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Transcript
Cell Structure and Function Go to Section: Slide # 3 Prokaryotic Cells 1. Prokaryotes: Do not have nucleus but they DO have DNA DNA a. Smallest and simplest cells b. DNA located in cytoplasm (nucleoid region) flagellum c. Have cell walls d. Have ribosomes e. Many have flagella for movement f. NEVER multicellular 2. Bacteria have prokaryotic cells Cytoplasm Cell wall Cell membrane ribosomes Bacteria are the only organisms that have prokaryotic cells. Slide # 3 Eukaryotic Cells 1.Eukaryotic: cells that have nucleus 2. Have specialized structures a.Larger & more complex than prokaryotic cells 3. Unicellular & multicellular organisms have eukaryotic cells mitochondria nucleus chloroplast nucleolus vacuole Cell membrane Cell wall Cellular Structures Structure and Functions of the Nucleus 1. Nuclear membrane is a double membrane (each is a lipid bi-layer) pourous (controls what enters / exits nucleus 2. Nucleolus produces ribosomes 3. DNA is organized into distinct units called chromosomes that carries the genetic material Nucleus controls cell’s activities because it contains the cell’s DNA Endoplasmic Reticulum (ER) 1. A network of membranous tubules and sacs (cisternae) 2. ER membrane is continuous with the nuclear membrane 3. Transports substances throughout the cell Smooth ER * no ribosomes 4. Rough ER * makes lipids & steroid * has ribosomes hormones * produces proteins (pancreas * breaks down toxins in produces insulin) liver cells *makes membrane proteins * controls release of calcium in muscle cells Golgi Apparatus (Body) (Complex) 1. Single membrane 2. Membrane covered sacs (5-8 layers) 3. Receives products from ER 4. Modifies products from ER 5. Packages products into vesicles 6. Sorts and targets products to different parts of the cell or to be exported from the cell Hydrolytic enzymes & lysosomal membranes that are made by the rough ER are packaged into lysosomes by the Golgi Ribosomes (Free & Attached) 1. NOT membrane bound * found in prokaryotes & eukaryotes 2. Proteins are synthesized (made) here 3. Free Ribosomes: * found throughout the cytoplasm * make proteins that function in the cytoplasm 4. Attached ribosomes (on ER) make proteins that are: * destined for insertion into membranes * put into lysosomes * many are exported from the cell Lysosomes 1. Single membrane 2. Contain hydrolytic enzymes that break down cell waste & “junk” from outside the cell into simple compounds * simple compounds transferred to cytoplasm as new cell building materials 3. Lysosomes originate in the Golgi but enzymes are made in rough ER 4. Most numerous in disease fighting cells (white blood cells) that engulf bacteria by phagocytosis Tay Sachs is a genetic disorder that prevents the formation of the enzyme that breaks down ganglioside (a lipid). Result is damage to nervous system, mental retardation, and death in early childhood. Mitochondria 1. Found in cytoplasm of ALL eukaryotic cells * number of mitochondria in the celldepends on the cell & its function 2. convert oxygen and nutrients into ATP (adenosine triphosphate) through aerobic respiration (metabolism) * ATP is the energy that cells use 3. Has its own DNA 4. Can reproduce independently of the cell Cytoskeleton 1. Made up almost entirely of protein filaments 2. Functions: * give cell shape * provides mechanical strength * aids in locomotion (especially in Amoeba and white blood cells -- pseudopods) * helps in separating chromosomes during mitosis * anchors organelles in cytoplasm Vacuoles 1. Both plant and animal cells have vacuoles * Temporary structure in animal cells * Large, permanent structure in plant cells 2. Function: Stores water 3. When filled with water: * helps cell maintain shape by exerting pressure on cell membrane & thus cell wall * When plants wilt, they have lost water from vacuole Large, central vacuole Plastids 1. Found in plant cells 2. Have a double membrane 3. Many different types * chromoplasts -- found in brightly colored flowers & fruits & leaves -- have accessory pigments involved in photosynthesis * amyloplasts -- found in root cells; store starch * leukoplasts (colorless) -- contain oils and lipids Chromoplasts Amyloplasts 1. Double membrane 2. Plastids that convert light energy into chemical energy (photosynthesis) * found in leaves & green stems 3. Addition membrane system inside the chloroplast * Thylakoids; flattened sacs * Grana; stacks of thylakoids * thylakoids are surrounded by fluid called stroma 4. Stroma contains circular DNA, ribosomes, and enzymes 5. Can replicate on own by binary fission Chloroplasts Chlorophyll is found inside the thylakoids Plasma (Cell) Membrane The Boundary 1. Described as a lipid bi-layer fluid mosaic model 2. Fatty acid tails face each other (hydrophobic) 3. Phosphate heads (hydrophilic) are on the inside and outside of the membrane 4. Lipid portion: isolates hydrophilic substances from entering / exiting the cell 5. Protein portion: allows hydrophilic molecules and ions (charged) in / out of cell & communicates with other cells Phosphate head hydrophilic Fatty Acid tails hydrophobic proteins Membrane Structures / Functions hydrophilic Changes shape 1. Transport: provides a hydrophilic channel across the membrane that is selective to a particular particle (salt, sugars, water, etc) 2. Some transport proteins change their shape to move substances from one side to another Cell Wall 1. Found in plant cells (NOT animals) 2. Protects cell, maintains cell shape, & prevents excessive uptake of water 3. Cellulose in cell wall – cross linked structure (like a chain linked fence) – makes cell wall very strong Theory of Endosymbiosis 1. Theory that Eukaryotes arose from symbiotic relationship between prokaryotes and aerobic bacteria that they took in 2. 2 organelles involved: mitochondria & chloroplasts 3. Evidence that supports theory: * bacteria, mitochondria, & chloroplasts all have circular DNA * bacteria, mitochondria, & chloroplasts all about the same size * bacteria, mitochondria, & chloroplasts can self replicate by binary fission Prokaryote takes in aerobic bacterium Prokaryote takes in cyano bacterium (capable of photosynthesis) Contractile Vacuoles 1. Found in animal-like PROTISTS, not plants or animals 2. Pump excess water out of cell; keeps them from bursting open Diffusion through phospholipid bilayer What molecules can get through directly? – fats & other lipids inside cell NH3 outside cell lipid salt sugar aa H 2O What molecules can NOT get through directly? – polar molecules • H2O – ions (charged) • salts, ammonia – large molecules • starches, proteins Slide # 10 Structures in Animal verses Plant Cells Animal Cells Several small vacuoles scattered throughout the cell Go to Section: Cell membrane Ribosomes Nucleus Endoplasmic reticulum Golgi apparatus Vacuoles Mitochondria Plant Cells Cell Wall Chloroplast 1 Large central vacuole