Transcript Chapter 7
Chapter 7 Cell Structure and Function Robert Hooke • 1665 constructed a simple microscope • Observed a piece of cork • Saw small boxlike structures he called cells. What is a Cell? • Basic structural and functional unit of all living organisms Other Important Discoveries • 1683 – Anton van Leewenhoehook discovers single-celled animal-like organisms • 1838 – Matthias Scheliden observes that all plant tissues are composed of cells • 1839 – Theodor Schwann observes that all animal tissues consist of individual cells • 1855 – Virchow proposes that all cells are produced by the division of existing cells Cell Theory • Includes 3 parts – All living organisms are composed of 1 or more cells – Cells are basic unit of structure and organization of all living things – Cells arise from previously existing cells and pass on genetic material Prokaryotes • Cells lacking internal membrane-bound structures • Unicellular • Ex: bacteria Eukaryotes • Cells containing membrane-bound structures • Mostly multicellular with some exceptions such as algae and yeast • Ex: plants and animals Comparing the two types of cells • Eukaryotic – separation of organelles into distinct compartments – has a true nucleus – different chemical reactions can be carried out at the same time in the different organelles • Prokaryotic – Metabolic functions take place in the cytoplasm – does not have true nucleus Section 2 – Eukaryotic Cell Structure • Membrane bound structures within eukaryotic cells are called organelles • Each has a specific function for cell survival Cytoplasm & Cytoskeleton • Cytoplasm - Semi fluid material inside the plasma membrane • Cytoskeleton - Long thin, protein fibers that form the framework of the cell – Anchors organelles in the cell and aids in cell movement Nucleus • Cell’s managing structure • Contains the cells DNA Ribosomes • Help manufacture proteins • Made of RNA and Protein • Not bound by a membrane Nucleolus • Found inside the nucleus • Site of ribosome production Endoplasmic Reticulum • Highly folded membrane that is the site of protein synthesis • 2 types – Rough – Smooth Golgi Bodies • Flattened stack of tubular membranes that modifies and packages proteins for distribution outside of the cell Vacuoles & Lysosomes • Vacuoles – membrane bound vesicle for temporary storage of materials • Lysosomes – vesicles that contain digestive enzymes for the breakdown of worn-out cellular structure Mitochondia • Membrane bound • Makes energy available to the rest of the cell • “power house” Centrioles • Found in pairs and help with cell division • Made of microtubules Chloroplasts • Contain chlorophyll • Site where photosynthesis takes place • Only found in plants Cell Wall • Inflexible barrier • Provides support and protection • Only in plant cells Cilia & Flagella • Cilia – hair like projections – Aid in locomotion and sweeping things along surfaces • Flagella – whip like projections – Aid in locomotion and feeding Section 3 – Cell Boundaries Plasma Membrane Plasma Membrane • Responsible for maintaining homeostasis • Thin, flexible boundary around a cell • Regulates what enters and exits the cell • Present in all prokaryotic and eukaryotic cells Selective Permeability • Allows some substances to pass though the plasma membrane while keeping others out • Ex: Fish Net Structure • Made of 2 layers of phospholipids called a phospholipid bilayer. • The heads are hydrophilic – Water loving • The tails are hydrophobic – Water hating Sunstances found in PM • Receptor Proteins – found on outer surface. Transmits signals to the cell • Transport Proteins – found within the cell and move substances in and out of the cell • Cholesterol – placed in the tails to keep the layers from sticking together • Carbohydrates – placed within the heads and help identify chemical signals. Fluid Mosaic Model • Fluids consist of particles that can change position without separating • A mosaic is a pattern made of small pieces of different colors and shapes • Bilayer can move sideways within the membrane Diffusion • Substances dissolved in water move constantly in random motion called Brownian motion • This random motion causes diffusion, which is the net movement of particles from an area where there are many particles of the substance to an area where there are fewer particles of the substance • Amount of a substance in a particular area is called concentration Diffusion • Substances diffuse from areas of high concentration to low concentration • Additional energy input is not required for diffusion because the particles are already in motion • One of the key characteristics of diffusion is the rate at which diffusion takes place Diffusion • Factors that affect the rate of diffusion: – concentration – temperature – pressure http://www.phschool.com/webcodes10/index.cfm?wcprefix=cbp&wcsuffi x=3073&fuseaction=home.gotoWebCode&x=11&y=15 Facilitated Diffusion • No additional energy is needed and is also called passive transport • Transport proteins are used to move ions and small molecules across the plasma membrane – Channel Protein : opens and closes to allow the substances to diffuse through the plasma membrane – Carrier Protein : change shape as the diffusion process continues to help move the particle through the membrane – http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html Osmosis • The diffusion of water across a selectively permeable membrane • Water molecule diffuse toward the side with the greater concentration of solute • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html Isotonic Solution • Concentration of solute of the inside and the outside of the cell are equal • Water enters and leaves at the same rate • Cell is at equilibrium with the solution and there is no net movement of water Hypotonic Solution • Concentration of solute outside of the cell is lower than the inside of the cell • Water moves into the cell • Cell swells and may burst Hypertonic Solution • The concentration of the solute outside of the cell is higher than the inside • Water moves out of the cell • Cell shrinks Active Transport • Movement from an area of low concentration to an area of high concentration • Movement of substances across the membrane against a concentration gradient and requires energy • Helps maintain homeostasis • Example – Na+/K+ ATPase pump Na+/K+ ATPase pump • Found in the plasma membrane of animal cells • This protein pump is an enzyme that catalyzes the breakdown of an energy-storing molecule • The pump uses the energy in order to transport sodium ions out of the cell while moving 2 potassium ions into the cell • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html Transport of Large Particles • Endocytosis – the process by which a cell surrounds a substance in the outside environment, enclosing the substance in a portion of the plasma membrane • Exocytosis - the secretion of materials at the plasma membrane. Used to expel wastes and to secrete substance such as hormones • Both processes require the input of energy • http://highered.mcgraw-hill.com/olc/dl/120068/bio02.swf