Ch. 6 Tour of the Cell 2007-2008
Microscopy Scientists use microscopes to visualize cells too small to see with the naked eye In a light microscope (LM), visible light is passed through a specimen and then through glass lenses Lenses refract (bend) the light, so that the image is magnified 2011 Pearson Education, Inc.
Three important parameters of microscopy Magnification, the ratio of an object s image size to its real size Resolution, the measure of the clarity of the image, or the minimum distance of two distinguishable points Contrast, visible differences in parts of the sample 2011 Pearson Education, Inc.
Electron microscopy Light microscopy Figure 6.2b 1 cm 1 mm Frog egg 100 m 10 m 1 m Human egg Most plant and animal cells Nucleus Most bacteria Mitochondrion 100 nm 10 nm 1 nm Smallest bacteria Viruses Proteins Lipids Ribosomes Small molecules Superresolution microscopy 0.1 nm Atoms
50 m Figure 6.3 Light Microscopy (LM) Brightfield (unstained specimen) Confocal Electron Microscopy (EM) Cilia Longitudinal section of cilium Cross section of cilium Brightfield (stained specimen) 2 m 1 m 10 m 50 m Deconvolution Scanning electron microscopy (SEM) 2 m Transmission electron microscopy (TEM) Phase-contrast Differential-interferencecontrast (Nomarski) Super-resolution Fluorescence 10 m
LMs can magnify effectively to about 1,000 times the size of the actual specimen Various techniques enhance contrast and enable cell components to be stained or labeled Most subcellular structures, including organelles (membrane-enclosed compartments), are too small to be resolved by an LM 2011 Pearson Education, Inc.
Two basic types of electron microscopes (EMs) are used to study subcellular structures Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen TEMs are used mainly to study the internal structure of cells 2011 Pearson Education, Inc.
Recent advances in light microscopy Confocal microscopy and deconvolution microscopy provide sharper images of threedimensional tissues and cells New techniques for labeling cells improve resolution 2011 Pearson Education, Inc.
Figure 6.3i Cilia 2 m Scanning electron microscopy (SEM)
Figure 6.3j Longitudinal section of cilium Cross section of cilium 2 m Transmission electron microscopy (TEM)
Cell Fractionation Cell fractionation takes cells apart and separates the major organelles from one another Centrifuges fractionate cells into their component parts Cell fractionation enables scientists to determine the functions of organelles Biochemistry and cytology help correlate cell function with structure 2011 Pearson Education, Inc.
Figure 6.4a TECHNIQUE Homogenization Tissue cells Homogenate Centrifugation
Figure 6.4b TECHNIQUE (cont.) Centrifuged at 1,000 g (1,000 times the force of gravity) for 10 min Supernatant poured into next tube 20,000 g 20 min Differential centrifugation Pellet rich in nuclei and cellular debris Pellet rich in mitochondria (and chloroplasts if cells are from a plant) 80,000 g 60 min Pellet rich in microsomes 150,000 g 3 hr Pellet rich in ribosomes
Types of cells Prokaryote bacteria cells - no organelles - organelles Eukaryote animal cells Eukaryote plant cells
The Work of Life What jobs do cells have to do for an organism to live breathe gas exchange: CO 2 vs. O 2 eat take in & digest food ATP make energy ATP build molecules proteins, carbohydrates, fats, nucleic acids remove wastes control internal conditions respond to external environment build more cells growth, repair, reproduction & development
Why organelles? Specialized structures specialized functions cilia or flagella for locomotion Containers partition cell into compartments create different local environments separate ph, or concentration of materials distinct & incompatible functions lysosome & its digestive enzymes Membranes as sites for chemical reactions unique combinations of lipids & proteins embedded enzymes & reaction centers chloroplasts & mitochondria mitochondria chloroplast Golgi ER
Cells gotta work to live! What jobs do cells have to do? make proteins proteins control every cell function make energy for daily life for growth make more cells growth repair renewal
Cell membrane Function separates cell from outside controls what enters or leaves cell O 2,CO 2, food, H 2 O, nutrients, waste recognizes signals from other cells allows communication between cells Structure double layer of fat phospholipid bilayer receptor molecules proteins phosphate head lipid tail
Proteins do all the work! proteins DNA organism cells Repeat after me Proteins do all the work!
