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Biology A Guide to the Natural World Chapter 4 • Lecture Outline Life’s Home: The Cell Fifth Edition David Krogh © 2011 Pearson Education, Inc. 4.1 Cells as Life’s Fundamental Unit © 2011 Pearson Education, Inc. Cells as Life’s Fundamental Unit • With the possible exception of viruses, every form of life on Earth either is a cell or is composed of cells. © 2011 Pearson Education, Inc. Cells as Life’s Fundamental Unit • Cells come into existence only through the activity of other cells. © 2011 Pearson Education, Inc. 4.2 Prokaryotic and Eukaryotic Cells © 2011 Pearson Education, Inc. Prokaryotic and Eukaryotic Cells • All cells can be classified as prokaryotic or eukaryotic. © 2011 Pearson Education, Inc. Prokaryotic and Eukaryotic Cells • Prokaryotic cells either are bacteria or another single-celled life-form called archaea. © 2011 Pearson Education, Inc. Prokaryotic and Eukaryotic Cells • Setting bacteria and archaea aside, all other cells are eukaryotic. © 2011 Pearson Education, Inc. Prokaryotic and Eukaryotic Cells • 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. © 2011 Pearson Education, Inc. Prokaryotic and Eukaryotic Cells • Eukaryotic cells tend to be much larger than prokaryotic cells. They have more of the specialized internal structures called organelles than do prokaryotic cells. © 2011 Pearson Education, Inc. Prokaryotic and Eukaryotic Cells • Many eukaryotes are multicelled organisms, whereas all prokaryotes are single-celled. © 2011 Pearson Education, Inc. Prokaryotic cells Eukaryotic cells DNA spread through much of cell 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 © 2011 Pearson Education, Inc. Figure 4.2 4.3 The Eukaryotic Cell © 2011 Pearson Education, Inc. The Eukaryotic Cell • There are five principal components to the eukaryotic cell: the nucleus, other organelles, the cytosol, the cytoskeleton, and the plasma membrane. © 2011 Pearson Education, Inc. The Eukaryotic Cell • Organelles are “tiny organs” within the cell that carry out specialized functions, such as energy transfer and materials recycling. © 2011 Pearson Education, Inc. The Animal Cell nuclear pores The nucleus contains DNA the cell’s primary nuclear envelope complement of DNA. nucleolus The smooth endoplasmic reticulum is the site of the production of lipid molecules such as estrogen and testosterone. free ribosomes plasma membrane cytoskeleton Mitochondria are the powerplant organelles that extract energy from food and put it into a form cells can use. lysosome The folds of the rough endoplasmic reticulum form a set of chambers within which proteins are processed. transport vesicle All the cell’s structures outside the nucleus are immersed in a jelly-like fluid called the cytosol. Composed mostly of water, the cytosol is a location for countless chemical reactions carried out within the cell. How are cell proteins sorted and shipped, so that they end up at the right location? Partly through the work of the Golgi complex. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. The Eukaryotic Cell Components of eukaryotic cells nucleus other organelles cytosol © 2011 Pearson Education, Inc. cytoskeleton plasma membrane Figure 4.3 4.4 A Tour of the Animal Cell’s Protein Production Path © 2011 Pearson Education, Inc. Tour of the Animal Cell’s Protein Production Path • Information for the construction of proteins is contained in the DNA located in the cell nucleus. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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). © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. The Protein Production Path • Some ribosomes are not embedded in the RER but instead remain free-standing in the cytosol. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. The Protein Production Path • Membrane-lined structures that carry cellular materials are called transport vesicles. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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). 3. Proteins are sorted and shipped… to cytosol for export out of cell to plasma membrane © 2011 Pearson Education, Inc. Figure 4.9 4.5 Cell Structures Outside the Protein Production Path © 2011 Pearson Education, Inc. Cell Structures Outside the Protein Production Path • The smooth endoplasmic reticulum is a network of membranes that functions to synthesize lipids and to detoxify potentially harmful substances. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Figure 4.10 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. © 2011 Pearson Education, Inc. Mitochondria and Energy Mitochondrion food oxygen outer membrane inner membrane water carbon dioxide ATP © 2011 Pearson Education, Inc. Figure 4.11 4.6 The Cytoskeleton: Internal Scaffolding © 2011 Pearson Education, Inc. The Cytoskeleton: Internal Scaffolding • Cells have within them a web of protein strands, called a cytoskeleton. © 2011 Pearson Education, Inc. The Cytoskeleton: Internal Scaffolding • The cytoskeleton provides the cell with structure, facilitates the movement of materials inside the cell, and facilitates cell movement. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. (a) Microfilaments (in red) (b) Intermediate filaments 7 nm 10 nm 25 nm Main function: changes Main function: maintenance in cell shape of cell shape © 2011 Pearson Education, Inc. (c) Microtubules Main functions: maintenance of cell shape, movement of organelles, cell mobility (cilia and flagella) Figure 4.12 Microfilaments • Microfilaments are made of the protein actin. © 2011 Pearson Education, Inc. Microfilaments • They help the cell move and capture prey by forming rapidly in the direction of movement and decomposing rapidly at their other end. © 2011 Pearson Education, Inc. Microfilaments © 2011 Pearson Education, Inc. Figure 4.13 Intermediate Filaments • Intermediate filaments provide support and structure to the cell. © 2011 Pearson Education, Inc. Microtubules • Microtubules play a structural role in cells and facilitate the movement of materials inside the cell by serving as transport “rails.” © 2011 Pearson Education, Inc. Microtubules • Cilia and flagella are extensions of cells composed of microtubules. © 2011 Pearson Education, Inc. Cilia • Cilia extend from cells in great numbers, serving to move the cell or to move material around the cell. © 2011 Pearson Education, Inc. Flagella • By contrast, one—or at most a few— flagella extend from cells that have them. © 2011 Pearson Education, Inc. Flagella • The function of flagella is cell movement. © 2011 Pearson Education, Inc. (a) Transport monorails transport vesicle motor proteins microtubule (b) Cilia (c) Flagellum © 2011 Pearson Education, Inc. Figure 4.14 4.7 The Plant Cell © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. The Plant Cell • Plant cells have three structures not found in animal cells: • a cell wall • a large central vacuole • the organelles called chloroplasts © 2011 Pearson Education, Inc. The Plant Cell Plant cells have a cell wall, chloroplasts, and a central vacuole, while cytoskeleton animal cells do not. nuclear envelope nuclear pores nucleus DNA nucleolus rough endoplasmic reticulum smooth endoplasmic reticulum free ribosomes cell wall chloroplast Golgi complex cytosol plasma membrane central vacuole mitochondrion © 2011 Pearson Education, Inc. Figure 4.17 The Central Vacuole • The central vacuole stores nutrients and degrades waste products. © 2011 Pearson Education, Inc. The Cell Wall • The cell wall gives the plant structural strength and helps regulate the intake and retention of water. © 2011 Pearson Education, Inc. Chloroplasts • Chloroplasts are the sites of photosynthesis. © 2011 Pearson Education, Inc. Chloroplasts water carbon dioxide minerals outer membrane inner membrane sugar (food) oxygen © 2011 Pearson Education, Inc. Figure 4.19 The Structure of Cells Animation 4.1: The Structure of Cells © 2011 Pearson Education, Inc. 4.8 Cell-to-Cell Communication © 2011 Pearson Education, Inc. Cell-to-Cell Communication • Cells are able to communicate with each other through special structures. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Communication Among Animal Cells • Adjacent animal cells have channels, called gap junctions, that are composed of protein assemblages that open only as necessary. © 2011 Pearson Education, Inc. Communication Among Animal Cells • These gap junctions allow the movement of small molecules and electrical signals between cells. © 2011 Pearson Education, Inc. Plant tissues (a) Plasmodesmata plasmodesmata Animal tissues In plants, a series of tiny pores plasma between plant cells, the membrane plasmodesmata, allow for the cell walls movement of materials among cells. Thanks to the cytoplasm 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. gap junction (b) Gap junctions plasma In animals, protein assemblies membranes come into alignment with one cytoplasm another, forming communication channels between cells. A cluster of many such assemblies—perhaps several hundred—is called a gap junction. © 2011 Pearson Education, Inc. Figure 4.20 Table 4.1 Structures in Plant and Animal Cells Function and Location Name Function and Location Nucleus Site of most of the cell’s DNA Location: Inside nuclear envelope Mitochondria Transform energy from food Location: Cytoplasm Nucleolus Synthesis of ribosomal RNA Location: Nucleus Rough endoplasmic reticulum Protein processing Location: Cytoplasm Ribosomes Sites of protein synthesis Location: Rough ER, Free-standing in cytoplasm Smooth endoplasmic reticulum Lipid synthesis, storage; detoxification of harmful substances Location: Cytoplasm Cytoskeleton Maintains cell shape, facilitates cell movement and movement of materials within cell Location: Cytoplasm Vesicles Transport of proteins and other cellular materials Location: Cytoplasm Cytosol Protein-rich fluid in which organelles and cytoskeleton are immersed Location: Cytoplasm Central vacuole (in plant cells only) Nutrient storage, cell pressure maintenance, pH balance Location: Cytoplasm Golgi complex Processing, sorting of proteins Location: Cytoplasm Chloroplasts (in plant cells only) Photosynthesis Location: Cytoplasm Lysosomes (in animal cells only) Digestion of imported materials and cell’s own used materials Location: Cytoplasm Cell walls (in plant cells only) Limit water uptake; maintain cell membrane shape, protect from outside influences Location: Outside plasma membrane Name © 2011 Pearson Education, Inc. Table 4.1