Plasma Membrane defines inside from outside. lasma membrane. Common features of all cells. Plasma Membrane defines inside from outside

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1 A Tour of the Cell Friday Sept 16, 2005 BCOR 011 Lecture 8 Common features of all cells Plasma Membrane defines inside from outside 10 µm 1 2 lasma Functions as a selective barrier Specific portals for selective transport of materials in and out of cell Outside of cell Common features of all cells Plasma Membrane defines inside from outside Figure 6.8 A, B Inside of cell (a) 0.1 µm TEM of a plasma. The plasma, here in a red blood cell, appears as a pair of dark bands separated by a Hydrophilic region Hydrophobic region Hydrophilic region Carbohydrate side chain Phospholipid Proteins (b) Structure of the plasma 3 Cytosol - Semifluid inside of the cell DNA chromosomes - Genetic material hereditary instructions Ribosomes 4

2 Two Broad Classes of Cells ure 6.11 ER Carry out protein synthesis TEM showing ER and ribosomes 0.5 µm Cytosol Free ribosomes Membrane Bound ribosomes Proteins To be exported ibosome RNA & Protein Complex Large subunit Diagram of a ribosome Small subunit 5 Prokaryotes Pro = before DO NOT HAVE A NUCLEUS NO internal s karyon = nucleus bacteria, cyanobacteria archaebacteria Eukaryotes Eu = true HAVE A NUCLEUS -bound organelles Plants, Animals, 6 Fungi, protists Pili: attachment structures on the surface of some prokaryotes Nucleoid: region where the cell s DNA is located (not enclosed by a ) Ribosomes: organelles that synthesize proteins Plasma : enclosing the cytoplasm Cell wall: rigid structure outside the plasma No internal s Bacterial chromosome (a) A typical rod-shaped bacterium Capsule: jelly-like outer coating of many prokaryotes Flagella: locomotion organelles of some bacteria 0.5 µm (b) A thin section through the bacterium Bacillus coagul (TEM) Bacterial Cell (Prokaryotic) 7 Figure 6.6 A, B 8

3 On the same size scale: 11 Relative Sizes 12 Typical ~ 1-2 µm Bacterium Typical Animal Cell ~ 5 to 20 µm diameter Bacterial cell (Prokaryotic Animal Cell Typical ~ 5 to 50 µm diameter Plant Cell µm = micrometer or micron =10-6 meter 9 10 (Eukaryotic) Internal -bound organelles Why Internal Membranes? Compartmentalization (Division of Labor) I m sleeping I m playing my sax I m watching TV I m cooking dinner

4 endoplasmic reticulum ENDOPLASMIC RETICULUM (ER) Rough ER Smooth ER Animal Cell NUCLEUS nucleus Nucleus: Information storage double Centrosome cytosol CYTOSKELETON Plasma Nuclear Envelope Microfilaments termediate filaments Microtubules Ribosomes ribosomes nucleolus Peroxisome Figure 6.9 Mitochondrion mitochondrion Lysosome lysosome Golgi apparatus In animal cells but not plant cells: Lysosomes Centrioles 13 Flagella (in some plant sperm) DNA housed, copied, read 14 he NUCLEUS nuclear envelope Nucleus ouble embrane uclear ores uclear amina Nucleolus DNA RNA protein lipid () 1 µm Surface of nuclear envelope µm Nuclear envelope: Inner Outer Nuclear pores Ribosome Nucleolus Chromatin Pore complex Nucle Rough ER 1 µm uchromatin 15 Figure 6.10 Close-up of nuclear envelope 16

5 19 20 Nucleolus Site of Ribosome Subunit Assembly Euchromatin region Site of mrna synthesis Expression Of Informational RNAs Note: No Endoplasmic reticulum (ER) Endoplasmic reticulum (ER) [Reticulum network] Continuous network of flattened sacs tubules, vesicles, throughout eukaryotic cytoplasm Smooth ER Rough ER Smooth ER Synthesizes lipids Synthesizes steroids Stores calcium Detoxifies poison

