Cells: The Working Units of Life Seminar PDF

5 Cells: The Working Units of Life Chapter 5 Cells: The Working Units of Life Key Concepts 5.1 Cells Are the Fundamental Units of Life 5.2 Prokaryotic Cells Are the Simplest Cells 5.3 Eukaryotic Cells Contain Organelles 5.4 Extracellular Materials Provide Struct...

5 Cells: The Working Units of Life Chapter 5 Cells: The Working Units of Life Key Concepts 5.1 Cells Are the Fundamental Units of Life 5.2 Prokaryotic Cells Are the Simplest Cells 5.3 Eukaryotic Cells Contain Organelles 5.4 Extracellular Materials Provide Structure 5.5 Eukaryotic Cells Evolved in Several Steps Concept 5.1 Cells Are the Fundamental Units of Life (1) Cell theory is an important unifying theory of biology: Cells are the fundamental units of life. All organisms are composed of cells. All cells come from preexisting cells. Modern cells evolved from a common ancestor. Concept 5.1 Cells Are the Fundamental Units of Life (2) Most cells are small because a high surface area-to-volume ratio is essential. As a cell volume increases, chemical activity increases, along with the need for resources and waste removal. Surface area becomes limiting. Thus, large organisms consist of many small cells. Concept 5.1 Cells Are the Fundamental Units of Life (3) To see most cells, we use microscopes: Magnification: Increases apparent size. Resolution: Clarity of magnified object—minimum distance two objects can be apart and still be seen as two objects. Concept 5.1 Cells Are the Fundamental Units of Life (4) Two basic types of microscopes: Light microscopes: glass lenses and light; resolution = 0.2 μm Electron microscopes: electromagnets focus an electron beam; resolution = 0.2 nm Many different techniques can be used in microscopy. Figure 5.4 Looking at Cells (Part 1) Figure 5.5 Prokaryotic versus Eukaryotic 1 Concept 5.1 Cells Are the Fundamental Units of Life (7) Two types of cells: Prokaryotic (Bacteria and Archaea): have no membrane- enclosed internal compartments. Eukaryotic (Eukarya): have membrane-enclosed organelles in which different functions occur. Concept 24.1 Bacteria and Archaea Represent the First Split in the Tree of Life (1) All organisms share features such as: – Cell membranes and ribosomes – A common set of metabolic pathways, such as glycolysis – Semiconservative DNA replication – Using DNA to encode proteins, same genetic code, and similar DNA sequences Figure 5.6 A Prokaryotic Cell 2 Figure 5.6 A Prokaryotic Cell 1 Concept 5.2 Prokaryotic Cells Are the Simplest Cells (1) Features of prokaryotic cells: Enclosed by a cell membrane DNA located in a region called the nucleoid Cytoplasm: the rest of the cell contents Ribosomes: sites of protein synthesis Concept 5.2 Prokaryotic Cells Are the Simplest Cells (2) Most prokaryotes have a rigid cell wall outside the cell membrane. Bacterial cell walls contain peptidoglycan and some have an additional outer membrane. Some bacteria have a slimy capsule of polysaccharides. Bacteria that carry out photosynthesis have an internal membrane system that contains the molecules needed for photosynthesis. Cytoskeleton: System of protein filaments that maintain cell shape and play roles in cell movement and cell division. Concept 24.1 Bacteria and Archaea Represent the First Split in the Tree of Life (8) Before DNA sequencing, taxonomy was based on shape, color, motility, nutrition, antibiotic sensitivity, and cell wall structure. Bacterial cell walls contain peptidoglycan, a polymer of amino sugars. Archeal cell walls don’t have peptidoglycan. https://www.creative- proteomics.com/services/peptidogly can-structure-analysis.htm Concept 5.2 Prokaryotic Cells Are the Simplest Cells (3) Bacteria that carry out photosynthesis have an internal membrane system that contains the molecules needed for photosynthesis. 5.2 What Features Characterize Prokaryotic Cells? Others have internal membrane folds (mesosomes) that are attached to the plasma membrane; they may function in cell division or in energy-releasing reactions. Concept 24.1 Bacteria and Archaea Represent the First Split in the Tree of Life (10) The Gram stain method separates bacteria into two groups. It uses two different stains—one violet and one red. Gram-positive bacteria retain the violet dye. Gram-negative bacteria retain the red dye. Differences are due to the structure of the cell wall. Concept 24.1 Bacteria and Archaea Represent the First Split in the Tree of Life (11) Gram-positive bacteria have a thick layer of peptidoglycan outside the cell membrane. Concept 24.1 Bacteria and Archaea Represent the First Split in the Tree of Life (11) Gram-negative bacteria have a thin layer of peptidoglycan in the periplasmic space between the cell membrane and another outer membrane. 