Chapter 7 & 6 Membrane Structure and Function PDF

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Chapter 7 Membrane Structure and Function:

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Membranes consist primarily of lipids, proteins, and carbs. These Proteins and Lipids(mostly phospholipids) are mostly amphipathic. This means that there exist a hydrophobic and hydrophilic region.

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Membrane movement Fluidity/Lipids: - A membrane is held together primarily through hydrophobic interactions, which are weaker than covalent bonds. - There is constant fast sideway movement of phospholipids in the membranes. - Length of hydrocarbons on membrane o The longer the tail, the more hydrophobic interactions take place, thus decreasing the fluidity of the membrane. - Temperature on Membrane o Cooler temperatures will decrease fluidity, higher temperature will increase fluidity. - Saturated and Unsaturated Fats ( double bonds) will impact the membranes differently o Unsaturated fats prevent dense packing, thus enhancing the fluidity of a cell o Saturated Fats can pack more densely and thus decrease the fluidity of that membrane, or increase the membrane viscosity. - Cholesterol on the membrane o Cholesterol is rigid and bulky. Not factoring temperature, cholesterol increases fluidity. o Cholesterol decreases the movement of phospholipids and therefore decreases fluidity at moderate temperatures. It can also o Cholesterol also lowers the temp at which the cell membrane would solidify, therefore increasing fluidity at lower temperatures. Called FLUIDITY BUFFER because it resist changes that temperature may cause. o At High temp cholesterol decreases fluidity. - Fluidity and Permeability are not the same. Fluidity focuses on later diffusion. Permeability is about the ability to get materials through the lipid bilayer. o Lipid bilayer with no Unsaturated fatty acids = low permeability o Lipid Bilayer with High amount of Unsaturated Fatty acids = High Permeability o If something impacts permeability in general it most likely will impact Fluidity.

Proteins can be tethered, keeping proteins in place to extracellular matrix, cytoskeleton, or other cells. GO BACK TO 3 EXPERIMENTS TO SEE HOW THIS COULD CHANGE RESULTS. - Any extreme end of fluidity cannot sustain protein function. Membrane Proteins and Function - Protein determines membrane’s function - 2 Major Membrane Proteins: Integral and Peripheral o Integral Proteins- Penetrate the hydrophobic lipid bilayer. They are TRANSMEMBRANE PROTEINS ONLY IF THEY PENETRATE ALL OF THE LIPID BILAYER. The hydrophobic regions consist of nonpolar amino acids usually 20-30 amino acids in length in coiled up helices. The polar/phillic ends of the protein are exposed to the polar solutions. They also have hydropjillic channels for polar molecules. Other kinds of Integral proteins do not extend through the entire lipid bilayer. o Peripheral Proteins- some bound to cytoskeleton or polar end of integral protein. Easier to dissociate from Integral Proteins. On the extracellular side some are attached to materials outside the cell/ - Function of Membrane Proteins: o Transport o Enzyme activity o Signal Transduction (Something can bind to a protein and relay certain messages) o Cell-Cell recognition (mainly through glycoproteins. o

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o Intercellular Joining o Attachment to Cytoskeleton and Extracellular Fluid (Protein Tehtering)  Membrane Carbohydrates - Cells recognize other cells by bonding to molecules containing carbs or proteins. - Membrane Carbohydrates are short branched chains covalently bonded to lipids (glycolipids) or proteins (glycoproteins).  Synthesis and Sidedness - Arrangement of proteins, carbs, and lipids in the plasma membrane is determined by the Golgi apparatus and the and Endoplasmic reticulum during membrane formation. Cell Fusions Experiment FRAP- FLOURESENCE, RECOVERY, 1. FLOURENCE- Ability to visualize. Purpose: Tracking movement of the membrane 2. Photobleaching- Light removes color. The removal of Fluorescence. Apply the Laser Only once. a. Exp: Can the membrane recover post treatment. GFP  Glows Green and attaches to a membrane protein. GFP is a protein. - The area that we treat is the area that we will measure. 2

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When we Photobleach the sun should go away, therefore we can no longer visualize the Protein. When we bleach these membranes, it is irreversible. If the membrane is fluid, you would expect color to come back, because the proteins of the cell that were not bleach will move into that area of the cell, while the proteins that were not bleached move out. Therefore the area treated will become green again. If the membrane is not fluid, the photobleached area will remain photobleached. o Note this movement is due to lateral diffusion, not movement down a concentration gradient. o Look at the graph provided. Is

it possible for graph to reach peak again? Yes it is possible. Imagine all the proteins with flouresence at one time move into that area, that would result in full recovery. LISTEN TO AUDIO!!

