Ch. 7 Inside the Cell BIOL 222 Overview: The Fundamental Units of Life All organisms are made of cells The cell is the simplest collec=on of ma>er that can live Cell structure is correlated to cellular func=on All cells are related by their descent from earlier cells Fig. 6-2 10 m 1 m 0.1 m 1 cm Human height Length of some nerve and muscle cells Chicken egg Unaided eye 1 mm Frog egg 100 µm 10 µm 1 µm 100 nm 10 nm Most plant and animal cells Nucleus Most bacteria Mitochondrion Smallest bacteria Viruses Ribosomes Proteins Light microscope Electron microscope 1 nm Lipids Small molecules 0.1 nm Atoms 1
Prokaryo=c cells Prokaryo=c and Eukaryo=c Cells Bacteria and Archaebacteria Eukaryo=c cells Pro=sts, fungi, plants, and animals Prokaryo=c and Eukaryo=c Cells Basic features of all cells: Plasma Semifluid substance called cytosol Cytoplasm = space inside cell filled with cytosol Chromosome(s) Gene=c info Ribosomes Protein synthesis Prokaryo=c cells characterized by: No nucleus Prokaryo=c Cells nucleoid region instead Fimbriae DNA in an unbound area No membranous organelles Bacterial chromosome Nucleoid Ribosomes Plasma Cell wall Capsule Ribosomes only Not bound (a) A typical rod-shaped bacterium Flagella (b) 0.5 µm A thin section through the bacterium Bacillus coagulans (TEM) Cytoplasm enclosed by the plasma 2
Eukaryo=c cells characterized by having: nucleus encloses DNA bounded by a double membranous envelope Many membranous organelles Eukaryota much larger than prokaryo=c cells 10x - 100x on average Eukaryo=c Cells plasma Cell Membrane Selec=vely permeable allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell Phospholipid bilayer amphipathic fluid mosaic Limits to the size of cells Diffusion can only work so far efficiency declines with distance Cell Membrane Surface area to volume ra=o of a cell is cri=cal As the surface area increases by a factor of n 2, the volume increases by a factor of n 3 Small cells have a greater surface area rela=ve to volume 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] 1 5 Surface area increases while total volume remains constant 6 150 750 1 1 125 125 6 1.2 6 3
Flagellum Centrosome CYTOSKELETON: Microfilaments Microtubules Microvilli Peroxisome ENDOPLASMIC RETICULUM (ER) Rough ER Mitochondrion Smooth ER Lysosome Nucleolus Chromatin Ribosomes NUCLEUS Internal s A Panoramic View of the Eukaryo=c Cell Nuclear envelope ENDOPLASMIC RETICULUM (ER) Nucleolus Rough ER Smooth ER Flagellum Chromatin NUCLEUS Par==on the cell into Centrosome Plasma organelles Same material and construc=on as cell CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi Peroxisome apparatus Mitochondrion Lysosome Nuclear envelope Rough endoplasmic NUCLEUS Nucleolus reticulum Chromatin Smooth endoplasmic reticulum Ribosomes Plant and animal cells have most of the same organelles Golgi apparatus Mitochondrion Peroxisome Plasma Cell wall Wall of adjacent cell Central vacuole Microfilaments Intermediate filaments CYTO- SKELETON Microtubules Chloroplast Plasmodesmata Nucleus Nucleus contains most of the cell s genes and is usually the most conspicuous (largest) organelle Mitochondria and/or chloroplasts also have their own DNA mtdna, ptdna Intermediate filaments Nuclear envelope Plasma Nuclear envelope encloses the nucleus, separa=ng it from the cytoplasm double ; each consists of a phospholipid bilayer Studded with nuclear pores Golgi apparatus Fig. 6-10 1 µm Nuclear envelope: Inner Outer Nucleolus Chromatin Nucleus Nuclear pore Pore complex Surface of nuclear envelope 0.25 µm Ribosome Rough ER 1 µm Close-up of nuclear envelope Pore complexes (TEM) Nuclear lamina (TEM) 4
Nucleus Nuclear Pores regulate the entry and exit of molecules from the nucleus 1 µm Nucleolus Chromatin Nuclear envelope: Inner Outer Nuclear pore Nucleus Nuclear lamina maintains shape of the nucleus Surface of nuclear envelope 0.25 µm Ribosome Pore complex Close-up of nuclear envelope Rough ER 1 µm composed of protein Pore complexes (TEM) Nuclear lamina (TEM) Intermediate filaments Similar to cytoskeleton Nucleus Chroma=n Diffuse form of Gene=c material made of DNA and proteins Chromosomes Condensed chroma=n Only during cell division Nucleolus site of ribosomal RNA (rrna) synthesis located within the nucleus Seen as large dark spot Ribosomes Ribosomes par=cles made of ribosomal RNA and protein Only organelle without a enclosure carry out protein synthesis in two loca=ons: In the cytosol (free ribosomes) On the outside of the endoplasmic re=culum or the nuclear envelope (bound ribosomes) 5
