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A Tour of the CellCell Structure and Function Membranes PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: The Fundamental Units of Life • All organisms are made of cells • The cell is the simplest unit of matter that can live • Cell structure is related to cellular function • All cells are related by their descent from earlier cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-1 Concept 6.1: To study cells, biologists use microscopes and the tools of biochemistry • Though usually too small to be seen by the unaided eye, cells can be VERY complex Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Microscopes and the tools of biochemistry • The quality of an image depends on – Magnification, the ratio of an object’s image size to its real size – Resolution, the measure of the clarity of the image, or the minimum distance of two distinguishable points – Contrast, visible differences in parts of the sample Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 10 m 1m Human height Length of some nerve and muscle cells 0.1 m Chicken egg 1 cm Unaided eye Frog egg 100 µm Most plant and animal cells 10 µm Nucleus Most bacteria 1 µm 100 nm 10 nm Mitochondrion Smallest bacteria Viruses Ribosomes Proteins Lipids 1 nm Small molecules 0.1 nm Atoms Electron microscope 1 mm Light microscope Fig. 6-2 Microscopes and the tools of biochemistry • LMs can magnify effectively to about 1,000 times the size of the actual specimen • Various techniques enhance contrast and enable cell components to be stained or labeled • Most subcellular structures, including organelles (membrane-enclosed compartments), are too small to be resolved by an LM Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-3ab TECHNIQUE RESULTS (a) Brightfield (unstained specimen) 50 µm (b) Brightfield (stained specimen) Fig. 6-4 TECHNIQUE (a) Scanning electron microscopy (SEM) RESULTS Cilia 1 µm (b) Transmission electron Longitudinal Cross section section of of cilium microscopy (TEM) 1 µm cilium Concept 6.2: Eukaryotic cells have internal membranes that compartmentalize their functions • The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic • Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells • Protists, fungi, animals, and plants all consist of eukaryotic cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Comparing Prokaryotic and Eukaryotic Cells • Basic features of all cells: – Plasma membrane – Semifluid substance called cytoplasm – Chromosomes (carry genes) – Ribosomes (make proteins) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Prokaryotic cells are characterized by having – No nucleus – DNA in an unbound region called the nucleoid (no nucleus remember?) – No membrane-bound organelles – Cytoplasm bound by the plasma membrane Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-6 Prokaryotic Bacteria Cell Fimbriae Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule 0.5 µm (a) A typical rod-shaped bacterium Flagella (b) A thin section through the bacterium Bacillus coagulans (TEM) • Eukaryotic cells are characterized by having – DNA in a nucleus that is bounded by a membranous nuclear envelope – Membrane-bound organelles – Cytoplasm in the region between the plasma membrane and nucleus • Eukaryotic cells are generally much larger than prokaryotic cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • The plasma membrane is a selective barrier: It allows the passage of oxygen, nutrients, and waste • This membrane is made of a double layer of phospholipids Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: Life at the Edge • The plasma membrane – Is the boundary that separates the living cell from its nonliving surroundings The plasma membrane • has selective permeability – It allows some substances to cross it more easily than others Figure 7.1 Fig. 6-7 Outside of cell (a) TEM of a plasma membrane The Plasma Membrane Inside of cell 0.1 µm Carbohydrate side chain Hydrophilic region Hydrophobic region Hydrophilic region Phospholipid Proteins (b) Structure of the plasma membrane The plasma membrane – Has a phospholipid bilayer – One side of a phospholipid is hydrophobic, the other is hydrophilic Hydrophilic head WATER Hydrophobic tail Figure 7.2 WATER Hydrophobic vs. Hydrophilic Hydrophobic Hydrophilic “Water hating” “Water loving” Is repelled by water’s polarity so it does not mix well. Think “oil and water” Is attracted to water’s polarity. Membrane proteins and lipids – Are created in the ER and Golgi apparatus ER 1 Transmembrane glycoproteins Secretory protein Glycolipid 2 Golgi apparatus Vesicle 3 4 Secreted protein Figure 7.10 Plasma membrane: Cytoplasmic face Extracellular face Transmembrane glycoprotein Membrane