FLIP Experiment- FOCUSED ON LOSS - Instead of finite amount of time we have laser on cell, the laser is left on the cell until experiment is done. - We now will have two regions of the cell that are observed. One treated area, and one measured area. - At the end of our experiment we expect to see no color. - We know that our laser is not moving, so that means the actual proteins are moving. Thus bleached proteins are now moving out of treated area, and new proteins moving in. Notice that we don’t have recovery because we don’t allow the restoration of color. How are these experiments similar, and different? If we denature a protein, it would be reduced to primary structure. By denaturing the protein it’s fluidity etc would be much less efficient and therefore would alter the results such that the conclusion would be incorrect.

Permeabillity, Diffusion, and Osmosis:  Nonpolar molecules do not the aid of membrane proteins to dissolve in the cell membrane.  Glucose can make it’s way through lipid bilayer however, not at a rate sufficient to meet our needs. 3

 H2O can make their way through the bilayer slowly.  Ions can not diffuse across cell membrane.  Ions and Polar molecules are impeded by the lipid bilayer and thus will need transport proteins to pass through the membrane. o Transport Proteins are sometimes called Channel Proteins. They have hydrophilic tunnels for polar molecules to pass through. They’re only specific to specified molecules. o Carrier Proteins change shape to be able to completely wrap around a molecule to shuttle them through the membrane.  Diffusion- the movement of solute particles from higher concentration to a lower concentration through a membrane.  Osmosis is the diffusion of water across a semipermeable membrane. o Tonicity- the ability of surrounding solution to make a cell lose or gain water. o Osmosis and Cells WITHOUT walls  NO net movement in ISOTONIC SOLUTIONS  Cell will lose water in a HYPERTONIC solution.  Cell will gain water in a HYPOTONIC SOLUTION solution  In cells such as Paramencium, contractile vacuoles are used to pump water out as quickly as it comes in o Osmosis and Cells With Walls  Plant cells are happiest in HYPOTONIC solutions. The cell keeps absorbing water until it creates a turgid pressure within the walls great enough to prevent further water intake. The cell will be very firm.  In a HYPERTONIC solution, as water leaves the cell, the membrane begins to separate from the cell wall in various places (PLASMOLYSIS). The plant will wilt leading to cellular death.  In an ISOTONIC Solution, the cells will become flaccid and wilt. Not as much as in a hypertonic solution, but it will nonetheless wilt.  Facilitated Diffusion o Transport proteins helping to diffuse polar molecules into the cell.  Channel Proteins that transport ions are called ion channels and function as gates that respond to specific stimuli

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 Carrier proteins will change their shape to wrap around polar molecule  Osmosis, Diffusion, and Facilitated Diffusion are ALL PASSIVE TRANSPORT

Active Transport  Active transport is done when a solute needs to be pumped across a membrane up it’s concentration gradient.  Only carrier proteins can do active transport.  ATP Hydrolysis is needed. The terminal end of the ATP will be transferred to the protein, making the protein change shape so that it will translocate a a solute bound to the protein. I.E. Sodium-Potassium pump o Na+ in cytoplasm binds to protein  Phosphorylation by ATP is now stimulated  Phosphorylation causes a change in protein shape, the protein can no longer hold 3 Na+ and releases it out into the cell.  the current shape of the protein has high affinity for K+ and now binds to 2 K+  This triggers release of the phosphate group on the extracellular side.  this then changes the shape of that protein to it’s original, causing the release of the 2 K+ into the membrane  Cytoplasmic Na+ are now reattracted to this protein.  How is Membrane Potential maintained: o The inside of a cell is negative in comparison the the extracellular solutions it’s usually placed in there much easier for cations to go in and anions to go out (Chemical force) and an (Electrical force) based on membrane potential.  Membrane Potential- the voltage across a cell membrane. Ranges from -5- to -200 Millivolts (mV)  Therefore Ions move down a electrical chemical gradient. o Proteins that contribute to membrane potential:  Electrogenic Pump.. I.E. Sodium-Potassium Pump in Animal Cells and Proton Pump in Bacteria, Fungi, and Plant cells o In a mechanism called Cotransport- a Cotransporter can couple the downhill diffusion of a solute with the uphill transport of a second substance. I.e. proton Pump in plants,

Bulk transport across Plasma Membrane:  Exocytosis- removal of various molecules by the fusion of vesicles with the plasma membrane 5

 Endocytosis- Cell takes in molecules by creating vesicles from the cellular membrane. There are 3 types: o Phagocytosis – Cellular eating. By extending Psuedopodia, engulfs particles by building A food vacoule around it. o Pinocytosis- Cellular Drinking. Gulps droplets of extracellular fluids into tiny vesicles. o Receptor Mediated Endocytosis- A specialized version of pinocytosis that allows a cell to gather bulk quantities of specific substances that are not very concentrated in the extracellular fluid.  Recognize the symbiotic relationship between endo and exocytosis in the remodeling or rejuvenation of the cell membrane.

