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by: Emily Liescheidt

Bio120Week5.pdf bio120

Emily Liescheidt
General Biology

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This section of notes contains information about the cell membrane and the functions that occur such as diffusion, osmosis, passive transport, and active transport.
General Biology
Class Notes
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This 4 page Class Notes was uploaded by Emily Liescheidt on Friday October 2, 2015. The Class Notes belongs to bio120 at Grand Valley State University taught by Simon in Fall 2015. Since its upload, it has received 20 views. For similar materials see General Biology in Biology at Grand Valley State University.


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Date Created: 10/02/15
1 membrane 1 selectively permeable 2 regulate what enters and leaves the cell 3 fluid mosaic of lipids and proteins 4 primarily composed of phospholipids 5 the proteins determine the function of the membrane plasma membrane is a double membrane also called a phospholipid bilayer 1 this membrane is very fluid meaning the components move within the membrane 1 the movement within the membrane is primarily lateral movement 2 phospholipids move left and right within the membrane 3 flip flops are rare because of the hydrophobic and hydrophilic regions of the phospholipid 1 The glycerol head is hydrophilic Flip flopping from the top to the bottom would mean the phospholipids would have to come in contact with the 3 Hydrocarbon tails and cholesterol 1 unsaturated fatty acids they have double bonds between the carbons of a carbon skeleton 1 as a result the fatty acids are kinked They don t hang straight 2 presence of unsaturated fatty acids increases the fluidity of the membrane 1 this prevents the tight packing of the phospholipids 2 glycerol headsspaces and gaps 3 fluidity selectively permeable membranes 1 have to be fluid for proteins to be functional 2 Saturated fatty acids viscous not fluid 4 Environment can affect the fluidity of a membrane 1 if the temperature decreases so does the fluidity of the membrane 2 membranes of animal cells contain cholesterol 1 at normal body temperature the cholesterol actually decreases the fluidity in membranes by slowing lateral movement of those phospholipids 2 When there s a decrease in temperature presence of cholesterol helps maintain fluidity by preventing the closepacking of the phospholipids 3 Decrease in temperature means the phospholipids want to get closer together 5 Selective permeability of membranes 1 Molecules and ions move back and forth across a membrane 2 Things are always moving in and out of the cell 3 molecules and ions move at different rates based on their characteristics 1 hydrocarbons other nonpolar molecules carbon dioxide and oxygen all move relatively quickly through the membrane 2 polar molecules water sugar and polar ions move more slowly through the membrane 3 Energy is not always required to move across a membrane 2 4 Passive transport Diffusion 1 Passive transport means there is no energy required 2 Thermal motion or heat of the molecules that result in diffusion 3 molecules move randomly in all directions but the net movement is from an area of higher concentration of that molecule type to an area of lower concentration of that same molecule type 1 As a result the molecule moves down it s concentration gradientfrom high to low 2 Ex perfume sprayed in the front of the room moving in all directions until it is distributed throughout the whole room 1 net overall movement is from the front of the room to the back of the room 4 Using two different solutes 1 when there are two solutes they each move down their own concentration gradient 1 presents of one doesn t affect the movement of the presence of another molecule 2 The rate of one doesn t affect the rate of the other 5 Osmosis type of passive transport simply the movementdiffusion of water across the membrane 1 membrane must be permeable to water 2 water is attracted to and it tightly clusters around hydrophilic molecules 1 They do not participate in osmosis 3 Free water molecules participate in osmosis 1 These are not associated in hydrophilic molecules 2 Concentration gradient based on free water molecules 6 Water balance of cells 1 Tonicity ability of a solution to cause a cell to gain or lose water due to concentration gradient and membrane permeability tonic refers to solute lso means same hypo means less hyper means more 1 When excess water moves into a plant cell the cell wall exerts back pressure 1 This limits the amount of water that can move into the plant cell 1 This is called Turgor pressurecell becomes turgid 2 this maintains the proper amount of water within a plant cell 3 cell wall prevents the plant cell from lysing 2 Plasmolysis Plant cells pulling away of the plasma membrane from the cell wall due to net water from the cell 0 39gt0 D 1 Plant cell maintains its overall shape Plasma membrane just shrinks 2 glycolipids are phospholipids with carbohydrates attached 2 Membrane structure 1 membrane proteinsfunction of membrane proteins 1 transport substances can pass through the membrane through diffusion or osmosis 1 sometimes substances need help to get through the membrane 1 this is called Facilitated diffusion 2 it is passive transport meaning it still doesn t need energy 3 2 types of proteins are involved in this assistance 1 Channel protein provides a hydrophilic channel through which substances can pass 1 anything that wants a hydrophilic environment uses channel proteins 1 polar molecules ions 2 Water channel proteins are called aquaporin 2 Carrier protein changes shape when transporting a substance 1 passive movement passive transport 2 moving down the concentration gradient 2 active transport energy is necessary for transportation 1 Substances are moved against concentration gradient from low to high concentration 2 active transport requires a carrier proteinone that changes shape as the substance is transported 2 Enzymatic Activity facilitate a reactionthey speed up the rate at which it occurs 1 one enzyme can work alone 2 more often two or more enzymes work together in a metabolic pathway 3 Signal Transduction sometimes these act as receptors for chemical messenger 1 chemical messenger is a signal molecule 1 the signal molecule bonds to the protein causing the protein to change shape 1 specific change in shape relays a specific message in to the interior of the cell 4 Cell to cell recognition this involves glycoproteins but also glycolipids present in the membranes 1 they act as identification tags which allows for the sorting of cells during embryonic development 1 Tissues are formed 2 organs are formed 3 one skin cell can recognize another skin cell 2 Cell to cell recognition is also used in the immune system 1 allows body to recognize foreign cells or entitiesviruses 2 ex HIV virus receptors on which the virus can dock create immunity 1 people with mutation lack some if not all receptors 5 Intercellular Joining Junctions are formed between cells which results in gap junctions in animal cells 1 protein in one cell recognizes and bonds with a protein of another cell 2 allows cytoplasm from one cell to continue to another Attachment to the Cytoskeleton and Extracellular matrix ECM 1 Fibers of ECM can be bonded to the protein enables communication between cells allows communication with the outside environment also helps maintain cell shape Stabilizes some of the membrane structures and lowers latteral movement of the membrane 0 39gt0 D 3 Transport across the Plasma Membrane 1 Transport of large quantities 1 2 Uses vesicles exocytosis movement of products to the plasma membrane in vesicles 1 motor proteins carry these vesiclesthey walk along the cytoskeleton 2 fibers of the cytoskeleton are primarily microtubules 3 getting substances from inside the cell to the outside of the cell Endocytosis Bringing substances into the cell 1 There is a forming of a pocket Endocytic vesicle forms 1 Fluid collects in the pocket 2 pocket deepens until it is pinched off 2 Three types of endocytosis 1 phagocytosis this is the intake of food particles from the environment 1 single cell organisms often use this mechanismhow amoebas take in food 2 food vacuole is formed 3 lysosomes are involved in the breakdown of the food 2 Pinocytosis this is the intake of large quantities of non specific substances 1 plasma membrane forms pocket and extracellular fluid enters 1 whatever solutes are in that fluid end up in the vesicleal types of solutes present in the extracellular fluid 1 reason for being non specific 2 There are varying amounts of each substance 3 Receptormediated endocytosis this allows for the intake of specific substances into the cell even if that substance is present in small quantities within the extracellular fluid 1 There are receptor proteins on the surface of the membrane and these receptor proteins are specific to the solute to which they bond 2 this guarantees the intake of that solute


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