5.2 What Features Characterize Prokaryotic Cells? Cytoskeleton: System of protein filaments that maintain cell shape and play roles in cell movement and cell division. This movie shows an E. coli cell near the end of cell division, harboring an E coli FtsZ-GFP fusion. FtsZ begins localized at the interface between the cells, but quickly relocalizes to the putative new cell division site in each of the daughter cells. https://www.bio.cmu.edu/courses/03441/TermPapers/99TermPapers/Caulo/ftsz-pic.html Concept 5.2 Prokaryotic Cells Are the Simplest Cells (4) Some prokaryotes swim using flagella, made of the protein flagellin. Pili are hairlike structures projecting from the cell surface. They help bacteria adhere to other cells. Fimbriae are shorter; they help cells adhere to surfaces such as animal cells. Figure 5.7 Prokaryotic Flagella 1 Figure 5.9 Eukaryotic Cells (Part 1) 2 Concept 5.3 Eukaryotic Cells Contain Organelles (1) Eukaryotic cells are about 10 times larger than those of prokaryotes. Membrane-enclosed organelles carry out specific functions. Most eukaryotic cells have similar organelles. Concept 5.3 Eukaryotic Cells Contain Organelles (2) Organelles were first studied using light microscopy and then electron microscopy. Stains targeted to specific molecules helped determine chemical composition of organelles. Cell fractionation separates organelles by size or density for chemical analyses. Figure 5.9 (1) Eukaryotic Cells 2 Concept 5.3 Eukaryotic Cells Contain Organelles (2) Organelles were first studied using light microscopy and then electron microscopy. Stains targeted to specific molecules helped determine chemical composition of organelles. Cell fractionation separates organelles by size or density for chemical analyses. Figure 5.9 Eukaryotic Cells (Part 3) Concept 5.3 Eukaryotic Cells Contain Organelles (4) Nucleus—usually the largest organelle Contains most of the DNA Site of DNA replication Site where gene transcription is turned on or off Assembly of ribosomes begins in a region called the nucleolus Figure 5.10 The Nucleus, Chromatin, and Chromosomes 3 Concept 5.3 Eukaryotic Cells Contain Organelles (5) The nucleus is surrounded by the nuclear envelope, a double membrane. Nuclear pores in the envelope control movement of molecules across the envelope. The outer membrane is continuous with the endoplasmic reticulum. Figure 5.10 The Nucleus, Chromatin, and Chromosomes 1 The Nucleus, Chromatin, and Chromosomes (A) Chromatin consists of nuclear DNA and the proteins associated with it. When the cell is not dividing, the chromatin is dispersed throughout the nucleus. This two- dimensional image was made using a transmission electron microscope. (B) The nuclear envelope has many pores that regulate traffic of large molecules such as RNA and proteins in and out of the nucleus. (C) The chromatin in dividing cells becomes highly condensed, so that the individual chromosomes can be seen. This three-dimensional image of isolated metaphase chromosomes was produced using a scanning electron microscope. Concept 5.3 Eukaryotic Cells Contain Organelles (7) Endomembrane system: Interconnected system of membrane-enclosed compartments. Tiny, membrane-surrounded vesicles shuttle substances between the various components. In the living cell, the membranes and the materials they contain are in constant motion. Figure 5.9 Eukaryotic Cells (Part 7) Concept 5.3 Eukaryotic Cells Contain Organelles (8) Endoplasmic reticulum (ER): Network of membranes in the cytoplasm; large surface area. Rough endoplasmic reticulum (RER): Ribosomes are attached. Newly made proteins enter the RER lumen and are modified, folded, and transported to other regions in vesicles that pinch off from the RER. Figure 5.9 Eukaryotic Cells (Part 10) Concept 5.3 Eukaryotic Cells Contain Organelles (9) Smooth endoplasmic reticulum (SER): No ribosomes. Chemically modifies small molecules such as drugs and pesticides Site of glycogen degradation in animal cells