Cell Structures and Functions PDF

BIOL S103F ESSENTIAL BIOLOGY CELL STRUCTURES AND FUNCTIONS Week 4 & 5 Learning Outcomes 2  Cell theory  Structures of prokaryotic vs eukaryotic cells  Structure & functions of cell membranes  Compartmentalization is important in eukaryotic cells  Structures of plant vs animal cells  4 function...

BIOL S103F ESSENTIAL BIOLOGY CELL STRUCTURES AND FUNCTIONS Week 4 & 5 Learning Outcomes 2  Cell theory  Structures of prokaryotic vs eukaryotic cells  Structure & functions of cell membranes  Compartmentalization is important in eukaryotic cells  Structures of plant vs animal cells  4 functional categories of organelles in eukaryotic cells  The nucleus and ribosomes  The endomembrane system  Energy-converting organelles  The cytoskeleton & cell surfaces @2015 Pearson Education, Inc. Microscopes Reveal the World of the Cell https://micro.magnet.fsu.edu/primer /museum/leeuwenhoek.html 3      First microscope in the 17th century  Robert Hooke & Antoni van Leeuwenhoek http://newsciencebiology.blogspot.hk/2012 /08/3-theory-of-cell-with-scientists.html Magnification  Increase in an object’s image size compared with its actual size Resolution  A measure of the clarity of an image  Ability of an instrument to show 2 nearby objects as separate Contrast  Visible differences in brightness between parts of the sample Cell theory (1800s)  All living things are composed of cells  All cells come from other cells @2015 Pearson Education, Inc. Light Microscope vs Electron Microscope 4  Light microscope (LM; 1665)  Magnification: 1,000X      Resolution: 2 m Microorganisms; animal & plant cells; some structures within cells Staining techniques to increase contrast & highlight parts of the sample Differential interference light microscopes  Amplify differences in density  structures in living cells appear almost 3-dimensional Electron microscope (EM; 1950s)  Magnification: 100,000X  Resolution: 2 nm  Ultrastructure of cells  Scanning electron microscopes (SEMs)  Detailed architecture of cell surfaces  Transmission electron microscopes (TEMs)  Details of internal cell structure  Cannot be used to study living specimens  Cells are killed in preparation of the specimens Prokaryotic Cells vs Eukaryotic Cells 5      Prokaryotic cells  Bacteria, archaea Eukaryotic cells  All other forms of life  Protists, fungi, plants, animals Eukaryotic cells are distinguished by having  Membrane-enclosed nucleus  Membrane-enclosed organelles that perform specific functions Prokaryotic cells are smaller & simpler in structure while sharing some common characteristics with eukaryotic cells Prokaryotic cells evolved before eukaryotic cells Prokaryotic Cells vs Eukaryotic Cells 6 Prokaryotic cells Smaller & simpler in structure Evolved before eukaryotic cells No membrane-enclosed nucleus Circular DNA is coiled into nucleoid No membrane-enclosed organelles Cell wall (usually chemically complex) Include: Bacteria, Archaea Eukaryotic cells Larger Plasma membrane Cytosol Cytoplasm One or more chromosomes Ribosomes Membrane-enclosed nucleus Linear DNA with histones Membrane-enclosed organelles Cell wall (chemically simpler, if present) Include: Protists, Fungi, Plants, Animals Both Prokaryotic & Eukaryotic Cells Have … 7 1. 2. 3. 4.  Plasma membrane Cytosol  Thick, jellylike fluid filling the interior of cells One or more chromosomes  Carry genes made of DNA Ribosomes  Tiny structures that make proteins according to instructions from genes Cytoplasm  The inside of both types of cells  In prokaryotic cells  Bound by the plasma membrane  In eukaryotic cells  Region between the nucleus & the plasma membrane Prokaryotic Cells are Characterized by Having … 8 1. No nucleus 2. DNA is coiled into an unbound region called the nucleoid (nucleus-like) 3. No membrane-bound organelles 4. 5. Cell wall  Outside the plasma membrane of most prokaryotes  Fairly rigid, chemically complex  Protects the cell  Helps maintain its shape Surface projections in some prokaryotes  Short projections  Help attach prokaryotes to each other or their substrate  Longer projections  Flagella (singular, flagellum)  Propel a prokaryotic cell through its liquid environment Fimbriae Attachment structures on the surface of some prokaryotes 9 Ribosomes For protein synthesis Nucleoid Region where the cell’s DNA is located (not enclosed by a membrane) Plasma membrane Membrane enclosing the cytoplasm Cell wall Bacterial chromosome Rigid structure outside the plasma membrane Capsule Jellylike outer coating of many prokaryotes A typical rodshaped bacterium Flagella A colorized TEM of the bacterium Escherichia coli Locomotion organelles of some bacteria @2015 Pearson Education, Inc. Eukaryotic Cells are Characterized by Having … 10 1. 