6 Example: detoxification in smooth ER enzo(a)pyrene charred meat, cigarette smoke Oxidations more soluble Some metabolites are more toxic Chronic use of barbiturates, alcohol- SER proliferation, resistance 21 Rough ER ribosomes attached to cytoplasmic face Large flattened sheets Synthesizes secreted proteins, proteins exported Protein modification; initial steps of carbohydrate addition - glycoproteins 22 1 Nuclear envelope is connected to rough ER, which is also continuous with smooth ER Nucleus Rough ER ough ER lips proteins hrough ER embrane lycosylation dds ligosaccharides Figure Lysosome available 5 Transport vesicle carries 6 23 Plasma 24 expands 3 2 Membranes and proteins produced by the ER flow in the form of transport vesicles to the Golgi Golgi pinches off transport Vesicles and other vesicles that give rise to lysosomes and Vacuoles Smooth ER cis Golgi trans Golgi Plasma

7 27 28 olgi Apparatus: protein secretion Processing, packaging nd sorting center Cis Golgi Close To RER Trans Golgi Far side Away From RER 25 Functions of the Golgi Apparatus cis Golgi near - processing center trans Golgi - sorting center far Present wrapping Service modifies proteins Fed Ex Central Sorts for delivery To specific 26 compartments Functions of the Golgi Apparatus Trimming of Oligosaccharide side chains on glycosylated proteins Addition of new Oligosaccharide residues to existing side chains of glycosylated proteins Maturation Cleavages of specific proteins e.g., insulin Phosphorylation of specific sugar residues on oligosaccharide side chains of glycosylated proteins Molecular tags route proteins to proper destination P added in cis Golgi Proteins with M-6-P tag bind receptor in trans Golgi

8 Lysosomes: Recycling Center sacs of digestive enzymes Endocytosis And Phagocytosis Lysosome Lysosome contains active hydrolytic enzymes Food vacuole fuses with lysosome Hydrolytic enzymes digest food particles Digestive enzymes Lysosome Plasma Digestion Food vacuole 29 Figure 6.14 A 30 (a) Phagocytosis: lysosome digesting food In phagocytosis, a cell engulfs a particle by Wrapping pseudopodia around it and packaging it within a enclosed sac large enough to be classified as a vacuole. The particle is digested after the vacuole fuses with a lysosome containing hydrolytic enzymes. In pinocytosis, the cell gulps droplets of extracellular fluid into tiny vesicles. It is not the fluid itself that is needed by the cell, but the molecules dissolved in the droplet. Because any and all included solutes are taken into the cell, pinocytosis is nonspecific in the substances it transports. PHAGOCYTOSIS EXTRACELLULAR CYTOPLASM FLUID Pseudopodium Food or other particle Plasma Food vacuole PINOCYTOSIS Vesicle Bacterium 1 µm Pseudopodium of amoeba Food vacuole An amoeba engulfing a bacterium via phagocytosis (TEM). 0.5 µm Pinocytosis vesicles forming (arrows) in a cell lining a small blood vessel (TEM). Receptor-mediated endocytosis enables the cell to acquire bulk quantities of specific substances, even though those substances may not be very concentrated in the extracellular fluid. Embedded in the are proteins with specific receptor sites exposed to the extracellular fluid. The receptor proteins are usually already clustered in regions of the called coated pits, which are lined on their cytoplasmic side by a fuzzy layer of coat proteins. Extracellular substances (ligands) bind to these receptors. When binding occurs, the coated pit forms a vesicle containing the ligand molecules. Notice that there are relatively more bound molecules (purple) inside the vesicle, other molecules (green) are also present. After this ingested material is liberated from the vesicle, the receptors are recycled to the plasma by the same vesicle. Receptor RECEPTOR-MEDIATED ENDOCYTOSIS Coat protein Plasma Ligand Coat protein Coated pit Coated vesicle A coated pit and a coated vesicle formed during receptormediated endocytosis (TEMs). Figure µm 32

9 two damaged organelles Vesicles move thru the endo system Autophagy Mitochondrion fragment Peroxisome fragment exocytosis Lysosome fuses with vesicle containing damaged organelle Hydrolytic enzymes digest organelle components Lysosome Figure 6.14 B Vesicle containing damaged mitochondrion Digestion 33 endocytosis 34 (b) Autophagy: lysosome breaking down damaged organelle Mitochondria: Powerhouses of the cell Mitochondria singular = mitochondrion powerhouse of the animal cell produces ~ 90% of ATP Carries out oxidative reactions 35 Believed Derived from prokaryotic ancestor -DNA - ribosomes - double inner and outer *define two functional spaces 36