Synthesis of lipids and steroids Stores calcium ions Figure 5.11 The Endomembrane System 1 Concept 5.3 Eukaryotic Cells Contain Organelles (3) Ribosomes: Sites of protein synthesis. – Similar structure in prokaryotes and eukaryotes. – Consist of two subunits: ribosomal RNA (rRNA) and more than 50 different protein molecules. Figure 5.11 The Endomembrane System The Golgi apparatus processes and packages proteins. Concept 5.3 Eukaryotic Cells Contain Organelles (10) Golgi apparatus: Flattened sacs (cisternae) and small vesicles. Receives proteins from the RER Modifies, concentrates, packages, and sorts proteins Figure 5.9 Eukaryotic Cells (Part 14) Figure 5.11 The Endomembrane System 2 Figure 5.11 The Endomembrane System Rough endoplasmic reticulum is studded with ribosomes that are sites for protein synthesis. They produce its rough appearance. Cytosol Protein-containing vesicles from the Nucleus endoplasmic reticulum transfer substances to the cis face of the Golgi apparatus. Lumen Cisterna The Golgi apparatus chemically cis modifies proteins in its lumen… region …and “targets” Golgi apparatus them to the correct destinations. Medial region trans region Proteins for use Cell within the cell membrane Proteins for use Lysosome outside the cell Smooth endoplasmic reticulum is a site for lipid Outside of cell synthesis and chemical modification of proteins. Concept 5.3 Eukaryotic Cells Contain Organelles (11) Lysosomes: Contain digestive enzymes that hydrolyze macromolecules into monomers. Lysosomes are sites for the hydrolysis of material taken into the cell by phagocytosis. Discarded components exit the cell by exocytosis. Primary lysosomes originate from the Golgi apparatus. Concept 5.3 Eukaryotic Cells Contain Organelles (12) Food molecules enter the cell by phagocytosis—a phagosome is formed. Phagosomes fuse with primary lysosomes to form secondary lysosomes. Enzymes hydrolyze the food molecules. Wastes are ejected by exocytosis. Figure 5.12 Lysosomes Isolate Digestive Enzymes from the Cytoplasm (Part 2) Figure 5.12 Lysosomes Isolate Digestive Enzymes from the Cytoplasm 1 Figure 5.13 A Mitochondrion Converts Energy from Fuel Molecules into ATP 3 Concept 5.3 Eukaryotic Cells Contain Organelles (13) Mitochondria: Energy in fuel molecules such as glucose is transformed to the bonds of energy-rich ATP (cellular respiration). Cells that require a lot of energy have many mitochondria. They can reproduce and divide independently of the central nucleus. Figure 5.13 A Mitochondrion Converts Energy from Fuel Molecules into ATP 2 Concept 5.3 Eukaryotic Cells Contain Organelles (14) Mitochondria have two membranes. Inner membrane folds inward to form cristae—creates large surface area for the embedded proteins involved in cellular respiration. Mitochondrial matrix contains DNA and ribosomes to make the proteins needed for cellular respiration. Figure 5.13 A Mitochondrion Converts Energy from Fuel Molecules into ATP 1 Concept 5.3 Eukaryotic Cells Contain Organelles (17) Peroxisomes: A peroxisome is a membrane-bound organelle, found in the cytoplasm of virtually all eukaryotic cells cells. Collect and break down toxic byproducts of metabolism such as H2O2, using specialized enzymes. Peroxisomes are involved in the catabolism of very long chain fatty acids, branched chain fatty acids, bile acid intermediates (in the liver), D-amino acids, and polyamines. Glyoxysomes: Only in plants—lipids are converted to carbohydrates for growth. Figure 5.9 Eukaryotic Cells (Part 12)  Centrioles are associated with nuclear division. Centrioles Concept 5.3 Eukaryotic Cells Contain Organelles (3) Ribosomes: Sites of protein synthesis. – Similar structure in prokaryotes and eukaryotes. – Consist of two subunits: ribosomal RNA (rRNA) and more than 50 different protein molecules. Figure 5.9 Eukaryotic Cells (Part 4) 1 Concept 5.3 Eukaryotic Cells Contain Organelles (20) Cytoskeleton: – Supports and maintains cell shape – Holds organelles in position – Moves organelles – Involved in cytoplasmic streaming – Interacts with extracellular structures to hold cell in place – Composed of three types of filaments Figure 5.17 The Cytoskeleton 2 Figure 5.17 The Cytoskeleton 1 Concept 5.3 Eukaryotic Cells Contain Organelles (21) Microfilaments: – Help a cell or parts of a cell to move – Determine cell shape – Made from the protein actin – Actin