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Cell Membranes: Osmosis and Diffusion ‹ # › ‹ # ‹ ›# › Membrane Functions 1. Protect cell 2. Guard incoming and outgoing substances 3. Maintain ion concentrations of various substances 4. Selectively permeable a. ‹ # › b. Allows some molecules in Others are kept out ‹ # › ‹ # ‹ ›# › ‹ # › Phospholipid Bilayer ‹ # › ‹ # ‹ ›# › ‹ # › Fluid Mosaic Model ‹ # › ‹ # ‹ ›# › ‹ # › Solutions Solutions are made of solute and a solvent Solvent - the liquid into which the solute is poured and dissolved Solute - substance that is dissolved or put into the solvent. Salt and sucrose are solutes ‹ # › Membrane Transport 1. Diffusion a. ‹ # ‹ ›# › b. 2. Osmosis a. ‹ # › Passive transport No energy expended b. Passive transport Water across membrane ‹ # › ‹ # ‹ ›# › ‹ # › Diffusion Movement of molecules from one side of a membrane to the other Occurs from a region of high concentration of substance to a region of lower concentration D i f f ‹ # ‹ u ›# › s i ‹ o # n › ‹ # › Osmosis ‹ # › Membrane Transport 3. Facilitated Diffusion a. ‹ # ‹ ›# › ‹ # › b. 4. Passive transport Use of proteins to carry polar molecules or ions across Active Transport a. b. Requires energy to transport molecules against a concentration gradient Energy is in the form of ATP ‹ # › Tonicity Hypotonic – ‹ # ‹ ›# › Inside has higher salt concentration Hypertonic – Solution Inside has lower salt concentration Isotonic – ‹ # › Solution Solution Both solutions have same concentrations of solute Plant and Animal Cells in Various Solutions ‹ # › ‹ # ‹ ›# › ‹ # › Active Transport • • Movement against a concentration gradient (from low to high concentration) Requires added energy (ATP) and a specific membrane carrier (“pump”) ‹ # › ‹ # ‹ ›# › Endocytosis Ingestion of large molecules or particles Cell surrounds and envelops substance forming a vesicle which fuses with lysosome – Phagocytosis Endocytosis ‹ # › – of organism Pinocytosis Endocytosis of large, soluble molecules ‹ # › ‹ # ‹ ›# › ‹ # › Exocytosis Cell secretes material Package in a vesicle Moves in vesicle to cell surface Vesicle membrane fuses with cell membrane Contents are secreted out Specialized animal cells produce and secrete digestive enzymes and hormones Cell Structure and Function ‹ # › Early Discoveries Mid 1600s - Robert Hooke observed and described cells in cork ‹ # ‹ ›# › observed sperm, microorganisms ‹ # › Late 1600s - Antony van Leeuwenhoek 1820s - Robert Brown observed and named nucleus in plant cells ‹ # › ‹ # ‹ ›# › ‹ # › Cell Theory Matthias Schleiden Theodor Schwann Rudolf Virchow ‹ # › Cell Theory 1) Every organism is composed of one or more cells ‹ # ‹ ›# › 2) Cell is smallest unit having properties of life 3) Continuity of life arises from growth and ‹ # › division of single cells ‹ # › ‹ # ‹ ›# › Cell Smallest Can survive on its own or has potential to do so Is highly organized for metabolism Senses ‹ # › unit of life Has and responds to environment potential to reproduce ‹ # › ‹ # ‹ ›# › Cells are Microscopic Why aren’t cells larger? Animal cells range from 7-50 μm, some are much larger: – – – ‹ # › Nerve cells Algae Eggs Plant cells are generally larger ‹ # › ‹ # ‹ ›# › Why aren’t Cells Larger? • • • ‹ # › As cells grow larger, volume increases faster than surface area Large cells do not have sufficient surface area for efficient diffusion of nutrients and wastes Nuclei control activities of smaller cells more easily ‹ # › Structure of Cells Must Have: ‹ # ‹ ›# › ‹ # › Two types: – Plasma membrane – Prokaryotic – DNA Region – Eukaryotic – Cytoplasm Structure of Cells The plasma membrane and internal cell membranes consist of lipids and proteins. The lipids are organized as two adjacent layers—as bi-layer. ‹ # › ‹ # ‹ ›# › ‹ # › Lipid Bilayer Main component of cell membranes Gives the membrane its fluid properties Two layers of phospholipids ‹ # › Fluid Mosaic Model ‹ # ‹ ›# › Membrane is a mosaic of – – – – ‹ # › Phospholipids Glycolipids Sterols Proteins Most phospholipids and some proteins can drift through membrane ‹ # › ‹ # ‹ ›# › ‹ # › ‹ # › ‹ # ‹ ›# › ‹ # › Membrane Proteins Transport proteins Receptor proteins Recognition proteins Adhesion proteins ‹ # › ‹ # ‹ ›# › Why Are Cells So Small? Surface-to-volume ratio The bigger a cell is, the less surface area there is per unit volume Above a certain size, material cannot be moved in or out of cell fast enough ‹ # › ‹ # › ‹ # ‹ ›# › Microscopes Create detailed images of something that is otherwise too small to see Light – microscopes Simple or compound Electron ‹ # › – microscopes Transmission EM or Scanning EM ‹ # › Light Microscope Limitations Wavelengths of light are 400-750 nm (nanometers) ‹ # ‹ ›# › ‹ # › If a structure is less than one-half of a wavelength long, it will not be visible Light microscopes can resolve objects down to about 200 nm in size ‹ # › ‹ # ‹ ›# › ‹ # › Electron Microscopy Uses streams of accelerated electrons rather than light Electrons are focused by magnets rather than glass lenses Can nm resolve structures down to 0.5 Plant cell Eukaryotic Cells Defined as a cell that starts out life with a nucleus Have a nucleus and other organelles Eukaryotic organisms – – – – Plants Animals Protista Fungi Animal cell Animal Cell Features Plasma membrane Cytoskeleton Nucleus Ribosomes Endoplasmic reticulum Vesicle Mitochondria Golgi body Plant Cell Features ‹ # › Nucleus Plasma Membrane Ribosomes Endoplasmic reticulum Golgi body Mitochondria ‹ # ‹ ›# › ‹ # › Cell wall Chloroplast Central Vacuole ‹ # › ‹ # ‹ ›# › ‹ # › Functions of Nucleus Keeps the DNA molecules of eukaryotic cells separated from metabolic machinery of cytoplasm Makes it easier to organize DNA and to copy it before parent cells divide into daughter cells ‹ # › ‹ # ‹ ›# › Components of Nucleus • Nuclear envelope - double membrane enclosing the nucleus • Nucleoplasm - fluid portion of the nucleus • Nucleolus - where other organelles are constructed • Chromosome – made of chromatin ‹ # › • Chromatin - DNA with all associated protein ‹ # › ‹ # ‹ ›# › ‹ # › Nuclear Envelope Two outer membranes (lipid bi-layers) Innermost surface has DNA attachment sites Pores span bi-layer ‹ # › ‹ # ‹ ›# › ‹ # › Nucleolus Dense mass of material in nucleus May be one or more Cluster of DNA and proteins Puts together ribosomal subunits ‹ # › Chromatin Cell’s collection of DNA and associated proteins Chromosome is one DNA molecule and its associated proteins Appearance changes as cell divides ‹ # ‹ ›# › ‹ # › ‹ # › ‹ # ‹ ›# › ‹ # › Cytomembrane System Group of related organelles in which lipids are assembled and new polypeptide chains are modified Products are sorted and shipped to various destinations ‹ # › Cyto-membrane System Endoplasmic reticulum ‹ # ‹ ›# › Golgi bodies Vesicles ‹ # › ‹ # › ‹ # ‹ ›# › ‹ # › Endoplasmic Reticulum In animal cells, continuous with nuclear membrane Extends Two throughout cytoplasm regions - rough and smooth ‹ # › ‹ # ‹ ›# › ‹ # › Rough ER Arranged into flattened sacs Ribosomes on surface give it a rough appearance Some polypeptide chains enter rough ER and are modified Cells that specialize in secreting proteins have lots of rough ER ‹ # › ‹ # ‹ ›# › ‹ # › Smooth ER A series of interconnected tubules No ribosomes on surface Lipids assembled inside tubules Smooth ER of liver inactivates wastes, drugs ‹ # › ‹ # ‹ ›# › ‹ # › Golgi Bodies Put finishing touches on proteins and lipids that arrive from ER Package finished material for shipment to final destinations Material arrives and leaves in vesicles ‹ # › ‹ # ‹ ›# › ‹ # › Vesicles Membranous sacs that move through the cytoplasm Lysosomes Peroxisomes ‹ # › ‹ # ‹ ›# › Mitochondria ATP-producing powerhouses Double-membrane Carry system out most efficient energy- releasing reactions that require ‹ # › oxygen ‹ # › ‹ # ‹ ›# › ‹ # › Mitochondrial Structure Outer membrane faces cytoplasm Inner membrane folds back on itself Membranes form two distinct compartments ATP-making machinery is embedded in the inner mitochondrial membrane ‹ # › Mitochondrial Origins ‹ # ‹ ›# › ‹ # › Mitochondria resemble bacteria – Have own DNA, ribosomes – Divide on their own May have evolved from ancient bacteria that were engulfed but not digested ‹ # › Plant Organelles Plastids organelles ‹ # ‹ ›# › that specialize in photosynthesis Central Vacuole store amino acids, sugars, ‹ # › ions and toxic wastes. ‹ # › ‹ # ‹ ›# › ‹ # › Chloroplasts Convert sunlight energy to ATP through photosynthesis ‹ # › Photosynthesis First stage – ‹ # ‹ ›# › – Second stage – ‹ # › Occurs at thylakoid membrane Light energy is trapped by pigments and stored as ATP Inside stroma, ATP energy is used to make sugars, then other carbohydrates ‹ # › ‹ # ‹ ›# › ‹ # › Central Vacuole Fluid-filled organelle Stores amino acids, sugars, wastes As cell grows, expansion of vacuole as a result of pressure that forces end cell walls to expand In mature cell, central vacuole takes up 50-90 percent of cell interior ‹ # › Cytoskeleton ‹ # ‹ ›# › Basis Present for cell shape and internal organization Allows ‹ # › in all eukaryotic cells organelle movement within cells and, in some cases, cell motility ‹ # › ‹ # ‹ ›# › ‹ # › ‹ # › ‹ # ‹ ›# › ‹ # › Flagella and Cilia Structures for cell