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Transcript
Chapter 3: Cells Cell Theory • Term “cell” was coined in 1665 by Robert Hooke when he looked at a slice of dried cork. He also observed that: 1. All living things are comprised of cells. 2. Cells are the smallest “living” unit in an organisms. 3. Cells come from previously existing cells. Other points: Cells of all living things carry on similar chemical activities. All cells carry on their metabolic activities in organelles There are two types of cells: 1. Prokaryotic- cells that DO NOT have a nucleus or other cell ORGANELLES 2. Eukaryotic- cells with a NUCLEUS & cell ORGANELLES • Which is more complicated? • REMEMBER YOU ARE EUKARYOTIC! Cell Diversity • Lots of shapes and sizes Typical Cell Cell Organization Cell Organization • The cell includes two basic parts: 1. Cell Membrane (outer covering of cell) 2. Cytoplasm • Cytosol (fluid portion of the cytoplasm) • Organelles (cell “organs” or functional parts) Cell (Plasma) Membrane • Cell Membrane Video – Cell Membrane by Bozeman Science • http://www.youtube.com/watch?v=S7CJ7xZOjm0 – Identify 3 key characteristics of the plasma membrane (13, 14, 15) Cell (Plasma) Membrane • Outer boundary • Comprised of two layers of lipids/fat – Phospholipid bilayer (Outer and inner layers) – Hydrophilic- attracts water – Hydrophobic- repels water Forming a bilayer satisfies the water preferences of both the “heads” and “tails” of phospholipids: the hydrophilic heads face the watery regions inside and outside the cell, and the hydrophobic tails face each other in a water-free junction. The bilayer forms spontaneously because this situation is so favorable. Cell (Plasma) Membrane • The cell membrane is SEMI-PERMEABLE – selectively regulates the flow of materials to and from the cell--thus maintaining chemical homeostasis within the cell – The membrane acts like a BOUNCER only allowing certain things in and out of the cell Cell (Plasma) Membrane: Globular Proteins • Contain globular proteins – Proteins give the cell its unique “personality” or function – transport through the plasma membrane likely occurs through these globular proteins (Fluid mosaic model) – According to the fluid-mosaic model of the cell membrane, special proteins called membrane proteins float in the phospholipid bilayer like icebergs in a sea. – The sea of phospholipid molecules and gatekeeper membrane proteins is in constant motion. The membrane’s fluidity keeps the cell from fracturing when placed under strain. Cell (Plasma) Membrane: Globular Proteins • Proteins embedded in membrane serve different functions 1. Channel Proteins - form small openings for molecules to diffuse through 2. Carrier Proteins- binding site on protein surface "grabs" certain molecules and pulls them into the cell 3. Receptor Proteins - molecular triggers that set off cell responses (such as release of hormones or opening of channel proteins) 4. Cell Recognition Proteins - ID tags, to identify cells to the body's immune system 5. Enzymatic Proteins - carry out metabolic reactions Cell (Plasma) Membrane: Globular Proteins Cell Membrane Cell (Plasma) Membrane: Junctions • plasma membranes of adjacent cells are pressed together. Four kinds of junctions occur – tight junctions – impermeable junctions that bind cells together into leak proof sheets that prevent substances from passing through the extracellular space between cells (prevent digestive enzymes from seeping into blood stream) – desmosomes– anchoring junctions that prevent cells subjected to mechanical stress from being pulled apart (skin cells) Cell (Plasma) Membrane: Junctions – gap junctions – allows communications to pass directly through gaps (hollow cylinders) from one cell to another (heart and embryonic cells) – adheren junctions -provides strong mechanical attachments between adjacent cells, holds cardiac muscle cells tightly together as the heart expands and contracts, holds epithelial cells together Cell Organization Cytoplasm • fluid like material between the cell membrane and the nucleus • over 80% water • “HOLDS” cell organelles in place • site of most organelles and cellular chemical reactions • Is comprised of: 1. Cytosol - fluid portion of the cytoplasm 2. Organelles - cell “organs” or functional parts Cytosol • Intracellular fluid • Contains inclusions - nonliving components of the cell that do not possess metabolic activity, may or may not be present, nonfunctioning, are commonly stored nutrients or cell products (glycogen granules, fat droplets, skin pigmentmelanin) Organelles • little “organs” of the cell • Carry out cellular functions! • Cell Organelle Video – A Tour of the Cell by Bozeman Science • http://www.youtube.com/watch?v=1Z9pqST72is Organelle: Nucleus • Control center of cell • Contains DNA/chromosomes – Chromatin -scattered through the nucleus, eventually form rod-like bodies-chromosomes when cell divides • self duplicating structure -divides when the cell divides • Genes control the synthesis of proteins in each cell. • Red blood cells don’t have a nucleus. • Skeletal muscle cells have multiple nuclei. Nucleus Nuclear membrane (envelope) • surrounds nucleus allowing certain materials to enter and leave (Semipermeable) Organelle: Nucleolus • round organelle in the nucleus • involved with the synthesis of RNA in the ribosomes Organelle: Cytoskeleton • Cytoskeleton –cell’s “bones and muscles”, internal framework that determines shape, supports other organelles and provides for intracellular transport and various cellular movements. Cytoskeleton • Made up of three elements, from largest to smallest elements – microtubules – determine overall shape and distribution of organelles – intermediate filaments – help form desmosomes and aids in resisting pulling forces on the cell – microfilaments – (such as actin and myosin) involved in cell motility and producing changes in cell shape Cytoskeleton Cytoskeleton The following are two fluorescence images of cells stained to show the cytoskeleton http://www.microscopyu.com/small world/gallery/index.html Organelle: Endoplasmic Reticulum (ER) • A network of membrane-bound tunnels throughout the cytoplasm - cytoplasmic channels from the cell membrane to the nuclear membrane • associated with the storage, synthesis, and transport of materials within the cell • “HIGHWAY” for cell transport Endoplasmic Reticulum (ER) • There are two forms of ER – Rough ER – the “membrane factory” studded with ribosomes, essentially all building materials of cellular membranes are formed either in it or on it – Smooth ER – plays no role in protein synthesis, functions in cholesterol synthesis and breakdown, fat metabolism and detoxification of drugs ER Rough ER Smooth ER ER Organelle: Ribosomes • sites of protein synthesis in the cytoplasm • may be free in the cytoplasm or attached to the endoplasmic reticulum Organelle: Golgi Apparatus (Body) • usually located near the nucleus • synthesizes, packages, and secretes cellular products • Packages waste & harmful materials Golgi Apparatus Organelle: Mitochondria • Bean shaped • Outer and inner membranes - Inner membrane folded into cristae • “Powerhouse of the cell" • Carries on cellular respiration - contains respiratory enzymes that make ATP – Adenosine triphosphate (ATP) produced on cristae. – ATP is high energy compound. (energy molecule) – ATP only produced in mitochondria. • Found in greater #s in active cells Mitochondria Organelle: Centriole • Centriole- a cylindrical structure found in the cytoplasm which appears to function during the division of certain animal cells (usually near the nucleus) • Helps animal cells divide Centriole Organelle: Lysosomes • Lysosomes -“break down bodies” – contains powerful digestive enzymes and function as cell’s “demolition site” capable of digesting worn-out or nonusable cell structures. Abundant in white blood cells to rid body of harmful substances Lysosomes Organelle: Peroxisomes • Peroxisomes - disarm dangerous chemicals (free radicals- highly reactive chemicals that can have devastating effects on cells) in the body Peroxisomes Organelle: Vacuole • membrane bound cytoplasmic spaces containing materials Two Types: – Food vacuole--store and digest ingested food – Contractile vacuole-pumps excess water from cells maintaining homeostasis Vacuole Types of Transport in Cells Video: Transport Across Cell Membranes • By Bozeman Science – http://www.bozemanscience.com/016-transport-across-cellmembranes Types of Transport in Cells • Passive transport - movement of substances through a membrane from a region of high to a region of low concentration - no energy needed (ATP) diffusion and osmosis are examples of this • Active transport - movement of substances through a membrane from a region of low concentration to a region of high concentration - requires cellular energy (ATP) Whether passive or active transport is needed depends on the CONCENTRATION GRADIENT • The concentration gradient is the difference in the concentration of a substance in two different spaces • Concentration - the amount of a particular substance in a contained area compared with the amount of the same substance in another area • Translation: Amount of