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Bulk/Active Transport

endocytosis - envelops food particles 

  • substances required for growth are sometimes too large to cross the bilayer
  • 3 main types
  • phagocytosis - enveloping particulate, organic matter
  • pinocytosis - enveloping liquid
  • receptor-mediated endocytosis - transfer of specific molecules
    • only food particles that fit attach to the receptor
    • clathrin - protein that coats the inner pit
    • each pit folds inward to form a vesicle
  • low-density lipoprotein - brings cholestrol into the cell to be used in the membranes

exocytosis - reverse of endocytosis 

  • discharges material from vesicles
  • used by plants to send material for cell wall construction through the membrane
  • used by animals to secrete hormones, neurotransmitters, enzymes, etc
  • protists use contractile vacuoles for exocytosis

active transport - moves substance against the concentration gradient 

  • powered by ATP
  • uses selective protein channels like facilitated diffusion
  • makes cells independent from environmental conditions

sodium-potassium pump - moves sodium and potassium ions across the membrane 

  1. 3 sodium ions bind to protein on the cytoplasm side, causing the protein to change shape
  2. protein turns ATP into ADP (adenine diphosphate) and a phosphate
  3. protein changes shape again, moves the 3 sodium to the exterior
  4. 2 potassium ions bond to protein once 3 sodium ions leave
  5. protein changes shape again, releasing phosphate group
  6. protein goes back to original shape, release potassium into the cell, attract new sodium
  • process found in all animal cells

coupled transport - uses energy from 1 molecule's gradient to move another molecule 

  • energy released from a molecule moving w/ its gradient is used to help move another molecule against its gradient
  • sodium moves back into the cell along its gradient to move glucose into the cell against its gradient
  • symport - both molecules moving the same direction through a membrane
  • countertransport - molecules move in opposite directions through a membrane; molecules attach to the protein known as an antiport in these situations
Subject: 
Biology
Subject X2: 
Biology

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