Cell Theory PDF

Figure 6.2 10 m Cell Theory 1m Human height Length of some nerve and All organisms are made of...

Figure 6.2 10 m Cell Theory 1m Human height Length of some nerve and All organisms are made of Unaided eye muscle cells 0.1 m Chicken egg cells 1 cm The cell is the simplest 1 mm Frog egg collection of matter Light microscopy Human egg that can be alive 100 m Most plant and animal cells 10 m Nucleus Cells are near the middle of Most bacteria the biological size range Electron microscopy Mitochondrion 1 m Smallest bacteria Super- 100 nm Viruses resolution microscopy Ribosomes 10 nm Proteins Lipids 1 nm Small molecules Atoms 1 0.1 nm Figure 6.3 Light Microscopy (LM) Electron Microscopy (EM) Brightfield Confocal Longitudinal section Cross section (unstained specimen) of cilium of cilium Cilia 50 m Brightfield (stained specimen) 50 m 2 m 2 m Transmission electron Scanning electron microscopy (TEM) Deconvolution microscopy (SEM) Phase-contrast Scanning electron microscopes (SEMs) focus 10 m Differential-interference- electrons onto the surface of contrast (Nomarski) Super-resolution a specimen, providing images that look 3-D Transmission electron Fluorescence microscopes (TEMs) focus a beam of electrons through a specimen 2 1 m 10 m  TECHNIQUE Figure 6.4 Homogenization Tissue cells Cell Centrifuged at Homogenate fractionation takes cells apart 1,000 g (1,000 times the Centrifugation force of gravity) for 10 min Supernatant poured into and separates the major organelles next tube Differential centrifugation 20,000 g 20 min from one another 80,000 g Centrifuges Pellet rich in nuclei and 60 min fractionate cells cellular debris 150,000 g into their component parts 3 hr Pellet rich in mitochondria (and chloro- plasts if cells are from a plant) Pellet rich in “microsomes” (pieces of plasma membranes and cells’ internal Pellet rich in membranes) ribosomes 3 Prokaryotic versus Eukaryotic Basic features of ALL prokaryotes and eukaryotes – Plasma membrane – Semifluid substance called cytosol – Chromosomes (carry genes) – Ribosomes (make proteins) 4  Fimbriae Nucleoid Ribosomes Plasma membrane Bacterial Cell wall chromosome Glycocalyx 0.5 μm Flagella (a) A typical rod-shaped (b) A thin section through the bacterium bacterium Corynebacterium diphtheriae (colorized TEM) Prokaryotic cells No nucleus DNA in an unbound region called the nucleoid No membrane-bound organelles  Eukaryotic cells are characterized by having – DNA in a nucleus with a membrane – Membrane-bound organelles – internal membranes = the endomembrane system Eukaryotic cells are generally much larger than prokaryotic cells Plant and animal cells have most of the same organelles 6 Figure 6.8a ENDOPLASMIC RETICULUM (ER) Nuclear Rough Smooth envelope Flagellum ER ER NUCLEUS Nucleolus Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome 7 Figure 6.8bc 1 m Cell wall Vacuole Nucleus Mitochondrion A single yeast cell (colorized TEM) 8 Figure 6.8c Nuclear Rough envelope endoplasmic NUCLEUS reticulum Smooth Nucleolus endoplasmic reticulum Chromatin Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate CYTOSKELETON filaments Microtubules Mitochondrion Peroxisome Plasma membrane Chloroplast Cell wall Plasmodesmata Wall of adjacent cell 9 The Nucleus: Information Central The nucleus contains most of the cell’s genes (DNA) The nuclear envelope encloses the nucleus The nuclear membrane is a lipid bilayer Nuclear pores regulate the entry and exit of molecules The shape of the nucleus is maintained by the nuclear lamina, which is composed of protein 10 Figure 6.9 1 m Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Rough ER Pore complex Surface of nuclear envelope Ribosome Close-up 0.25 m of nuclear Chromatin envelope 1 m Pore complexes (TEM) Nuclear lamina (TEM) 11  chromatin = DNA associated with proteins in the nucleus Chromatin condenses to chromosomes as a cell prepares to divide Each chromosome = a single DNA molecule associated with proteins The nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis 12 Figure 6.10 Ribosomes are particles made of ribosomal RNA and protein Ribosomes carry out protein synthesis 0.25 m Free ribosomes in cytosol Endoplasmic reticulum (ER) Ribosomes bound to ER Large subunit Small subunit TEM showing ER and ribosomes Diagram of a ribosome 13 The Endoplasmic Reticulum The endoplasmic reticulum (ER) = more than half of the total membrane in the cell The ER membrane is continuous with the nuclear envelope There are two distinct regions of ER – Smooth ER = without ribosomes – Rough ER = with ribosomes 14 Figure 6.11 Smooth ER Nuclear envelope Rough ER ER lumen Cisternae Transitional ER Ribosomes Transport vesicle 200 nm Smooth ER Rough ER 15  The smooth ER – Synthesizes lipids – Metabolizes carbohydrates – Detoxifies drugs and poisons – Stores calcium ions The rough ER Has bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates) Distributes transport vesicles Is a membrane factory for the cell 16 The Golgi Apparatus: Shipping and Receiving Center The Golgi apparatus = flattened membrane sacs called cisternae Functions of the Golgi apparatus – Modifies products of the ER – Manufactures certain macromolecules – Sorts and packages materials into transport vesicles 17 Figure 6.12 cis face (“receiving” side of 0.1 m Golgi apparatus) Cisternae trans face (“shipping” side of TEM of Golgi apparatus Golgi apparatus) 18 Lysosomes: Digestive Compartments A lysosome is a membranous sac of enzymes that can digest macromolecules Lysosomal enzymes work best in the acidic environment inside the lysosome 19 Figure 6.13 1 m Vesicle containing Nucleus two damaged 1 m organelles