also recognize foreign bodies. which allows for the immune system to take action.
intercellular joining: proteins of adjacent cells may hook together with various junctions like gap or tight junctions. this is a long-term bind.
ECM (extracellular matrix): elements of the cytoskeleton can be noncovalently bound to membrane proteins. this function helps maintain cell shape and stabilize locations of certain proteins within the membrane.
membranes have inside and outside faces, and the two lipid layers may differ in composition. each protein also has a directional orientation within the membrane.
the cell membrane is semi-permeable. also called selective permeability. this means that only certain substances can cross through the membrane. these molecules must be small, uncharged, and nonpolar.
transport proteins can help other molecules pass through the membrane. Ex. an aquaporin is a channel protein that deals with osmosis. another example is carrier proteins. these proteins hold onto their passengers and change their shape to move across the membrane.
Exocytosis and endocytosis
Exocytosis is when a cell takes certain molecules and with vesicles made from the golgi apparatus it brings those vesicles to the membrane, and the content within those vesicles spill out of the cell.
Endocytosis is when the cell takes in molecules by forming vesicles from the membrane. there are three types of endocytosis: phagocytosis, pinocytosis, and receptor mediated endocytosis.
phagocytosis is "eating" for the cell.
pinocytosis is "drinking" for the cell.
receptor mediated endocytosis is used for cholesterol, and is caused by receptors accepting the molecules.
diffusion: this is the movement of particles from a high concentration to a low concentration until they reach dynamic equilibrium.
a concentration gradient is where the density of a substance increases or decreases. it is a part of diffusion, where the substance goes down its own concentration gradient.
passive diffusion: this type of diffusion requires no energy. it is when a substance goes from a high concentration and into a low concentration. if it is a low to high concentration, this action requires ATP.
Osmosis is a type of diffusion: it is when
water
diffuses across a selectively permeable membrane.
Tonicity: when a solution surrounding the cell causes it to gain or lose water. if in an environment where no water is gained or lost it is isotonic.
hypertonic: when a solution is hypertonic it takes water from the cell due to water wanting to balance the solution. Ex. salt on a snail.
hypotonic: the solution here will make water enter the cell faster than it leaves. this could cause the cell to burst (lyse).
Plasmolysis: when walled cells the cytoplasm shrivels, and the plasma membrane pulls from the cell wall. this happens in a hypertonic environment.
facilitated diffusion: molecules or ions down their electrochemical gradient and across a membrane with assistance of specific transmembrane transport proteins, with no energy being expended.
a type of channel protein is an ion channel, and many of those are gated channels. this means they open and close due to stimulus.
membrane potential is the difference in electrical charge across the plasma membrane of a cell due to the distribution of ions. it affects the activity of cells and the transmembrane movement of charged substances.
electrochemical gradient: this is the diffusion of gradient of an ion, affected by the concentration difference of an ion across a chemical force (membrane), and the ion tendency to move in relatively to the membrane potential ( electrical force).