2.   A membrane-bound nucleus  Enclosed by a membranous nuclear envelope  Houses DNA Membrane-bound organelles  Internal membranes of eukaryotic cells partition it into compartments  Cellular metabolism (chemical activities of cells) occurs within organelles Eukaryotic cells are generally much larger than prokaryotic cells Structures & organelles of eukaryotic cells perform 4 basic functions  Genetic control of the cell  Manufacture, distribution & breakdown of molecules  Energy processing  Structural support, movement & communication between cells Plasma Membrane 11    Selective barrier that allows sufficient passage of oxygen, nutrients & waste between the living cell & its surroundings Phospholipid bilayer (Phospholipids form a 2-layer sheet)  Hydrophilic heads  Face outward, exposed to water  Hydrophobic tails Point inward, shielded from water Membrane proteins embedded  Channels  Passage of ions & other hydrophilic molecules  Pumps  Active transport (using energy) of molecules into / out of the cell The Small Size of Cells Relates to the Need to Exchange Materials Across the Plasma Membrane 12   Metabolic requirements set upper limits on the size of cells The surface area to volume ratio of a cell is critical  As a cell increases in size, its volume grows proportionately more than its surface area  Cell size must be large enough to house DNA, proteins, & structures needed to survive & reproduce  Remain small enough to allow for a surface-to-volume ratio that will allow adequate exchange with the environment Cell Size and Volume 13  Prokaryotic cells  Diameter: 1 - 10𝝻m  Eukaryotic cells ◍ Diameter: 10 - 100𝝻m What’s the difference in cell volume? Cell Size and Volume 14  Prokaryotic cells ◍ Volume: 4.189𝝻m3 – 4189𝝻m3 (4.189 x 10-6 mm3 )  Eukaryotic cells ◍ Diameter: 4.189 x 10-6 mm3 – 4.189 x 10-3 mm3 10X increase in diameter causes 1000X increase in volume Cell Size and Volume 15 10X increase in diameter causes 100X increase in surface area Raven P. et. al. (2017). Biology (11ed). NY: McGraw-Hill Animal vs Plant Cells 16   Almost all of the organelles & other structures of animals cells are present in plant cells, except 1. Lysosomes & centrosomes (containing centrioles) are absent in plant cells 2. Only the sperm cells of a few plant species have flagella Plant, but not animal cells, have 1. A rigid cell wall that contains cellulose 2. Plasmodesmata  Cytoplasmic channels through cell walls, connecting adjacent cells 3. Chloroplasts  Where photosynthesis occurs 4. A central vacuole  A compartment that stores water & a variety of chemicals ENDOPLASMIC RETICULUM (ER) Rough ER Smooth ER 17 Nuclear envelope Nucleolus Flagellum NUCLEUS Chromatin Centrosome with pair of centrioles Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome @2015 Pearson Education, Inc. Nuclear envelope NUCLEUS Nucleolus Chromatin 18 Rough ER Smooth ER Ribosomes Golgi apparatus Central vacuole Microfilaments Microtubules CYTOSKELETON Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell @2015 Pearson Education, Inc. Structures & Organelles of Eukaryotic Cells Perform 4 Basic Functions 19 1. Genetic control of the cell Nucleus Ribosomes 2. Manufacture, distribution, & breakdown of molecules Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles 3. Energy processing Mitochondria Chloroplasts (in plant cells) 4. Structural support, movement, & communication between cells Plasma membrane Cell junction Cell wall (in plant cells) Nucleus 20     Cell’s control center  Contains most of the cell’s DNA  Controls cell’s activities  Direct protein synthesis via synthesis of messenger RNA (mRNA) DNA is associated with many proteins & is organized into chromosomes  When a cell is not dividing, chromatin (the complex of proteins & DNA) appears as a diffuse mass within the nucleus Double membrane nuclear envelope  With pores  Regulate the entry & exit of large molecules  Connect with the endoplasmic reticulum (ER; cell’s network of membranes) Nucleolus  A prominent structure in the nucleus  Site of ribosomal RNA (rRNA) synthesis