Lecture 7 - Cell Structure & Function PDF

Unit 2 Cellular and Subcellular Structure and Function Lesson 7 (chapter 4) L. Ayuso Sizes of Living Things...

Unit 2 Cellular and Subcellular Structure and Function Lesson 7 (chapter 4) L. Ayuso Sizes of Living Things 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 0.1 1 10 100 1 m 1 m 10 m 1 1 0.1 1 10 100 1 nm nm nm nm 0 0 mm cm m m m m km protein chloroplas t plant and mous ros animal frog egg e e amino cells acid viru s ostric most human egg ant h atom bacteria egg blue electron human whale microscope light microscope human eye Why are larger organism made of many cells? Cell Size Cells range in size from one millimeter down to one micrometer As a cell grows, its volume increases much faster than its surface area. Think of blowing up a balloon. It may pop! Therefore, there is a limit to cell size. This is important because material needed by a cell (eg. nutrients and oxygen) and waste produced by a cell (such as CO2) must pass into and out of the cell through its surface. 4 Why Are Cells So Small? If the cell’s volume gets too large it cannot transport enough wastes out or nutrients in. Thus, surface area limits cell volume/size. The surface-area-to-volume ratio tells you how much surface area there is per unit of volume Surface to Volume Ratio One 4-cm cube Eight 2-cm cubes Sixty-four 1-cm cubes Total surface area (height × width × number of sides × number of cubes) 96 cm2 192 cm2 384 cm2 Total volume (height × width × length × number of cubes) 64 cm3 64 cm3 64 cm3 Surface area: Volume per cube (surface area ÷ volume) 1.5:1 3:1 6:1 7  The surface‑area‑to‑volume ratio requires that cells be small Large cells - surface area relative to volume decreases Volume is living cytoplasm, which demands nutrients and produces wastes Cells specialized in absorption utilize membrane modifications such as microvilli to greatly increase surface area per unit volume Why Are Cells So Small? Strategies for increasing surface area, so cell can be larger: “Frilly” edged……. Long and narrow….. Round cells will always be small. Eukaryotic Cells: Organelles Eukaryotic cells are compartmentalized They contain small structures called organelles Perform specific functions Isolates reactions from others Two classes of organelles: Endomembrane system: Organelles that communicate with one another Via membrane channels Via small vesicles Energy related organelles Mitochondria & chloroplasts Basically independent & self-sufficient 11  What are the names of the organelles in the cell? 1. Cytoplasm 2. Nucleus 3. Mitochondrion 4. Chloroplast 5. Endoplasmic reticulum 6. Ribosome 7. Golgi body 8. Lysosome 9. Centriole 10. Cell wall 11. Cell membrane Plasma membrane Double layer of phospholipid in which a wide variety of proteins embedded. 3 functions: 1. isolate cells content form the external environment 2. regulates flow of materials into and out of the cell (eg. acquire nutrients and expels waste) 3. allows interaction with other cells.  Cytoplasm/Cytosol: function Aqueous medium contained within plasma membrane (made of mostly water-70%-90%) Cytoplasm contains: Essential ions Soluble organic compounds (sugars, amino acids) Soluble proteins (enzymes) Organelles Network of protein strands (microtubules, microfilaments) that make up cytoskeleton – provides structural support THE N U C L E U S ART E R OF M OS T CELL THE HEADQU NUCLEUS Prominent & Characteristic features “Eukaryon” means “true nucleus” Very essence of eukaryotic-membrane bounded nucleus It is spherical, and the most prominent part of the cell, making up 10% of the cell’s volume Nucleus: Structure Largest organelle ~10-20 μm diameter All cell in the body contain nucleus except mature RBCs & uppermost layer of skin Consists of proteins, RNA and DNA (chromosomes) Nucleus: Function Bag of chromosomes: it contains most of the cell’s genetic material Physically separates DNA from the cytoplasm complex metabolic machinery Storage of DNA DNA maintenance Replication & repair of DNA The control center of a cell: controls the activities of cell by regulating gene expression DNA (Deoxyribonucleic acid) - DNA: stores and transmits genetic information - What information? instructions about what proteins to make. Proteins control and organism's traits. DNA→proteins—>traits - DNA is described as a Double Helix, two single strands of DNA wound around - each other.  Fun Fact If you put all the DNA molecules in your body end to end, the DNA would reach from the Earth to the Sun and back over 600 times! DNA is double stranded. What do you notice about how the 2 strands are joined?  