glycolipid Diffusion – Is the tendency for molecules of any substance to spread out evenly into the available space (a) Diffusion of one solute. The membrane has pores large enough for molecules of dye to pass through. Random movement of dye molecules will cause some to pass through the pores; this will happen more often on the side with more molecules. The dye diffuses from where it is more concentrated to where it is less concentrated (called diffusing down a concentration gradient). This leads to a dynamic equilibrium: The solute molecules continue to cross the membrane, but at equal rates in both directions. Figure 7.11 A Molecules of dye Membrane (cross section) Net diffusion Net diffusion Equilibrium Concentration Gradient • Substances diffuse down their concentration gradient, the difference in concentration of a substance from one area to another (b) Diffusion of two solutes. Solutions of two different dyes are separated by a membrane that is permeable to both. Each dye diffuses down its own concentration gradient. There will be a net diffusion of the purple dye toward the left, even though the total solute concentration was initially greater on the left side. Net diffusion Net diffusion Figure 7.11 B Net diffusion Net diffusion Equilibrium Equilibrium Effects of Osmosis on Water Balance • Osmosis – Is the movement of water across a semipermeable membrane Isotonic – The concentration of solutes in the environment is the same as it is inside the cell – There will be no net movement of water Hypertonic – The concentration of solutes in the environment is greater than it is inside the cell – The cell will lose water Hypotonic – The concentration of solutes in the environment is less than it is inside the cell – The cell will gain water Water balance in cells without walls Hypotonic solution (a) Animal cell. An animal cell fares best in an isotonic environment unless it has special adaptations to offset the osmotic uptake or loss of water. H2O Lysed Figure 7.13 Isotonic solution Hypertonic solution H2O H2O Normal H2O Shriveled Water Balance of Cells with Walls • Cell walls – Help maintain water balance If a plant cell is turgid – It is in a hypotonic environment – It is very firm, a healthy state in most plants If a plant cell is flaccid – It is in an isotonic or hypertonic environment Water balance in cells with walls (b) Plant cell. Plant cells are turgid (firm) and generally healthiest in a hypotonic environment, where the uptake of water is eventually balanced by the elastic wall pushing back on the cell. H2O Turgid (normal) Figure 7.13 H2O H2O Flaccid H2O Plasmolyzed Cell Size is Important • There is a size limit in cells • The surface area to volume ratio of a cell is critical • Small cells have a greater surface area relative to volume Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-8 Surface area increases while total volume remains constant Cell Size is Important 5 1 1 Total surface area [Sum of the surface areas (height width) of all boxes sides number of boxes] Total volume [height width length number of boxes] Surface-to-volume (S-to-V) ratio [surface area ÷ volume] 6 150 750 1 125 125 6 1.2 6 Fig. 6-9a Nuclear envelope ENDOPLASMIC RETICULUM (ER) Flagellum Rough ER NUCLEUS Nucleolus Smooth ER Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome Fig. 6-9b NUCLEUS Nuclear envelope Nucleolus Chromatin Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate filaments Microtubules Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell CYTOSKELETON Concept 6.3: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes • The nucleus contains most of the DNA in a eukaryotic cell • Ribosomes use the information from the DNA to make proteins Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Nucleus: Information Central • The nucleus contains most of the cell’s genes • The nuclear envelope encloses the nucleus, separating it from the cytoplasm • The nuclear membrane is a double membrane; each membrane consists of a lipid bilayer Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-10 1 µm The Nucleus: Information Central Nucleolus Nucleus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Pore complex Surface of nuclear envelope Rough ER Ribosome 1 µm 0.25 µm Close-up of nuclear envelope Pore complexes (TEM) Nuclear lamina (TEM) The Nucleus: Information Central • In the nucleus, DNA and proteins form genetic material called chromatin • Chromatin condenses to form discrete chromosomes • The nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Chromosomes Ribosomes: Protein Factories • Ribosomes are particles made of ribosomal RNA and protein • Ribosomes make proteins! Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-11 Ribosomes: Protein Factories Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit 0.5 µm TEM showing ER and ribosomes Small subunit Diagram of a ribosome Concept 6.4: The endomembrane system • The endomembrane system includes: – Nuclear envelope – Endoplasmic reticulum – Golgi apparatus – Lysosomes – Vacuoles – Plasma membrane • These components are either continuous or connected via transfer by vesicles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Endomembrane system- What does it do? • regulates protein traffic • performs metabolic functions in the cell Endomembrane System The Endoplasmic Reticulum: Biosynthetic Factory • The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells • Two distinct regions (types) of ER: – Smooth ER, which lacks ribosomes – Rough ER, with ribosomes studding its surface Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-12 Smooth ER Rough ER The Endoplasmic Reticulum: Biosynthetic Factory ER lumen Cisternae Ribosomes Transport vesicle Smooth ER Nuclear envelope Transitional ER Rough ER 200 nm Functions of Smooth ER • The smooth ER – Synthesizes or makes lipids (Fats) – Metabolizes (or breaks downs) carbohydrates – Detoxifies poison – Stores calcium Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Functions of Rough ER • The rough ER – Has ribosomes – Distributes transport vesicles, proteins surrounded by membranes – Is a membrane factory for the cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Golgi Apparatus: Shipping and Receiving Center • The Golgi apparatus consists of flattened membranous sacs • Functions of the Golgi apparatus: – Modifies products of the ER – Manufactures certain macromolecules – Sorts and packages materials into transport vesicles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-13 The Golgi Apparatus: Shipping and Receiving Center cis face (“receiving” side of Golgi apparatus) 0.1 µm Cisternae trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus Lysosomes: Digestive Compartments • A lysosome is a sac of enzymes that can digest macromolecules (such as proteins, fats, sugars and nucleic acids) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Lysosomes: Digestive Compartments • Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole • Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-14 Lysosomes: Digestive Compartments Nucleus 1 µm Vesicle containing two damaged organelles 1 µm Mitochondrion fragment Peroxisome fragment Lysosome Lysosome Digestive enzymes Plasma membrane Lysosome Peroxisome Digestion Food vacuole Vesicle (a) Phagocytosis (b) Autophagy Mitochondrion Digestion Fig. 6-14a Nucleus 1 µm Lysosomes: Digestive Compartments Lysosome Lysosome Digestive enzymes Plasma membrane Digestion Food vacuole (a) Phagocytosis Fig. 6-14b Lysosomes: Digestive Compartments Vesicle containing two damaged organelles 1 µm Mitochondrion fragment Peroxisome fragment Lysosome Peroxisome Vesicle (b) Autophagy Mitochondrion Digestion Vacuoles: Storage Compartments • A plant cell or fungal cell may have one or several vacuoles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-15 Vacuoles: Storage Compartments Central vacuole Cytosol Nucleus Central vacuole Cell wall Chloroplast 5 µm Fig. 6-16-1 The Endomembrane System: A Review Nucleus Rough ER Smooth ER Plasma membrane Fig. 6-16-2 The Endomembrane System: A Review Nucleus Rough ER Smooth ER cis Golgi trans Golgi Plasma membrane Fig. 6-16-3 The Endomembrane System: A Review Nucleus Rough ER Smooth ER cis Golgi trans Golgi Plasma membrane Mitochondria and Chloroplasts • change energy from one form to another Concept 6.5: Mitochondria and chloroplasts • Mitochondria are the sites of cellular respiration, a metabolic process that generates ATP • Chloroplasts, found in plants and algae, are the sites of photosynthesis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Mitochondria and chloroplasts – Are not part of the endomembrane system – Have a double membrane of their own – Contain their own DNA Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Mitochondria: Chemical Energy Conversion • Mitochondria are in nearly all eukaryotic cells • Membranes have a large surface area Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-17 Mitochondria: Chemical Energy Conversion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix 0.1 µm Energy Processing inside Mitochondria Chloroplasts: Capture of Light Energy • The chloroplast is a member of a family of organelles called plastids • Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis • Chloroplasts are found in leaves and other green organs of plants and in algae Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Chloroplast structure includes: – Thylakoids, membranous sacs, stacked to form a granum – Stroma, the internal fluid Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-18 Chloroplasts: Capture of Light Energy Ribosomes Stroma Inner and outer membranes Granum Thylakoid 1 µm Energy Processing inside the Chloroplasts: Concept 6.6: The Cytoskeleton • The cytoskeleton is a network of fibers throughout the cytoplasm • Organizes the cell’s structures and activities, anchoring many organelles • It is composed of: – Microtubules – Microfilaments – Intermediate filaments Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-20 The cytoskeleton Microtubule 0.25 µm Microfilaments The Cytoskeleton: Function • Support • Motility • Regulation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Table 6-1a 10 µm Column of tubulin dimers 25 nm Tubulin dimer Table 6-1b 10 µm Actin subunit 7 nm Table 6-1c 5 µm Keratin proteins Fibrous subunit (keratins coiled together) 8–12 nm Centrosomes and Centrioles • The centrosome is a “microtubule-organizing center” • In animal cells, the centrosome has a pair of centrioles. **Becomes VERY important in next weeks discussion on Mitosis! Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cilia and Flagella- give the cell movement • Microtubules control the beating of cilia and flagella • Cilia and flagella differ in their beating patterns Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-23 Direction of swimming (a) Motion of flagella 5 µm Direction of organism’s movement Power stroke Recovery stroke (b) Motion of cilia 15 µm Cell Walls of Plants • The cell wall is an extracellular (outside) structure. Plants have them, animals don’t! • Prokaryotes, fungi, and some protists also have cell walls • The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water • Plant cell walls are made of cellulose fibers Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-28 Secondary cell wall Primary cell wall Middle lamella 1 µm Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata The Cell: A Living Unit Greater Than the Sum of Its Parts • Cells rely on the integration of structures and organelles in order to function Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-UN1a Structure Cell Component Concept 6.3 The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes Nucleus Function Surrounded by nuclear envelope (double membrane) perforated by nuclear pores. The nuclear envelope is continuous with the endoplasmic reticulum (ER). Houses chromosomes, made of chromatin (DNA, the genetic material, and proteins); contains nucleoli, where ribosomal subunits are made. Pores regulate entry and exit os materials. Two subunits made of ribosomal RNA and proteins; can be free in cytosol or bound to ER Protein synthesis (ER) Ribosome Fig. 6-UN1b Cell Component Concept 6.4 Endoplasmic reticulum The endomembrane system (Nuclear regulates protein traffic and envelope) performs metabolic functions in the cell Golgi apparatus Lysosome Vacuole Structure Function Extensive network of membrane-bound tubules and sacs; membrane separates lumen from cytosol; continuous with the nuclear envelope. Smooth ER: synthesis of lipids, metabolism of carbohydrates, Ca2+ storage, detoxification of drugs and poisons Stacks of flattened membranous sacs; has polarity (cis and trans faces) Rough ER: Aids in sythesis of secretory and other proteins from bound ribosomes; adds carbohydrates to glycoproteins; produces new membrane Modification of proteins, carbohydrates on proteins, and phospholipids; synthesis of many polysaccharides; sorting of Golgi products, which are then released in vesicles. Breakdown of ingested subMembranous sac of hydrolytic stances cell macromolecules, enzymes (in animal cells) and damaged organelles for recycling Large membrane-bounded vesicle in plants Digestion, storage, waste disposal, water balance, cell growth, and protection Fig. 6-UN1c Cell Component Concept 6.5 Mitochondrion Mitochondria and chloroplasts change energy from one form to another Structure Bounded by double membrane; inner membrane has infoldings (cristae) Function Cellular respiration Chloroplast Typically two membranes around fluid stroma, which contains membranous thylakoids stacked into grana (in plants) Photosynthesis Peroxisome Specialized metabolic compartment bounded by a single membrane Contains enzymes that transfer hydrogen to water, producing hydrogen peroxide (H2O2) as a by-product, which is converted to water by other enzymes in the peroxisome Now create the following graphic organizer in your journal and fill in with what you know about cell structures: Things that are Things they have in common you write in the overlapping space! unique to that cell type you write in the individual space! Bacteria (Prokaryote) Animal cell (eukaryote) Plant cell (eukaryote)