Ribosomes 21   Involved in the cell’s protein synthesis  Cellular components that use instructions from the nucleus, written in mRNA, to build proteins  Cells that make a lot of proteins have a large number of ribosomes 2 types of ribosomes  Free ribosomes  Suspended in the cytosol  Make proteins for use in the cell  Bound ribosomes  Attached to the outside of the ER or nuclear envelope  Make proteins for export Rough ER Bound ribosome Endoplasmic reticulum Protein Ribosome Free ribosome mRNA @2015 Pearson Education, Inc. Endomembrane System 22      Many of the membranes within a eukaryotic cell are part of (connected through) the endomembrane system Some of these membranes are physically connected Others are linked when tiny vesicles (sacs made of membrane) transfer membrane segments between them Many of these organelles interact in the  Synthesis, distribution, storage & export of molecules The endomembrane system includes 1. Nuclear envelope 2. Endoplasmic reticulum (ER) 3. Golgi apparatus 4. Lysosomes 5. Vacuoles 6. Plasma membrane Endoplasmic Reticulum (ER) 23    The largest component of the endomembrane system  An extensive network of flattened sacs & tubules A biosynthetic workshop 2 kinds of ER  Physically interconnected  Differ in structure & function 1. Smooth ER Lacks attached ribosomes Rough ER  2.  Rough ER Smooth ER Ribosomes Rough ER Smooth ER @2015 Pearson Education, Inc. Bound ribosomes that stud the outer surface of the membrane Endoplasmic Reticulum (ER) 24  Smooth ER  Rough ER  Lacks attached ribosomes  Bound ribosomes that stud the outer surface of the membrane  Involved in a variety of metabolic processes  Abundant in cells that secret proteins 1. Most secretory polypeptides are  Production of enzymes glycoproteins (proteins covalently important in the bonded to carbohydrates) 1. Synthesis of lipids, oils, 2. Secretory proteins are packaged phospholipids & steroids in transport vesicles, to be carried 2. Metabolism of from one part of the cell to another carbohydrates 3. Membrane-bound proteins are 3. Detoxification of drugs, synthesized directly into the ER alcohol & other potentially membrane harmful substances  Adding additional membrane 4. Storage of calcium ions for itself (membrane factory) The Rough ER Synthesize, Modifies & Packages Secretory Proteins 25 1. 2. 3. 4. Polypeptide is synthesized by a bound ribosome following instructions of an mRNA, & threaded into the cavity of the rough ER Short chains of sugars are often linked to the polypeptide, making glycoprotein It is packaged in a transport vesicle for export from the ER The vesicle (containing the secretory protein) buds off from the ER membrane to the Golgi apparatus Transport vesicle buds off 4 Secretory protein inside transport vesicle mRNA Bound ribosome 3 Sugar chain 1 2 Growing polypeptide Glycoprotein Rough ER @2015 Pearson Education, Inc. Golgi Apparatus 26    Stack of flattened sacs  Not connected Functions  Modifies products of the ER  Manufactures certain macromolecules  Sorts & packages materials into transport vesicles Products travel in transport vesicles from the ER to the Golgi apparatus Lysosomes 27  Digestive compartments within a cell  Membrane-enclosed sac of digestive enzymes  Provides an acidic environment for its enzymes, @2015 Pearson Education, Inc. while safely isolating them from the rest of the cell (compartmentalization)  Several types of digestive functions  Fuses with food vacuoles & digest food  Destroys bacteria engulfed by white blood cells  Fuses with other vesicles containing damaged organelles or other materials to be recycled within a cell  Acts as recycling center  Breaks down damaged organelles, recycling the organic molecules @2015 Pearson Education, Inc. Nucleus Vacuoles Smooth ER Rough ER Nuclear envelope Golgi apparatu Transport vesicle Plasma membrane 28 Lysosome  Large vesicles function in the general maintenance of the cell  Derived from the ER & Golgi apparatus  Have a variety of functions  Food vacuole  Forms as a cell ingests food Contractile  Contractile vacuoles vacuoles  Found in many freshwater protists Nucleus  Pump excess water out of cells  Central vacuoles  Found in many mature plant cells  Hold organic compounds & water Central vacuole Chloroplast  Have digestive functions Nucleus  Contain pigments  Contain poisons that protect the plant Transport vesicle @2015 Pearson Education, Inc. Mitochondria & Chloroplasts Change Energy from One Form to Another 29   Mitochondria  Found in nearly all eukaryotic cells  Sites of cellular respiration  Cellular respiration converts the chemical energy in foods to chemical energy in ATP (adenosine triphosphate; the main energy source for cellular work) Chloroplasts  Found in leaves & other green organs of plants & in algae  Contain the green pigment chlorophyll, enzymes & other molecules that function in photosynthesis  Photosynthesizing organelles of plants & algae  Photosynthesis converts light energy from the sun (solar energy) to the chemical energy of sugar molecules Mitochondria & Chloroplasts Evolved by Endosymbiosis 30   Mitochondria & chloroplasts have similarities with bacteria  Enveloped by a double membrane  Contain free ribosomes & circular DNA molecules  Grow & reproduce somewhat independently in cells Endosymbiont theory  Mitochondria & chloroplasts were formerly small prokaryotes  They began living within larger cells @2015 Pearson Education, Inc. Mitochondria 31  Have 2 internal compartments Mitochondrion 1. Intermembrane space Intermembrane  Marrow region between the inner space Outer & outer membranes membrane Inner 2. Mitochondrial matrix contains membrane  Mitochondrial DNA Crista Matrix  Ribosomes  Enzymes that catalyze some of the @2015 Pearson Education, Inc. reactions of cellular respiration  Cristae  Folds of the inner mitochondrial membrane  Many embedded protein molecules that function in ATP synthesis  Increase the membrane’s surface area, enhancing the mitochondrion’s ability to produce ATP Chloroplasts 32   Partitioned into compartments Between the outer & inner membrane is a thin intermembrane space  Stroma  Thick fluid inside the inner membrane  Chloroplast DNA  Ribosomes  Many enzymes  Thylakoids  A network of interconnected sacs where green chlorophyll molecules trap solar energy  Stacked like poker chips (granum) in some regions 3 Types of Cell Junctions are Found in Animal Tissues 33  Adjacent cells adhere, interact & communicate through specialized junctions between them 1. Tight junctions Tight junctions  Prevent leakage of fluid prevent fluid from across a layer of epithelial cells moving across a layer of cells 2. Anchoring junctions  Fasten cells together Tight junction into sheets Anchoring 3. Gap junctions junction  Channels that allow small Gap junction molecules to flow through protein-lined pores Plasma membranes of adjacent cells between cells Ions or small molecules Extracellular matrix @2015 Pearson Education, Inc. Cell Wall 34  Rigid  Enclose & support plant cells  Absent in animal cells   Protects & provides skeletal support that helps keep the plant upright against gravity  Primarily composed of cellulose Plant cell walls  Embedded in a matrix of other polysaccharides & proteins Vacuole Plasmodesmata (singular: plasmodesma)  Cell junctions in plant cells  Allow plant tissues to share  Water  Nourishment  Chemical messages Plasmodesmata Primary cell wall Secondary cell wall Plasma membrane Cytosol @2015 Pearson Education, Inc. Plasma Membranes 35  Fluid mosaic model  Describe a membrane’s structure  A patchwork of diverse protein molecules (performing various functions) embedded in a phospholipid bilayer  Plasma membrane exhibits selective permeability  Spontaneous formation of membranes was a critical step in the origin of life   Phospholipids  Key ingredient of biological membranes  Spontaneously self-assemble into simple membranes Formation of membrane-enclosed collections of molecules was a critical step in the evolution of the first cells Cytoplasmic side of membrane Extracellular side of membrane CO2 O2 36 Enzymatic activity Diffusion of small nonpolar molecules Fibers of extracellular matrices (ECM) Enzyme Enzyme Phospholipid Cholesterol Transport Attachment protein Attachment to cytoskeleton & ECM Membrane proteins Receptor protein Cell-cell recognition Junction protein Signal transduction Channel Active protein transport protein Junction protein ATP Microfilaments of cytoskeleton Intercellular junctions Glycoprotein @2015 Pearson Education, Inc. Diffusion 37      Passive transport across a membrane with no energy investment Tendency of particles to spread out evenly in an available space Particles move from an area of more concentrated particles to an area where they are less concentrated (diffuse down their concentration