5-carbon sugar (deoxyribose) phosphate group nitrogenous base (A,T,C,G)  DNA in the Nucleus has 2 forms: 1. Chromatin: Unwound DNA (thread-like) 2. Chromosomes: condensed form of DNA Anatomy of the Nucleus nuclear envelope nucleolus Nuclear envelope: nuclear inner membrane pore outer membrane chromatin nucleoplasm nuclear pore phospholipid 28 (Bottom): Courtesy Ron Milligan/Scripps Research Institute; (Top right): Courtesy E.G. Pollock Components of the Nucleus 1. Nuclear Membrane Also known as the nuclear envelope of nucleolemma Separates the nuclear material from cytoplasm Consists of two lipid bilayers Outer membrane Connected to the ER, communicating with cytoplasm of the cell. The exchange of the large molecules (proteins & RNA) between the nucleus and cytoplasm happens here Nuclear pore bilayer facing cytoplasm Nuclear envelope bilayer facing nucleoplasm Fig. 4-17, 2. Nuclear Pore Most distinctive feature of the NE Small Cylindrical channels- direct contact b/w cytosol & Nucleoplasm Exchange of polar materials between nucleus and cytoplasm Structural complexity- control transport of key molecules Each pore is a ring of 8 proteins with an opening in the center of the ring 3. Nucleoplasm A jelly-like (mostly made of water matrix within the nucleus Also known as karyoplasm All the materials “float” inside Helps the nucleus keep its shape and serves as a median for the transportation of important molecules within the nucleus Is completely enclosed within the nuclear membrane of nuclear envelope 4. Nucleolus Ribosome factory Large, prominent structure Doesn’t have a membrane Directs synthesis of rRNA (crucial component of ribosomes which are responsible for protein synthesis) Ribosome assembly Takes up around 25% of the volume of the nucleus Made of proteins and ribonucleic acids (RNA). Ribosomes First observed in 1953s by the romanian cell biologist George Emil Palade Cell’s factory; site for protein synthesis Non-membranous organelle Composed of protein and a type of RNA called rRNA (ribosomal RNA) Consists of a large subunit and a small subunit Subunits made in nucleolus Classified according to their location: Membrane-Bound Ribosomes: on the endoplasmic reticulum (thereby making it “rough”), or Free Ribosomes: in the cytoplasm, either singly or in groups, called polyribosomes 36 Nucleus, Ribosomes, & ER Cytoplasm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endoplasmic reticulum (ER) ER membrane protei n 4. An enzyme removes the signal Lumen of peptide. ER 5. Ribosomal subunits and mRNA break away. The enzyme protein remains in the ER and folds into its receptor mRNA final shape. SRP signal recognition particle (SRP) 2. Signal recognition 3. SRP attaches to receptor (purple); particle a channel opens; and (SRP) binds the to signal polypeptide enters ER.. peptide. signal ribosoma peptide l nuclear ribosom subunits pore e mRNA mRNA DNA 1. mRNA is leaving the nucleus and Nucleus is attached to the ribosome; protein synthesis is occurring. 37 Endomembrane System Series of intracellular membranes that compartmentalize the cell Restrict enzymatic reactions to specific compartments within cell Consists of: Nuclear envelope Membranes of endoplasmic reticulum Golgi apparatus Vesicles Several types Transport materials between organelles of system 38 Endomembrane System: The Endoplasmic Reticulum A system of membrane channels and saccules (flattened vesicles) continuous with the outer membrane of the nuclear envelope The ER is the site of membrane synthesis both RER and SER cooperate in membrane synthesis Rough ER Studded with ribosomes on cytoplasmic side Protein anabolism Synthesizes proteins Modifies and processes proteins Adds sugar to protein Results in glycoproteins 39  Smooth ER No ribosomes Synthesis of lipids substances like steroid hormones, cholesterol … Detoxification of organic compounds in the liver cells Forms transport vesicles Storage space for calcium Endoplasmic Reticulum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ribosome nuclear s envelope rough endoplasmic reticulum smooth endoplasmic reticulum 0.0 m © R. Bolender & D. Fawcett/Visuals Unlimited 8 41  Endomembrane System: The Golgi Apparatus Golgi Apparatus Consists of 3-20 flattened, curved saccules Resembles stack of hollow pancakes Modifies proteins and lipids Receives vesicles from ER on cis (or inner face) Packages them in vesicles Prepares for “shipment” & Packages them in vesicles from trans (or outer face) Within cell 44 Export from cell (secretion, exocytosis) Golgi Apparatus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. secretion transport saccule vesicle s transport vesicle trans face cis face Golgi apparatus Nucleu s 45 0.1 m Courtesy Charles Flickinger, from Journal of Cell Biology 49: 221-226, 1971, Fig. 1 page 224 Endomembrane System: Lysosomes 0.2 – 0.5 μm or larger (diameter) Spherical vesicles Single membrane-bound vesicles (not in plants) Produced by the Golgi apparatus or RER