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LIFE102 Week 5 Notes

by: Sydney Dingman

LIFE102 Week 5 Notes Life 102

Marketplace > Colorado State University > Biology > Life 102 > LIFE102 Week 5 Notes
Sydney Dingman
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Week 5 lecture notes.
Attributes of Living Systems
Erik N Arthun
Class Notes
Biology, LIFE102
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This 8 page Class Notes was uploaded by Sydney Dingman on Friday February 19, 2016. The Class Notes belongs to Life 102 at Colorado State University taught by Erik N Arthun in Winter 2016. Since its upload, it has received 23 views. For similar materials see Attributes of Living Systems in Biology at Colorado State University.


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Date Created: 02/19/16
Week 5 LIFE 102 Notes 2/15/16, Chapter 7: Membrane Structure and Function… MARCH 7, NEXT TEST  Structure of membranes is more fluid than we would expect and is very, very thin.  Cells & Organelles are surrounded by membranes o Molecules can move in and out of the cell, and separates the inside from the outside environments o Selectively permeable: some substances cross easily, others don’t  Cellular membranes are fluid mosaics of lipids and proteins o Form by themselves because they are amphipathic  Membrane structure o Myseal, the phospholipids will form a sphere by themselves because of the amphipathic tendencies.  Lipids move freely in the plasma membrane o Multiple factors determine whether the membrane is fluid or viscous  Fluid: liquid  Viscous: gummy o Temperature  Phospholipids can move side to side easily, but not switch up to down easily.  High temperature will move side to side quickly  Cold temperature will not move as much o Type of phospholipids  More saturated fatty acids means more viscosity  Less saturated fatty acids makes the phospholipids not pack together as tightly which makes it more fluid o Cholesterol content  In the bilayer  Acts as a fluidity buffer  High temperatures, moderates the movement of the phospholipids  Lower temperatures, moderates the packing of the phospholipids  Freeze Fracture o When you freeze the cell then chop the membrane in half o Lots of proteins on in the bilayer  Phospholipid bilayer is embedded with proteins o Peripherals- bound to membrane surface o Integrals- incorporated into membrane  Integral Membrane Protein o In the proteins, hydrophobic ones will hang out inside the structure of the bilayer, hydrophilic ones hang out outside the structure of the bilayer  Membrane proteins and lipids are synthesized in the ER and Golgi o Proteins determine most of the membrane’s specific functions o Some proteins will be released, while other embed with the phospholipid bilayer  Membrane Protein Functions o Transport  Help move molecules from one side to the other  Channel proteins: specific doorways through which molecules can get through the hydrophobic interior  Carrier o Enzyme Activity  Help with chemical reactions and can be grouped into metabolic pathways  Modifies protein in some way so that it is more usable. o Signal transduction  Send chemical messages across the membrane  How cells communicate with other cells or their environment o Cell-Cell recognition 2  Glycoproteins in membrane serve as identification  Blood Types o Intercellular joining  Bind cells together  Tight junctions  Gap junctions o Cytoskeleton & extracellular matrix attachments  Helps maintain cell shape and location of proteins  Why do cells require movement across their membranes? o Metabolic needs:  Nutrients and oxygen in  Wastes and carbon dioxide out o Maintain potential energy of the cell:  Inorganic ions in and out  How are molecules moved across membranes? o Not all substances cross the same o Passive transport requires no energy o Active energy requires a little bit of ATP energy o Some go straight through the bilayer o Others need to go through a channel or carrier protein  Passive transport o No additional energy used to move the substance from high to low concentration o Concentration gradient: things move from high to low concentrations for free o Can move through in 3 ways:  Lipid bilayer  Channel proteins  Carrier proteins o Charged molecules and polar molecules need some sort of channel to move through the bilayer 3 o Occurs by diffusion: the movement of molecules from where there is a lot of them to where there is few of them o Molecules tend to spread out evenly  Active transport o Uses additional energy to pump energy from a low concentration to a high concentration. 2/17/16, Chapter 7 cont.  