motility ‹ # › Cell Wall Plasma membrane Structural ‹ # ‹ ›# › ‹ # › component that wraps around the plasma membrane Occurs in plants, some fungi, some protista ‹ # › ‹ # ‹ ›# › ‹ # › Prokaryotic Cells Archaebacteria and Eubacteria DNA is NOT enclosed in nucleus Generally the smallest, simplest cells No organelles Prokaryotic Structure pilus cytoplasm with ribosomes DNA flagellum capsule cell plasma wall membrane ‹ # › ‹ # ‹ ›# › ‹ # › Things to know: The first cell seen under a microscope was cork. One portion of the cell theory states that all living organisms are made up of cells. The cell theory was proposed by Theodor Schwann and Matthias Schleiden. The idea that all living cells come from pre-existing living cells was proposed by Rudolf Virchow. ‹ # › ‹ # ‹ ›# › ‹ # › Things to know: The phospholipid molecules of most membranes have a hydrophilic head and two hydrophobic tails. Hydrophobic reactions of phospholipids may produce clusters of their fatty acid tails, which form a lipid bilayer. ‹ # › ‹ # ‹ ›# › ‹ # › Things to know: The relative impermeability of membranes to water-soluble molecules is a result of the presence of phospholipids in the lipid bilayer. Membranes have holes due to proteins that extend through the membrane. Some membranes have proteins with channels or pores that allow for the passage of hydrophilic substances. ‹ # › ‹ # ‹ ›# › ‹ # › Things to know: The current concept of a membrane can be best summarized by the fluid mosaic model. The lipid bilayer serves as a hydrophobic barrier between two fluid regions. Receptor proteins are responsible for binding hormones that can switch on a cell. There are 1,000,000,000 nanometers in a meter. ‹ # › ‹ # ‹ ›# › ‹ # › Things to know: The maximum power of magnification of a light microscope is 4,000. The highest magnification generally used to study cells is provided by the transmission electron microscope. The transmission electron microscope has the highest magnification. The ribosomes are made of two subunits of RNA and protein. ‹ # › ‹ # ‹ ›# › ‹ # › Things to know: Organelles composed of a system of canals, tubes and sacs that transport molecules inside the cytoplasm are endoplasmic reticula. Mitochondria are the primary cellular sites for the recapture of energy from carbohydrates. Golgi bodies are the primary structures for the packaging of cellular secretions for export from the cell. ‹ # › ‹ # ‹ ›# › ‹ # › Things to know: The cell part responsible for maintaining cell shape, internal organization, and cell movement is the cytoskeleton. The cell wall is found in plant cells but not in animal cells. The nucleolus is found in the nucleus. The nuclear envelope has two lipid layers; there are pores in the membrane; ribosomal subunits can pass out of the nucleus; protein filaments are attached to inner surface. ‹ # › ‹ # ‹ ›# › ‹ # › Things to know: Scientists use the word “chromosome” to describe an individual DNA molecule. Endoplasmic reticula are sometimes referred to as rough or smooth. Ribosomes are the primary cellular sites for the production of protein. The Golgi body has been likened to a stack of pancakes. ‹ # › ‹ # ‹ ›# › ‹ # › Things to know: The lysosomes contain enzymes and are the main organelles of intracellular digestion. Animal cells dismantle and dispose of waste materials by several lysosomes fusing with a sac that encloses the wastes. A tadpole’s tail disappears when it changes into an adult frog by action of lysosomes. ‹ # › ‹ # ‹ ›# › ‹ # › Things to know: The nuclei and mitochondria contain DNA. Mitochondria contain enzymes used in the breakdown of glucose and generation of ATP. Energy stored in carbon compounds is converted by mitochondria to a form usable by the cell. There are two membranes surrounding the mitochondrion. ‹ # › ‹ # ‹ ›# › ‹ # › Things to know: The inner membranes of mitochondria are called cristae. Fluid-filled sacs that may store food or water in cells are called vacuoles. Plastids in plant cells function in photosynthesis or storage. Stroma and grana are portions of chloroplasts. ‹ # › ‹ # ‹ ›# › ‹ # › Things to know: Vacuoles dramatically increase the cell size and surface area. Flagellum is compared to a whip and used for mobility. Bacteria are examples of prokaryotes. Prokaryotic cells do NOT have membrane bound nucleus. Prokaryotes have DNA regions; are unicellular; have cell walls; and are bacteria. ‹ # › ‹ # ‹ ›# › ‹ # › Bibliography 1. 2. http://filebox.vt.edu/users/malsaghi/ 6 Dec 2004, Mohannad AL-Saghir, Biology Department, Virginia Tech http://pls.atu.edu/biology/, 6 Dec 2004, Arkansas Tech University, Biology Department, Beck,