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BIOLOGY A GUIDE TO THE NATURAL WORLD FOURTH EDITION DAVID KROGH Life’s Home: The Cell Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. 4.1 Cells are the Fundamental Units of Life Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Cells are the Fundamental Units of Life • With the possible exception of viruses, every form of life on Earth either is a cell or is composed of cells. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Cells are the Fundamental Units of Life • Cells come into existence only through the activity of other cells. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 4.2 All Cells are Either Prokaryotic or Eukaryotic Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. All Cells are Either Prokaryotic or Eukaryotic • All cells can be classified as prokaryotic or eukaryotic. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. All Cells are Either Prokaryotic or Eukaryotic • Prokaryotic cells either are bacteria or another single-celled life-form called archaea. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. All Cells are Either Prokaryotic or Eukaryotic • Setting bacteria and archaea aside, all other cells are eukaryotic. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. All Cells are Either Prokaryotic or Eukaryotic • Eukaryotic cells have most of their DNA contained in a membrane-lined compartment, called the cell nucleus, whereas prokaryotic cells do not have a nucleus. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. All Cells are Either Prokaryotic or Eukaryotic • Eukaryotic cells tend to be much larger than prokaryotic cells. They have more of the specialized internal structures called organelles than do prokaryotic cells. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. All Cells are Either Prokaryotic or Eukaryotic • Many eukaryotes are multicelled organisms, whereas all prokaryotes are single-celled. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. All Cells are Either Prokaryotic or Eukaryotic Prokaryotic cells Eukaryotic cells DNA in “nucleoid” region within membrane-bound nucleus much smaller much larger always single-celled often multicellular only one type of organelle many types of organelles Size Organization Organelles Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 4.2 4.3 The Eukaryotic Cell Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Eukaryotic Cell • There are five principal components to the eukaryotic cell: the nucleus, other organelles, the cytosol, the cytoskeleton, and the plasma membrane. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Eukaryotic Cell • Organelles are “tiny organs” within the cell that carry out specialized functions, such as energy transfer and materials recycling. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Eukaryotic Cell nuclear pores DNA nucleus nuclear envelope nucleolus smooth endoplasmic reticulum free ribosomes cytosol cytoskeleton lysosomes rough endoplasmic reticulum Golgi complex plasma membrane transport vesicle mitochondria Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 4.4 The Eukaryotic Cell • The cytosol is the jelly-like fluid outside the nucleus in which these organelles are immersed. • The cytosol should not be confused with the cytoplasm, which is the region of the cell inside the plasma membrane but outside the nucleus. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Eukaryotic Cell • The cytoskeleton is a network of protein filaments. • It functions in cell structure, cell movement, and the transport of materials within the cell. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Eukaryotic Cell • The plasma membrane is the outer lining of the cell. • A membrane can be defined as the flexible, chemically active outer lining of a cell or of its compartments. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Eukaryotic Cell Components of eukaryotic cells nucleus other organelles cytosol cytoskeleton Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. plasma membrane Figure 4.3 4.4 A Tour of the Animal Cell: Along the Protein Production Path Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Tour of the Animal Cell: Along the Protein Production Path • Information for the construction of proteins is contained in the DNA located in the cell nucleus. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Protein Production Path • This information is copied onto a length of messenger RNA (mRNA) that departs the cell nucleus through its nuclear pores and goes to the sites of protein synthesis, structures called ribosomes, which lie in the cytoplasm. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Protein Production Path • Many ribosomes that receive mRNA chains process only a short stretch of them before migrating to, and then embedding in, one of a series of sacs in a membrane network called the rough endoplasmic reticulum (RER). Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Protein Production Path • The polypeptide chains produced by the ribosomal “reading” of the mRNA sequences are dropped from ribosomes into the internal spaces of the RER. • There, the polypeptide chains fold up, thus becoming proteins, and undergo editing. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Tour of an Animal Cell Suggested Media Enhancement: Tour of an Animal Cell To access this animation go to folder C_Animations_and_Video_Files and open the BioFlix folder. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Protein Production Path • Some ribosomes are not embedded in the RER but instead remain free-standing in the cytosol. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Protein Production Path • Materials move from one structure to another in the cell via the endomembrane system. • Here a piece of membrane, with proteins or other materials inside, can bud off from one organelle, move through the cell, and then fuse with another membrane-lined structure. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Protein Production Path • Membrane-lined structures that carry cellular materials are called transport vesicles. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Protein Production Path • Once protein processing is finished in the rough ER, proteins undergoing processing move, via transport vesicles, to the Golgi complex. • They are processed further and marked for shipment to appropriate cellular locations. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Golgi Complex Golgi complex 1. Transport vesicle from RER fuses with Golgi 2. Protein undergoes more processing in Golgi cisternae cisternal space vesicle Side chains are edited (sugars may be trimmed, phosphate groups added). to cytosol 3. Proteins are sorted and shipped… for export out of cell to plasma membrane Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 4.8 4.5 Outside the Protein Production Path: Other Cell Structures Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Outside the Protein Production Path: Other Cell Structures • The smooth endoplasmic reticulum is a network of membranes that functions to synthesize lipids and to detoxify potentially harmful substances. