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Tour of the Cell (Internal Structures of Cells (Endomembrane System…

- - - - Focused beam of electrons onto the surface of a specimen, providing a 3-D like image.
    - - Focused beam of electrons through a specimen, used to study the internal structure of cells.
- - - - No Nucleus
      - DNA in an unbound region called the nucleoid
      - No membrane-bound organelles
      - Cytoplasm bound by the plasma membrane
    - - DNA in Nucleus, bound by a double membrane
      - Membrane-bound organelles
      - Cytoplasm in region between the Nucleus and Plasma Membrane
      - Generally larger in size
    - - Plasma mebrane
      - Semifluid substance called Cytosol (cytoplasm)
      - Chromosomes (Genetic Material)
      - Ribosomes (make Proteins)
  - - - Contains most of the genetic material in a eukaryotic cell.
      - Enclosed by Nuclear Envelope, separating it from the cytoplasm.
        
        Double membrane, each consisting of a lipid bilayer.
        
        Pores, lined with a pore complex, regulate the entering and exit of molecules from the nucleus.
        
        Nuclear Envelope lined by the nuclear lamina, composed of proteins to maintain the nucleus shape.
      - DNA is organized into units called Chromosomes.
        
        One chromosome contains one DNA molecule associated with proteins called chromatin.
      - Nucleolus located within the nucleus and is the site of Ribosomal RNA (rRNA) synthesis.
    - - Use the information from the DNA to make Proteins.
        
        Carry out protein synthesis in two locations
        
        In the Cytosol (Free Ribosomes)
        
        On the outside of the Endoplasmic Reticulum or Nuclear Envelope (Bound Ribosomes)
  - - - Connected to the Nuclear Envelope
      - Two regions of the ER
        
        Smooth Endoplasmic Reticulum: Lacks bound Ribosomes
        
        Functions
        
        Synthesizes lipids
        
        Metabolizes Carbohydrates
        
        Detoxifies drugs and poisons
        
        Stores calcium ions
        
        Rough Endoplasmic Reticulum: Contains surface bound Ribosomes
        
        Functions
        
        Bound Ribosomes produce Glycoproteins
        
        Distributes Transport Vesicles, secretory proteins surrounded by membranes
        
        Is the membrane factory of the cell
    - - Consists of flattened membranous sacs called Cisternae.
      - Functions
        
        Modifies products of ER
        
        Manufactures certain macromolucles
        
        Sorts and packages materials into Transport Vesicles
    - - Membranous sacs of hydrolytic enzymes
      - Hydrolytic enzymes and lysosomal membranes are produced by the rough ER and then transferred to the Golgi apparatus for processing.
        
        Lysosomal enzymes work best within the acidic environment of the lysosome.
      - Some types of cells can engulf another cell by phagocytosis; forming food vacuoles.
        
        Lysosomes fuse with the food vacuole to digest the molecules.
      - Lysosomes recycle the cell's own organelles and macromolecules; via autophagy
    - - Large vesicles derived from the ER and Golgi apparatus.
      - Functions vary in different types of cells
        
        Food Vacuoles: Formed by Phagocytosis
        
        Contractile Vacuoles: Pump excess water out of the cells; mostly found in freshwater protists.
        
        Central Vacuoles: Holds organic compounds and water; found in mature plant cells.
  - - - Enveloped by a double membrane
        
        Contain free ribosomes and circular DNA molecules
        
        Grow and reproduce somewhat independently in cells
      - Similarities led to the Endosymbiont Theory
        
        Suggests that an early ancestor of eukaryotic cells engulfed an oxygen using non-photosynthetic prokaryotic cell; which formed a symbiotic relationship with the host cell, becoming an endosymbiont.
        
        Endosymbiont later evolved into mitochondria.
        
        At least one cell may have taken up a photosynthetic prokaryote; which later evolved into a chloroplast.
    - - Site of Cellular Respiration, metabolic process that uses oxygen to generate ATP
      - Made up of a smooth outer membrane and an inner folded membrane called Cristae
        
        Inner membrane crates two compartments: Intermembrane space and Mitochondrial matirx
        
        Some steps of cellular respiration are catalyzed in the mitochondrial matrix.
        
