Cells CH02 - PDF

CELLS Reading (Campbell Biology – Concepts and Connections, 10th edition): Chapter 4, Cell Structure Introduction Section 4.0, Microscopes reveal a starling new view of life Section 4.1, microscopes reveal the world of the cell Section 4.2, The small size of cells relates to the nee...

CELLS Reading (Campbell Biology – Concepts and Connections, 10th edition): Chapter 4, Cell Structure Introduction Section 4.0, Microscopes reveal a starling new view of life Section 4.1, microscopes reveal the world of the cell Section 4.2, The small size of cells relates to the need to exchange materials across the plasma membrane Section 4.3, Prokaryotic cells are structurally simpler than eukaryotic cells Section 4.4, Eukaryotic cells are partitioned into functional compartments Section 4.5, The nucleus contains the cell’s genetic instructions Section 4.6, Ribosomes make proteins for use in the cell and for export Section 4.7, Many organelles are connected in the endomembrane system Section 4.8, The endoplasmic reticulum is a biosynthetic workshop Section 4.9. The Golgo apparatus modifies, sorts and ships cell products Section 4.10, Lysosomes are digestive compartments within a cell Section 4.11, Vacuoles function in general maintenance of the cell Section 4.12, A review of structures involved in manufacturing and breakdown Section 4.13, Mitochondria harvest chemical energy from food Section 4.14, Chloroplasts convert solar energy to chemical energy Section 4.16, The cell’s internal skeletal helps organize it structure and activities Section 4.18, Cilia and flagella move when microtubules bend Section 4.19, The extracellular matrix of animal cells functions in support and regulation Section 4.20, Three types of cell junctions are found in animal tissues Section 4.21, Cell walls enclose and support plant cells Section 4.22, Review: eukaryotic cell structures can be grouped on the basis of four main functions Section 5.1, Membranes are fluid mosaics of lipids and proteins What you should know about going into this topic – the major classes of biomolecules Cells 2 the importance of cells in the structure and function of organisms What you will know by the end – the differences between prokaryotic and eukaryotic cells the structure and function of the major organelles and macromolecular assemblies in eukaryotic cells how these structures interact A. Cell Theory Cell theory states that organisms consist of cells and the products of cells, and that all cells come from pre-existing cells. The cell is the unit of biological structure and biological function. In other words, the cell is the level of biological organization at which the properties of life emerge from interactions of non-living matter. B. How Cells Are Studied (Campbell Biology – Concepts and Connections, Sections 4.0, 4.1) 1. Cells can be studied by microscopy. light microscopy transmission electron microscopy Cells 3 2. Cells can also be studied by separating their contents using a centrifuge, and then using biochemical techniques to study the fractionated components. 3. Cells can be studied by classical and molecular genetics. This is especially useful in understanding multistep processes, such as biochemical pathways. C. Why Cells Are Small (Campbell Biology – Concepts and Connections, Section 4.2) 1. Surface / volume considerations The surface / volume ratio of a cell deceases with increasing cell size. Surface / volume ratio deceases with increasing sphericity. Cells 4 For a small cell, compared to a larger one of the same shape, each unit of volume is served by a larger area of surface. Therefore the traffic of materials into and out of the cell is more rapid with smaller cells. Fig. 4.2 Surface / volume ratio increases as cell size decreases. from Campbell Biology – Concepts and Connections, 10th edition, Taylor et al., 2021. 2. There is a limit to the amount of products of gene expression (proteins) that can be produced by expression in one nucleus, from two alleles. Cells 5 3. Some cells can be very large. They are either metabolically inactive, or they are non-spherical, or they have many nuclei. D. Prokaryotic Cells and Eukaryotic Cells (Campbell Biology – Concepts and Connections, Sections 4.3, 4.4) 1. Prokaryotic cells include bacteria and archaea. They are smaller than eukaryotic cells, do not have membrane-bound compartments, have no nucleus or cytoskeleton, and have small genomes (in most species, 1500-4000 genes). 