polymerizes to form long helical chains (reversible) – Have distinct ends: plus and minus Concept 5.3 Eukaryotic Cells Contain Organelles (22) Actin filaments are associated with localized changes in cell shape, including cytoplasmic streaming and amoeboid movement. Microfilaments are also involved in the formation of pseudopodia. In some cells, microfilaments form a meshwork just inside the cell membrane. This provides structure, for example in the microvilli that line the human intestine. Figure 5.22A (1) The Role of Microfilaments in Cell Movement — Showing Cause and Effect in Biology (Experiment) 1 Figure 5.18 Microfilaments for Support 2 Figure 5.18 Microfilaments for Support 1 Cells that line the intestine are folded into tiny projections called microvilli, which are supported by microfilaments. The microfilaments interact with intermediate filaments at the base of each microvillus. Concept 5.3 Eukaryotic Cells Contain Organelles (24) Intermediate filaments: – 50 different kinds in 6 molecular classes – Tough, ropelike protein structures – Anchor cell structures in place – Resist tension Concept 5.3 Eukaryotic Cells Contain Organelles (25) Microtubules: – Long, hollow cylinders – Form a rigid internal skeleton – Act as a framework for motor proteins – Made from dimers of the protein tubulin – Can change length rapidly by adding or losing dimers at plus or minus ends Figure 5.19 Cilia 3 Concept 5.3 Eukaryotic Cells Contain Organelles (26) Cilia and eukaryotic flagella are made of microtubules in “9 + 2” array. Cilia—short, hundreds on one cell, move stiffly to propel the cell or move fluid over a cell. Flagella—longer, usually one or two present, movement is snakelike. Figure 5.19 Cilia 1 Figure 5.20 Motor Protein Moves Microtubules in Cilia and Flagella 3 Concept 5.3 Eukaryotic Cells Contain Organelles (28) Microtubules serve as tracks for motor proteins, which move vesicles or organelles from one part of a cell to another. Kinesin binds to a vesicle and “walks” it along by changing shape. Kinesins move materials toward the plus end; dyneins move materials toward the minus end. Figure 5.20 Motor Protein Moves Microtubules in Cilia and Flagella 1 Figure 5.21 A Motor Protein Pulls Vesicles along Microtubules 1 Kinesins move materials toward the plus end; dyneins move materials toward the minus end. Concept 5.4 Extracellular Materials Provide Structure (1) Extracellular structures are secreted to the outside of the cell membrane. Example: the peptidoglycan cell wall of bacteria In eukaryotes, extracellular structures consist of fibrous macromolecules embedded in a gel-like medium. Many animal cells are surrounded by an extracellular matrix composed of fibrous proteins such as collagen, gel-like proteoglycans, and other proteins. Concept 5.4 Extracellular Materials Provide Structure (5) The extracellular matrix: – Holds cells together in tissues – Contributes to properties of bone, cartilage, skin, etc. – Filters materials passing between different tissues – Orients cell movements in development and tissue repair – Plays a role in chemical signaling Figure 5.24 An Extracellular Matrix 1 Concept 5.5 Eukaryotic Cells Evolved in Several Steps (1) Evidence of the first eukaryote cells appears in the fossil record 2.7 billion years ago. The advent of compartmentalization and evolution of eukaryotic cells was a major event in the history of life. How did compartmentalization arise? Figure 5.25 The Origins of Organelles 1 Concept 5.5 Eukaryotic Cells Evolved in Several Steps (2) The nucleus and endomembrane system may have originated from the inward folds of the cell membrane in prokaryotes. Enclosed compartments would be advantageous: chemicals could be concentrated and chemical reactions would proceed more efficiently. Concept 5.5 Eukaryotic Cells Evolved in Several Steps (3) Some organelles arose by symbiosis. The theory of endosymbiosis proposes that mitochondria and plastids arose when one cell engulfed another cell. Many of the ingested cell’s genes were transferred to the host’s DNA but the symbionts retained specialized functions.  