BSC2010 Exam 2 Chapter 6 Cell Theory o All living things are composed of cells o All cells arise by division of preexisting cells o All cells have a lipid bilayer membrane that separates inside of the cell from the external environment Microscopes Probably not important might as well just put it in anyway allows scientists to observe different parts of the cell o Light Microscope Staining Achieves a resolution of about 200nm Studies living organisms o Electron Microscope Invented by Anton Van Leewenhoek and Robert Hooke Focuses a beam of electrons through the specimen or onto its surface Achieves a resolution of 0 002nm Cells have to be dead and cut in half Use electromagnets as lenses to bend the paths of the electrons Scanning Electron Microscope SEM Topography of a specimen Scans surface usually with a thin film of gold Shows surface in 3D Transmission Electron Microscope TEM Focuses on internal structures Shows structures in 2D Bacteria and Archaea DNA is concentrated in a region called the nucleoid Not membrane enclosed Fimbriae Pili attachment structures on the surface of some prokaryotes Capsule jellylike outer coating used for protection Lacks membrane enclosed internal structures and the structures Cells o Prokaryotic themselves Sizes range between 1 and 5 m o Eukaryotic Membrane bound organelles Sizes range between 10 and 100 m Contain a nucleus o Both Selectively permeable plasma membrane Contain cytoplasm Chromosome contains DNA Ribosomes protein synthesis Smooth ER Rough ER o Synthesizes lipids and calcium o Make membrane proteins and proteins to be secreted Some have flagella which is used for locomotion LOOK AT ALL THE FUNCTIONS FROM THE IMAGE BELOW o Mitochondria and Chloroplasts Both appeared in the cell through endosymbiosis Prokaryote mit or chlor living in eukaryote Evidence o Contain their own DNA and make some of their own proteins o Chloroplast DNA is similar to that of certain bacteria Chloroplasts Photosynthesis Granum o Stack of thylakoids Double lipid membrane Mitochondria Cellular respiration Cristae o Spaces within the folds Chapter 7 Plasma membrane o Phospholipid bilayer Amphipathic Hydrophilic head Hydrophobic tail o Fluid mosaic model The membrane is a mosaic of protein molecules drifting laterally in the phospholipid bilayer EX Partygoers elbowing their way in a crowded room Cholesterol Fluidity Buffer Wedged between phospholipids Helps maintain membrane fluidity during fluctuating temperatures o Restrains phospholipid movement in high temperatures o Hinders close packing in low temperatures o Membrane Proteins Integral protein Penetrate the hydrophobic interior of the lipid bilayer Majority are transmembrane proteins o span the membrane Hydrophobic regions consist of one or more stretches of nonpolar amino acids usually coiled in helices Hydrophilic parts are exposed to the aqueous solutions on both sides of the layer Transport o Some have one or more protein channels that allow passage through the membrane of hydrophilic substances o Others move a substance from one side of the bilayer to the other by changing shape Enzymatic activity adjacent solution Signal transduction o An enzyme with its active site exposed to substances in the o Receptor may have a binding site with a specific shape that fit the shape of a chemical messenger o Signaling molecule may cause the protein to change shape which allows it to relay the message to the inside of the cell Cell cell recognition o Some glycoproteins serve as identification tags that are specifically recognized by membrane proteins of other cells Intercellular joining o Membrane proteins may hook together on various kinds of junctions i e gap junctions or tight junctions o Longer lasting than cell cell recognition Attachment to the cytoskeleton and extracellular matrix o Microfilaments or other elements of the cytoskeleton noncovalently bind to membrane proteins Helps maintain cell shape and stabilizes the location of certain membrane proteins Appendages loosely bound to the surface of the membrane Peripheral protein o Selective permeability Decides which molecules can enter and leave the cell Nonpolar hydrophobic molecules can dissolve in the lipid bilayer and cross it easily without aid of membrane proteins O2 and CO2 Ions and polar molecules are hydrophilic and therefore are blocked from direct passage into the plasma membrane they move slowly Membrane proteins play key roles in regulating transport Passive Transport o Doesn t require energy o Diffusion simple The movement of particles of any substance that spread out into available Moves from an area with high concentration to an area with low space concentration Concentration gradient increases or decreases Osmosis The region along which the density of a chemical substance The diffusion of free water across a selectively permeable membrane Moves from an area with low concentration to an area with high concentration Hypotonic Isotonic Hypertonic o More concentration inside the cell o Animal cell the cell lyses or bursts o Plant cell cell swells and becomes turgid stiff but normal o No net movement of water across the cell membrane o Animal cell normal o Plant cell flaccid o More concentration outside of the cell o Animal cell shrivels o Plant cell shrivels plasmolyzed causes wilting or death o Diffusion facilitated The passage of molecules or ions down their electrochemical gradient Hydrophilic substances diffuse through membranes with assistance from across a membrane transport proteins Assisted by specific transmembrane transport proteins Requires no energy Channel proteins provide a pore for molecules to move through Carrier proteins flip flop substances across o Active transport The movement of a substance across a membrane against its gradient Requires energy Allows a cell to maintain internal concentrations of small solutes that differ from the extracellular environment Sodium potassium pump Electrogenic pump o Transport protein that generates voltage across a membrane ATP supplies energy for pump to change shape after transporting 3 sodium ions for 2 potassium ions to come in The removal of the phosphate group allows the pump to return to its original shape generates a negative membrane potential and Na and K gradients which can be used to drive the uptake of other solutes Membrane potential The voltage across a membrane Electrochemical gradient Ranges from about 50 to 200 mV inside is negative relative to outside Favors passive transport
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