Cells functions Building proteins read DNA instructions build proteins process proteins folding modifying removing amino acids adding other molecules e.g, making glycoproteins for cell membrane address & transport proteins
Building Proteins Organelles involved nucleus ribosomes endoplasmic reticulum (ER) Golgi apparatus vesicles The Protein Assembly Line nucleus ribosome ER Golgi apparatus vesicles
Nucleus Function protects DNA Structure nuclear envelope double membrane nuclear pores nucleolus DNA histone protein membrane fused in spots to create pores allows large macromolecules to pass through What kind of molecules need to pass through? chromosome nuclear pore nuclear envelope
1 nuclear membrane DNA production of mrna from DNA in nucleus Nucleus mrna mrna travels from nucleus to ribosome in cytoplasm through nuclear pore 2 nuclear pore mrna small ribosomal subunit large ribosomal subunit cytoplasm
Nucleolus Function ribosome production build ribosome subunits from rrna & proteins exit through nuclear pores to cytoplasm & combine to form functional ribosomes large subunit small subunit rrna & proteins ribosome nucleolus
Ribosomes Function protein production Structure rrna & protein 2 subunits combine Ribosomes Rough ER large subunit small subunit 0.08 m Smooth ER
Types of Ribosomes Free ribosomes suspended in cytosol synthesize proteins that function in cytosol Bound ribosomes attached to endoplasmic reticulum synthesize proteins for export or for membranes membrane proteins
Endoplasmic Reticulum Function processes proteins manufactures membranes synthesis & hydrolysis of many compounds Structure membrane connected to nuclear envelope & extends throughout cell
Types of ER rough smooth
Smooth ER function Membrane production Many metabolic processes synthesis synthesize lipids oils, phospholipids, steroids & sex hormones hydrolysis hydrolyze glycogen into glucose in liver detoxify drugs & poisons in liver ex. alcohol & barbiturates
Membrane Factory Build new membrane synthesize phospholipids builds membranes ER membrane expands bud off & transfer to other parts of cell that need membranes
Rough ER function Produce proteins for export out of cell protein secreting cells packaged into transport vesicles for export Which cells have lot of rough ER?
Synthesizing proteins cisternal space polypeptide signal sequence mrna ribosome ribosome membrane of endoplasmic reticulum cytoplasm
Golgi Apparatus Function Which cells have lots of Golgi? finishes, sorts, tags & ships cell products like UPS shipping department ships products in vesicles membrane sacs UPS trucks secretory vesicles transport vesicles
Golgi Apparatus
Vesicle transport protein vesicle budding from rough ER migrating transport vesicle fusion of vesicle with Golgi apparatus ribosome
nucleus 1. DNA 2. RNA endoplasmic reticulum 5. vesicle 9. protein on its way! TO: TO: 8. vesicle TO: 3. ribosomes TO: Making Proteins Regents Biology 4. protein 6. Golgi apparatus 7. finished protein
Putting it together nucleus nuclear pore cell membrane rough ER Making proteins protein secreted ribosome vesicle proteins smooth ER cytoplasm transport vesicle Golgi apparatus
Lysosomes small food particle vacuole lysosomes Function digest food clean up & recycle digest broken organelles Structure membrane sac of digestive enzymes digesting broken organelles digesting food
Food & water storage plant cells central vacuole food vacuoles animal cells contractile vacuole
Concept 6.6: The cytoskeleton is a network of fibers that organizes structures and activities in the cell The cytoskeleton is a network of fibers extending throughout the cytoplasm It organizes the cell s structures and activities, anchoring many organelles It is composed of three types of molecular structures Microtubules Microfilaments Intermediate filaments 2011 Pearson Education, Inc.
Roles of the Cytoskeleton: Support and Motility The cytoskeleton helps to support the cell and maintain its shape It interacts with motor proteins to produce motility Inside the cell, vesicles can travel along monorails provided by the cytoskeleton Recent evidence suggests that the cytoskeleton may help regulate biochemical activities 2011 Pearson Education, Inc.
ATP Vesicle Receptor for motor protein (a) Motor protein (ATP powered) Microtubule of cytoskeleton Microtubule Vesicles 0.25 m (b)
Components of the Cytoskeleton Three main types of fibers make up the cytoskeleton Microtubules are the thickest of the three components of the cytoskeleton Microfilaments, also called actin filaments, are the thinnest components Intermediate filaments are fibers with diameters in a middle range 2011 Pearson Education, Inc.
Table 6.1 10 m 10 m 5 m Column of tubulin dimers 25 nm Actin subunit Keratin proteins Fibrous subunit (keratins coiled together) Tubulin dimer 7 nm 8 12 nm
Centrosomes and Centrioles In many cells, microtubules grow out from a centrosome near the nucleus The centrosome is a microtubule-organizing center In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring 2011 Pearson Education, Inc.
Figure 6.22 Centrosome Microtubule Centrioles 0.25 m Longitudinal section of one centriole Microtubules Cross section of the other centriole
Figure 6.22a 0.25 m Longitudinal section of one centriole Microtubules Cross section of the other centriole
Cilia and Flagella Microtubules control the beating of cilia and flagella, locomotor appendages of some cells Cilia and flagella differ in their beating patterns 2011 Pearson Education, Inc.
2011 Pearson Education, Inc. Video: Chlamydomonas
2011 Pearson Education, Inc. Video: Paramecium Cilia
Figure 6.23 Direction of swimming (a) Motion of flagella 5 m Direction of organism s movement Power stroke Recovery stroke (b) Motion of cilia 15 m
Microfilaments (Actin Filaments) Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of actin subunits The structural role of microfilaments is to bear tension, resisting pulling forces within the cell They form a 3-D network called the cortex just inside the plasma membrane to help support the cell s shape Bundles of microfilaments make up the core of microvilli of intestinal cells 2011 Pearson Education, Inc.
Figure 6.26 Microvillus Plasma membrane Microfilaments (actin filaments) Intermediate filaments 0.25 m
Microfilaments that function in cellular motility contain the protein myosin in addition to actin In muscle cells, thousands of actin filaments are arranged parallel to one another Thicker filaments composed of myosin interdigitate with the thinner actin fibers 2011 Pearson Education, Inc.
Figure 6.27 Muscle cell Actin filament Myosin filament Myosin head (a) Myosin motors in muscle cell contraction 0.5 m Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits 100 m Extending pseudopodium (b) Amoeboid movement Chloroplast (c) Cytoplasmic streaming in plant cells 30 m
Figure 6.27a Muscle cell Actin filament Myosin filament Myosin head (a) Myosin motors in muscle cell contraction 0.5 m
Peroxisomes: Oxidation Peroxisomes are specialized metabolic compartments bounded by a single membrane Peroxisomes produce hydrogen peroxide and convert it to water Peroxisomes perform reactions with many different functions How peroxisomes are related to other organelles is still unknown 2011 Pearson Education, Inc.
Mitochondria Function make ATP energy from cellular respiration sugar + O 2 ATP fuels the work of life Structure double membrane ATP in both animal & plant cells
Plants make energy two ways! Mitochondria make energy from sugar + O 2 cellular respiration sugar + O 2 ATP Chloroplasts make energy + sugar from sunlight photosynthesis sunlight + CO 2 ATP & sugar ATP = active energy sugar = stored energy build leaves & roots & fruit out of the sugars sugar ATP ATP
Mitochondria are in both cells!! animal cells plant cells mitochondria chloroplast
Figure 6.18a Chloroplast structure includes Thylakoids, membranous sacs, stacked to form a granum Stroma, the internal fluid The chloroplast is one of a group of plant organelles, called plastids Ribosomes Stroma Inner and outer membranes Granum DNA Thylakoid Intermembrane space (a) Diagram and TEM of chloroplast 1 m
See p. 114 What is not in Animal Cells
See p. 115 What is not in Plant Cells
Concept 6.7: Extracellular components and connections between cells help coordinate cellular activities Most cells synthesize and secrete materials that are external to the plasma membrane These extracellular structures include Cell walls of plants The extracellular matrix (ECM) of animal cells Intercellular junctions 2011 Pearson Education, Inc.
Cell Walls of Plants The cell wall is an extracellular structure that distinguishes plant cells from animal cells Prokaryotes, fungi, and some protists also have cell walls The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein 2011 Pearson Education, Inc.
Plant cell walls may have multiple layers Primary cell wall: relatively thin and flexible Middle lamella: thin layer between primary walls of adjacent cells Secondary cell wall (in some cells): added between the plasma membrane and the primary cell wall Plasmodesmata are channels between adjacent plant cells 2011 Pearson Education, Inc.
Figure 6.28 Secondary cell wall Primary cell wall Middle lamella 1 m Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata
The Extracellular Matrix (ECM) of Animal Cells Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin ECM proteins bind to receptor proteins in the plasma membrane called integrins 2011 Pearson Education, Inc.
Figure 6.30 Collagen EXTRACELLULAR FLUID Polysaccharide molecule Proteoglycan complex Carbohydrates Fibronectin Core protein Integrins Plasma membrane Proteoglycan molecule Proteoglycan complex Microfilaments CYTOPLASM
Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid Desmosomes (anchoring junctions) fasten cells together into strong sheets Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells 2011 Pearson Education, Inc.
Cellular Visions: Inner Life of the Cell http://aimediaserver4.com/studi odaily/videoplayer/?src=ai4/harv ard/harvard.swf&width=640&hei ght=520