BISC 102 Notes - Chapter 3: Cells
BISC 102 Notes - Chapter 3: Cells Bisc 102
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This 5 page Class Notes was uploaded by Alexis Neely on Friday September 2, 2016. The Class Notes belongs to Bisc 102 at University of Mississippi taught by Carla Beth Carr in Fall 2016. Since its upload, it has received 67 views. For similar materials see Inquiry Into Life Human Biology in College of Liberal Arts at University of Mississippi.
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Date Created: 09/02/16
3.1 Cells Are the Units of Life Simple Lenses Revealed the First Glimpses of Cells Cells: the smallest units of life that can function independently Study of cells began in 1660 by English physicist Robert Hooke Named “cells” because they looked like the cubicles (Latin , ellae) where monks studied and prayed. Cell theory: formulated by German biologists Mathias J. Schleiden and Theodor Schwann. Two main components: All organisms are made of one or more cells, and the cell is the fundamental unit of life. German physiologist Rudolf Virchow added a third component, that all cells come from preexisting cell Microscopes Magnify Cell Structures The unaided eye can see objects that are larger than about 0.2mm, studying cellular level require magnification Light Microscopes: 2 types, compound and confocal. A compound microscope uses two or more lenses to focus visible light through a specimen. Most powerful magnify up to 16x and resolve objects 200 nanometers apart. A confocal microscope enhances resolution by focusing white or laser light through a lens to the object, passing image through pinhole and resulting in a scan of highly focused light on one tiny part of specimen at a time Transmission and Scanning Electron Microscopes: P rovide greater maginfication and resolution using electrons. However, extremely expensive, require altered specimen and all images are black and white. A T EM sends beam of electrons through specimen and translates into a highresolution, twodimensional image. Can magnify up to 50 million times and resolve objects less than 1 angstrom apart. A SEM scans a beam of electrons over metalcoated 3D specimen. Lower resolution than TEM. Ability to reveal textures on a specimen’s external surface. All Cells Have Features in Common All cells contain DNA (genetic info) and RNA (production of proteins) Ribosomes: s tructures that manufacture proteins Cell membrane: lipidrich, forms a boundary between the cell and its environment Cytoplasm: includes all cell contents (except the nucleus, in cells that have one) Cytosol: f luid portion of the cytoplasm Size of cell maximizes the ratio of surface area to volume 3.2 Different Cell Types Characterize Life’s Three Domains Domains Bacteria and Archaea Contain Prokaryotic Organisms Prokaryotes: the simplest and most ancient forms of life, organisms lack a nucleus (pro = before; k aryon = kernel) Eukaryotes: have cells that contain a nu cleus and other membranous organelles (e u = true) Bacteria are the most abundant and diverse organisms on Earth. Nucleoid: the area where the cell’s circular DNA molecule congregates Cell wall: rigid, surrounds the cell membrane of most bacteria, protecting the cell and preventing it from bursting from absorbing too much water, gives shape Flagella: (singular: flagellum) are taillike appendages that enable cells to move Archaean cells resemble bacteria cells in some ways (smaller, lack nucleus/organelles, cell walls, flagella, onecelled organisms). Archaea have their own domain because they build cells outs of biochemicals that are different from those in bacteria or eukaryotes. Closest relatives of eukaryotes. Domain Eukarya Contains Organisms with Complex Cells All eukaryotic organisms share many features on a cellular level. (But plant cells have chloroplasts and a cellular wall, which animal cells lack) Eukaryotic cells are typically 10 to 100 times greater than prokaryotic cells Cytoplasm of a eukaryotic cell is divided into organelles Organelles: “little organs”, compartments that carry out specialized functions (e.g.nucleus, mitochondria, chloroplasts). Elaborate system of internal membranes creates these compartments. Keep related biochemicals and structures close enough to make them function efficiently without altering or harming other cellular contents. Compartmentalization: t he cell maintains high concentrations of each biochemical only in certain organelles, not throughout the entire cell 3.3 A Membrane Separates Each Cell from Its Surroundings Cell membrane separates the cytoplasm from the cell’s surroundings. Composed of phospholipids