Tour of the Cell What is the difference between a Eukaryote and a Prokaryote? The membrane and nonmembrane bound organelles How do cellular components cooperate to help the cell function? Fig. 6-1 Comparing Prokaryotic and Eukaryotic Cells • Basic features of all cells: • Plasma membrane • Semifluid substance called cytosol • Chromosomes (carry genes) • Ribosomes (make proteins) Prokaryotic cells are characterized by having • No nucleus • DNA in an unbound region called the nucleoid • No membrane-bound organelles • Cytoplasm bound by the plasma membrane Fimbriae Nucleoid Ribosomes Plasma membrane Cell wall Bacterial chromosome Capsule 0.5 µm (a) A typical rodshaped bacterium Fig. 6-6 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 nucleus in the region between the plasma membrane and Based on what you have learned, which is generally much larger? Eukaryotic Or Prokaryotic Cell? The Plasma Membrane • selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell • The general structure of a biological membrane is a double layer of phospholipids Outside of cell Inside of cell 0.1 µm (a) TEM of a plasma membrane Carbohydrate side chain Hydrophilic region Hydrophobic region Hydrophilic region Fig. 6-7 Phospholipid Proteins (b) Structure of the plasma membrane Surface Area to Volume Ratio Surface Area Volume Fig. 6-8 Surface area increases while total volume remains constant 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 https://www.google.com/imgres?imgurl=https%3A%2F%2F78.media.tumblr.com%2F04b3937643040ec68e2c4af9cf63bbf6%2Ftumblr_inline_p5ssry5cJv1vsm738_500.png&imgrefurl=https%3A%2F%2Fasstudypeach.tumblr.com%2Fpost%2F172004171854%2Fsavol-ratios-gas-exchange-ininsects&docid=bokHGIVRn0FygM&tbnid=YVv5uptQEqEQEM%3A&vet=10ahUKEwjXgJaxlYTcAhVprFQKHXvOAqQQMwheKBswGw..i&w=500&h=375&bih=565&biw=1280&q=surface%20area%20to%20volume%20ratio&ved=0ahUKEwjXgJaxlYTcAh VprFQKHXvOAqQQMwheKBswGw&iact=mrc&uact=8 What is the importance of knowing the Surface to Volume Ratio? Exchange of materials happens at the organism’s surface Used to supply the cells that make up the volume Situation Analysis Determine if there will be an efficient exchange of materials by simple diffusion in the given situations A. Small Organism with larger surface area compared to its volume B. Large Organism with larger volume but smaller surface area What can be done to overcome Situation B? A. Flat shape so no cell is far from the surface B. Have a specialized exchange surface to increase surface area to volume ratio A. These limitations can restrict cell size and shape. Smaller cells typically have a higher surface area-to-volume ratio and more efficient exchange of materials with the environment. B. As cells increase in volume, the relative surface area decreases and the demand for internal resources increases. C. More complex cellular structures (e.g., membrane folds) are necessary to adequately exchange materials with he environment. D. As organisms increase in size, their surface area-to-volume ratio decreases, affecting properties like rate of heat exchange with the environment. Surface area-to-volume ratios affect the ability of a biological system to obtain necessary resources, eliminate waste products, acquire or dissipate thermal energy, and otherwise exchange chemicals and energy with the environment. 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. 6-9a Nuclear envelope Nucleolus Chromatin NUCLEUS Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate filaments Microtubules CYTOSKELETON Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell Fig. 6-9b The Nucleus: Information Central 1 µm Pores regulate the entry and exit of molecules from the nucleus The shape of the nucleus is maintained by the nuclear lamina, which is composed of protein Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Pore complex Fig. 6-10 Surface of nuclear envelope Rough ER Ribosome 1 µm 0.25 µm Close-up of nuclear envelope Pore complexes (TEM) Nuclear lamina (TEM) Chromatin Chromosomes The nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis Ribosomes: Protein Factories Where do ribosomes carry out protein synthesis? Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit 0.5 µm TEM showing ER and ribosomes Fig. 6-11 Small subunit Diagram of a ribosome The endomembrane system regulates protein traffic and performs metabolic functions in the cell • • Components of the endomembrane system: • Nuclear envelope • Endoplasmic reticulum • Golgi apparatus • Lysosomes • Vacuoles • Plasma membrane These components are either continuous or connected via transfer by vesicles The Endoplasmic Reticulum: Biosynthetic Factory • The smooth ER • The rough ER – Synthesizes lipids – secrete glycoproteins – Metabolizes carbohydrates – Detoxifies poison – Distributes transport vesicles, proteins surrounded by membranes – Stores calcium – Is a membrane factory for the cell Smooth ER Rough ER ER lumen Cisternae Ribosomes