        Folded Cristae allows for more surface area for enzymes to synthesize ATP.
    - - Found in plants and algae and are the sites of photosynthesis.
      - Contain green pigment, Chlorophyll, as well as enzymes and other molecules that function in photosynthesis
      - Structures
        
        Thylakoids: Membranous sacs stacked to form Granum.
        
        Stroma: Internal fluid
      - Chloroplast is one of a group of plant organelles called plastids.
    - - Specialized metabolic compartments bound by a single membrane
      - Produce Hydrogen Peroxide and converts it into water.
        
        Peroxisomes perform reactions with different functions; it is unknown how peroxisomes are related to other organelles.
  - - - Network of fibers extending throughout the cytoplasm. That organizes cell's structures and activities, anchoring many organelles.
      - Composed of
        
        Microtubules
        
        Hollow rods about 25 nm in diameter, and 200 nm to 25 microns long. constructed from dimers of tubulin.
        
        Functions
        
        Shaping the cell
        
        Guiding movement of organelles
        
        Separating Chromosomes during cell division
        
        Grow out from Centrosomes near the Nucleus
        
        Each Centrosome has a pair of Centrioles; each with nine triplets of microtubules.
        
        Cilia and Flagella
        
        Control the beating of Flagella and Cilia, Microtubule-containing extensions that project from some cells.
        
        Many unicellular Eukaryotes are propelled through water by Cilia or Flagella; they differ by their beating pattern
        
        Common structures between Cilia and Flagella
        
        Group of microtubules sheathed by an extension of the plasma membrane
        
        Basal body anchors the Cilium or Flagellum
        
        Dynein, a motor protein, which drive the bending movement of a Cilium or Flagellum.
        
        Has two "feet" that "walk" along microtubules. One foot maintains contact, while the other releases and reattaches on step farther along; causing the microtubules to bend, rather than slide, because the microtubules are held in place.
        
        Microfilaments (Actin filaments)
        
        Solid rod about 7 nm in diameter, build as a twisted double chain of actin subunits.
        
        Cortex, a network of microfilaments just inside the plasma membrane
        
        Bundles of microfilaments make up the core of microvilli in intestinal cells
        
        Microfilaments that function in cellular motility contain Myosin in addition to Actin.
        
        Cells crawl along a surface by extending pseudopodia (cellular extensions) and moving towards them.
        
        Cytoplasm Streaming: Circular flow of cytoplasm within cells, driven by actin-myosin interactions.
        
        Intermediate Filaments
        
        Range in diameter from 8 to 12 nm; larger than microfilaments bus smaller than microtubules.
        
        More permanent cytoskelton fixtures that microfilaments and microtubules.
        
        Supports cell shape and fixes organelles in place
  - - - Protects the plant cell, maintains it's shape and prevents excessive intake of water
      - Made up of cellulose fibers embedded in other polysaccharides and protein.
      - Extracellular structure that distinguishes plant cells from animal cells
        
        Prokaryotes, Fungi, and some unicellular Eukaryotes have cell walls.
      - Layers
        
        Primary Cell Wall: Relatively thin and flexible
        
        Middle Lamella: Thin layer between primary cell walls of adjacent cells.
        
        Secondary Cell Wall: Added between the plasma membrane and primary cell wall in some cells.
    - - Made up of glycoproteins, such as collegen, proteoglycans, and fibronectin
      - ECM can regulate cells behaviors by communicating with a cell through integrins
        
        ECM proteins bind to receptor proteins in the plasma membrane called integrins
        
        Can influence the activity of genes in the nucleus
      - Animal cells lack cell walls but are covered by an elaborate extracellular matrix
- - - - Phospholipids, the most abundant lipid in the plasma membrane, are amphipathic molecules. Containing hydrophobic and hydrophilic regions.
        
        The hydrophobic tails of the phospholipids are sheltered inside the membrane, while the hydrophilic heads are exposed to water on either side.
      - Fluid Mosaic Model: Membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids.
        
