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Chapter 5: Membrane Structure, Synthesis, and Transport - Coggle Diagram

- - - - do not interact with the hydrophobic interior of the phospholipid bilayer
        
        non covalently bound to the polar head groups of phospholipids.
        
        are typically attached to the membrane by hydrogen and/or ionic bonds.
    - - Integral membrane proteins
        
        Transmembrane proteins
        
        have one or more regions that are physically inserted into the hydrophobic interior of the phospholipid bilayer
        
        each transmembrane segment is folded into an α helix
        
        a segment is stable in a membrane because the non polar amino acids interact favourably with the non polar lipid tails
        
        can rotate, move laterally, no flipflop
        
        Lipid anchored proteins
        
        lipid molecule that is covalently attached to an amino acid side chain within the protein
        
        lipid tails are inserted into the hydrophobic portion of the membrane and thereby keep the protein firmly attached to the membrane
- - - - lipid raft is a group of lipids that float together as a unit within a larger sea of lipids
        
        they have high amounts of cholesterol
        
        contain unique sets of lipid-anchored proteins and transmembrane proteins
        
        lipid rafts may play an important role in endocytosis
  - - - at lower temperatures
- - - - building blocks are made via enzymes in the cytosol
        
        fatty acids are activated by attachment to an organic molecule CoA
        
        activation promotes the bonding of the two fatty acids to a glycerol-phosphate molecule
        
        resulting molecule is inserted into the cytosolic leaflet of the ER membrane
        
        phosphate is removed from glycerol
        
        a polar molecule already linked to phosphate is attached to glycerol, the polar head group contains choline
        
        phospholipid is initially inserted into the cytosolic leaflet
        
        flippases in the ER membrane transfer about half of the newly made phospholipids to the other leaflet so similar amounts of lipids are found in both leaflets
        
        phospholipids in the ER can diffuse laterally to the nuclear envelope
        
        lipids are transported via vesicles to the Golgi, lysosomes, vacuoles or plasma membrane
        
        lipid exchange proteins, which extract a lipid from one membrane, diffuse through the cell, and insert the lipid into another membrane
        
        this transfer can occur between any two membranes, even between the endomembrane system and semiautonomous organelles
  - - - after the ER signal sequence is removed by signal
        peptidase, a membrane protein with a ER signal single transmembrane segment is the result
        
        each time a
        polypeptide sequence contains a region of 20 amino acids that are mostly
        hydrophobic and form an α helix, an additional transmembrane
        segment is synthesized into the membrane
        
        from the ER, membrane proteins can be transferred via vesicles to other regions of the cell, e.g. golgi, lysosomes, vacuoles, or plasma membrane.
  - - - play a role in cell surface recognition
        
        carbohydrates often have a protective effect
        
        carbohydrate rich zone on the surface of certain animal cells shields the cell from mechanical and physical damage
        
        carbohydrate portion of glycosylated proteins protects them from the harsh conditions of the extracellular environment and degradation by extracellular proteases
        
        Two forms of protein glycosylation occur in eukaryotes
        
        N- linked
        
        occurs in archaea
        
        carbohydrate is attached to a nitrogen atom of the asparagine side chain
        
        a group of 14 sugar molecules, called a carbohydrate tree, is first built onto a lipid found in the ER membrane
        
        enzyme in the ER, oligosaccharide transferase, transfers the carbohydrate tree from the lipid to an asparagine in the polypeptide
        
        commonly occurs on membrane proteins that are transported to the cell surface
        
        O- linked
        
        occurs only in the Golgi apparatus
        
        involves the addition of a string of sugars to the oxygen atom of a serine/threonine side chain in a polypeptide
        
        important for the production of proteoglycans, which are highly glycosylated proteins that are secreted from cells and help to organize the extracellular matrix that surrounds cells - proteoglycans are also a component of mucus, a slimy material that coats many cell surfaces and is secreted into fluids such as saliva
        
        high concentrations of carbohydrates give mucus its slimy texture
- - - - Diffusion
        
        Simple
        
        substances directly pass through the phospholipid bilayer
        
        Facilitated
        
        transport protein provides a passageway for a substance
      - Osmosis
        
        involves the movement of water molecules
        
        Tonicity
        
        isotonic
        
        concentrations of solutes on both sides of the plasma membrane are equal
        
        hypertonic
        
        concentration of solutes outside the cell is higher than the inside of the cell
        
        hypotonic
        
        outside of the cell has a lower concentration of solutes than the inside
        
        Animal cells
        
        hypertonic solution
        
        water will exit the cell via osmosis and equalize solute concentrations on both sides of the membrane
        
        cell shrinks
        
        crenation
        
        hypotonic solution
        
        water will enter the cell to equalize solute concentrations on both sides of the membrane
        
        osmotic lysis
        
        Plant cells
        
        hypertonic solution
        
        volume inside the plasma membrane shrinks
        
        membrane pulls away from the cell wall (plasmolysis) due to the exit of water
        
        hypotonic solution
        
        small amount of water may enter the cell
        
        cell wall prevents major expansion
  - - - primary
        
        uses a pump, directly using energy to transport solutes
      - secondary
        
        uses pre existing gradient to drive transport
- - - - uniporter
        
        single solute in one direction
      - symporter
        
        2 solutes in one direction
      - antiporter
        
        2 solutes in opposite directions
- - - - Phagocytosis
        
        formation of an enormous membrane vesicle called a phagosome, or phagocytic vacuole, which engulfs a large particle such as a bacterium
        
        macrophages, which are cells of the immune system in mammals, kill bacteria via phagocytosis
        
        macrophages engulf bacterial cells into phagosomes
        
        once inside the cell, the phagosome fuses with a lysosome, and the digestive enzymes within the lysosome destroy the bacterium
      - Pinocytosis
        
        formation of membrane vesicles from the plasma membrane as away for cells to internalize the extracellular fluid
        
        allows cells to
        sample the extracellular solutes
        
        important in cells that are actively involved in nutrient absorption eg cells that line the intestine in animals