Molecules that can diffuse across lipid bilayers (without help of proteins): o Non-polar molecules o Small, uncharged polar molecules  Larger polar molecules and ions need transport proteins to get across membrane  Osmosis o Passive diffusion of water across a selectively permeable membrane o Tonicity: the ability of a surrounding solution to cause a cell to gain or lose water o Hypotonic: solute concentration is less than that inside the cell; cell gains water o Hypertonic: solute concentration is greater than that inside the cell; cell loses water o Isotonic: solute concentration is the same as that inside the cell; no net water movement across the plasma membrane o Water follows salt  What drives osmosis? o Solutes that don’t cross the membrane o Water diffuses  Towards the highest solute concentration  Towards lowest free water concentration  Implications of osmosis for cells o Animal cells prefer an isotonic environment o Plant cells prefer a hypotonic environment 4  Facilitated diffusion through proteins o Channel proteins  Specific hydrophilic tunnel across membrane o Carrier proteins  Pass specific substances down in concentration gradients through changes in the shape of the membrane protein  Shift their binding site across the membrane o Faster than diffusion across the plasma membrane o Ions and large polar molecules can cross the membrane  Active transport o Moves molecules against concentration gradient (requites ATP energy) o ATP’s terminal phosphate is transferred to the membrane protein o Induces change in protein shape, moving molecule across membrane o Sodium potassium pump: pumps 3 Na+ out and Pumps 2 K+ in  Active transport through protein ion pumps creates a membrane potential o Membrane potential: voltage difference across a membrane generated by ion pump o Create electrochemical gradients o 2 forces act on ions:  Chemical force: ion’s concentration gradient  Electrical force: effect of membrane potential on ions movement  Active and passive transport may be coupled through a cotransporter o The gradient created by the active transport of one molecule can move a second molecule up its concentration gradient o “Cotransporter”: transport of two different molecules at the same time by one carrier o Plants: load glucose into the veins of leaves o Animals: Na+/Glucose cotransporter keeps Na levels up  Transport of particles/large molecules 5 o Proteins, polysaccharides, complex particles o Packaged in vesicles o Exocytosis: secretion of vesicle content via fusion with membrane o Endocytosis: Captures content from outside of the cell o Phagocytosis: cell engulfs a particle and forms food vacuole, which is digested by a lysosome o Pinocytosis: cell captures extracellular fluid (which contains dissolved solutes) o Receptor Mediated Endocytosis: cell acquires a specific substance that is found in low abundance 2/19/16, Chapter 8, Metabolism  Metabolism: all biochemical reactions that occur in cells o Transformation of matter and energy  Catabolism and Anabolism o Anabolism: any process that results in synthesis or assembly of large molecules from smaller molecules  Usually requires the input of energy  Synthesis of proteins from amino acids o Catabolism: the breakdown of large molecules into smaller molecules  Involves breakage of chemical bonds  Often releases energy  Cellular respiration o Catabolism produces energy used in anabolism, you can rarely have one without the other  Energy: the capacity to cause change (rearrange matter, physically move or change bonds) o Potential energy: energy provided by location or structure o Kinetic energy: energy of motion o Chemical energy: potential energy in chemical bonds, released in chemical reactions  First Law of Thermodynamics 6 o Law of Energy Conservation  Energy can be transferred and transformed to other forms of energy, but it cannot be created or destroyed  Plants transform light energy  chemical energy  The energy of the universe is constant  Energy needed for anabolic reaction = energy released in catabolic reaction  Second Law of Thermodynamics o During every energy transfer or transformation, some energy is unusable and is often lost as heat o All energy transformations result in an increase of disorder o Afterwards, there is less “useful” energy o Useful energy= “Gibbs free energy” o Implications for metabolism: spontaneous reactions are only possible if the free energy (G) decreases  Only process with a negative change in G are spontaneous o Exergonic and Endergonic Reactions in Metabolism  An exergonic reaction proceeds with a net release of free energy and is spontaneous  An endergonic reaction absorbs free energy from its surroundings and nonspontaneous o Amount of energy needed to let a reaction proceed: free (Gibbs) energy change, G  If G < 0: exergonic reaction  If G > 0: endergonic reaction  ATP’s Role in Metabolism o In cells: energy from exergonic reactions is used to fuel endergonic reactions o We use our catabolism (to breakdown glucose into ATP), we store the ATP and use it in anabolic reactions (Look at graphic on slide 15 of PowerPoint) o ATP: adenosine triphosphate: molecule that transfers energy from exergonic to endergonic reactions 7 o Made of Adenine+Ribose+3 phosphate groups (negative charges on each phosphate group pushing against each other, creating energy)  How ATP transfers energy o Hydrolysis of ATP  Water is added to it and the third phosphate is removed, releasing energy  ATP Role in Metabolism o ATP gives P to reactant (G>0) o Reactant is energized o Reaction can proceed (G<0)  ATP and Metabolism o ATP is needed for most endergonic processes and has to be created constantly o ATP is produced through respiration: breakdown of C compounds to CO2 and H2O o See slide 19 on Chapter 8 PowerPoint on Canvas 8


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