something in a space (water, salt, sugar, iron,) Passive Transport • There are two types of passive transport: Diffusion and Osmosis • The goal of both diffusion and osmosis is to reach EQUILIBRIUM within the cell • Equilibrium is a condition in which the movement in one direction is equal to the movement in another direction Diffusion • the tendency of molecules to move from an area of higher concentration to an area of lower concentration • (concentration gradient- different in concentration between 2 regions) Osmosis • movement of water through a membrane from a region of higher to lower con. • Solute - substance being dissolved in a liquid (ex. salt) • Solvent - substance doing the dissolving (ex. water) • Permeability - the extent to which a membrane will allow particular sized molecules to pass Semi-permeable membrane (selectively permeable)-allows some molecules to pass but not others Osmosis Think about it… • So, describe how “Kool-Aid”® is made with regard to the terms “solute” and “solvent”. What is the “universal solvent”? And the answer is… • Water is the solvent and the solute is the kool-aid powder because it dissolves in water resulting in a solution. • Water is known as the “universal solvent” Comparing Solutions • Three possible relationships – based on determining what would happen if a cell were placed in the solution. • Hypertonic- A solution that causes a cell to shrink because of osmosis, meaning water leaves the cell. • Hypotonic- A solution that causes a cell to swell because of osmosis, meaning water rushes into the cell. • Isotonic-A solution that causes no change in cell size, meaning there is no movement of water. Hypertonic solution Hypotonic solution This can occur to such an extent that the cell actually bursts to release its contents. This bursting of cells is called lysis, and of a red blood cell, hemolysis Isotonic solution The normal Saline solution which is 0.9% NaCl is isotonic with blood and is used in patients suffering from dehydration or if they can't take any liquids or food. Think about it… • So, answer this question…. Why do “establishments” offer free popcorn, peanuts, and pretzels to their patrons if they are serving beverages? What changes are taking place in the body to initiate the need for more beverages? • What type of solution occurs? • What form of membrane transport is taking place? • What is the concentration gradient movement during this membrane transport process? Think about it… • What type of solution occurs? – Sodium in bloodstream creates a hypertonic solution • What form of membrane transport is taking place? – Osmosis • What is the concentration gradient movement during this membrane transport process? – High to low movement of water across the cell membrane, water form inside cell moving to outside cell. And the answer is… • After it is consumed, salt is absorbed into your bloodstream. Salt acts as a magnet for water, sucking it out of the body’s cells. Water is polar and attracted to sodium's electrical ions. The cells resist, but lose. • Both your dehydrated cells and salty blood send messages to the brain, asking for more water to respectively quench and dilute. This is why you become thirsty after eating salty snacks Facilitated Diffusion • requires transport proteins in the cell membrane to move materials into and out of the cell either because the molecules that are transported are too big or they are polar (act against the nonpolar fatty acid tail of the lipid bilayer) Facilitated diffusion • Channel proteins provide corridors that allow a specific particle to cross the membrane. • Carrier proteins undergo a change in shape that translocates the solutebinding site across the membrane. Active Transport • the movement of a substance against the concentration gradient. (uphill) • Active transport requires cell to USE ENERGY Types of Active Transport • • • • Sodium pump - transports three sodium ions out of the cell and two potassium ions into the cell Both are against the concentration gradient The energy needed to perform this activity is supplied by ATP (adenosine tri-phosphate) ATP is a unit of energy made by the cell Types of Active Transport • Endocytosis- the movement of a substance into the cell by a vesicle. A vesicle is a form of packaging that is used by cells. – Phagocytosis- cytoplasm of cell surrounds and engulfs particle--ex. ameba and white blood cell – Pinocytosis- plasma membrane "pinches in" to permit entry of molecules too large to diffuse through • Exocytosis- the movement of a substance out of the cell by a vesicle. Endocytosis Exocytosis