        Proteins are not randomly distributed in the membrane.
        
        Phospholipids form the main fabric of the membrane.
      - Fluidity of Membranes
        
        Held together mainly by weak hydrophobic interactions.
        
        Most of the lipids, and some proteins, can move sideways within the membrane. Rarely a lipid may flip-flop across the membrane from one phospholipid layer to the other.
        
        As temperatures cool, membranes switch from a fluid state to a solid state.
        
        The temperature at which a membrane solidifies depends on the types of lipids
        
        Membranes rich in unsaturated fatty acids are more fluid than those rice in saturated fatty acids.
        
        Variations of lipid composition of cell membranes appear to be adaptations to specific environmental conditions.
        
        Ability to change lipid composition have evolved in organisms that live where temperatures vary.
        
        Membranes must be fluid to work properly
        
        Steroid cholesterol effects membrane fluidity at different temperatures
        
        At warm temperatures, cholesterol restrains movement of phospholipids.
        
        At cool temperatures, cholesterol maintains fluidity by preventing tight packing.
        
        Plants use a related steroid lipid to buffer membrane fluidity.
      - Membrane Proteins and their Functions
        
        Membrane is a collage of different proteins, clustered in groups, embedded in the fluid matrix of the lipid bilayer.
        
        Proteins determine most of the membrane's functions
        
        Def. Peripheral Proteins: Proteins bound to the surface of the membrane.
        
        Def. Integral Proteins: Proteins that penetrate the hydrophobic core.
        
        Proteins that span the membrane are called Transmembrane Proteins.
        
        Cell-surface membranes carry out several functions
        
        Signal Transduction
        
        Cell-Cell recognition
        
        Enzymatic activity
        
        Intercellular joining
        
        Transport
        
        Attachment to the cytoskeleton and extracellular matrix
    - - Cells recognize each other by binding to molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane
        
        Carbohydrates maybe covalently bonded to lipids, or to proteins.
        
        Carbohydrates vary among species, individuals, and even cell types in an individual.
    - - Cells must exchange materials with it's surrounding, the plasma membrane is selectively permeable to regulate the cell's molecular traffic.
      - Permeability of the Lipid Bilayer
        
        Hydrophobic (Nonpolar) molecules can dissolve into the lipid bilayer and pass through the membrane rapidly.
        
        Hydrophilic molecules, such as ions and polar molecules, cannot cross the membrane easily.
        
        Proteins built into the membrane regulate transport.
      - Synthesis and Sidedness of Membranes
        
        Have distinct inside and outside faces.
        
        asymmetrical distribution of proteins, lipids, and carbohydrates in the membrane are determined when the membrane is built by the ER and Golgi apparatus.
  - - - Diffusion
        
        Def. Diffusion: The tendency for molecules to spread evenly into the available space.
        
        Each molecule moves randomly, diffusion of a population of molecules may be directional.
        
        Def. Dynamic Equilibrium: As many molecules cross the membrane in one direction as the other.
        
        Substances diffuse down their own concentration gradient, the region along which the density of a chemical substance increases or decreases.
        
        No work is required
        
        Diffusion of a substance across a biological membrane is passive transport because no energy is expended by the cell to make it happen.
      - Water Balance
        
        Osmosis is the diffusion of water across a selectively permeable membrane.
        
        Water diffuses from a region of lower solute concentration to a region of higher solute concentration until the solute concentration is equal on both sides.
        
        Tonicity
        
        Def. Tonicity: The ability of a surrounding solution to cause a cell to gain or lose water.
        
        Depends on it's concentration of solutes that cannot cross the membrane relative to that inside the cell.
        
        Types of Solutions
        
        Def. Hypertonic Solution: Solute concentration is greater than that of inside the cell; Cell loses water.
        
        Def. Hypotonic Solution: Solute concentration is less than that of inside the cell; Cell gains water.
        
        Def. Isotonic Solution: Solute concentration is the same as inside the cell; no net water movement.
        