Fig. 6-11 Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit 0.5 µm TEM showing ER and ribosomes Small subunit Diagram of a ribosome Components of the endo system: Nuclear envelope Endoplasmic re=culum Golgi apparatus Lysosomes Vacuoles Plasma These components are either con=nuous or connected via transfer by vesicles Endo System Biosynthesis: Endoplasmic Re=culum Endoplasmic re=culum (ER) accounts for more than half of the total in many eukaryo=c cells con=nuous with the nuclear envelope Two regions of ER: Smooth ER No ribosomes Rough ER Ribosomes a>ached 6
Fig. 6-12 Smooth ER Rough ER Nuclear envelope ER lumen Cisternae Ribosomes Transport vesicle Smooth ER Rough ER Transitional ER 200 nm Smooth Endoplasmic Re=culum The smooth ER Synthesizes lipids Phospholipids Steroids Metabolizes carbs Glycogenolysis / gluconeogenesis Detoxifies poisons Stores calcium Sarcoplasmic re=culum Rough Endoplasmic Re=culum Rough ER Ribosomes a>ached Sites of and secretory protein synthesis Transport vesicles Proteins surrounded by s Bud from RER Is a manufacturing and assembly factory for the cell Along with SER 7
Golgi apparatus The Golgi Apparatus Cisternae fla>ened membranous sacs Func=ons: Modifies products of the ER Manufactures some cis face ( receiving side of Golgi apparatus) Cisternae 0.1 µm polysaccharides (pec=n) Sorts and packages materials into transport vesicles trans face ( shipping side of Golgi apparatus) TEM of Golgi apparatus Lysosomes Lysosome membranous sac of hydroly=c enzymes digest macromolecules hydrolyze proteins, fats, polysaccharides, and nucleic acids Lysosomes Phagocytosis One cell engulfing another forms a food vacuole fuses with lysosome Autophagy Lysosomes use enzymes to recycle the cell s own organelles and macromolecules 8
Fig. 6-14 Nucleus 1 µm Vesicle containing two damaged organelles 1 µm Mitochondrion fragment Lysosome Lysosome Digestive enzymes Peroxisome fragment Lysosome Plasma Digestion Peroxisome Food vacuole Vesicle Mitochondrion Digestion (a) Phagocytosis (b) Autophagy Vacuoles A plant cell or fungal cell may have one or several vacuoles Food vacuoles formed by phagocytosis Contrac=le vacuoles found in many freshwater pro=sts, pump excess water out of cells Central vacuole Cytosol Central vacuoles found in many mature plant cells, hold organic compounds and water Nucleus Cell wall Chloroplast Central vacuole 5 µm Mitochondria and Chloroplasts Mitochondria sites of cellular respira=on In plants too Chloroplasts in plants and algae only sites of photosynthesis Both change energy from one form to another 9
Mitochondria and chloroplasts Mitochondria and Chloroplasts Are not part of the endo system Have a double Have proteins made by free ribosomes Contain their own DNA?! Endosymbiont theory hmp://www.sciencedaily.com/releases/ 2011/07/110725190046.htm hmp://www.nature.com/srep/2011/110614/ srep00013/full/srep00013.html Mitochondria Mitochondria in nearly all eukaryo=c cells All have evolu=onary descendants of mitochondria Cristae Folds of inner to increase surface area inner creates two compartments: inter space For H+ gradient of electron transport chain mitochondrial matrix For Krebs Cycle Fig. 6-17 Inter space Outer Free ribosomes in the mitochondrial matrix Inner Cristae Matrix 0.1 µm 10
Chloroplasts Chloroplast structure includes: Thylakoids membranous sacs, stacked to form a granum Stroma internal fluid Ribosomes Stroma Inner and outer s Granum Thylakoid 1 µm Peroxisomes Peroxisomes: Oxida=on Specialized metabolic compartments Bound by a single Oxygen used to break down different types of molecules H 2 O 2 by-product converted to water Cytoskeleton Cytoskeleton network of protein fibers extending throughout the cytoplasm organizes the cell s structures and ac=vi=es anchors many organelles composed of three types of molecular structures: Microtubules Microfilaments Intermediate filaments 11
