The endomembrane system and bulk transport processes Flashcards
What does the endomembrane system include?
- Nuclear envelope
- Endoplasmic reticulum (smooth and rough
- Golgi apparatus
- Vesicles
- Lysosomes
- Vacuoles
- Plasma membrane
What is the endomembrane system?
A membrane system interconnected by direct physical contract or transfer by vesicles.
What are the functions of the SMOOTH endoplasmic reticulum?
- Metabolism of Carbs
- Lipid syntesis for membranes
- Detoxification of drugs and posions
- Storage of calcium ions (used as a signal in the cell)
What can the amount of sER in a cell be determined by?
Depends on how active the cell is in sER processes. The amount can be increased of decreased to meet demand.
What are the functions of the rER?
Involved in protein synthesis of secreted and membrane bound proteins that will enter the lumen of the rER. These proteins are processes by the rER and the rest of the endomembrane system for release from the cell or retention on the cell membrane.
Why is the rER rough?
Due to the ribosomes bound on it.
Where does synthesis of cytoplasmic proteins occur?
On free ribosomes.
What are the functions of the golgi complex?
Receives, modifies, sorts and ships proteins arriving from the rER.
What is the golgi complex?
A series of membrane sacs and associated vesicles
The golgi complex has polarity. What does this mean?
Means it has a cis and trans face. Vesicles arrive at the cis face and processed vesicles leave at the trans face.
What is glycosylation?
Addition or modification of carbs to proteins
- Important for secreted or cell surface proteins
- Golgi also produces many polysaccharides which may also be secreted from the cell
How does the golgi sort proteins?
Adds molecular markers to direct proteins to the correct vesicles before ‘budding’ from the trans face.
How does the golgi direct vesicle trafficking?
Adds molecular “tags” to vesicles leaving the trans face to direct them to the correct targets
- Such tags are often short proteins exposed on the vesicle surface
- Act as docking sites when the reach their target.
Where do vesicles go when they leave the trans face?
- Some tages direct vesicles to the lysosome
- Others direct to secretory pathways
- Important for release and surface expression
What is exocytosis?
Transports material (glycoproteins) out of the cell or delivers it to the cell surface
What is constitutive exocytosis?
Releases extracellular matrix proteins. Un-regulated.
What is regulated exocytosis?
Releases hormones and neurotransmitters. Highly regulated.
What is endocytosis?
The cell takes in molecules and particulate matter at the plasma membrane.
What is phagocytosis?
Cell “eating”
- Uptake of “food” particles
- Forms a phagocytic vacuole which is “digested” by the lysosomes
- In humans this occurs in marcophages
What is pinocytosis?
Cell “drinking”
- up-take of extracellular fluid containing various solutes such as protein and sugars
- up-take vesicle is formed with the aid of a coat protein
- up-take is non-selective.
What is receptor-mediated endocytosis?
Specialised form of pinocytosis
- Allows the cell to take up bulk quantities of specific substances which may be present at only low concentrations in the extracellular fluid.
- Receptor proteins are used to selectively capture the required solute.
What are lysosomes?
Membrane bound organelles made by the rER and golgi body containing hydrolytic enzymes.
What do lysosomes do?
Phagocytic vacuoles fuse with lysosomes.
- They degrade proteins, lipids, carbs, and nucleic acids and release breakdown products into the cell.
- They digest and recycle unwanted cellular material, process is called “autophagy” and is important for cell health.
Why is lysosomal digestion important in cell health?
Important in programmed cell death in which whole cells “intentionally” die. Defects lysosomal enzymes can result in lysosomal storage diseases.
