LMs can magnify effectively to about 1,000 times the size of the actual specimen. Various techniques enhance contrast and enable cell components to be stained or labeled. Most subcellular structures, or organelles, are too small to be resolved by a LM.
Cell fractionation takes cells apart and separates the major organelles from one another. Ultracentrifuges fractionate cells into their component parts. Cell fractionation enables scientists to determine the functions of organelles. Isolating Organelles by Cell Fractionation. Cell fractionation enables the researcher to prepare specific components of cells in bulk quantity to study their composition and functions. By following this approach, biologists have been able to assign various functions of the cell to the different organelles, a task that would be far more difficult with intact cells. For example, one cellular fraction collected by centrifugation has enzymes that function in the metabolic process known as cellular respiration. The electron microscope reveals this fraction to be very rich in the organelles called mitochondria. This evidence helped cell biologists determine that mitochondria are the sites of cellular respiration. Cytology and biochemistry complement each other in correlating cellular structure and function.
LE 6-2 10 m Human height 1m Length of some nerve and muscle cells Unaided eye 0.1 m Chicken egg 1 cm Frog egg 1 mm Measurements Light microscope 1 centimeter (cm) = 10–2 meter (m) = 0.4 inch 100 µm 1 millimeter (mm) = 10–3 m 1 micrometer (µm) = 10–3 mm = 10–6 m Most plant and 1 nanometer (nm) = 10–3 µm = 10–9 m animal cells 10 µm Nucleus Most bacteria Mitochondrion Electron microscope 1 µm Smallest bacteria 100 nm Viruses Ribosomes 10 nm Proteins Lipids 1 nm Small molecules 0.1 nm Atoms
LE 6-4 Electron Microscopes 1 µm Cilia Used to study subcellular structures Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3D Longitudinal Cross section section of of cilium cilium 1 µm Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen TEMs are used mainly to study the internal ultrastructure of cells
The two types of cells Prokaryotic vs. Eukaryotic CellsNucleus- no yesMembraneBound organelles no yesPlasma membrane yes yesCytosol yes yesChromosomes yes yesRibosomes yes yesDomain Bacteria, Archea protist ,fungi, plant animal
LE 6-6 Pili Nucleoid Ribosomes Plasma membrane Cell wall Bacterial chromosome Capsule 0.5 µm Flagella A typical A thin section through the rod-shaped bacterium Bacillus bacterium coagulans (TEM)
LE 6-7 Surface area increases while Total volume remains constantLarger organisms do not havelarger cells- simple more cells 5 1 1 Total surface area (height x width x 6 150 750 number of sides x number of boxes) Total volume (height x width x length 1 125 125 X number of boxes) Surface-to-volume ratio 6 1.2 6 (surface area ÷ volume)
The boundary of every cell – Plasma membrane Outside of cell Carbohydrate side chain Hydrophilic regionInside of cell 0.1 µm Hydrophobic region Hydrophilic Phospholipid Proteins region TEM of a plasma membrane Structure of the plasma membrane Function - selective barrier that allows sufficient passage of oxygen, nutrients, and waste Structure - double layer of phospholipids
A Panoramic View of the Eukaryotic Cell ENDOPLASMIC RETICULUM (ER Nuclear envelope Flagellum Rough ER Smooth ER Nucleolus NUCLEUS Chromatin In animal cells but not Centrosome Plasma membrane plant cells: Lysosomes CYTOSKELETON Centrioles MicrofilamentsIntermediate filaments Flagella (in Microtubules some plant Ribosomes: sperm) Microvilli Golgi apparatus Peroxisom e Mitochondrion Lysosome
Nuclear A Panoramic View of the Eukaryotic Cell envelope RoughNUCLEUS Nucleolus endoplasmic reticulum Chromatin Smooth Centrosome endoplasmic reticulum Ribosomes (small brown dots) Central vacuole Golgi apparatus Microfilaments Intermediate CYTOSKELETON filaments Microtubules In plant cells but not animal cells: Mitochondrion Chloroplasts Peroxisome Plasma Chloroplast membrane Central vacuole and Cell wall tonoplast Plasmodesmata Wall of adjacent cell Cell wall Plasmodesmata