Cytoskeleton: Support, Mo=lity, and Regula=on Cytoskeleton support the cell and maintain its shape motor proteins produce mo=lity PLAY vesicles can travel along monorails provided by the cytoskeleton Recent evidence suggests cytoskeleton may help regulate biochemical ac=vi=es Components of the Cytoskeleton Three main types of fibers make up the cytoskeleton: Microtubules thickest Intermediate filaments Medium sized diameter Microfilaments Thinnest also called ac=n filaments Centrosomes Microtubules and Cell Division Structure near nucleus from where microtubules grow a microtubule-organizing center In animal cells Centrosome Consists of two centrioles Centrioles Paired structures consis=ng of nine triplets of microtubules arranged in a ring Centrioles Longitudinal section of one centriole Microtubules Microtubule 0.25 µm Cross section of the other centriole 12
Most cells synthesize and secrete materials that are external to the plasma Extracellular Matrix These extracellular structures include: Cell walls of plants The extracellular matrix (ECM) of animal cells Intercellular junc=ons cell wall Cell Walls of Plants extracellular structure dis=nguishes plant cells from animal cells made of cellulose fibers embedded in other polysaccharides and protein protects the plant cell, maintains its shape, and prevents excessive uptake of water Prokaryotes, fungi, and a few pro=sts also have cell walls Bacteria - pep=doglycan Fungi - chi=n The Extracellular Matrix (ECM) of Animal Cells Extracellular matrix (ECM) Animal cells lack cell walls but are covered by ECM made up of glycoproteins Collagen Proteoglycans fibronec=n Integrins Receptor proteins in the plasma to which ECM proteins bind 13
Func=ons of the ECM: Extracellular Matrix Support Anchorage and separa=on of different =ssues Adhesion Bind cells together within =ssues Movement Guide for cell migra=on in embryonic development Regula=on Propaga=on of external s=muli to nucleus Fig. 6-30 Collagen EXTRACELLULAR FLUID Proteoglycan complex Polysaccharide molecule Carbohydrates Fibronectin Core protein Integrins Plasma Proteoglycan molecule Proteoglycan complex Microfilaments CYTOPLASM Intercellular Junc=ons Intercellular junc=ons facilitate contact between neighboring cells in =ssues, organs, or organ systems adhere, interact, and communicate through direct physical contact Types Plasmodesmata Plants only Tight junc=ons Desmosomes Gap junc=ons 14
Plasmodesmata in Plant Cells Plasmodesmata channels that perforate plant cell walls water and small solutes some=mes proteins and RNA can pass from cell to cell Plasma con=nuous from one cell to another Fig. 6-31 Interior of cell Cell walls Interior of cell 0.5 µm Plasmodesmata Plasma s Tight Junc=ons, Desmosomes, and Gap Junc=ons =ght junc=ons Leak-proof barrier Plasma s squeezed together Diges=ve system Tight junctions prevent fluid from moving across a layer of cells Desmosomes anchoring junc=ons fasten cells together into strong sheets rivets Tight junction Intermediate filaments Desmosome Gap junctions Gap junc=ons communica=ng junc=ons provide cytoplasmic channels between adjacent cells Space between cells Plasma s of adjacent cells Extracellular matrix 15
You should now be able to: 1. Dis=nguish between the following pairs of terms: magnifica=on and resolu=on; prokaryo=c and eukaryo=c cell; free and bound ribosomes; smooth and rough ER 2. Describe the structure and func=on of the components of the endo system 3. Briefly explain the role of mitochondria, chloroplasts, and peroxisomes 4. Describe the func=ons of the cytoskeleton 5. Compare the structure and func=ons of microtubules, microfilaments, and intermediate filaments 6. Explain how the ultrastructure of cilia and flagella relate to their func=ons 7. Describe the structure of a plant cell wall 8. Describe the structure and roles of the extracellular matrix in animal cells 9. Describe four different intercellular junc=ons 16