CHAPTER 6  The Cell is the simplest form of matter that can be considered a living entity  Microscopy o Magnification- ratio of an object’s image size to it’s real size. o Resolution- a measure of clarity of an object. The minimum distance two points can be separated and still be distinguished as a separate entity. o Contrast- difference between light and dark areas of an image. o Light Microscope- Visible light is being passed through the specimen and then through the glass lense. o Electron Microscopy- Focuses a beam of electrons through a specimen or onto it’s surface. Here resolution is inversely related to the wavelength of the light. Can achieve resolution of about .002nm. o Scanning Electron Microscope- Shows a 3D image of a specimen. Useful for detailed study of Topography. Electron beam scans the surface of the sample usually coated with a thin film of gold, secondary electrons are then detected by a device that turns them into electrical signals on a screen, thus creating a 3-d image. o Transmission Electron Microscope- Used to study the internal structure of cells. Aims an electron beam through a very thin slice of 6

the specimen. Specimens are stained with heavy metal atoms that attach to various cell structures. Also Instead of glass lenses,  The Drawback is that this preparation of cells kills the organism. o Cell Fractation- The process of separating cell structures using a centrifuge(machine that spins test tubes). Lower speeds provide larger components of the cell, faster speeds provide larger components.  This allows researchers to be able to prepare specific cell materials in bulk than and identify their functions. CELLS

Eukaryotic: -DNA located in double membane bound nucleus - Membrane bound organelles - Larger than Prokaryotes

Both: - All bounded by a plasma membrane -Cystosol - Chromosomes - Ribosomes

Prokaryotic: - DNA in non-membrane region called nucleoid - Organelles almost completely absent, instead have regions surrounded by proteins where specific pricesses take place - Smaller than Eukaryotes

 Metabolic requirements provide upper limits on the size of a single cell. o As a cell grows in size it’s surface area grows proportionately less than It’s volume. o Area is proportionate to linear dimension squared, volume is proportionate to linear dimension cubed. o Smaller Objects have greater surface area to volume ratios. 7

THE NUCLEUS (Information Central):  Contains most genes of the Eukaryotic Cell. (Other genes located in Mitochondria and Chloraplasts)  Double Membrane Nuclear Envelope keeps Nucleus separate from cytoplasm.  Protein named the Pore Complex lines each poor, regulating the entry and exit of proteins, RNAs, and other large complexes of RNA.  A netlike array of protein filaments/Nuclear Lamina maintain the shape of the nucleus by providing mechanical support to the envelope. o Nuclear Matrix also may help in the maintenance of these structures.  Chromosomes- Structures that carry genetic information. o Chromosomes are made up of one long DNA molecule and associated proteins. The associated proteins help DNA coil to fit into the Nucleus. o Chromatins are the complex of DNA and Proteins that make up chromosomes.  When the cell is not dividing chromosomes appear as a diffuse mass, they can not be distinguished from one another  During Preperation for division chromsomes condense further, becoming thick enough to be distinguished. o 46 Chromosomes in non-sex Human Cells, 23 in Sex cells o In a non-dividing nucleus there is a structure called the nucleolus.  Here is where Ribosomal RNA is synthesized based on info from DNA  Proteins from the cytoplasm are also assembled with RNA to create large and small subunits of ribosomes. These small and large subunits then exit through a pore where they are assembled into a ribosome. Note that a Ribosome is One small unit joined with one large unit. RIBOSOMES (Protein Factories):  Ribosome- Complexes made of Ribosomal RNAs and Proteins. Ribosomes carry out Protein Synthesis.  Cells that have high rates of protein synthesis have many ribosomes. I.E. Pancreatic cells.