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Lysosomes and Cellular Recycling • Lysosomes are organelles that break down worn-out cellular structures or foreign materials that come into the cell. • Once this digestion is completed, the lysosomes return the molecular components of these materials to the cytoplasm for further use. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Lysosomes and Cellular Recycling lysosome worn-out organelle digestive enzymes 1. Lysosome fuses with worn-out organelle. 2. Organelle broken down. 5. Usable molecules recycled to make new organelles. 3. Small molecules returned to cytosol. 4. Waste molecules expelled from cell. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 4.9 Mitochondria and Energy • Mitochondria are organelles that function to extract energy from food and to transform this energy into a chemical form the cell can use, the molecule ATP. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Mitochondria and Energy Mitochondrion food oxygen outer membrane inner membrane water carbon dioxide ATP Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 4.10 4.6 The Cytoskeleton: Internal Scaffolding Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Cytoskeleton: Internal Scaffolding • Cells have within them a web of protein strands, called a cytoskeleton. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Cytoskeleton: Internal Scaffolding • The cytoskeleton provides the cell with structure, facilitates the movement of materials inside the cell, and facilitates cell movement. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Cytoskeleton: Internal Scaffolding • There are three principal types of cytoskeleton elements. • Ordered by size, going from smallest to largest in diameter, they are microfilaments, intermediate filaments, and microtubules. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Microfilaments (a) Microfilaments 7 nm (b) Intermediate filaments 10 nm Main function: changes in cell shape (c) Microtubules 25 nm Main function: maintenance of cell shape Main functions: maintenance of cell shape, movement of organelles, cell mobility (cilia and flagella) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 4.11 Microfilaments • Microfilaments are made of the protein actin. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Microfilaments • They help the cell move and capture prey by forming rapidly in the direction of movement and decomposing rapidly at their other end. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Microfilaments Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 4.12 Intermediate Filaments • Intermediate filaments provide support and structure to the cell. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Microtubules • Microtubules play a structural role in cells and facilitate the movement of materials inside the cell by serving as transport “rails.” Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Microtubules • Cilia and flagella are extensions of cells composed of microtubules. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Cilia • Cilia extend from cells in great numbers, serving to move the cell or to move material around the cell. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Flagella • By contrast, one—or at most a few—flagella extend from cells that have them. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Flagella • The function of flagella is cell movement. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Functions of Microtubules (a) Transport monorails transport vesicle motor proteins microtubule (b) Cilia (c) Flagellum Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 4.13 4.7 The Plant Cell Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Tour of a Plant Cell Suggested Media Enhancement: Tour of a Plant Cell To access this animation go to folder C_Animations_and_Video_Files and open the BioFlix folder. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Plant Cell • Plant cells have most of the structures found in animal cells— ribosomes, a cell nucleus, a rough ER, and so forth—although plant cells do not have the lysosomes found in animal cells. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Plant Cell • Plant cells have three structures not found in animal cells: – a cell wall – a large central vacuole – the organelles called chloroplasts Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Plant Cell Plant cells have a cell wall, chloroplasts, and a central vacuole, while animal cells do not. cytoskeleton cell wall nuclear envelope nuclear pores nucleus DNA nucleolus rough endoplasmic reticulum smooth endoplasmic reticulum free ribosomes chloroplast Golgi complex central vacuole cytosol plasma membrane mitochondrion Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 4.16 The Central Vacuole • The central vacuole stores nutrients and degrades waste products. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Cell Wall • The cell wall gives the plant structural strength and helps regulate the intake and retention of water. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Chloroplasts • Chloroplasts are the sites of photosynthesis. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Chloroplasts water carbon dioxide minerals outer membrane inner membrane sugar (food) oxygen Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 4.18 The Structure of Cells PLAY Animation 4.1: The Structure of Cells Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 4.8 Cell-to-Cell Communication Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Cell-to-Cell Communication • Cells are able to communicate with each other through special structures. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Communication Among Plant Cells • Plant cells have channels, called plasmodesmata, that are always open and hence have the effect of making the cytoplasm of one plant cell continuous with that of another. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Communication Among Animal Cells • Adjacent animal cells have channels, called gap junctions, that are composed of protein assemblages that open only as necessary. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Communication Among Animal Cells • These gap junctions allow the movement of small molecules and electrical signals between cells. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Cell Communication Plant tissues plasma membrane cell walls cytoplasm plasmodesmata Animal tissues gap junction plasma membranes cytoplasm (a) Plasmodesmata In plants, a series of tiny pores between plant cells, the plasmodesmata, allow for the movement of materials among cells. Thanks to the plasmodesmata channels, the cytoplasm of one cell is continuous with the cytoplasm of the next; the plant as a whole can be thought of as having a single complement of continuous cytoplasm. (b) Gap junctions In animals, protein assemblies come into alignment with one another, forming communication channels between cells. A cluster of many such assemblies—perhaps several hundred—is called a gap junction. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 4.19 Structures in Plant and Animal Cells Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Table 4.1