2. Eukaryotic cells make up protists, plants, animals, and fungi. They are larger than prokaryotic cells, have membrane-bound compartmentalization of functions, have a nucleus and a cytoskeleton, and have larger genomes (in most species, 6,000-25,000 genes). Cells 6 E. The Plasma Membrane and Membranes in General (Campbell Biology – Concepts and Connections, Section 5.1) 1. Surrounding all cells is the plasma membrane, which acts as a selective barrier. A selective barrier is a barrier than allows some things to pass through, but not others. Fig. 5.1 The plasma membrane of an animal cell. from Campbell Biology – Concepts and Connections, 10th edition, Taylor et al., 2021. Cells 7 2. The membranes that surround the organelles in a eukaryotic cell are also selective barriers. The many functions in the cell are therefore compartmentalized. F. Nucleus (Campbell Biology – Concepts and Connections, Section 4.5) 1. The nucleus is a protected area, bound by two membranes (the nuclear envelope), where chromosomes are located and where genes are transcribed. Fig. 4.5 The nucleus of a eukaryotic cell. Campbell Biology – Concepts and Connections, 10th edition, Taylor et al., 2021. Cells 8 2. Contents of the nucleus chromatin (organized into chromosomes) nucleolus enzymes that work on DNA G. Ribosomes (Campbell Biology – Concepts and Connections, Sections 4.6) 1. Ribosomes are where protein synthesis takes place. 2. Ribosomes consist of two subunits, a larger one and a smaller one, each composed of ribosomal RNA (rRNA) and many proteins. Cells 9 Fig. 10.12 A ribosome engaged in making a new polypeptide. from Campbell Biology – Concepts and Connections, 10th edition, Taylor et al., 2021. 3. Free ribosomes are located in the cytosol (the aqueous part of the cytoplasm outside the organelles). Free ribosomes make proteins that will be active in cytosol chloroplast mitochondrion nucleoplasm peroxisomes 4. Bound ribosomes are attached to the endoplasmic reticulum (rough ER). See the next section. H. Endomembrane System (Campbell Biology – Concepts and Connections, Sections 4.7 – 4.12) 1. The endomembrane system is a network of components connected either directly, or interacting by means of transport vesicles that move between them. Cells 10 These components are involved in the synthesis, modification, packaging and shipping of proteins bound for various destinations in the cell and on the outside of the cell. 2. Components of the endomembrane system nuclear envelope endoplasmic reticulum (ER) rough ER smooth ER transport vesicles Golgi apparatus Cells 11 lysosomes vacuole plasma membrane Fig. 4.12 The endomembrane system (smooth ER, vacuole and lysosome not shown). from Campbell Biology – Concepts and Connections, 10th edition, Taylor et al., 2021. Cells 12 I. Mitochondrion (Campbell Biology – Concepts and Connections, Section 4.13) 1. The mitochondrion hosts reactions that provide most of the ATP that cells need as an immediate source of energy in biochemical reactions and processes. 2. The organelle has two membranes. The inner membrane separates two aqueous compartments: the mitochondrial matrix and the intermembrane space. mitochondrial matrix – site of the citric acid cycle inner mitochondrial membrane – site of electron transport and proton pumping intermembrane space – site of H+ accumulation Cells 13 Fig. 4.13 The mitochondrion. from Campbell Biology – Concepts and Connections, 10th edition, Taylor et al., 2021. 3. The mitochondrion has its own genome and gene expression system. Cells 14 J. Chloroplast (Campbell Biology – Concepts and Connections, Section 4.14) 1. Plastids are a family of interconvertible organelles that perform many functions in algae and plants. The chloroplast is a type of plastid that performs photosynthesis. 4.14 The chloroplast. from Campbell Biology – Concepts and Connections, 10th edition, Taylor et al., 2021. 