Mitochondrion fragment Lysosome Peroxisome fragment Digestive enzymes Lysosome Lysosome Plasma membrane Peroxisome Digestion Food vacuole Mitochondrion Digestion Vesicle (a) Phagocytosis (b) Autophagy engulfing food particles or other lysosomes digesting old organelles cells fuse with lysosome 20 Figure 6.15-3 Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi 21 Vacuoles Food vacuoles are formed by phagocytosis Contractile vacuoles pump excess water out of cells Central vacuoles, found in many mature plant cells, hold organic compounds and water 22 Figure 6.14 Central vacuole Cytosol Central Nucleus vacuole Cell wall Chloroplast 5 m 23 Membrane bound organelles Mitochondria are the sites of cellular respiration, generation of ATP Chloroplasts, in plants and algae, are the sites of photosynthesis Mitochondria and chloroplasts contain their own ribosomes and DNA the endosymbiont theory: these organelles were originally bacteria Peroxisomes are oxidative organelles (involved in metabolism) 24 Mitochondria: Chemical Energy Conversion in nearly all eukaryotic cells They have a smooth outer membrane and an inner membrane folded into cristae The inner membrane creates 2 compartments: intermembrane space and mitochondrial matrix Different enzymes, and different metabolic reactions, are in each compartment 25 Figure 6.17a Intermembrane space Outer membrane DNA Inner Free membrane ribosomes in the Cristae mitochondrial Matrix matrix 0.1 m (a) Diagram and TEM of mitochondrion 26 Chloroplasts: Capture of Light Energy Chloroplasts contain the green pigment chlorophyll, plus the enzymes and molecules of photosynthesis Like mitochondria, they have 2 membranes Chloroplast structure includes – Thylakoids, membranous sacs, stacked to form a granum – Stroma, the internal fluid 27 Figure 6.18a Ribosomes Stroma Inner and outer membranes Granum DNA Thylakoid Intermembrane space 1 m (a) Diagram and TEM of chloroplast 28 Peroxisomes: Oxidation Peroxisomes have a single membrane Peroxisomes produce hydrogen peroxide and convert it to water Peroxisomes perform many different metabolic reactions How peroxisomes are related to other organelles is still unknown 29 Figure 6.19 1 m Chloroplast Peroxisome Mitochondrion 30 Cytoskeleton: Support and Motility a network of fibers extending throughout the cytoplasm 1) shape, 2) support, and 3) transport guides The cytoskeleton is composed of three types of molecular structures: Microtubules: thickest fibers, made of  and  tubulin Microfilaments: thinnest fibers, made of actin, also called actin filaments Intermediate filaments: intermediate sized, made of a variety of proteins. 31  10 m 10 m 5 m Column of tubulin dimers Keratin proteins Actin subunit Fibrous subunit (keratins 25 nm coiled together) 7 nm 812 nm   Tubulin dimer 32 Figure 6.21 Vesicle ATP Receptor for motor protein Motor protein Microtubule (ATP powered) of cytoskeleton (a) Microtubule Vesicles 0.25 m (b) 33 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 34 Figure 6.22 Centrosome Microtubule Centrioles 0.25 m Longitudinal section of one centriole Microtubules Cross section 35 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 36 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 37  Cilia and flagella share a common structure – A core of microtubules sheathed by the plasma membrane – A basal body that anchors it – A motor protein called dynein, which drives the bending movements 38 Figure 6.24 0.1 m Outer microtubule Plasma membrane doublet Dynein proteins Central microtubule Radial spoke Microtubules Cross-linking proteins between outer doublets (b) Cross section of Plasma motile cilium membrane Basal body 0.5 m 0.1 m (a) Longitudinal section Triplet of motile cilium (c) Cross section of basal body 39  Actin and Myosin Microfilaments that function in cellular motility use myosin in addition to actin In muscle cells,thicker filaments composed of myosin interdigitate with the thinner actin fibers Actin and myosin also drive amoeboid movement via Pseudopodia (cellular extensions) Cytoplasmic streaming = a circular flow of cytoplasm within cells, is also actin-myosin driven 40 Figure 6.27 Muscle cell 0.5 m Actin filament Myosin filament Myosin head (a) Myosin motors in muscle cell contraction Cortex (outer cytoplasm): gel with actin network 100 m Inner cytoplasm: sol with actin subunits Extending pseudopodium (b) Amoeboid movement Chloroplast 30 m (c) Cytoplasmic streaming in plant cells 41  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 42 Cell Walls of Plants The cell wall: 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 shape, and prevents excessive uptake of water Plant cell walls are made of cellulose fibers along with other polysaccharides and protein 43 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 Functions of the ECM Support, Adhesion, Movement, Regulation 44 Figure 6.30a Collagen EXTRACELLULAR FLUID Proteoglycan complex Fibronectin Integrins Plasma membrane CYTOPLASM Micro- filaments 45 Cell Junctions Neighboring cells often adhere, interact, and communicate Intercellular junctions facilitate this contact – Plasmodesmata (plants only, transport of material* between cells) – Tight junctions (hold cells together) – Desmosomes (hold cells together) – Gap junctions (transport of material* between cells) *(water, ions, small molecules, rarely macromolecules) 46 Figure 6.32 Tight junctions prevent fluid from moving Tight junction across a layer of cells TEM 0.5 m Tight junction Intermediate filaments Desmosome TEM 1 m Gap junction Ions or small molecules Space between cells TEM Extracellular Plasma membranes matrix of adjacent cells 0.1 m 47