Chapter 6: tour of the cell
•Microscopes provide a window to the cell.
•Most important tool in cytology
•Resolution has improved understanding of cells.
oResolving power – the smallest distance between two objects that allows them to be seen as distinct objects. oResolving power of the human eye is 0.1 mm
•Light microscope – uses glass lenses and visible light to form a magnified image of an object. oResolving power of about 100 nm (.0002 mm)
oAdvantage: View of cells and organelles
oDisadvantage: Cannot visualize ribosomes
oTypes of light microscopy:
Brightfield microscopy- passes light directly through specimen. Very little contrast (will show natural colors). Brightfield stained specimen- same as above except dyes have stained specimen. WE USE Phase contrast – useful for viewing living cells. Increases contrast of unstained cells. Differential interference contrast- exaggerates contrast making image appear almost 3D. Fluorescence – shows location of specific molecules with the use of fluorescent dyes or antibodies. Confocal – uses lasers and special optics for optical sectioning of fluorescently stained specimens. Clearer Picture than fluorescence. •Electron microscopes –use powerful magnets to focus an electron beam. oElectron micrograph- the image created.
oResolving power of .2 nm
oScanning electron microscope - electrons are directed at the surface of the cells, providing a 3D image. Electrons don’t penetrate. oTransmission electron microscope – allows you to see inside of the cell. Specimen is sliced thin so that electrons can penetrate. •Cell fractionation – rupturing cells, followed by systematic centrifugation to take cells apart, separating out organelles. oCells must be ruptured with care so as to not break the internal membrane bound compartments. Mortar and pestle, glass homogenizer, blender, or place cell in a hypotonic solution so that it pops. oDifferential centrifugation – when cell suspension is placed in a centrifuge to create large forces causing the components of the suspension to pellet at the bottom of the tube. (Burst cell, separates more dense.) oCentrifuge- lab instrument that spins materials at high speeds. View of the Cell
oEvery cell is composed of one or more prokaryotic or eukaryotic cells. oCells come from preexisting cells
oAll cells have certain features in common: plasma membrane, cytosol, chromosomes, and ribosomes. oCells must maintain a surface area –to-volume ratio (SA/V) that is beneficial for metabolic processes to occur. As a cells volume increases, so does surface area. Not to the same extent Volume is related to the amount of chemical activity a cell can undertake. Surface area indicates its ability to exchange nutrients and waste products with the environment. If a cell was larger, its waste production would outwork its ability to deal with that waste. Cells maintain a large SA/V ration by being small in volume The large amount of surface area is important for many biological functions. oProkaryotic and eukaryotic differ in size and complexity
•From Greek meaning pre-nucleus (nucleoid)
•Generally smaller in size
•No membrane bound organelles
•Have cell walls
•Have smaller ribosomes.
•Includes kingdoms eubacteria and archeabacteria
•Generally single celled organisms, often seen in chains, clusters, or colonies. •Some can use light energy to generate needed materials
•Others can generate needed materials from inorganic compounds. •Some are chemoheterotrophs
•Some move with the aid of flagella
•Pilli – used for attachment to substrates or used for conjugation. •Biofilm – conglomeration of bacteria or different species that form a polysaccharide coat so that they are hard to get rid of. Eukaryotic
•Meaning “true nucleus”
oRed blood cells have no nucleus
•Found in plantae, fungi, protista, and animalia
•Have membrane enclosed...