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 TWO TYPES of RIBOSOMES. Bound Ribosomes and Free Ribosomes. They are structurally identical. They can also switch roles at different times. o Bound Ribosomes are located on the ER and Nuclear Envelope. They make Proteins that are destined for insertion to membranes for packaging for those organelles that package such as lysosomes o Free Ribosomes- make proteins and enzymes that primarily function in the cytosol. Endomembrane System:  The Endomembrane system includes: o Nuclear Envelope o Endoplasmic Reticulum (Biosynthetic Factory)- An extensive network of membranes accounting for more than half of the membrane.Two Types:  Smooth E.R.- diverse metabolic processes depending on the cell. Synthesizes lipids, metabolizes carbs, detoxifies drugs and poisons, storage of calcium ions. Sex Hormones (Steroids) are an example of one of the lipids that are synthesized in the Smooth E.R.. To Detoxify most drugs and alcohol hydroxyl groups must be added, these enzymes are created in the smooth E.R..  Rough E.R.- Makes Secretory Proteins, also produces most of membrane for cells. Most secretory proteins are glycoproteins. o Golgi Apparatus(Shipping and Receiving Center)- A warehouse for receiving, sorting, shipping, and even manufacturing. Products of the E.R. Mostly proteins are modified, stored, then sent to other destinations. Also produces a variety of carbohydrates.  Structurally the Golgi Apparatus consists of flattened membranous sacs called CISTERNAE. The cisternae on the Cis Face (Face closest to ER/ Facing the ER), Trans Face on opposite side. The cisternae on different sides differ slightly in molecular makeup and thickness.  Vesicles of molecules from the ER fuse with the membrane on the cis side to provide and those molecules are then processed, when released from the G.A. they bud off from the membrane on the Trans side.

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o Lysosomes (Digestive spheres)- a membranous sac of hydrolytic enzymes to digest macromolecules and perform AUTOTOGRAPHY (Breaking down defective, nonfunctioning matterials in the cell tp be reused and processed into other things). The insides pf these sacs are acidic.  Hydrolytic enzymes and lysosomal membranes are made by the rough E.R., then transferred to Golgi Apparatus for further packaging. Most lysosomes then bud from trans face of G.A.  During Endocytosis the vacuole formed to intake material then fuses it’s outer membrane with the membrane of a lysosome so that materials can be broken down.  Ex: Macrophage WBC. o Vacoules- Large vesicles created from the E.R. and Golgi Apparatus.  The Vacuolar membrane is selective in transporting solutes, and therefore fluid in membrane differs drom cytosol.  Food Vacuole- formed by Phagocytosis  Contractile Vacuole- Found primarily in unicellular Eukaryotes living in fresh water.  Central Vacoule- Found in older plant cells. Coalescence of smaller vacuoles combining creating a repository of inorganic material. Plays a major role in cell growth, as it absorbs water the cell grows. This allows the cell to become larger without investment into cytoplasm.  In plants some vacuoles will serve as a small reserve of various organic materials. o Vesicles o Plasma Membrane ORGANELLES FOR ENERGY  Endosymbiotic Theory- At some point Eukaryotic cells engulfed Mitochondria and Chloroplast Bacteria creating symbiotic relationships with them. o Unlike other organelles, these organelles are wrapped in double membranes. o Both have ribosomes and circular DNA. o They are autonomous organelles, growing and reproducing on their own accord. 10

 Mitochondria- The site of cellular respiration, the process of using oxygen to create ATP by extracting from Sugar, Fats, and other fuels. Found in all Eukaryotic Cells. o Outer membrane is smooth, inner membrane convoluted. With cristae infoldings. Cristae increase surface area thus increasing metabolic activity. Inner Membrane divides Mitochondria into two distinct compatments:  Intermembrane space- the narrow region between inner and outer membrane  Mitochondrial Matrix- contains different enzymes, DNA, and ribosomes. Exact location of Cellular Respiration.  Chloroplast- sites of photosynthesis. Algea and Plant cells. Converting solar energy into chemical energy, creating synthetic sugars, from carbon dioxide and water. o Inside chloroplast is a membranous system of interconnected sacs called Thylakoids. Thlakoids are stacked like poker chips. A stack is called a granum. o Fluid outside of Thykaloid is called Stroma. Stroma contains chloroplasts DNA, ribosomes, and enzymes.  Chloroplasts belong to a group of plant organelles called Plastids.  Amlyoplast- colorless. stores starch(Amylose) in the roots and tubers.  Chromoplast- Pigment gives flowers orange and yellow hues.  Peroxisomes( Oxidation): o Remove Hydrogen from various subtrates and add them to O2 creating Hydrogen Peroxide. o Some use Oxygen to breakdown fatty acids into smaller molecules that are then used in the Mitochondria for cellular respiration. o Peroxisomes in liver detoxify alcohol and drugs. o Glyoxysomes are found un fat storing tissue of plant seeds. They produce their own sugar until plant can do photosynthesis. Cytoskeleton  A network of fibers extending throughout the cytoplasm. These networks provide anchorage, mechanical support to cell, and maintenance of shape.

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 The Cytoskeleton is very dynamic and can be quickly broken apart and reassembled in the cell.  Cell Moti...