Chapter 6 The Cell 1665 Cell walls were first seen by Robert Hooke o Looked at dead cell walls from the bark of an oak tree o Antoni van Leeuwenhoek made the lenses used to view the cells Light microscope o Visible light is passed through the specimen and then through glass lenses The lenses refract the light so that the image of the specimen is magnified as it is projected into the viewers eye o Up to 1 000x magnification and 0 2 m resolution Magnification Ratio of an object s image size to its real size Resolution Measure of the clarity of the image o Fully developed in the 1870s by German engineers Electron microscopes o Focuses a beam of electrons through the specimen or onto its surface o Up to 1 000 000x magnification and about 1 nm resolution o Invented in 1930 mostly used in the 1950s o Two types of images Scanning electron microscopy SEM Shows surfaces in 3D Transmission electron microscope TEM Profiles a thin section of the internal structures of a specimen in 2D 1 100 m Diameter of most plant and animal cells and most bacteria o Easily viewed with the light microscope Cell Fractionation Takes cells apart and separates major organelles and other subcellular structures from one another o Process is carried out by a centrifuge which spins test tubes at increasing speeds o At each speed the resulting forces causes a subset of the cell components to settle to the bottom of the tube forming a pellet At lower speeds the pellet consists of larger components At higher speeds the pellet consists of smaller components o Allows researchers to prepare specific cell components in bulk and identify their functions which is usually not possible with intact cells Cell Theory All living things are composed of cells and arise by division of o All cells have a lipid bilayer membrane that separates the inside of the cell from the external environment preexisting cells Cells o All cells Bounded by a selective barrier plasma membrane Have a semifluid jellylike substance inside where the subcellular components are found cytoplasm Contain chromosomes which carry genes in the form of DNA Contain ribosomes which are tiny complexes that make and protein proteins o Prokaryotic Most prokaryotic cells are 1 5 m in diameter DNA is concentrated in a region called the nucleoid not membrane enclosed Do not have membrane bounded organelles Bacteria and archea o Eukaryotic Most of the DNA is found in the nucleus which is bounded by a double membrane Plasma membrane Functions as a selective barrier that allows passage of enough oxygen nutrients and wastes to service the entire cell Participate directly in the cell s metabolism because many enzymes are built into the membranes Each type of membrane has a unique composition of lipids and proteins suited to that membrane s specific functions Larger than prokaryotic cells between 10 100 m Cell structure o Cytoskeleton Composed of Microtubules Tubulin protein thickest o Hollow rods constructed from a globular protein called tubulin In animal cells these grow out from a centrosome Involved in the separation of chromosomes during cell division Microfilaments Actin protein thinnest o Thin solid rods build from molecules of actin Intermediate filaments Keratin protein o Only found in the cells of some animals vertebrates Gives mechanical support to the cell and maintain its o Important for animal cells because they lack a Function shape o Nucleus contains most of the genes cell wall Surrounded by nuclear envelope double membrane Chromosomes Structures that carry the genetic information inside the nucleus proteins Contains one long DNA molecule associated with many Chromatin The complex of DNA and proteins that makes up chromosomes Each human cell has 46 chromosomes in its nucleus Nucleolus A mass of densely stained granules and fibers adjoining part of the chromatin Nonmembranous structure involved in the production of ribosomes RNA is synthesized ribosomes are produced Proteins imported from the cytoplasm are assembled with rRNA ribosomal RNA into large and small subunits of ribosomes o Ribosomes Complexes made of ribosomal RNA and protein Carry out protein synthesis Not membrane bounded and not considered organelles Made up of two subunits of ribosomal RNA and proteins Free ribosomes Suspended in the cytoplasm Bound ribosomes Attached to the outside of the endoplasmic reticulum or nuclear envelope Endomembrane system o Function Carries out the synthesis of proteins Transport of proteins into membranes and organelles or out of the cell Metabolism and movement of lipids Detoxification of poisons o Nuclear envelope Encloses the nucleus separating its contents from Double membrane each has a lipid bilayer with associated the cytoplasm proteins Has pore structures Pore complex lines each pore and regulates the entry and exit of proteins and RNA o Endoplasmic reticulum Accounts for more than half the total membrane in eukaryotic Consists of a network of membrane bounded tubules and sacs cells called cisternae Two distinct regions Smooth ER Outer surface lacks ribosomes o Function Synthesis of lipids including sex hormones Metabolism of carbohydrates detoxification of drugs and poisons especially in liver cells Storage of calcium ions Rough ER Studded with ribosomes on the outer surface of the membrane o Function Ribosomes on the rough ER aids in synthesis of secretory and other proteins from bound ribosomes Adds membrane proteins and phospholipids to its own membrane o Golgi apparatus Consists of flattened membranous sacs cisternae Function Modifies and stores proteins made in the ER then sends them to other destinations Vesicles are engaged in the transfer of material between parts of the golgi and other structures Transport vesicles move material from the ER to the Golgi apparatus After leaving the ER proteins inside the transport vesicles travel to the Golgi apparatus from the golgi in transport vesicles the proteins will eventually fuse with the plasma membrane o Lysosomes membranous sac of hydrolytic enzymes that many eukaryotic cells use to digest macromolecules Has a lipid bilayer Function Carry out intracellular digestion Enzymes digest food or defective macromolecules to recycle their components by using phagocytosis Phagocytosis Eating by engulfing smaller organisms using a Lysosomes will merge with the food vacuoles and the enzymes Lysosomes also use their enzymes to recycle the cell s own vacuole digest the food organic material Autophagy A damaged
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