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Biology Ch.6 (Biology Ch.7 (Ch. 7.1 (Membrane Proteins (Cell-surface…

- - - - In exocytosis, transport vesicles migrate to the membrane, fuse with it, and release their contents outside the cell
      - Many secretory cells use exocytosis to export their products
    - - In endocytosis, the cell takes in macromolecules by forming vesicles from the plasma membrane
      - Endocytosis is a reversal of exocytosis, involving different proteins
      - There are three types of endocytosis
      - Phagocytosis (“cellular eating”)
        
        engulfs particle in a vacuole
        
        vacuole fuses with lysosome to digest
      - Pinocytosis (“cellular drinking”)
        
        in pinocytosis, molecules dissolved in droplets are taken up when extracellular fluid is “gulped” into tiny vesicles
      - Receptor-mediated endocytosis
        
        In receptor-mediated endocytosis, binding of specific solutes to receptors triggers vesicle formation
        
        Receptor proteins, receptors, and other molecules from the extracellular fluid are transported in the vesicles
        
        Emptied receptors are recycled to the plasma membrane
  - - - most abundant lipid in plasma membrane
      - amphipathic with hydrophilic heads and hydrophobic tails
    - - membranes mainly held together by weak hydrophobic interactions
      - most lipids and some proteins can move sideways rarely a lipid may flip-flop
      - as temp. cool membranes switch from fluid state to solid
      - membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids
      - must be fluid to work properly
      - steroid cholesterol can have effects
      - at warm temp. cholesterol restrains movement of phospholipids at cool temp. it maintains fluidity by preventing tight packing
    - - a membrane is a collage of different proteins, often clustered in groups, embedded in the fluid matrix of the lipid bilayer
      - Phospholipids form the main fabric of the membrane
      - Proteins determine most of the membrane’s functions
      - Peripheral proteins are bound to the surface of the membrane
      - Integral proteins penetrate the hydrophobic core
      - Integral proteins that span the membrane are called transmembrane proteins
      - The hydrophobic regions of an integral protein consist of one or more stretches of nonpolar amino acids, often coiled into α helices
      - Cell-surface Membranes Functions
        
        Transport
        
        Enzymatic activity
        
        Signal transduction
        
        Cell-cell recognition
        
        Intercellular joining
        
        Attachment to the cytoskeleton and ECM
    - - Cells recognize each other by binding to molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane
      - Membrane carbohydrates may be covalently bonded to lipids (forming glycolipids) or, more commonly, to proteins (forming glycoproteins)
      - Carbohydrates on the extracellular side of the plasma membrane vary among species, individuals, and even cell types in an individual
  - - - Hydrophobic (nonpolar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly
      - Hydrophilic molecules including ions and polar molecules do not cross the membrane easily
      - Proteins built into the membrane play key roles in regulating transport
    - - allow 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 greatly facilitate the passage of water molecules
      - other called carrier proteins bind to molecules and change shape to shuttle them across the membrane
  - - - The diffusion of a substance across a biological membrane with no energy required
      - Diffusion is the tendency for molecules to spread out evenly into the available space
      - At dynamic equilibrium as many molecules cross the membrane in one direction in the other
      - Substances diffuse down their concentration gradient which shouldn't require any work
    - - Is the diffusion of water across a selective permeable membrane
      - Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration until the solute concentration is equal
      - Tonicity
        
        the ability of a surrounding solution to cause a cell to gain or lose water
        
        depends on concentration of solutes that cant cross the membrane
        
        Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
        
        Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water
        
        Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water
        
        Cells without cell walls will shrivel in hypertonic solution and lyse (burst) in a hypotonic solution
    - - cell walls help maintain water balance
      - hypo. solution a plant cell swells becoming turgid (firm)
      - iso. solution in plant cell theres no net movement of water cell becomes flaccid(limp)
      - hyper. solution plant cells lose water causing plant to wilt a potentially lethal effect called plasmolysis
    - - transport proteins speed the passive movement of molecules across plasma membrane
      - include channel and carrier proteins
      - channel proteins provide corridors that allow a specific molecule or ion to cross the membrane
      - Aquaporins facilitate the diffusion of water
      - Ion channels facilitate the transport of ions
      - Some ion channels, called gated channels, open or close in response to a stimulus
  - - - requires energy, usually in the form of ATP hydrolysis, to move substances against their concentration gradients
      - All proteins involved in active transport are carrier proteins
      - allows cells to maintain concentration gradients that differ from their surroundings
    - - Membrane potential is the voltage across a membrane
      - Voltage is created by differences in the distribution of positive and negative ions across a membrane
      - The cytoplasmic side of the membrane is negative in charge relative to the extracellular side
      - Two combined forces, collectively called the electrochemical gradient, drive the diffusion of ions across a membrane
      - A chemical force (the ion’s concentration gradient)
      - An electrical force (the effect of the membrane potential on the ion’s movement)
      - An electron pump is a transport protein that generates voltage across a membrane and help store energy that can be used for cellular work
      - The sodium-potassium pump is the major electrogenic pump of animalcells
      - Proton pump- activily transports hydrogen ions out od the cell
    - - Cotransport occurs when active transport of a solute indirectly drives transport of other substances
      - The diffusion of an actively transported solute down its concentration gradient is coupled with the transport of a second substance against its own concentration gradient
- - - - suggests that an early ancestor of eukaryotes engulfed an oxygen-using nonphotosynthetic prokaryotic cell
      - the engulfed cell formed a relationship with the hos cell becoming an endosymbiont
      - endosymbionts evolved into mitochondria
      - at least one of these cells may have taken up photosynthetic prokatyote which involved into chloroplast
  - - - network of fibers extending throughout cytoplasm
      - organizes cells structures and activities, anchoring many organelles
      - Microfilaments
        
        twisted double chain of actin subunits
        
        form a cortex inside the plasma membrane to help support shape
        
        make up core of microvilli or intestinal cells
        
        that function in cellular motility contain protein myosin alon with actin
        
        are the smallest; about 7nm in diameter
      - Microtubules
        
        constructed of dimers of tubulin
        
        Shaping the cell
        
        Guiding movement of organelles
        
        Separating chromosomes during cell division
        
        The largest; about 25mn with 15 um lumen
      - Intermediate filaments
        
        diameter about 8-12nm
        
        more permanent cytoskeleton fixtures than the other twoo
        
        support cell shape and fix organelles in place
        
        fibrous subunit are keratin protein coiled together
      - supports cell and shape
      - interacts with motor proteins to produce cell mtility
    - - nine triplets of microtubules arranged in a ring
      - in animal cells microtubules grow out from a centrsome near the nucleus
    - - microtubules control the beating of cilia and flagella but they differ in the beating patterns
      - many unicellular eukaryotes are propelled through water by these
      - groups of microtubules sheated by an extension of the plasma membrane
      - basal body
      - motor protein called dynein that drives the bending movements
- - - - visible light is passed through a specimen and then through glass lenses
      - magnify about 1,000 times the size of specimen
      - Resolution too low to study organelles
    - - Scanning electron microscopes (SEMs)
        
        Focus's a beam of electrons onto the surface of a specimen, providing images that look 3D
      - Transmission electron microscopes (TEMs)
        
        Focus's a beam of electrons through a specimen
        
        mainly study's the internal structure of cells
  - - - internal membranes that compartmentalize their functions
      - consist of Protists, fungi, animals, and plants
      - Nucleus bounded by a double membrane
      - Membrane-bound organelles
      - Cytoplasm in the region between the plasma membrane and nucleus
    - - Consist of bacteria and archaea
      - No nucleus; has a Nucleoid
      - No membrane-bond organelles
      - Cytoplasm bound by the plasma membrane
      - Normally smaller compared to eukaryotes
    - - Plasma membrane
      - Semifluid substance called cytosol
      - Chromosomes (carry genes)
      - Ribosomes (make proteins)
    - - Critical to cell
      - Metabolic requirements set upper limits on the size of cells
      - As cell increases volume grows proportionately more than surface area
    - - Cytoskeleton: Microfilaments and Microtubules
      - Chloroplast: Photosynthetic convert energy of sunlight to chemical
      - Central Vacuole: storage, breakdown waste, hydrolysis macromolecules
      - Ribosomes
      - Plasmodesmata: cytoplasmic channels through cell walls that connect the cytoplasma of adjacent cells
      - Cell wall: outer layer that maintains shape, and protects from damage. made of cellulose other polysaccharides and protein
      - Plasma membrane
      - Peroxisome
      - Smooth and rough ER
      - Mitochondrion
      - Nucleus
        
        Nuclear envelope
        
        Nucleolus
        
        Chromatin
      - Golgi apparatus
    - - Mitochondrion: cellular respiration and make of ATP
      - Peroxisome: metabolic functions; produces hydrogen peroxide and converts to water
      - Lysosome: digest organelles where macromolecules are hydrolyzed
      - Microvill: increase surface area
      - Golgi Apparatus: Organelle active in synthesis, modification, sorting, and secretion of cell products
      - Ribosomes: make protein
      - Cytoskeleton: cells shape, movement, made of protein and includes Microfilaments, Microtubules, and Intermediate filaments
      - Plasma Membrane: encloses the cell
      - Nucleus
        
        Nuclear envelope surrounds the nucleus with a double membrane with multiple pores. The pores regulate the passage of macromolecules
        
        Nucleolus: production of ribosomes
        
        Chromatin:Consisting of DNA and proteins
      - Centrosome: organize microtubules and provide structure for the cell and help in cell division
      - Flagellum: microtubules help cell move
      - Smooth and Rough ER: active in membrane synthesis and other synthetic and metabolic processes
- - - - Endoplasmic Reticulum (ER)
        
        Smooth ER
        
        Synthesizes lipids
        
        Metabolizes carbohydrates
        
        Detoxifies drugs and poisons
        
        Stores calcium ions
        
        Lacks ribosomes
        
        Rough ER
        
        Studded with ribosomes
        
        Has bound ribosomes, which secrete glycoproteins
        
        Distributes transport vesicles, secretory proteins surrounded by membranes
        
        Is a membrane factory for the cell
      - Nuclear envelope
      - Golgi apparatus
        
        Shipping, receiving center
        
        Modifies products of the ER
        
        Manufactures certain macromolecules
        
        Sorts and packages materials into transport vesicles
        
        Flattened membrane sacs called cisternae
      - Lysosomes
        
        membraneous sac of hydrolytic enzymes.
        
        fusees with food vacuole and digest macromolecules
        
        Made by rough ER and transferred to Golgi for further processing
        
        recycle cells own organelles and marcomolecules process called autophagy
      - Vacuoles
        
        lare vesicles derived from ER and Golgi
        
        Food vacuoles are formed by phagocytosis
        
        Contractile vacuoles, found in many freshwater protists, pump excess water out of cells
        
        Central vacuoles, found in many mature plant cells, hold organic compounds and water