A Tour of the Cell Chapter 6 Objectives Distinguish between prokaryotic and eukaryotic cells. Distinguish between free and bound ribosomes in terms of location and function. List the components of the endomembrane system, and describe the structure and functions of each component. Briefly describe the roles of the mitochondrion, chloroplast and peroxisome. Describe the functions of the cytoskeleton and compare the structure and functions of microtubules, microfilaments, and intermediate filaments. 2 Explain how the ultrastructure of cilia and flagella relates to their functions. Describe the basic structure of a plant cell wall. Describe the structure and function of the extracellular matrix in animal cells. Describe four different intercellular junctions 3 1
Introduction Cell is smallest functional unit of life cell theory: all organisms composed of cells all existing cells arise from pre-existing cells Common characteristics of all cells: cell contents surrounded by plasma membrane cytoplasm consists of semifluid matrix organelles are embedded in cytoplasm contain genes in the form of DNA 4 Fundamental Features of Life Features of cells are characteristic of life cells are highly structured cell structure and function are related cell membranes separate the cell from the external environment each cell has DNA as the genetic material each cell carries out metabolism 5 Cell Organization Two types of cells-prokaryotic and eukaryotic Prokaryotic: small lacks nucleus the DNA is in the nucleoid region cytoplasm surrounded by plasma membrane and outer cell wall flagella and pili may be present 6 2
Cell Organization Eukaryotic Larger than prokaryotic cells complex internal structure with membranous and non-membranous organelles membranous: nucleus, endoplasmic reticulum, Golgi apparatus,mitochondria, lysosomes and peroxisomes non-membranous: ribosomes, microtubules, centrioles, flagella and cytoskeleton 8 3
The plasma membrane functions as a selective barrier allows sufficient passage of nutrients and waste 10 A Panoramic View of the Eukaryotic Cell Eukaryotic cells have extensive and elaborately arranged internal membranes, which form organelles Plant and animal cells have most of the same organelles animal cells surrounded by plasma membrane only 11 4
plant cells surrounded by plasma membrane and rigid cell wall; also have central vacuole and chloroplasts 13 5
Eukaryotic Cell Organization Eukaryotic organelles form four functional groups: manufacture breakdown energy processing support, movement and communication 16 Manufacturing nucleus ribosomes endoplasmic reticulum: rough and smooth Golgi apparatus 17 The Nucleus: Genetic Library of the Cell Nucleus is cell s genetic control center surrounded by double membrane contains pores to allow passage of material between nucleus and cytoplasm DNA normally present as strands of chromatin During cell division, chromatin coils up to form chromosomes Nucleolus-organelle within nucleus-responsible for ribosome synthesis 18 6
Ribosomes: Protein Factories in the Cell Ribosomes synthesize proteins two populations of ribosomes within cells free ribosomes suspended in cytosol bound ribosomes attached to the outside of endoplasmic reticulum or nuclear membrane 20 7
The Endoplasmic Reticulum: Biosynthetic Factory Endomembrane system smooth endoplasmic reticulum synthesizes lipids, metabolizes carbohydrates, detoxifies drugs and poisons stores Ca 2+ in muscle cells rough endoplasmic reticulum synthesizes proteins on attached ribosomes which are distributed by transport vesicles known as secretory proteins many modified in rough ER by addition of carbohydrates also synthesize membrane proteins and phospholipids 22 The Golgi Apparatus: Shipping and Receiving Center Golgi apparatus finishes, sorts and ships cell products transported in vesicles from ER consists of flattened membranous sacs called cisternae Functions of the Golgi apparatus include modification of the products of the rough ER manufacture of certain macromolecules 24 8
Breakdown lysosomes vacuoles 26 Lysosomes: Digestive Compartments Lysosomes contain enzymes to digest food and wastes defective lysosomes cause fatal diseases Lysosomes carry out intracellular digestion by phagocytosis autophagy 27 9
Vacuoles: Diverse Maintenance Compartments Vacuoles function in general cell maintenance a plant or fungal cell may have one or several vacuoles food vacuoles are formed by phagocytosis contractile vacuoles pump excess water out of protist Central vacuoles are found in plant cells hold reserves of important organic compounds and water 29 10