organic molecules that resemble triglycerides. The cell’s surface transports substances into and out of cell. Responds to external stimuli. Inside eukaryotic cells, internal membranes enclose the organelles Phospholipid: glycerol bonds to only two fatty acids; the third carbon binds to a phosphate group attached to additional atoms. The phosphate “head”, with polar covalent bonds, is hydrophilic. The other end, two fatty acid “tails”, is hydrophobic. Phospholipid bilayer: a double layer of phospholipids, resembles a cheese sandwich. The hydrophilic heads are bread, exposed to watery medium outside and inside cell. Hydrophobic tails face each other in sandwich. Forms a 3D sphere. Has selective permeability. Lipids and small, nonpolar molecules pass freely into and out of cell. Tails in interior block ions and polar molecules like glucose. Fluid mosaic: phospholipid bilayer is often called this because of many molecules that drift laterally within the bilayer Steroid molecules maintain the membrane’s fluidity as temperature fluctuates. Both animal and plant cell membranes contain steroids (cholesterol in animal membranes). Proteins are important to function. Transport proteins e mbedded in the phospholipid bilayer create passageways through which ions, glucose and other polar substances pass into or out of the cell. Enzymes facilitate chemical reactions that otherwise would proceed too slowly to sustain life. R ecognition proteins s erve as “name tags” that help the body’s immune system recognize its own cells. Adhesion proteins e nable cells to stick to one another. R eceptor proteins b ind to molecules outside the cell and trigger a response inside the cell. 3.4 Eukaryotic Organelles Divide Labor Organelles have specialized functions that carry out the work of the cell. “Walls” of these cellular compartments are membranes. Folded and studded with enzymes and other proteins. Folds provide tremendous surface area where many of the cell’s chemical reactions occur. Many of the cell’s internal membranes form a coordinated endomembrane system: consisting of several interacting organelles (nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, cell membrane) Organelles of the endomembrane system are connected by v esicles small membranous spheres that transport materials inside the cell. “Bubbles” of membrane. Pinch off from one organelle, travel within the cell, fuse with another. Also considered part of the endomembrane system. The Nucleus, Endoplasmic Reticulum, and Golgi Interact to Secrete Substances Nucleus: the organelle that contains DNA in eukaryotic cells Nuclear pores: h oles in the doublemembrane n uclear envelope, which separates the nucleus from the cytoplasm Nucleolus: dense spot that assembles the components of ribosomes Remainder of cell between nucleus and membrane is cytoplasm which includes cytosol: a watery mixture of ions, enzymes, RNA and dissolved substances. In eukaryotes, the cytoplasm also includes organelles and arrays of protein rods and tubules called cytoskeleton. mRNA (messenger RNA) coming from the nucleus binds to a ribosome, which manufactures proteins. Ribosomes produce proteins for use inside cell. Freefloating in the cytosol. Entire complex of ribosome, mRNA, and partially made protein anchors to the membrane of endoplasmic reticulum Endoplasmic reticulum (ER) is a network of sacs and tubules composed of membranes. Originates at nuclear envelope and winds throughout cell. Surface is studded with ribosomes making proteins that that enter the inner compartment of the ER, destined to be secreted. This section is called r ough ER. Smooth ER is adjacent to rough ER. Synthesizes lipids and other membrane components. Golgi apparatus is a stack of flat, membraneenclosed sacs that function as a processing center. Proteins from the ER pass through Golgi sacs. Complete intricate folding and become functional. Enzymes in Golgi apparatus also manufacture and attach carbohydrates to proteins or lipids, forming “name tags” recognized by the immune system. Sorts and packages materials into vesicles, which move toward cell membrane. Lysosomes, Vacuoles, and Peroxisomes Are Cellular Digestion Centers Lysosomes: organelles containing enzymes that dismantle and recycle food particles, captured bacteria, wornout organelles, and debris. “Lyse” or cut apart, substrates. Membrane maintains the pH of the organelle’s interior at 4.8, much more acidic than the neutral pH of the rest of the cytoplasm (so it does not digest entire cell) Vacuole: large, central. Contains a watery solution of enzymes that degrade and recycle molecules and organelles. Acquires water and exerts turgor pressure to help plants stay rigid and upright. Contains a variety of salts, sugars and weak acids. pH is somewhat acidic. Peroxisomes are contained in all eukaryotic cells. Organelles contain several types of enzymes that dispose of toxic substances. Although they resemble lysosomes in size and function, peroxisomes originate at the ER and contain different enzymes. Mitochondria Extract Energy from Nutrients Mitochondria: organelles that use a process called cellular respiration to extract needed energy from food. Two membrane layers: outer and intricately folded inner that encloses the mitochondrial matrix. Within the matrix is DNA that encodes proteins essential for function; ribosomes occupy matrix. Cristae are folds of inner membrane. Add tremendous surface area to inner membrane, which houses enzymes that catalyze reactions of cellular respiration. Photosynthesis Occurs in Chloroplasts Chloroplast is the site of photosynthesis in eukaryotes. Each contains multiple membrane layers. Outer membrane enclose an enzymerich fluid called stroma, within it is a third membrane system folded into flattened sacs called thylakoids which stack like pancakes to form grana. Chlorophyll pigment are embedded in thylakoid membranes. Chloroplast is one representative of a larger category of plant organelles called plastids, which synthesize lipidsoluble carotenoid pigments. Plastids that assemble starch molecules are important in cells specialized for food storage. Endosymbiosis theory states that some ancient organism(s) engulfed bacterial cells. Rather than digest as food, the hosts kept them as partners: mitochondria and chloroplasts. The structures and genetic sequences of today’s bacteria, mitochondria and chloroplasts supply powerful evidence of this theory. 3.5 The Cytoskeleton Supports Eukaryotic Cells The cytosol of eukaryotic cell contains a c ytoskeleton, an intricate network of protein “tracks” and tubules. A structural framework with many functions. Maintains the cell’s 3D shape, aids in cell division, and helps connect cells to one another. Enables cells or parts of a cell to move. Microfilament is the thinnest component of cytoskeleton. Long rod composed of protein actin. Each microfilament is only 7 nanometers in diameter. Part of nearly all eukaryotic cells. Provide strength for cells to survive stretching and compression. Anchor one cell to another. Intermediate filaments have 10nanometer diameters. Between microfilaments and microtubules. Made of a variety of proteins. Maintain cell shape by forming an internal scaffold in cytosol and resisting mechanical stress. Bind cells together. Microtubule is composed of a protein called tubulin assembled into hollow tube (23 nanometers in diameter). Cell can change the length of a microtubule by adding or removing tubulin molecules. Have many functions in eukaryotic cells. Centrosomes (in animal cells) Organize microtubules. Contains two centrioles. Centrioles indirectly produce the extensions that enable cells to move (cilia and flagella) Cilia are short, numerous extensions resembling a fringe. Some protists have thousands that enable cells to “swim”. 3.6 Cells Stick Together and Communicate with One Another Cell walls surround membranes of nearly all bacteria, archaea, fungi, algae, and plants. Not just a barrier. Impart shape, regulate cell volume and prevent bursting when a cell takes in too much water. Plasmodesmata are channels that connect adjacent plant cells. “Tunnels” in the cell wall, through which the cytoplasm of one plant cell interacts with another. Animal cells lack cell walls, but secrete a complex extracellular matrix that holds together and coordinates many aspects of cellular life. Cells are not in direct contact with one another. Plasma membranes of adjacent cells directly connect to one another via several types of junctions. Tight junction fuses animal cells together. Forms impermeable barrier. Proteins anchored in membranes connect to actin in cytoskeleton and join cells into sheets. Connections allow the body to control where biochemicals move, since fluids cannot leak between the joined cells. Anchoring (or adhering) junction: c onnects an animal cell to its neighbors or to extracellular matrix. Proteins at each junction span the cell membrane and link to each cell’s cytoskeleton. These junctions hold skin cells in place by anchoring them to the extracellular matrix. Gap junction: protein channel that links cytoplasm of adjacent animal cells. Allows exchange of ions, nutrients, and other small molecules. Analogous to plasmodesmata in plants.
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