gradient) Molecules of dye Membrane Pores Net diffusion Net diffusion Equilibrium Eventually, the particles reach dynamic equilibrium, where there is no NET change in concentration on either side of the membrane The sole means by which oxygen enters & carbon dioxide passes out of cells Net diffusion Net diffusion Equilibrium Net diffusion Net diffusion Equilibrium @2015 Pearson Education, Inc. Osmosis 38    Diffusion of water across a selectively permeable membrane Passive transport If a membrane  Separates 2 solutions with different solute concentrations  Permeable to water but not to a solute  Water will cross the membrane, moving down its own concentration gradient, until the solute concentration on both sides is equal Lower Higher concentration concentration of solute of solute Solute molecule More equal concentrations of solute H2O Selectively permeable membrane Water molecule Solute molecule with cluster of water molecules Osmosis @2015 Pearson Education, Inc. Tonicity 39   Ability of a surrounding solution to cause a cell to gain or lose water Tonicity of a solution mainly depends its solute concentration relative to the solute concentration inside the cell  In an isotonic solution  Solute concentration is the same on both sides of a membrane  Cell volume will not change  In a hypotonic solution  Solute concentration is lower outside the cell  Water molecules move into the cell  The cell will expand & may burst  In a hypertonic solution  Solute concentration is higher outside the cell  Water molecules move out of the cell  The cell will shrink Water Balance between Cells & Their Surroundings is Crucial to Organisms 40   For an animal cell to survive in a hypotonic or hypertonic environment, it must engage in osmoregulation (control of water balance) Cell walls of plant cells, prokaryotes & fungi make water balance issues somewhat different Hypotonic solution Isotonic solution Hypertonic solution (lower solute levels) (equal solute levels) (higher solute levels)  In a hypotonic environment HO HO HO HO  Cell wall of a plant cell Animal exerts pressure that cell prevents the cell from Lysed Normal Shriveled Plasma HO taking in too much water HO HO membrane & bursting Plant  In a hypertonic environment cell Shriveled Turgid  Plant & animal cells Flaccid (plasmolyzed) (normal) @2015 Pearson Education, Inc. both shrivel 2 2 2 2 2 2 2 Facilitated Diffusion 41   Hydrophobic substances easily diffuse across a cell membrane Polar or charged substances do not easily cross cell membranes  Specific transport proteins helps specific substances (e.g. sugar, amino acids, ions) diffuse across the membrane down their concentration gradient & requires no energy input Transport protein  Some function by becoming a hydrophilic tunnel  For passage of ions or other molecules  Others bind their passenger  Change shape  Release their passenger on the other side  Water is polar, so its diffusion through a membrane’s hydrophobic interior is relatively slow  Very rapid diffusion of water into & out of certain cells is made possible by an aquaporin (a protein channel) Solute molecule @2015 Pearson Education, Inc. Active Transport 42  A cell must expend energy to move a solute against its concentration gradient  The energy molecule ATP supplies the energy for most active transport Transport protein ATP Solute 2 ATP provides 1 Solute binds to 3 Protein returns to transport protein. energy for change original shape and in protein shape. more solute can bind. @2015 Pearson Education, Inc. Exocytosis & Endocytosis 43    A cell uses 2 mechanisms to move large molecules across membranes 1. Exocytosis is used to export bulky molecules Phagocytosis CYTOPLASM EXTRACELLULAR e.g. proteins, polysaccharides FLUID Pseudopodium 2. Endocytosis is used to take in large molecules In both cases, material to be transported is packaged within a vesicle that fuses with the membrane “Food” or other particle Food vacuole Receptor-mediated endocytosis There are 2 kinds of endocytosis Coat protein Coated 1. Phagocytosis Receptor vesicle  Engulfment of a particle by the cell wrapping Coated cell membrane around it, forming a vacuole Specific pit molecule @2015 Pearson Education, Inc. 2. Receptor-mediated endocytosis  Uses membrane receptors for specific solutes  Region of membrane with receptors pinches inward to form a vesicle  e.g. Used to take in cholesterol from the blood