membrane transport of large molecules

what are the 2 main types of vesicular transport of large molecules

endocytosis and exocytosis

describe what endocytosis is and name three types

• Moves large molecules into the cell (ingestion / uptake)

• Three types: phagocytosis, pinocytosis and receptor-mediated

describe exocytosis and 3 uses of it

• Moves large molecules out of the cell (excretion / secretion)

• Used for:
  • Hormone secretion
  • Neurotransmitter release
  • Mucous secretion

define (transport) vesicles (4)

• Bubble-like, membranous sacs

• Made of a phospholipid bilayer containing fluid

• Transport bubble - move substances (like proteins or lipids) within a cell or to the cell membrane.

• Protects substances being transported

explain phagocytosis as a process of endocytosis (5)

• ‘cell eating’

• Ingestion of large particles by specialised cells (phagocytes; in the immune system) : macrophages and certain white blood cells

• used for removing bacteria and debris

• When a particle (e.g. bacteria) binds to a phagocyte, the cell membrane wraps itself around the particle

• Resulting in a phagosome containing the particle

explain pinocytosis as a process of endocytosis (4)

• ‘cell-drinking’

• Occurs in most cells

• Process used to take in extracellular fluid with dissolved
  substances

• Droplet enters the cell and fuses with an endosome (sorting vesicle)

explain receptor mediated endocytosis (5)

• Main mechanism for specific uptake of macromolecules

• Very selective method

• Uptakes substances (hormones, cholesterol) found in small amounts

• Receptors for this are specific membrane proteins

• Some viruses can hijack this route and enter our cells

list 3 substances that are moved out of the cell during exocytosis

hormones, waste products and neurotransmitters

explain the full process of exocytosis (5)

• process is stimulated by a cell-surface signal that results in a cascade of events:
  • Substance is enclosed in a vesicle
  • Transported to plasma membrane
  • Vesicle attaches to ‘docking’ sites on the
  membrane
  • Fuses with membrane and ejects
  substance

how do endocytosis and exocytosis contribute to the dynamic nature of the cell membrane

• a balance in cell membrane content

• While exocytosis adds membrane material to the cell membrane, endocytosis removes it from the cell membrane

• These processes help the membrane stay flexible, adaptive, and balanced — allowing the cell to respond to its environment, grow, repair, and communicate.