2. Structure of the chloroplast double membrane thylakoid membrane, where light is absorbed and converted to useful energy; chlorophyll functions in the light absorption Cells 15 stroma, where this useful energy is used to fix CO2 (i.e. make sugars using CO2) circular DNA – about 150 genes, 120 kb K. Cytoskeleton (Campbell Biology – Concepts and Connections, Sections 4.16, 4.18) 1. The cytoskeleton constitutes what you might call the bones and muscles of the cell. It is an extensive, dynamic network of protein filaments and other associated proteins in eukaryotic cells. It helps to support cells mechanically and maintain cell shape. It enables changes in cell shape. It provides movement within the cell, and movement of the cell as a whole. Cells 16 4.16 Types of cytoskeletal elements, each of them made from different proteins from Campbell Biology – Concepts and Connections, 10th edition, Taylor et al., 2021. 2. Intermediate filaments – tough protein fibers An extensive network of intermediate filaments in the cytosol provides shape and order to the cell and to the nucleus. 3. Microtubules are hollow fibers that can polymerize (get longer), depolymerize (get shorter), or remain stable. Cells 17 They are constructed from -tubulin and -tubulin proteins. Microtubules are associated with motor proteins that use ATP energy to move cargo (such as vesicles and chromosomes) along the microtubules, like locomotives pulling cars along a train track. Microtubules form the core of flagella and cilia. 4. Microfilaments are polymerized molecules of actin (a protein). The motor proteins associated with microfilaments are myosins. The actin-myosin interaction underlies muscle contraction, cytoplasmic streaming, cell crawling and animal cell cytokinesis (cell division). Cells 18 L. The Cell Surface (Campbell Biology – Concepts and Connections, Sections 4.19 – 4.22) 1. Thin plant cell walls are constructed of cellulose microfibrils in a matrix of other polysaccharides and proteins. Thicker walls are fortified with lignin. Cell wall functions – ▪ protection ▪ maintenance of cell shape ▪ structural support for the whole plant ▪ prevention of excess water uptake by osmosis s Fig. 4.21 The plant cell wall. from Campbell Biology – Concepts and Connections, 10th edition, Taylor et al., 2021. Cells 19 2. The animal cell surface junctions between cells ▪ tight junctions – diffusion barriers ▪ desmosomes – strong connections ▪ gap junctions – communication junctions Fig. 4.20 Junctions between animal cells. from Campbell Biology – Concepts and Connections, 10th edition, Taylor et al., 2021. the extracellular matrix – glycoproteins (eg. collagen), proteoglycans, and other proteins cross-linked to one another by extracellular adhesion proteins Cells 20 LIST of IMPORTANT TERMS and CONCEPTS Cells cell theory light microscopy transmission electron microscopy centrifugation biochemistry genetics surface / volume ratio gene expression products prokaryotic cells eukaryotic cells membrane-bound compartments nucleus cytoskeleton plasma membrane selective barrier compartmentalization nucleus nuclear envelope chromatin chromosomes nucleolus ribosome large subunit small subunit ribosomal RNA ribosomal proteins free ribosomes bound ribosomes endomembrane system rough ER smooth ER transmembrane proteins secreted proteins transport vesicles Golgi apparatus Cells 21 lysosomes vacuole mitochondrion inner and outer mitochondrial membranes electron transport chain intermembrane space H+ accumulation mitochondrial genome plastids chloroplast inner and outer chloroplast membranes thylakoid membrane stroma CO2 fixation chloroplast DNA cytoskeleton intermediate filaments microtubules - and -tubulin ATP-dependent motor proteins cilia flagella microfilaments actin myosin plant cell wall cellulose lignin plasmodesmata animal intercellular junctions tight junctions desmosomes gap junctions extracellular matrix glycoproteins collagen glycoplipids extracellular adhesion proteins Cells 22 Questions from Campbell Biology – Concepts and Connections, 10/e, Taylor et al. Chapter 4 Testing Your Knowledge Questions 2 – 5, 8 – 11 STUDY QUESTIONS – Cells 1. The surface area of a sphere, A, is given by A=4r2. The volume of a sphere, V, is given by V=(4r3)/3. Compare the surface area of plasma membrane of a spherical cell that services each unit of volume in cells with the following diameters: 1 m, 20 m, 1000 m. What is the biological significance of your answer? 