Transport vesicle Smooth ER Nuclear envelope Transitional ER Rough ER 200 nm Fig. 6-12 The Golgi Apparatus: Shipping and Receiving Center • Modifies products of the ER • Manufactures certain macromolecules • Sorts and packages materials into transport vesicles cis face (“receiving” side of Golgi apparatus) 0.1 µm Cisternae trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus Fig. 6-13 Lysosomes: Digestive Compartments • membranous sac of lysosomal or hydrolytic enzymes that can digest macromolecules • Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole •A lysosome fuses with the food vacuole and digests the molecules • Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy 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 Mitochondrion Digestion (b) Autophagy Fig. 6-14 Vacuoles: Diverse Maintenance Compartments 1. Food vacuoles 2. Contractile vacuoles 3. Central vacuoles Match the function of the different types of vacoules a. found in many freshwater protists, pump excess water out of cells b. are formed by phagocytosis c. found in many mature plant cells, hold organic compounds and water Source https://davidwangblog.wordpress.com/structure-and-functions/ Source https://www.google.com/imgres?imgurl=https%3A%2F%2Fqph.fs.quoracdn.net%2Fmain-qimg-53e297c93945ea0d186d07f276dc9d00-c&imgrefurl=https%3A%2F%2Fwww.quora.com%2FWhy-are-contractilevacuolesimportant&docid=cgi1AGYXGvS66M&tbnid=uUYjIZ1xv765qM%3A&vet=10ahUKEwjK2PbjooTcAhUMG3wKHUddDY0QMwhbKBAwEA..i&w=288&h=164&bih=565&biw=1280&q=function%20of%20contractile%20vacuole& ved=0ahUKEwjK2PbjooTcAhUMG3wKHUddDY0QMwhbKBAwEA&iact=mrc&uact=8 Central vacuole Cytosol Nucleus Central vacuole Cell wall Fig. 6-15 Chloroplast 5 µm Mitochondria and chloroplasts change energy from one form to another • Mitochondria and chloroplasts – Are not part of the endomembrane system – Have a double membrane – Have proteins made by free ribosomes Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix 0.1 µm Fig. 6-17 Chloroplasts: Capture of Light Energy • Chloroplast structure includes: – Membranes – Thylakoids, membranous sacs, stacked to form a granum – Stroma, the internal fluid Ribosomes Stroma Inner and outer membranes Granum Thylakoid 1 µm Fig. 6-18 Peroxisomes: Oxidation • bounded by a single membrane • Peroxisomes produce hydrogen peroxide and convert it to water • Oxygen is used to break down different types of molecules Chloroplast Peroxisome Mitochondrion Fig. 6-19 1 µm The cytoskeleton is a network of fibers that organizes structures and activities in the cell It is composed of three types of molecular structures: 1. Microtubules = thickest 2. Microfilaments = or actin filaments - bear tension, resisting pulling forces within the cell 3. Intermediate filaments Microtubule 0.25 µm Microfilaments Fig. 6-20 Roles of the Cytoskeleton: Support, Motility, and Regulation • helps to support the cell and maintain its shape • interacts with motor proteins to produce motility • may help regulate biochemical activities Centrosomes and Centrioles • The centrosome is a “microtubule-organizing center” where microtubules grow out from • In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring Centrosome Microtubule Centrioles 0.25 µm Fig. 6-22 Longitudinal section of one Microtubules centriole Cross section of the other centriole Cilia and Flagella • Microtubules control the beating of cilia and flagella, locomotor appendages of some cells Direction of swimming (a) Motion of flagella 5 µm Direction of organism’s movement Power stroke (b) Motion of cilia Recovery stroke 15 µm Fig. 6-23 Muscle cell Actin filament Myosin filament Myosin arm (a) Myosin motors in muscle cell contraction Fig, 6-27a Extracellular components and connections between cells help coordinate cellular activities • Most cells synthesize and secrete materials that are external to the plasma membrane • These extracellular structures include: 1. Cell walls of plants 2. The extracellular matrix (ECM) of animal cells 3. Intercellular junctions Cell Walls of Plants • Prokaryotes, fungi, and some protists also have cell walls Functions • protects the plant cell • maintains its shape • prevents excessive uptake of water The Extracellular Matrix (ECM) of Animal Cells • The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin • ECM proteins bind to receptor proteins in the plasma membrane called integrins • Functions of the ECM: – Support – Adhesion – Movement – Regulation Collagen Proteoglycan complex EXTRACELLULAR FLUID Polysaccharide molecule Carbohydrates Fibronectin Core protein Integrins Proteoglycan molecule Plasma membrane Proteoglycan complex Microfilaments CYTOPLASM Fig. 6-30 Intercellular Junctions Plasmodesmata 2. Tight junctions 3. Desmosomes 4. Gap junctions 1. Plasmodesmata in Plant Cells • Through plasmodesmata, water and small solutes can pass from cell to cell Cell walls Interior of cell Interior of cell Fig. 6-31 0.5 µm Plasmodesmata Plasma membranes
