Chapter 6 Notes I HOW WE STUDY CELLS A Microscopes 1 Resolution vs Magnification a magnification making an object look larger relative to its real size b resolution minimum distance you can distinguish between 2 points image sharpness you can make out chloroplasts and mitochondria in light microscopes because they are ancient bacteria and contain circular DNA like bacteria 2 Types a light microscope visible light is passed through the specimen and then through glass lenses the lenses refract bend the light in such a way that the image of the specimen is magnified as it is projected into the eye or into a camera can magnify effectively to about 1 000 times the actual size of the specimen can t resolve detail finer than about 0 2 micrometers um or 200 nanometers nm Magnification is the ratio of an object s image size to its real size Resolution is a measure of the clarity of the image it is the minimum distance two points can be separated and still be distinguished as two points i objective lens ii ocular lens iii condenser lens focuses light on the specimen iv resolution 0 2 um bacteria nucleus what other organelles b electron microscope focuses a beam of electrons through the specimen or ratio surface usually can t resolve structures smaller than about 2nm across resolves just short of the atomic level can see cell ultrastructure small organelles B Isolation of organelles permit studying their function Cell fractionation takes cells apart and separates major organelles from other subcellular structures from one another isolates cell components based on size and density useful technique for studying cell structure and function Cell fractionation enables researchers to prepare specific cell components in bulk and identify their functions a task not usually possible with intact cells II PRINCIPLES OF CELL SIZE AND COMPLEXITY A Size Constraints 1 Lower limit At the lower limit the smallest cells known are bacteria called mycoplasmas which have diameters between 0 1 and 1 0 um These are perhaps the smallest packages with enough DNA to program metabolism and enough enzymes and other cellular equipment to carry out the activities necessary for a cell to sustain itself and reproduce a DNA cell must have sufficient amount to encode all structures necessary for life b Essential hardware cell must have minimum number of structures necessary to execute life processes 2 Upper limit if a cell gets too big the surface to volume ration is too small Metabolic requirements also impose theoretical upper limits on the size that is practical for a single cell At the boundary of every cell the plasma membrane functions as a selective barrier that allows passage of enough oxygen nutrients and wasters to service the entire cell For each square micrometer of membrane only a limited amount of particular substance can cross per second so the ratio of surface area to volume is critical As a cell increases in size its volume grows proportionately more than its surface area A smaller object has a greater ratio of surface are to volume Larger organisms do not generally have larger cells than smaller organisms they simply have more cells A sufficiently high ratio of surface area to volume is especially important in cells that exchange a lot of material with their surroundings such as intestinal cells Such cells may have many long thin projections from their surface called microvilli which increase surface area without an appreciable increase in volume Restricted by surface area SA volume ratio The SA of the plasma membrane must have a large enough exchange capacity for O2 nutrients and wastes to support the size of the cell Surface volume relationship surface area increases while total volume stays constant B Membrane compartmentalization enables increased size and complexity of eukaryotic cells distinguishes prokaryotic and eukaryotic cells 1 folding increases surface area SA 2 partitioning incompatible reactions a provides tailored local environments for specific metabolic processes b segregates incompatible reactions in the cell c provides surface for enzyme implantation Eukaryotic cells have more compartments so it can do more specialized things O2 reactions are incompatible to things in the nucleus Bacterium cells only have one compartment so it can only do things that are compatible with each other because everything is in contact with each other III PROKARYOTIC CELL STRUCTURE 1 cell wall protection 2 plasma membrane selective barrier 3 cytoplasm DNA confined to nucleoid region 4 ribosomes protein synthesis 5 flagella propeller like locomotion 6 pillus hair like structure for attachment to surfaces or other organisms IV EUKAYOTIC CELL STRUCTURE A Nucleus 1 DNA chromosomes genetic information 2 Nucleolus ribosome assembly B Cytoplasm 1 Cytosol water portion 2 Organelles involved in production a Ribosomes i free synthesize cytosolic proteins ii bound to RER synthesize proteins requiring modification to permit inclusion in membranes or exported as extracellular matrix ECM b Endoplasmic Reticulum Smooth SER i lipid steroid synthesis ii detoxifying enzymes to destroy drugs and poisons Rough RER i ribosome studded ii synthesize proteins that will be inserted into a membrane or secreted from the cell c Golgi apparatus i sorts adds finishing touches to proteins then ships them ii vesicles transport proteins between various membrane structures by melting into one membrane and budding from next membrane iii proteins mature as they cross the Golgi 3 Organelles involved in breakdown a Lysosomes have acidic environment and collection of hydrolytic enzymes that digest macromolecules i phagocytize bacteria ii breakdown and recycle decrepit cell machinery b Peroxisome breaks down toxic peroxides which are natural waste by products of chemical reactions eg H 2O2 4 Organelles involved in energy processing a Mitochondria i generate cellular energy ATP consuming O2 in the process ii contain unique prokaryotic ribosomes and DNA distinct from the cell s cytosolic ribosomes b Chloroplasts plants only i photosynthesis utilize light energy CO2 H2O glucose ii contain unique prokaryotic ribosomes DNA distinct from the cell s cytosolic ribosomes 5 Plasma membrane 6 ECM extracellular matrix i locally secreted meshwork ii provides anchorage support involved in cell cell communication 7 Cytoskeleton Supports the cell and is involved in cell and organelle movement Consists of microtubules microfilaments and intermediate filaments all