The Endomembrane System: A Review The organelles involved in synthesis of macromolecules form the endomembrane system primarily responsible for protein synthesis lipids synthesized to form transport vesicles which fuse with other membrane-bound organelles 31 Energy Processing mitochondria chloroplasts peroxisomes 33 11
The Evolutionary Origins of Mitochondria and Chloroplasts Mitochondria and chloroplasts have similarities with bacteria Enveloped by a double membrane Contain free ribosomes and circular DNA molecules Grow and reproduce somewhat independently in cells 34 The Endosymbiont theory An early ancestor of eukaryotic cells engulfed a nonphotosynthetic prokaryotic cell, which formed an endosymbiont relationship with its host The host cell and endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrion At least one of these cells may have taken up a photosynthetic prokaryote, becoming the ancestor of cells that contain chloroplasts 35 12
Mitochondria: Chemical Energy Conversion Mitochondria: found in all eukaryotic cells, except anaerobic protozoans surrounded by double membrane a smooth outer membrane an inner membrane folded into cristae site of cellular respiration 37 Chloroplasts: Capture of Light Energy Chloroplasts are specialized members of a family of closely related plant organelles called plastids contain chlorophyll found in plants and algae site of photosynthesis convert solar energy to chemical energy 39 13
Surrounded by double membrane Separate inner membrane system divided into two parts thylakoids, membranous sacs stroma, the internal fluid 40 Peroxisomes: Oxidation Peroxisomes are involved in the breakdown of fatty acids and amino acids Detoxify blood toxins in liver and kidney Examples alcohol, peroxide 42 14
Support, Movement, and Communication cytoskeleton centrioles and centrosomes cilia and flagella intracellular connections 44 Roles of the Cytoskeleton: Support, Motility, and Regulation Internal cell skeleton-cytoskeleton composed of 3D meshwork of proteins extending through the cytoplasm gives mechanical support to the cell 45 15
Components of the Cytoskeleton There are three components of the cytoskeleton rods of globular proteins-microfilaments ropelike strands of fibrous proteins-intermediate filaments hollow tubes of globular proteins-microtubules 47 16
Microtubules Microtubules provide anchors for organelles, act as conveyor belts and form cilia and flagella 49 Centrosomes and Centrioles The centrosome is considered to be a microtubule-organizing center In animals contains a pair of centrioles 51 17
Cilia and Flagella Cilia and flagella function to move whole cell 53 18
Cilia and flagella share a common ultrastructure structure consists of 9 microtubule doublets arranged around central pair (9+2) 55 Movement of cilia and flagella occurs when arms consisting of the protein dynein move the microtubule doublets past each other 57 19
Microfilaments (Actin Filaments) Microfilaments are built from molecules of the protein actin microfilaments cause contraction of muscle cells they also function in amoeboid movement, cytoplasmic streaming and support for cellular projections 59 20
Intermediate Filaments Intermediate filaments support cell shape fix organelles in place 61 Eukaryotic Cell Surface Organization Extracellular components and connections between cells help coordinate cellular activities Cell surfaces protect, support and join cells 62 Cell Walls of Plants In plants, neighboring cells joined to form interconnected and coordinated group cell walls are multi-layered composed of mixtures of polysaccharides and proteins 63 21
The Extracellular Matrix (ECM) of Animal Cells In multi-cellular animals cells are often surrounded by sticky mixture of polysaccharides and proteins-no support Functions of the ECM include support adhesion movement regulation 65 22
Intercellular Junctions Several type of junctions between cells In plants, plasmodesmata are channels through cell walls connecting cytoplasm of adjacent cells 67 In animal cells, there are three types of cellular connections tight junctions-leak proof anchoring junctions-join cells and allow passage of materials in spaces between cells or anchor to extracellular matrix communicating junctions-provide channels between cells 69 23
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 For example, a macrophage s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane 71 24