10 itochondria are enclosed by two s A smooth outer An inner folded into cristae Mitochondrion Inter space Outer Cell organelles = Cytosol Gel Important chemical reactions cytoskeleton - eukaryotes Free ribosomes in the mitochondrial matrix Inner Cristae Figure 6.17 Mitochondrial DNA Matrix µm 38 The cytoskeleton Is a network of fibers extending throughout the cytoplasm Structural Support Movement of Materials and Organelles Microtubule There are three types of fibers that make up the cytoskeleton Microtubules Microfilaments Intermediat Filaments Tubulin Actin various 25 µm dia 7 µm dia 8-15 µm dia Cell shape Organelle movt Chromosome separation Flagellar movt Motors: Dynein Kinesis Cell shape Cell cleavage Cytoplasmic streaming Muscle contract Motors: Myosin Nuclear lamina Tension bearing elements Anchors Figure µm Microfilaments 39 40

11 Movement of Vesicles along Microtubules Motor MAPs transport vesicles ATP Vesicle Receptor for motor protein Motor protein (ATP powered) Microtubule of cytoskeleton (a) Motor proteins that attach to receptors on organelles can walk the organelles along microtubules or, in some cases, microfilaments. Microtubule Vesicles 0.25 µm Dynein inbound outbound kinesin MTOC (b) Vesicles containing neurotransmitters migrate to the tips of nerve cell axons via the mechanism in (a). In this SEM of a squid giant axon, two vesicles can be seen moving along a microtubule. (A separate part of the Figure 6.21 A, B experiment provided the evidence that they were in fact moving.) Contains a pair of centrioles Animal cells Lack cell walls Are covered by an elaborate matrix, the ECM Centrosome The ECM Is made up of glycoproteins Centrioles Microtubule 0.25 µm microtubuleorganizing center Collagen Fibronectin Plasma EXTRACELLULAR FLUID A proteoglycan complex Integrins Polysaccharide molecule Carbohydrates Core protein Proteoglycan molecule Figure 6.22 Longitudinal section of one centriole Microtubules Cross section of the other centriole 43 Integrin Figure 6.29 Microfilaments CYTOPLASM 44

12 Functions of the ECM include Cell-Cell adhesion Cell-Cell recognition Regulation of cellular processes plant cell NUCLEUS Golgi apparatus Rough endoplasmic reticulum Smooth endoplasm reticulum Central vacuole/tonopla Microfilaments Intermediate filaments CYTOSKELETON Microtubules Mitochondrion Peroxisome Plasma Cell wall Chloroplast 45 Figure 6.9 Wall of adjacent cell Plasmodesmata 46 lant Central vacuoles - Tonoplasts Are found in plant cells Hold reserves of important organic compounds and water Regulates Turgor In plant cells, chloroplasts capture energy from the sun Chloroplast Photosynthesis Central vacuole Cytosol Chloroplast DNA Ribosomes Stroma Inner and outer s Tonoplast Nucleus Central vacuole Granum Cell wall 1 µm Figure 6.15 Chloroplast 47 Figure 6.18 Thylakoid 48

13 51 52 Chloroplasts -Contain DNA -Contain bacterial-like ribosomes -Believed derived from prokaryotic ancestor cyanobacterium = blue-green alga Thylakoid Space Stroma -Double organelle defines three functional spaces 3 Central Players Membrane OuterChlorpla Membrane 49 Thylakoid Membrane Inter Space (transports things in and out of the chloroplast, but not central to photosynthesis itself 50 Cell Walls of Plants The cell wall Is an extracellular structure of plant cells that distinguishes them from animal cells

14 55 Plant cell walls Are made of cellulose fibers embedded in other polysaccharides and protein May have multiple layers Central vacuole of cell Plasma Secondary cell wall Plasmodesmata Are channels that perforate plant cell walls Primary cell wall Cell walls Central vacuole of cell Middle lamella Interior of cell Central vacuole 1 µm Cytosol Plasma Plant cell walls Interior of cell Figure µm Plasmodesmata Plasma s Figure Plasmodesmata Summary Features of all cells Features of Prokaryotes Organelles of Animal Cells Organelles of Plant Cells