10/13/11. Cell Theory. Cell Structure

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1 Cell Structure Grade 12 Biology Cell Theory All organisms are composed of one or more cells. Cells are the smallest living units of all living organisms. Cells arise only by division of a previously existing cell. 1 2 Cell Characteristics Genetic material single circular molecule of DNA in prokaryotes double helix located in nucleus in eukaryotes nuclear envelope (double membrane Cytoplasm fills cell interior sugars, amino acids, proteins - organelles Plasma membrane encloses the cell phospholipid bilayer Phospholipid Membrane proteins 3 Generalized Eukaryotic Cell 4 Cell Size Visualizing Cells Most cells are relatively small because as size increases, volume increases much more rapidly. longer diffusion time Resolution - minimum distance two points can be apart and still be distinguished as two separate points Compound microscopes - magnify in stages using multiple lenses Transmission electron microscope - electrons transmitted through specimen Scanning electron microscope - electrons beamed onto surface of the specimen 5 6 1

2 Visualizing Cells Prokaryotic Cells Simplest organisms Cytoplasm is surrounded by plasma membrane and encased in a rigid cell wall composed of peptidoglycan. no distinct interior compartments gram-positive thick single layer wall that retains a violet dye from Gram stain procedure gram-negative multilayered wall does not retain dye Susceptibility of bacteria to antibiotics depends on cell wall structure. 7 8 Prokaryotic Cells Some use flagellum for locomotion threadlike structures protruding from cell surface Bacterial cell wall Rotary motor Flagellin Sheath Eukaryotic Cells Characterized by compartmentalization by an endomembrane system, and the presence of membrane-bound organelles. Central vacuole plants, storage Vesicles (smaller) Chromosomes - DNA and protein Cytoskeleton (internal protein scaffolding) Cell walls plants and fungi

3 Nucleus Repository for genetic material Directs activities of the cell Usually single, some cells several, RBC none Nucleolus - region of intensive ribosomal RNA synthesis Surface of nucleus bound by two phospholipid bilayer membranes nuclear membrane Nuclear pores protein gatekeepers Usually proteins going in and RNA going out 13 Nucleus 14 Chromosomes DNA of eukaryotes is divided into linear chromosomes. exist as strands of chromatin, except during cell division associated with packaging histones, packaging proteins nucleosomes Endomembrane System Compartmentalizes cell, channeling passage of molecules through cell s interior. Endoplasmic reticulum Rough ER - studded with ribosomes Smooth ER - few ribosomes Endoplasmic reticulum Largest internal membrane Composed of Lipid bilayer Serves as system of channels from the nucleus Functions in storage and secretion Rough ER is rough because of associated ribosomes (sites of protein synthesis Smooth ER - lack associated ribosomes contained embedded enzymes, catalyze synthesis of carbohydrate and lipid molecules 17 Golgi apparatus Endomembrane System collection of Golgi bodies collect, package, and distribute molecules synthesized at one location in the cell and utilized at another location Front - cis, Back trans Cisternae stacked membrane folds 18 3

4 Ribosome Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Proteins Transport vesicle cis face Cisternae Protein Vesicle Migrating budding transport from rough vesicle endoplasmic reticulum Fusion of vesicle with Golgi apparatus trans face Golgi apparatus 19 Endomembrane System Vesicles Lysosomes - membrane-bound vesicles containing digestive enzymes from Golgi Microbodies - enzyme-bearing, membrane-enclosed vesicles. Peroxisomes - contain enzymes that catalyze the removal of electrons and associated hydrogen atoms Peroxisome named for hydrogen peroxide produced as a by-product Enzyme breaks down to water and oxygen 20 Plasma membrane Extracellular fluid Cytoplasm Phagocytosis Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Food vesicle Digestion of phagocytized food particles or cells Endoplasmic reticulum Golgi apparatus Lysosomes Transport vesicle Old or damaged organelle Breakdown of old organelle Ribosomes Ribosomes are RNA-protein complexes composed of two subunits that join and attach to messenger RNA. site of protein synthesis assembled in nucleoli Mitochondria Organelles With DNA bounded by exterior and interior membranes interior partitioned by cristae Chloroplasts have enclosed internal compartments of stacked grana, containing thylakoids found in photosynthetic organisms Mitochondria A. "Powerhouse of the cell" - cellular metabolism B. Structure- outer and inner membranes, cristae C. Have their own DNA

5 Chloroplasts Chloroplasts are larger and more complex than mitochondria Grana closed compartments of stacked membranes Thylakoids disc shaped structure light capturing pigment Stroma fluid matrix Endosymbiosis Endosymbiotic theory suggests engulfed prokaryotes provided hosts with advantages associated with specialized metabolic activities Theory of Endosymbiosis Evidence for the endosymbiont theory is that mitochondria and chloroplasts: 27 - Are appropriate size to be descendants of eubacteria. - Have inner membranes similar to those on prokaryotic plasma membranes. - Replicate by splitting, as in prokaryotes. - DNA is circular and different from the DNA of the cell's nucleus. - Contain their own components for DNA transcription and translation into proteins. - Have ribosomes similar to prokaryotic ribosomes. - Molecular systematics lend evidence to support this theory. - Many extant organisms are involved in endosymbiotic relationships. 28 Cytoskeleton Cytoskeleton Network of protein fibers supporting cell shape and anchoring organelles Actin filaments cell movement Microtubules Hollow tubes Microtubules Intermediate filaments Facilitate cell movement Centrioles barrel shaped organelles occur in pairs help assemble animal cell s microtubules Intermediate filaments Stable - don t break down Actin

6 Plant Cells Plant Cell Central vacuole often found in the center of a plant, and serves as a storage facility for water and other materials Cell wall primary walls laid down while cell is growing middle lamella glues cells together secondary walls inside the primary cell walls after growth Animal Cells Animal cells lack cell walls. form extracellular matrix provides support, strength, and resilience