If the cells that line the intestine lost their microvilli structure, what could be a possible result? a. Decreased movement of nutrients through the intestinal tract b. Loss of nutrients from the cell into the intestinal tract due to a decrease in surface area-to-volume ratio c. No effect, since cells would continue their normal cellular activity d. Decreased absorption of nutrients into the cell due to a decrease in surface area-to-volume ratio e. Increased transport of nutrients into the blood stream 2. Which statement about ribosomes is correct? a. They are complexes of DNA and proteins. b. They can be visualized under a light microscope. c. They are found only in eukaryotic cells. d. They are the sites of protein synthesis. 3. The Golgi a. is the site for glycogen degradation in animal cells. b. concentrates, packages, and sorts proteins. c. contains thylakoids. d. contains cristae.  Which of the following three components of the cytoskeleton is involved in structural support, but not movement? a. b. c. 5. Which of the following is not a function of the extracellular matrix? a. Helping filter materials passing between cells b. Helping orient cell movements during embryonic development c. Playing a role in chemical signaling d. Contributing to the physical properties of bone e. Acting as a barrier to fungal infection Which of the following represents the correct order of the outer layers found on some prokaryotes, from the interior to the exterior? a. Plasma membrane, peptidoglycan cell wall, polysaccharide-rich phospholipid membrane, capsule b. Plasma membrane, polysaccharide-rich phospholipid membrane, peptidoglycan cell wall, capsule c. Capsule, polysaccharide-rich phospholipid membrane, peptidoglycan cell wall, plasma membrane d. Capsule, plasma membrane, peptidoglycan cell wall, polysaccharide-rich phospholipid membrane e. Peptidoglycan cell wall, plasma membrane, polysaccharide-rich phospholipid membrane, capsule 21. In some prokaryotic organisms, the plasma membrane folds to form an internal membrane system that is able to a. carry out photosynthesis. b. engulf and phagocytize bacteria. c. synthesize proteins. d. propel the cell. e. hydrolyze carbohydrates to ATP. 25. Prokaryotic cells are generally smaller than eukaryotic cells because a. prokaryotes have more diverse energy sources. b. prokaryotes have a capsule that limits cell growth. c. the rigid cell wall of prokaryotes limits cell size. d. prokaryotes lack the genetic material needed to support larger cells. e. prokaryotic cells do not have compartments, a feature of eukaryotic cells that takes up more space in the cell. In a mixture of cellular structures, which structure would require the greatest amount of centrifugal force in order for it to sediment at the bottom of a centrifuge tube? a. Mitochondria b. Nuclei c. Golgi apparatus d. Chloroplast e. Ribosome Proteins packaged by the Golgi apparatus are delivered to the correct location by means of a. identifying carbohydrate groups covalently bound to the packaged proteins. b. the general flow of vesicles within the cell. c. the control provided by the nucleus. d. motor proteins that direct the Golgi apparatus. e. microfilaments. Which of the following spherical cells would exchange the greatest amount of substances and waste products with its environment relative to its internal chemical activity? a. A 1-mm cell b. A 2-mm cell c. A 3-mm cell d. A 4-mm cell e. All cells exchange substances and waste products with the environment at the same rate with respect to their ability to carry out chemical activity, irrespective of size. The role of cellular organelles is to a. provide structural support for the cell. b. decrease the flow of materials into and out of the cell. c. increase the efficiency of cellular activities. d. provide a means of cellular reproduction. e. regulate the flow of traffic inside the cell. If a bacterial cell were fed radioactive sulfur such that all of its proteins were labeled, all of the following specialized structures would contain the labeled protein except for the a. pili. b. capsule. c. flagella. d. fimbriae. e. cytoskeleton. If you removed the pili from a bacterial cell, the bacterium would a. no longer be able to swim. b. lose some of its ability to adhere to other cells. c. no longer be able to regulate the movement of molecules into and out of the cell. d. dry out. e. change its shape. Proteins that are transported in vesicles are made by a. the Golgi apparatus. b. ribosomes within the mitochondrion. c. the smooth endoplasmic reticulum. d. ribosomes on the rough endoplasmic reticulum. e. ribosomes within chloroplasts.