Week 2 Notes
Week 2 Notes Life Sciences 2
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This 6 page Class Notes was uploaded by Jenna Kovsky on Friday October 16, 2015. The Class Notes belongs to Life Sciences 2 at University of California - Los Angeles taught by Dr. Cooper/Dr. Esdin in Fall 2015. Since its upload, it has received 25 views. For similar materials see Cells, Tissues, and Organs in Biology at University of California - Los Angeles.
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Date Created: 10/16/15
10515 Lecture 4 Cell Structure II 0 Looking at cells 0 Light microscope o Stainedbright o fluorescence o confocal look at one field in the plane of view gives good picture 0 Survival of cells is dependent on o obtaining and processing energy 0 converting genetic info into protein 0 allowing biochemical reactions to occur 0 Organization of cells 0 Prokaryotes lack a nucleus I DNA coiled into nucleoid region no membrane around nucleoid region so DNA in direct contact w cytoplasm Eubacteria and Archaebacteria have plasma membrane cytoplasm ribosomes flagellum and cell wall some have specialized features cell wall containing peptidoglycan in bacteria outer membrane may enclose cell wall capsule around cell wall and membrane some bacteria cyanobacteria can do photosynthesis our present atmosphere is thought to have arisen bc of these we have an aerobic environment some use flagella to swim flagella are made of flagellin pili involved in mating project from the surface of some bacteria o Eukaryotes I all plants animals fungi and protists eg algae I generally much larger than prokaryotic I features 0 plasma membrane cytoplasm and ribosomes 0 have internal cytoskeleton to maintain cell shape and move materials 0 membranous compartments membraneenclosed organelles 0 plants have a cell wall mainly made of cellulose I thought to have arisen from prokaryotes by endosymbiosis endoinside symbiosisiving together 0 microtubules with actin give cells more stability microtubules allowed flagellum to form developed peroxisomes engulfed bacteria which gave rise to mitochondria similarly cells that engulfed cyanobacteria which gave rise to chloroplasts TODAY S LECTURE 0 Human Genome Project 0 most cells in body except sperm and eggs have 23 pairs of chromosomes 0 appearance of the 23 pairs is called a karyotype o Nucleus 0 largest organelle has Mof the cell s DNA 0 enclosed by nuclear envelope 2 membranes perforated by nuclear pores I envelope is phospholipid bilayer DNA combined with protein to form chromatin when nucleus is about to divide chromatin condense and could tightly forming chromosomes each chromosome colored body contains one long molecule of DNA with many genes I chromosomes form just prior to division I x shape means chromosome has already been replicated so the x is made of two sister chromatids I sister chromatids separate for form chromosomes 0 mitotic spindle microtubules from opposite poles attach to each sister at the kinetochorecentromere and pull the sisters apart I made when chromatin is wrapped tightly around proteins called histones o mature erythrocytes Red Blood CellsRBC do not have a nucleus they are full of hemoglobin and have a lifespan of 120 days so they don t really need a nucleus and it takes up too much space they do have them when they are developing 0 contains nucleolus may be more than one where genetic material is concentrated site of ribosome assembly 0 nucleoplasm fluid material within the nuclear envelop 0 nuclear lamina is a network of proteins lamins which maintains the shape of the nucleus 0 Ribosomes 0 all cells synthesize proteins on ribosomes o in eukaryotes I free in cytoplasm I attached to surface of Rough Endoplasmic Reticulum I in energyproducing organelles mitochondrial matrix chloroplast stroma o consist of a type of RNA together with protein comprising a large and small subunit which associate during protein synthesis 0 an enzyme ribozyme actually makes the peptide bonds during protein synthesis 0 Endomembrane system 0 a series of interrelated membranes and compartments in eukaryotes 0 made up of Endoplasmic Reticulum and Golgi Apparatus I Endoplasmic Reticulum o extensive system of folded membranes forming sacs and tubes 0 cells which synthesize proteins for export contain large amounts of ER 0 smooth ER lacks ribosomes 0 site for hydrolysis of glycogen 0 synthesis of steroids 0 Rough ER contains attached ribosomes o manufactures proteins for export from cell incorporation into membranes or moved into organelles to the endomembrane system 0 site for addition of short sugar chains to proteins glycoproteins o Insulin hormone protein 0 important in blood glucose homeostasis o destined to be exported from the cell 0 made in pancreatic beta cells I Golgi apparatus 0 looks like