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Transcript
NOTES: CH 6 – A Tour Of The Cell Overview: The Importance of Cells ● All organisms ● The cell is the simplest collection of matter ● Cell structure is correlated to ● All cells are related by their 6.1 – Biologists use microscopes and the tools of biochemistry to study cells MICROSCOPES 1) Light Microscope: 2) Electron Microscope (1950’s) Transmission Electron Microscope Scanning Electron Microscope Light Microscope works by passing visible light through a thin section of specimen and then through glass lenses resolving power = 0.2 µm (size of small bacteria) Electron Microscope (1950’s) uses electron beams which have shorter wavelengths of light resolving power = 0.2 nm (most cell structures) 1) Transmission Electron Microscope - electrons transmitted through specimen are focused and image is magnified using electromagnets 2) Scanning Electron Microscope - electron beam scans the surface of a specimen **Disadvantages to EM: can only view dead cells (elaborate preparation) very expensive WE CAN ALSO STUDY CELLS BY... Cell Fractionation = Centrifugation = spinning mixtures of cells and their parts at very high speeds; separates the components 6.2 – Eukaryotic cells have internal membranes that compartmentalize their functions Types of CELLS: ● The basic structural and functional unit of every organism is one of two types of cells: ● Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells ● Protists, fungi, animals, and plants all consist of eukaryotic cells (& are in the domain Eukarya) ALL CELLS: ● ● have cytoplasm / cytosol ● ● (make proteins) material (DNA / chromatin / chromosomes) CELLS CAN BE CLASSIFIED AS: 1) PROKARYOTES (3.5 billion years) 2) EUKARYOTES “newer” cells (1.5 billion years) . . lack nucleus & membrane-bound organelles have a “ genetic material in a single, circular molecule (PLASMID) in region called NUCLEOID genetic material organized into CHROMOSOMES in NUCLEUS . Domains Bacteria and Archaea ” & membrane-bound organelles . Domain Eukarya, includes Kingdoms Protista, Fungi, Plantae, Animalia ● although eukaryotic cells are larger than prokaryotes, there is a limit on cell size due to the logistics of carrying out cellular metabolism PLASMA MEMBRANE: the boundary of every cell ● The plasma membrane is a nutrients, and waste to service the volume of the cell ● The general structure of a biological membrane is a that allows sufficient passage of oxygen, A Panoramic View of the Eukaryotic Cell: ● A eukaryotic cell has internal membranes that partition the cell into organelles ● Plant and animal cells have most of the same organelles 6.3 - The eukaryotic cell’s genetic instructions are housed in the NUCLEUS and carried out by the ribosomes ● the nucleus contains most of the DNA in a eukaryotic cell ● ribosomes use the information from the DNA The Nucleus: Genetic Library of the Cell ● the nucleus contains most of the cell’s genes and is usually the most conspicuous organelle ● the encloses the nucleus, separating it from the cytoplasm ● houses the information / instructions for …the “control center” of the cell ● averages NUCLEAR ENVELOPE - each of the 2 membranes is a phospholipid bilayer w/specific proteins - is perforated by pores which regulate molecular traffic into and out of the nucleus - RNA and proteins enter or leave the nucleus through these pores - breaks down prior to cell division CHROMATIN fibrous, threadlike complex of CHROMOSOMES visible under microscope; form just prior to cell division; human cells have NUCLEOLUS dense, spherical region in the nucleus - visible when cell is NOT dividing - may be 2 or more per cell which make up chromosomes in eukaryotic cells ; - : 1) rRNA: transcribed in nucleolus 2) RNA produced elsewhere in nucleus - ribosomal subunits pass through nuclear pores to the cytoplasm where assembly into ribosomes is completed RIBOSOME cytoplasmic organelle; - made of RNA and protein - cells with high rates of protein synthesis have large numbers of nucleoli & ribosomes (e.g. human liver cells have millions) ● Ribosomes carry out protein synthesis in two locations: -in the cytosol ( ) -attached to the outside of the endoplasmic reticulum (ER) or the nuclear envelope ( The Endomembrane System **all structures are essentially compartments, closed off by their membranes from the cytoplasm 6.4 - The endomembrane system regulates protein traffic and performs metabolic functions in the cell ● Components of the endomembrane system: -Nuclear envelope -Lysosomes -Endoplasmic reticulum -Vacuoles -Golgi apparatus -Plasma membrane ● These components are either continuous or connected via transfer vesicles ● The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells ● The ER membrane is continuous with the nuclear envelope ENDOPLASMIC RETICULUM (ER): ● extensive network of tubules and sacs ● used for transport and/or modification of proteins; ● can be (ribosomes) or (no ribosomes) Rough ER: ● manufactures secretory proteins and membranes ; ● proteins made here may be modified (i.e. folded into their tertiary structure) ● usually closer in to nucleus than smooth ER Smooth ER: ● ● participates in carbohydrate metabolism ● ● stores calcium ions (for muscle contraction) The GOLGI APPARATUS: Shipping and Receiving Center ● The Golgi apparatus consists of flattened membranous sacs called cisternae ● Functions of the Golgi apparatus: -Manufactures certain macromolecules ● cis face (forming face; faces the rough ER) into transport vesicles by accepting transport vesicles from the rough ER ● trans face (maturing face; faces the cell membrane) pinches off vesicles from the Golgi and transports molecules to