2. Name the structure(s) in the cell where the following activities take place. a) protein synthesis; b) photosynthesis; c) synthesis of proteins to be secreted from the cell; d) storage of genetic information; e) synthesis of small and large ribosomal subunits; f) hydrolysis and recycling of damaged organelles; g) phospholipid synthesis. 3. How many lipid bilayers would a water molecule cross if it travelled from the interior of the nucleus, out to the cytoplasm, all the way through a mitochondrion, to the exterior of the cell? Assume the water molecule does not pass through a nuclear pore or any transport protein, and does not encounter the endoplasmic reticulum. 4. How does a secreted protein get outside the cell without crossing a membrane? 5. What cytoskeletal elements are involved in the following activities? a) movement of chromosomes during mitosis and meiosis; b) operation of cilia and flagella; c) muscle contraction; d) cytoplasmic streaming; e) traffic of vesicles between the Golgi apparatus and the plasma membrane. 6. How can adjacent cells in plants and animals communicate with each other? Cells 23 Answers to Text Questions – Cells Chapter 4 2. c; 3. b; 4. b; 5. a; 8. d; 9. b; 10. a; 11. c. Answers to Study Questions – Cells 1. Cell Surface Surface / Volume Diameter Area Volume Ratio 1 m 3.14 m2 0.52 m3 6.0 20 m 1257 m2 4190 m3 0.3 1000 m 3.14 x 106 m2 5.2 x 108 m3 0.006 The biological significance of these numbers can best be understood by comparing the smallest and the largest cell. The smallest cell has 6 m2 of plasma membrane (with its receptors and transporters) serving every 1 m3 of volume; while in the largest cell, each 1 m3 of volume is served by only 0.006 m2 of plasma membrane. The largest cell would therefore interact much more slowly with its environment and/or neighboring cells. One additional note: these values are for spherical cells. Some very large cells, like animal neurons and cells in the plant stem, are long and thin, not spherical, and their surface/volume ratios are not as unfavorable as those calculated above. 2. a) ribosome; b) chloroplast; c) rough ER; d) nucleus (chromatin); e) nucleus (nucleolus); f) lysosome; g) rough ER and smooth ER. 3. 7 4. A secreted protein is synthesized in the rough ER: the ribosome doing the protein synthesis is attached to the ER membrane, and the nascent polypeptide is fed into the lumen of the ER as it is being made. Once made, the protein stays inside the ER until a vesicle blebs off the ER carrying it, and makes its way to the trans face of the Golgi apparatus. When the vesicle fuses with the Golgi membrane, the protein finds itself in Cells 24 the lumen of that Golgi cisterna. There, the protein is modified as the cisterna matures, and another vesicle pinches off, carrying the protein in its lumen to the plasma membrane. After one final membrane fusion event, the protein is outside the cell. Because of these membrane fusion events, the protein gets outside the cell without ever crossing a membrane. 5. a) microtubules; b) microtubules; c) microfilaments (actin); d) microfilaments (actin); e) microtubules. 6. Two ways. First, a cell could secrete a chemical signal across its plasma membrane, which might diffuse to a receptor in the plasma membrane of the neighbouring cell. Second, substances dissolved in the cytosol of one cell could travel directly to the other cell through cytoplasmic connections between the cells – plasmodesmata in plants, gap junctions in animals. Fair Dealing Statement This copy was made pursuant to the Fair Dealing Guidelines of the University, library database licenses, and other university license and policies. The copy may only be used for the purpose of research, private study, criticism, review, news reporting, education, satire or parody. If the copy is used for the purpose of review, criticism or news reporting, the source and the name of the author must be mentioned. The use of this copy for any other purpose may require the permission of the copyright owner. Figure Citations Figures from Campbell Biology, Concepts and Connections, Tenth edition, by M.R. Taylor, E.J. Simon, J.L. Dickey, K. Hogan, and N.A. Campbell. Pearson 2021. Figs. 4.2, 4.5, 4.12, 4.13, 4.14, 4.16, 4.20, 4.21, 5.1, 10.12 © 2025 by Greg Beaulieu