Contain powerful digestive enzymes and are highly acidic (hydrolytic digestive enzymes) Digestion of large molecules Recycling of cellular resources Apoptosis (programmed cell death, like tadpole losing tail) Involved in autolysis Some genetic diseases Caused by defect in lysosomal enzyme 47 Lysosomal storage diseases (Tay-Sachs)  They are found in animal cells, while in plant cell the same role are performed by the vacuole Discovered by Christan de Duve in 1955, named as “suicide bags” or “suicide sacs” They are most abundant in cells which are related with the enzymatic reactions such as liver cells, pancreatic cells, kidney cells, spleen cells, leucocytes, macrophages etc. STRUCTURE Are surrounded by a single membrane unique in composition. Lysosomes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. lysosome mitochondrion peroxisome fragment a. Mitochondrion and a peroxisome in a lysosome 51 b. Storage bodies in a cell with defective lysosomes a: Courtesy Daniel S. Friend; b: Courtesy Robert D. Terry/Univ. of San Diego School of Medicine Endomembrane System: A Visual Summary Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. secretion plasma membrane incoming vesicle secretory vesicle brings substances into the fuses with the plasma cell that are digested membrane as secretion when occurs the vesicle fuses with a lysosome enzyme Golgi apparatus modifies lipids and lysosome proteins contains digestive enzymes from the ER; sorts them that break down worn-out and packages them in cell parts or substances vesicles entering the cell at the plasma membrane protei n transport vesicle transport vesicle shuttles proteins to shuttles lipids to various various locations such locations such as the as Golgi apparatus the Golgi apparatus lipi d rough endoplasmic smooth endoplasmic reticulum reticulum synthesizes proteins and synthesizes lipids packages them in vesicles; and vesicles commonly go to also performs various the Golgi apparatus other functions ribosom Nucleus e 52 Vacuoles Membranous sacs that are larger than vesicles Store materials that occur in excess Others very specialized (contractile vacuole) Plants cells typically have a central vacuole Up to 90% volume of some cells Functions in: Storage of water, nutrients, pigments, and waste products Development of turgor pressure Some functions performed by lysosomes in other eukaryotes 53 Vacuoles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 100 nm 54 © Newcomb/Wergin/Biological Photo Service Energy-Related Organelles: Chloroplast Structure 4 – 10 μm long, 2 – 3 μm wide Biconvex disc shape Only in plants Double membrane structure Site of photosynthesis – found in green parts of a plant – converts solar energy into chemical energy light-dependent photosynthesis Chloroplast Structure a. b. 58 a: Courtesy Herbert W. Israel, Cornell University Energy-Related Organelles: Chloroplasts Membranous organelles that serve as the site of photosynthesis Captures light energy to drive cellular machinery Photosynthesis Synthesizes carbohydrates from CO2 & H2O Makes own food using CO2 as only carbon source Energy-poor compounds converted to energy-rich compounds solar energy + carbon dioxide + water → carbohydrate + oxygen 60 Only plants, algae, and certain bacteria are capable of conducting photosynthesis Energy-Related Organelles: Mitochondria Power house of the cell 0.5 – 1.5 μm wide, 3.0 – 10.0 μm long Rod-shaped, numerous Contain ribosomes and their own DNA Has double membrane Inner membrane folded to form cristae (finger-like projections) Fluid interior known as matrix Site of aerobic respiration (Glycolysis→ Krebs cycle→ETC): produces energy that is stored as ATP Mitochondrial Structure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. 200 nm outer membrane cristae matrix double inner membrane membrane b. 63 a: Courtesy Dr. Keith Porter Mitochondria replicating Endosymbiotic Theory The Endosymbiotic Theory The theory of Endosymbiosis explains the origin of chloroplasts and mitochondria and their double membranes. Mitochondria and Chloroplasts Have their own DNA What could that mean? ○ These were prokaryotes that were ingested or eaten by eukaryotes ○ The prokaryotes were a parasite inside the eukaryotes The prokaryotic cells were protected and produced energy for the eukaryote Evidence There will likely not be any true evidence ○ Just theories Mitochondria and chloroplasts have their own DNA ○ Arranged in a circular pattern M and C have ribosomes that more closely resemble those in prokaryotic cells M and C reproduce by fission, independent of the rest of the cell Cell Wall Plant cells (*bacteria and fungi have different types of cell walls) Outermost structure of cell Rigid layer consisting of cellulose chains held together by a matrix of other polysaccharides