other sites. ) Lysosomes: Digestive Compartments ● A lysosome is a membranous sac of ● Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids ● Lysosomes also use enzymes to recycle organelles and macromolecules, a process called autophagy ● probably pinch off from the trans face of Golgi; ● ; ● the cell’s own organic material; ● destroy cells VESICLES / VACUOLES: ● membrane-enclosed sac used for animal cells, vacuoles are small and look like vesicles **Vacuoles in PLANTS have special characteristics: -plants have a LARGE central vacuole that stores water and water-soluble organic compounds and inorganic ions (K + and Cl-); -contain soluble pigments in some cells (red and blue pigments in flowers); -play a role in plant growth by ; -helps protect from predators by storing waste products that may also be poisonous compounds; -are surrounded by a membrane called the . -some fresh-water protists have a that pumps excess water from cell MORE ORGANELLES… 6.5 - Mitochondria and chloroplasts change energy from one form to another ● Mitochondria are the ● Chloroplasts, found only in plants and algae, are the ● Mitochondria and chloroplasts are not part of the endomembrane system ● Peroxisomes are MITOCHONDRIA: ● . ● found in nearly all eukaryotic cells. ● the # in cells varies and is related to the cell’s metabolic activity ● inner membrane is convoluted and contains enzymes involved in cellular respiration ● inner membranes many infoldings are called CRISTAE; they increase the surface area for cellular respiration reactions to occur ● region within inner membrane is the . CHLOROPLASTS: (a.k.a. “the organelles that feed the world”) ● ; ● (convert light energy into chemical energy; ● found in eukaryotic algae, leaves and other green plant organs; ● can change shape, move and divide ● Chloroplast structure includes: -Thylakoids, -Stroma, PEROXISOMES: ● contain special enzymes for specific metabolic pathways ● found in nearly all eukaryotic cells ● contain peroxide-producing enzymes that transfer hydrogen ions to oxygen producing hydrogen peroxide ● contain catalase enzyme which 6.6 - The CYTOSKELETON is a network of fibers that organizes structures and activities in the cell ● anchors and/or provides “tracks” for many organelles ● It is composed of three types of molecular structures: -Microtubules -Microfilaments -Intermediate filaments Components of the Cytoskeleton ● Microtubules are the thickest of the three components of the cytoskeleton ● Microfilaments, also called , are the thinnest components ● Intermediate filaments are fibers with diameters in a middle range Roles of the Cytoskeleton: Support, Motility, and Regulation ● the cytoskeleton helps to and ● it interacts with motor proteins to ( ) ● inside the cell, vesicles can travel along “monorails” provided by the cytoskeleton ● recent evidence suggests that the cytoskeleton may help regulate biochemical activities Microtubules: ● straight, hollow rods made of protein called ; ● can serve as “tracks” to guide organelle movement; ● involved in separation of chromosomes in cell division; make up ; Cilia and Flagella ● Microtubules control the beating of cilia and flagella, locomotor appendages of some cells ● Cilia and flagella differ in their beating patterns ● FLAGELLA: ; usually found singly or in pairs; ● CILIA: shorter than flagella; usually present ; wavelike motion used to ● Cilia and flagella share a common ultrastructure: -A core of microtubules sheathed by the plasma membrane -A basal body that anchors the cilium or flagellum -A motor protein called DYNEIN, which drives the bending movements of a cilium or flagellum Microfilaments: ● can exist as single filaments or in bundles; ● formed from the protein ; ● help the cell (or parts of the cell) to contract; ● they stabilize cell shape; ● Involved in “pinching” contractions during cell division; ● Involved in forming “pseudopodia” that enable some cells to move. Intermediate Filaments ● Intermediate filaments range in diameter from 8–12 nanometers, larger than microfilaments but smaller than microtubules ● They and ● Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes Extracellular Structures: 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: - The extracellular matrix (ECM) of animal cells ● CELL WALL: -semirigid structure outside of cell membrane of ; -consists of fibers + complex polysaccharides & proteins -provides support, limits cell’s volume, and protects against fungi and/or microorganism infection. Cell Walls of Plants ● 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 The Extracellular Matrix (ECM) of Animal Cells: ● Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) ● Functions of the ECM: -Support -Adhesion -Movement -Regulation EXTRACELLULAR MATRIX: -fibrous proteins such as and glycoproteins are secreted by and surround cells; - ; -helps filter materials passing between different tissues; -orients cell movement during development; - . Intercellular Junctions ● Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact ● Intercellular junctions facilitate this contact Plants: Plasmodesmata ● Plasmodesmata are channels that perforate plant cell walls ● Through plasmodesmata, (and sometimes proteins and RNA) can pass from cell to cell Animals: Tight Junctions, Desmosomes, and Gap Junctions ● At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid ● Desmosomes (anchoring junctions) ● Gap junctions ( into strong sheets ) provide cytoplasmic channels between adjacent cells The Cell: A Living Unit Greater Than the Sum of Its Parts ● Cells rely on the integration of structures and organelles in order to function ● For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane