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CHAPTER 4 A Tour of the Cell PowerPoint® Lectures for Essential Biology, Third Edition – Neil Campbell, Jane Reece, and Eric Simon Essential Biology with Physiology, Second Edition – Neil Campbell, Jane Reece, and Eric Simon Lectures by Chris C. Romero Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Biology and Society: Cells That Cure • During a heart attack, – Heart muscle cells die because they are starved for oxygen. • Unfortunately, these kinds of cells do not regenerate. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings • In recent years, a new treatment called “cell therapy” has emerged. • In this procedure, cells are taken from other parts of the body – And delivered to the ailing heart, facilitating healing. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 4.1 The Microscopic World of Cells • Organisms are either: – Single-celled, such as most bacteria and protists – Multicelled, such as plants, animals, and most fungi Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The Microscopic World of Cells • The human body is made up of trillions of cells many of which are specialized – Muscle cells, Nerve cells, & blood cells… Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Cells were first discovered in 1665 by Robert Hooke. • The accumulation of scientific evidence led to the cell theory. – All living things are composed of cells. – All cells are formed from previously existing cells. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Microscopes provide windows to the world of the cell The light microscope enables us to see the overall shape and structure of a cell Image seen by viewer Eyepiece Ocular lens Objective lens Specimen Condenser lens Light source Figure 4.1A Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Microscopes as a Window on the World of Cells • The light microscope is used by many scientists. – Light passes through the specimen. – Lenses enlarge, or magnify, the image. • Magnification – Is an increase in the specimen’s apparent size. • Resolving power – Is the ability of an optical instrument to show two objects as being separate. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • The electron microscope (EM) uses a beam of electrons. – It has a higher resolving power than the light microscope. • The electron microscope can magnify up to 100,000X. – Such power reveals the diverse parts within a cell. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Microscopes as a Window on the World of Cells • The scanning electron microscope (SEM) is used to study the detailed architecture of the surface of a cell. • Produces a 3D image • Used to study cell surfaces Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Microscopes as a Window on the World of Cells • The transmission electron microscope (TEM) is useful for exploring the internal structure of a cell. • An electron beam is aimed through a thin section. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The Two Major Categories of Cells • The countless cells on earth fall into two categories: – Prokaryotic cells – Eukaryotic cells • Both cells – Are surrounded by a plasma membrane – Consist of cytoplasm and organelles and contain DNA • Prokaryotic and eukaryotic cells differ in several respects. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 4.4 Most cells are 10-100 micrometers in size Cell size and shape relate to function Figure 4.2 Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Natural laws limit cell size The lower limit of cell size is determined by the fact that a cell must be large enough to house the parts it needs to survive and reproduce The maximum size of a cell is limited by the amount of surface needed to obtain nutrients from the environment and dispose of wastes. • The ratio of surface are to volume imposes limits on cell size • Muscle and nerve cells can be very long because they are thin and have more surface area compared to volume Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings A small cell has a greater ratio of surface area to volume than a large cell of the same shape 30 µm Figure 4.3 10 µm Surface area of one large cube = 5,400 µm2 Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Total surface area of 27 small cubes = 16,200 µm2 • Prokaryotic cells – Are smaller than eukaryotic cells. – Lack internal structures surrounded by membranes. – Lack a nucleus. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings A prokaryotic cell is enclosed by a plasma membrane and is usually encased in a rigid cell wall • The cell wall may be covered by a sticky capsule Prokaryotic flagella Nucleoid Region (DNA) Capsule Cell wall • Inside the cell are its DNA and other parts Plasma membrane Ribosome Pili Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 4.4 Structures of Prokaryotic Cells Nucleoid region – area where DNA is coiled in the cytoplasm. DNA is in direct contact with the rest of the cell Plasmid – smaller circular DNA molecules Ribosomes – where proteins are made Plasma membrane – encloses the cytoplasm of the prokaryotic cell Cell wall – rigid, composed of lipids, carbohydrates and protein. Protects the cell and maintains its shape Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Cell Wall components determine if bacteria is classified as •gram positive (+) • or gram negative • In general more toxic and resistant to antibiotics http://www.bio.upenn.edu/computing/media/Instructional.Stain.Gram.php Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Structures of the Prokaryotic Cell Capsule – sticky outer coat that surrounds some prokaryotes. Protects the cell surface. Helps bacteria attach to surfaces Pili – short surface projections found in some prokaryotes. Helps attach bacteria to surfaces Flagella – long whiplike extensions found in some prokaryotes. Propel cell through liquid environments Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The Role of Bacteria in the Nitrogen Cycle Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Eukaryotic cells are partitioned into functional compartments All other life forms are made up of one or more eukaryotic cells These are larger and more complex than prokaryotic cells Eukaryotes are distinguished by the presence of a true nucleus Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings A Panoramic View of Eukaryotic Cells • An idealized animal cell Cytoplasmic Streaming Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 4.6b The Plasma Membrane Would this organelle/ structure also be found in prokaryotes? If so, are there any important differences in structure or function? Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The Plasma Membrane: A Fluid Mosaic of Lipids and Proteins • The plasma membrane separates the living cell from its nonliving surroundings. • The membranes of cells are composed mostly of: – Lipids – Proteins Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings The plasma membrane • The lipids belong to a special category called phospholipids. • Phospholipids form a two-layered membrane, the phospholipid bilayer. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The plasma membrane • Most membranes have specific proteins embedded in the phospholipid bilayer. • Membranes also contain cholesterol wedged between the phospholipids. • Carbohydrates are found on the external surface attached to phospholipids or protein. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Membrane phospholipids and proteins can drift about in the plane of the membrane. • This behavior leads to the description of a membrane as a fluid mosaic: – Molecules can move freely within the membrane. – A diversity of proteins exists within the membrane. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Cell Surfaces • Most cells secrete materials for coats of one kind or another – That are external to the plasma membrane. • These extracellular coats help protect and support cells – And facilitate interactions between cellular neighbors in tissues. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Animal cells have an extracellular matrix, – Which helps hold cells together in tissues and protects and supports them. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The Cell Wall Would this organelle/ structure also be found in prokaryotes? If so, are there any important differences in structure or function? Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Plant cells have cell walls, – Which help protect the cells, maintain their shape, and keep the cells from absorbing too much water. – Made of Cellulose and other components in plant cells – Prokaryotes’ cell wall performs the same function, though it is composed of different organic molecules Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Cell Junctions – “Tunnels” that Connects the cytoplasm of one plant cell with the cytoplasm of another plant cell, thus allowing small substances to move from cell to cell. – There are other types of junctions, but that is for Advanced bio I Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Ex: cell Junctions The Nucleus Would this organelle/ structure also be found in prokaryotes? Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The Nucleolus Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 4.8 The Nucleus and Ribosomes: Genetic Control of the Cell • The nucleus is the manager of the cell – Genes in the nucleus store information necessary to produce proteins which direct the cell’s activities • It is usually the largest organelle. • It contains chromatin (DNA) • The nucleus is separated from the cytoplasm by the nuclear envelope. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings Structure and Function of the Nucleolus • The nucleolus is found within the nucleus – It is a mass of fibers and granules – It is where ribosomes are made Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Ribosomes Would this organelle/ structure also be found in prokaryotes? If so, are there any important differences in structure or function? Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Ribosomes • Ribosomes are responsible for protein synthesis. • DNA controls the cell by transferring its coded information into RNA. – The information in the RNA is used by ribosomes to make proteins. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The Endomembrane System: Manufacturing and Distributing Cellular Products The endomembrane system is a collection of membranous organelles • These organelles manufacture and distribute cell products • The endomembrane system divides the cell into compartments Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings Figure 4.10 The Endoplasmic Reticulum • The endoplasmic reticulum (ER) – Produces an enormous variety of molecules. – Is composed of smooth and rough ER. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Rough Endoplasmic Reticulum Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Rough ER makes membrane and proteins • The “roughness” of the rough ER is due to ribosomes that stud the outside of the ER membrane. • The functions of the rough ER include: – Producing two types of membrane proteins – Producing new membrane Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Rough Endoplasmic REticulum • After the rough ER synthesizes a molecule, it packages the molecule into transport vesicles. Transport vesicle buds off 4 Ribosome Sugar chain 1 3 Secretory (glyco-) protein inside transport vesicle Glycoprotein 2 Polypeptide Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings ROUGH ER Smooth Endoplasmic Reticulum Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Smooth ER • Continuous with the rough ER • Lacks the surface ribosomes of ER • Produces lipids, including steroids. – For example how cells in your ovaries or testes produce steroid based sex hormones like estrogen and testosterone • In some cells, it regulates carbohydrate metabolism • In liver cells breaks down toxins and drugs – Antibiotics, barbiturates, alcohol • In other cells- especially muscle cells it stores calcium ions. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The Golgi Complex Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 4.12 The Golgi Apparatus • The Golgi apparatus – Works in partnership with the ER. – It consists of stacks of membranous sacs – Refines, stores, and distributes the chemical products of cells. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Vesicles Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Lysosomes • A lysosome is a membrane-enclosed sac. – It contains digestive enzymes. – The enzymes break down macromolecules. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 4.13a Figure 4.13b • Lysosomes have several types of digestive functions. – They fuse with food vacuoles to digest the food. – They break down damaged organelles. Lysosome Formation Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Connection: Abnormal lysosomes can cause fatal diseases Lysosomal storage diseases are hereditary • They interfere with other cellular functions • Examples: Pompe’s disease, Tay-Sachs disease Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Vacuoles • Vacuoles are membranous sacs. – Two types are the contractile vacuoles of protists and the central vacuoles of plants. Paramecium Vacuole Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The Central Vacuole Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Vacuoles function in the general maintenance of the cell Plant cells contain a large central vacuole • The vacuole absorbs water, stores vital chemicals, stores waste products Central vacuole Nucleus Figure 4.13A Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Protists may have contractile vacuoles • These pump out excess water Nucleus Contractile vacuoles Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 4.13B Figure 4.15 Chloroplasts and Mitochondria: Energy Conversion • Cells require a constant energy supply to do all the work of life. • This function is carried out by the chloroplasts and the mitochondria Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings Chloroplasts Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Chloroplasts • Chloroplasts are found in plants and some protists. • Chloroplasts are the sites of photosynthesis, the conversion of light energy to chemical energy in sugars. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Mitochondria Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Mitochondria • Mitochondria are the sites of cellular respiration, which involves the production of ATP from food molecules. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Mitochondria and chloroplasts share another feature unique among eukaryotic organelles. – They contain their own DNA. • The existence of separate “mini-genomes” is believed to be evidence that – Mitochondria and chloroplasts evolved from free-living prokaryotes in the distant past. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Cytoskeleton Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The Cytoskeleton: Cell Shape and Movement • The cytoskeleton is an infrastructure of the cell consisting of a network of fibers. • One function of the cytoskeleton is to provide mechanical support to the cell and maintain its shape. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings The Cytoskeleton • The cytoskeleton can change the shape of a cell. • This allows cells like amoebae to move. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Flagella Would this organelle/ structure also be found in prokaryotes? If so, are there any important differences in structure or function? Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Cilia and Flagella • Cilia and flagella are motile appendages. • Flagella propel the cell in a whiplike motion. • Cilia move in a coordinated back-andforth motion. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Cilia and Flagella • Some cilia or flagella extend from nonmoving cells. • The human windpipe is lined with cilia. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Evolution Connection: The Origin of Membranes • Phospholipids were probably among the organic molecules on the early Earth. • When mixed with water, phospholipids spontaneously form membranes. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings