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

- - - - two types
        
        lipid-anchored proteins
        
        attached to the membrane via a lipid molecule that is covalently attached to an amino acid sidechain within the protein
        
        the lipid molecules keep the protein attached to the membrane
        
        transmembrane proteins
        
        one or more regions (transmembrane segments) physically embedded in the interior of the phospholipid bilayer
        
        transmembrane segments are stretches of non-polar amino acids that traverse the membrane through both leaflets
        
        transmembrane segments are folded into a-helices and are stable due to the favourable interaction with non-polar lipid tails
      - cannot be removed unless there was an interaction disrupting the integrity of the protein (e.g., dissolved with an organic solvent or detergent)
    - - do not interact with the interior of the phospholipid bilayer
      - they are non-covalently bound to regions of integral membrane proteins that stick out of the membrane or to the polar head groups of phospholipids
      - typically attached to the membrane by hydrogen bonds and ionic bonds
- - - - carbohydrate + lipid = glycolipid
      - carbohydrate + protein = glycoprotein
    - - N-linked
        
        involves the attachment of carbohydrate to amino acid asparagine in a polypeptide
        
        "N" because the carbohydrate is attached to a nitrogen atom of the asparagine side chain
        
        for the attachment to happen, a group of 14 sugar molecules (carbohydrate tree) is built onto a lipid found in the ER membrane. Oligosaccharide transferase transfers the carbohydrate tree from the lipid to an asparagine in the polypeptide
      - O-linked
        
        only occurs in the golgi apparatus
        
        involves the addition of a string of sugars to the oxygen atom of a serine or threonine side chain in a polypeptide
        
        important for production of proteoglycans
- - - - enzyme flippase uses ATP to carry this movement out since the polar head group will have to pass through the hydrophobic part of the bilayer
  - - - longer tails = less fluidity due to stronger van der Waal bonds
      - shorter tails = less likely to interact with each other, membrane more fluid
    - - double bond present = lipid tail is unsaturated and has a kink, more difficult for neighboring tails to interact, bilayer becomes more fluid
    - - high temperature = cholesterol makes the membrane less fluid
      - low temperature = cholesterol makes the membrane more fluid
    - - if a membrane is too fluid (can occur at high temp.) it can become leaky
      - if a membrane is too solid (at low temp.) membrane protein function gets inhibited
      - changes in temperatures are dealt with by the cell changing the composition of lipids in its cytoplasmic membrane
- - - - includes simple diffusion and facilitated diffusion
        
        simple diffusion = movement of substance across a membrane from a region of high to low concentration by passing directly through the phospholipid bilayer
        
        facilitated diffusion = transport protein provides a passageway for a substance to cross a membrane from an area of higher concentration to lower concentration
    - - transport of a substance across a membrane from an area of low concentration to one of higher concentration with the aid of a transport protein
      - requires energy
      - primary active transport = type of transport that involves pumps that directly use energy to transport a solute against a gradient
      - secondary active transport = type of membrane transport that involves the utilization of a pre-existing gradient to drive the active transport of another solute (established by a pump)
  - - - small solutes can cross faster than larger ones
    - - nonpolar solutes cross faster than polar ones
    - - non-charged solutes cross faster
    - - higher conc. = higher rate of movement across the membrane
  - - - extreme cases in animal cells lead to crenation, in plant cells cause plasmolysis
    - - cell wall in plant cell prevents it from bursting, in animal cells, extreme cases lead to osmotic lysis
- - - - receptor mediated
        
        a receptor in the membrane is specific for a given cargo
      - pinocytosis
        
        involves the formation of membrane vehicles from the plasma membrane as a way for cells to internalize extracellular fluid
      - phagocytosis
        
        type of endocytosis that involves the formation of a phagosome or phagocytic vesicle which engulfs particles such as bacteria