        Effects of Tonicity on Cells With and Without Cell Walls
        
        Hyper/Hypotonic environments create osmotic problems for organisms that lack rigid cell walls.
        
        Cells without cell walls with shrivel in hypotonic environments and lyse (burst) in hypertonic environments.
        
        Cells with cell walls can better maintain water balance.
        
        Cells in hypotonic solutions swell entill the cell wall opposes intake; cell becomes turgid (firm)
        
        If the cells surroundings are isotonic the cell becomes flaccid (limp)
        
        In a hypertonic solution the cell loses water and the membrane pulls wasy from the cell wall.
        
        In plant cells this causes the plant to wilt with a potentially lethal effect, Plasmolysis.
        
        Osmoregulation
        
        Def. Osmoregulation: The control of solute concentrations and water balance.
        
        Bacteria and Archaea that live in hypersaline environments have cellular mechanisms to balance internal and external solute concentrations.
      - Bulk Transport
        
        Small molecules and water enter or leave the cell through the lipid bilayer or via transport proteins, Large molecules cross the membrane in bulk via vesicles.
        
        Def. Exocytosis: When transport vesicles migrate to the membrane, fuse, and release their contents outside the cell.
        
        Secretory cells use endocytosis to export products.
        
        Def. Endocytosis: When cells take in macromolecules forming vesicles from the plasma membrane.
        
        Types
        
        Def. Pinocytosis ("Cellular Drinking"): Molecules dissolved in droplets are taken up when extracellular fluids are "gulped" into tiny vesicles.
        
        Def. Receptor-Mediated Endocytosis: When specific solutes bind to receptors on the cell's surface which triggers the formation of a vesicle.
        
        Emptied receptors are recycled into the plasma membrane.
        
        Human cells use receptor-mediated endocytosis to take in cholesterol, which is carried in particles called low-density lipoproteins (LDLs).
        
        Receptor Proteins, Receptors and other molecules from extracellular fluid are transported in vesicles.
        
        Def. Phagocytosis ("Cellular Eating"): Cell engulfs a particle in a vacuole which then fuses with a lysosome to digest the particle.
      - Facilitated Diffusion
        
        Transport proteins speed up passive movement of molecules across the plasma membrane, includes channel proteins and carrier proteins.
        
        Facilitated Diffusion is still passive, because solutes move down it's concentration gradient, without requiring energy.
    - - Allow the passage of hydrophilic substances across the membrane.
      - Some, called Channel Proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel.
        
        Channel Proteins, called aquaporins, facilitate passage of water molecules.
      - Others, called Carrier Proteins, bind to molecules and change shape to shuttle them across the membrane.
      - Some ion channels, called Gated Channels, open or close in response to stimulus.
      - Transport Proteins are specific for the substance it moves.
    - - Some Transport Proteins can move solutes against their concentration gradient. Allowing cells to maintain concentration gradients that differ from their surroundings.
      - Requires energy, usually in the form of ATP hydrolysis, to move substances against their concentration gradient.
        
        All proteins involved are Carrier Proteins.
      - Ion Pumps/Membrane Potential
        
        Membrane potential is the voltage across the membrane.
        
        Voltage is created by differences in a distribution of positive and negative ions across the membrane.
        
        The Cytoplasmic side is negatively charged relative to the Extracellular side.
        
        Def. Electrochemical Gradient: Drives the diffusion of ions across the membrane.
        
        Def. chemical Force: Ions concentration gradient.
        
        Def. Electrical Force: The effect of the membrane potential on the ion's movement.
        
        Def. Electrogenic Pump: Transport proteins that generates voltage across the membrane.
        
        The main pump of plants, Fungi and Bacteria is a Proton Pump; which actively transports Hydrogen Ions (H+) out of the cell.
        
        Helps store energy that can be used for cellular work.
      - Cotransport
        
        Def. Cotransport: Occurs when active transport of a solute indirectly drives transport of other substances.
        
        Diffusion of an actively transported solute down it's concentration gradient is coupled with he transport of a second substance against it's own concentration gradient.