a stack of pancakes o modifies packages and sorts proteins 0 series of flattened sacs cis region lies closest to nucleus trans region closer to cell surface o synthesizes some polysaccharides for the cell wall 0 Role of Slgnal Sequences in Directing Proteins to Various Organelles 0 signal sequences in proteins direct them to their cellular destination eg to the nucleus mitochondria o a specific hydrophobic sequence of approx 25 amino acids at the beginning of a polypeptide chain directs it to the ER which will get it across the cell membrane only the signal sequence is encoded in the cytoplasm then translation stops hydrophobic signal sequence threads through the rough ER and translation continues so insulin or other protein ends up inside the Rough ER from which it is moved to the Golgi Apparatus for export 10715 Lecture 5 Cells cont amp Membrane Structure 0 secretory vesicles stored in pancreatic beta cells until they are needed to carry insulin their release is triggered by increased blood glucose hyperglycemia o lnsulinbinds to certain cell types to promote the intake of glucose into those cells effectively lowering blood glucose 0 Mitochondria powerhouse of the cell O o converts energy from food into ATP adenosine triphosphate the energy currency of the cell 0 small similar in size to many bacteria 0 consist of inner and outer membranegtinner membrane highly folded forming cristae o mitochondrial matrix contains ribosomes and DNA 0 almost all eukaryotes contain mitochondria except those living in environments without oxygen 0 more mitochondria are present if cells are very active eg heart muscle 0 need electron microscope to view 0 respiratory chain for converting O2 and glucose into ATP spans the inner mitochondrial membrane cristae increase the surface area of this membrane leaving more room for ATP synthesis 0 certain proteins are made in mitochondria using mitochondrial DNA 0 Plastids 0 present in plants and some protist serves for food manufacture or storage eg chloroplasts carry out photosynthesis like mitochondria is surrounded by 2 membranes both unfolded inner membrane forms a stack of flattened disklike things thylakoids are inside and contain chlorophyll which harvests light energy granum stacks of thylakoids o stroma fluid surrounding granums o Endosymbiotic Theory 0 a long time ago 0 a larger cell absorbed smaller 0 explains how organelles mitochondria and chloroplasts have two membranes and their own DNA 0 Organelles for Breakdown and Storage 0 lysosomes suicide bags pinch off from the membrane of the Golgi apparatus break down almost any organic substance interior is very acidic pH 55 which is optimal for the following enzymes none in plants I proteases break down proteins I lipases break down lipids OOOOO I nucleases break down nucleic acids I carbohydratedigesting enzymes I Tay Sachs Disease 0 person is unable to break down gangliosides type of lipid 0 these gangliosides build up especially in neurons 0 age 6 monthsgtblind deaf unable to swallow 0 age 45 yearsgtdeath I autophagy breaking down worn out old organelles performed by lysosomes o peroxisomes in plants and animals one membrane RH2OZgtR H202 hydrogen peroxide involved in breaking down lipids o glyoxysomes in plants specialized peroxisomes break down lipids particularly during cell germination o vacuoles present in plant cells store waste products and provide turgor water in the cell provides pressure to keep it rigid perform a similar role to lysosomes which plants do not have 0 Organelles for Support and Movement 0 cytoskeleton maintains cell shape facilitates cell movement some fibers act as tracks for motor proteins I components 0 microfilaments strands of actin39 involved in movement during cell division to divide nucleus and the cytoplasm during cytokinesis and muscle contraction smallest diameter of the cytoskeleton components also used for support 0 intermediate filaments tough fibrous protein molecules twisted into ropelike structures stabilize cell structure keratin in hair and nails 0 microtubules hollow cylinders made of tubulin involved in structure and function of cilia and flagella centrioles and movement of organelles larger diameter than microfilaments or intermediate filaments form mitotic spindle during cell division 0 cilia made of 9 microtubules wavelike motion back and forth caused by movement of dynein along microtubules 0 motor proteins eg dynein and kinesin use energy from ATP to change their shape and move things use microtubules to move things around the cell have feet to walk around microtubule tend to go towards negative end of the microtubule I kinesin can move vesicles or organelles around the cell 0 cell wall 0 Differences between plant and animal cells 0 no cell wall in animal cells but is in plants chloroplasts absent in animal cells vacuoles absent or small in animal cells some animal cells have flagella usually absent in plants centrioles absent in plant cells 0000 10915 Lecture 6 Cell Membra 0 Role of lipids in membrane structure 0 basic foundation is lipid bilayer o phospholipids are the main structural components 0 phospholipids spontaneously form bilayer sheets in which the hydrophobic tails point inward o lipid bilayer is fluid I fluidity of a bilayer depends on its composition and temperature I as temperature falls lipid bilayer changes from a fluid state to a rigid gel state undergoes phase transition at a characteristic temperature I temp at which this occurs is lower ie membrane more difficult to freeze if hydrocarbon chains are short or have double bonds 0 cholesterol intercalates slip in between phospholipid bilayer and provides stability 0 Fluid Mosaic Model 0 lipid bilayer provides membrane integrity 0 fluid mosaic model explains how proteins are incorporated into the bilayer o carbohydrates are attached to either proteins or lipids facing outwards from the cell c Membrane proteins 0 categories I integral penetrate into the bilayer 0 most are transmembrane contain an alpha helix of nonpolar amino acids spanning the hydrophobic interior of the membrane I peripheral located outside of the bilayer attached by noncovalent bonds to the polar headgroups of the phospholipids or to integral proteins 0 mobility of proteins in membranes I some move freely within the bilayer while others are held in place I many cells eg RBC have a cytoskeletal protein network 0 RBCs are good work with in membrane research bc of the ease of obtaining them and o if you lyse break open and centrifuge them only plasma membrane is present I beneath the cytoplasmic surface of the RBC spectrin forms a mesh I spectrin is attached to membrane junctional complexes by actin and to ankyrin peripheral protein which in turn is attached to an anion channel integral protein I role of membrane proteins 0 transport proteins 0 receptors for molecular messengers from other cells 0 responds to signal transmitted via some kind of ligand eg a hormone for example insulin binds to receptor membrane protein which causes the cell to increase intake of glucose 0 form junctions between cells 0 Membrane carbohydrates 0 project from exterior surface of the membrane when attached to proteins of phospholipids within the membrane serve as recognition sites on the cell surface most carbohydrates in membranes ar bound to proteins forming glycoproteins I bound carbs are oligosaccharide chains I enable cells to recognize foreign substances 0 glycolipids form cell identity markers 0 Cell adhesion o in an organism or tissue cells recognize and bind to each other via surface membrane proteins 0 in animal cells specific cell junctions allow cells to adhere to each other I tight junctions o epithelial cells form sheets of tightly packed cells that form boundaries 0 these sheets of cells are held together by tightjunction proteins 0 tightjunctions prevent molecules from slipping between cells protective mechanism I desmosomes like spot welds cytoplasmic plaque on inside of each cell with adhesion proteins running between each cell s plaque could be attached to cytoskeletal proteins providing extra support I gapjunc ons particular protein that has 6 subunits creates a small pore in each cell connexons line up between the two cells aqueous pore between two adjacent cells very important in the heart allow ions to move between cells and facilitate the spread of action potentials from cell to cell causing the heart muscles to contract 0 in plantsgtaqueous pore plasmodesmata o extracellular matrix 0 contains the protein collagen most prevalent protein in the human body 0 also the protein fibronectin connects to integrin in a noncovalent bond which in turn is connected to actin which is within the cell 0 integrin anchors the extracellular matrix to the cell s internal cytoskeleton o and polysaccharide complex protein proteoglycan 0 Movement of Molecules across cell membranes 0 4 main methods I diffusion simplest method passive for molecules that are lipidsoluble or a gas random molecular motion produces net migration of molecules toward regions of lower concentration when molecules are uniformly distributed they are in equilibrium small nonpolar molecules can diffuse higher lipid solubilitygtdiffuse faster O2 and 002 can readily diffuse across biological membranes osmosis diffusion of water molecules I ion channel passive uses channel protein aqueous pore in membrane through which something can move I carriermediated mechanismtransporter passive allows polar molecule to shovel through then releases it on the other side I active transport uses energy bc molecules going against concentration gradient