Endomembrane System & Bulk Transport Processes Flashcards
what is the endomembrane system?
a membrane system interconnected by direct physical contact or transfer by vesicles.
what does the endomembrane system include?
- nuclear envelope
- endoplasmic reticulum (smooth & rough)
- Golgi apparatus
- vesicles
- lysosomes
- vacuoles
- plasma membrane (made up of phospholipid bilayer)
How to move proteins out of the cell?
- synthesize
- tag and package
- deliver
How to move proteins out of the cell through synthesise?
- endoplasmic reticulum (ER)
How to move proteins out of the cell through tag and package?
- Golgi apparatus
How to move proteins out of the cell through deliver?
- vesicles transport protein
- vesicles can fuse with membranes of organelles/the cell
what are the two types of ER?
- smooth ER
- rough ER
what are the functions of the smooth endoplasmic reticulum (sER)?
- Metabolism of carbohydrates
- Lipid synthesis for membranes
- Detoxification of drugs and poisons
- Storage of calcium ions (used as a signal in the cell)
- Extensive sER in cells active in these processes
- The amount of sER can be increased or decreased to meet the demand
why does rough endoplasmic reticulum appear rough?
because of ribosomes that sit on the surface
what are the functions of the Rough Endoplasmic Reticulum (rER)?
- Rough appearance due to ribosomes
- Involved in protein synthesis
- Secreted and membrane-bound proteins enter the lumen (interior) of the rER
- and are processed by the rER and the rest of the endomembrane system for release from the cell or retention on the cell membrane
where does the synthesis of cytoplasmic proteins occur?
Synthesis of cytoplasmic proteins occurs on free ribosomes
what are the functions of Golgi apparatus?
- Series of membrane sacs and associated vesicles
- Receives, modifies, sorts and ships proteins arriving from the rER
how does Golgi apparatus have polarity?
- Vesicles from the endoplasmic reticulum arrive at the cis face
- Processed vesicles leave at the trans face (away from the ER towards the plasma membrane)
what happens in the cis face of the Golgi apparatus?
- Vesicles from the endoplasmic reticulum arrive at the cis face
- faces towards the ER - receive vesicles from the endoplasmic reticulum
- modification and sorting happen throughout the Golgi
what are the functions of the Golgi apparatus?
- Series of membrane sacs and associated vesicles
- Receives, modifies, sorts, and ships proteins arriving from the rER
what functions happen in between the golgi complex?
- glucosylation
- sorting proteins
- directing vesicle trafficking
what happens during glucosylation in the Golgi?
- Addition (or modification) of carbohydrates to proteins
- Important for secreted or cell surface proteins
- Golgi also produces many polysaccharides which may
also, be secreted from the cell e.g. pectin & hemicellulose
what happens during sorting protein function in the Golgi?
- Adds molecular markers to direct proteins to the correct vesicles before ”budding” from the trans face
what happens during directing vesicle trafficking function in the Golgi?
- 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
- Tags direct vesicles to lysosomes, or secretory pathways, or to the plasma membrane to add membrane proteins
- Act as docking sites when they reach their target
what are the different types of vesicles?
Names reflect the function:
- Transport vesicles
- Secretory vesicles
- Vacuoles
what is a vesicle?
Membrane-bound (phospholipid bilayer), cytoplasm/fluid-filled organelles
what is exocytosis?
- out of the cell - releases stuff we just made and tagged
- Transports material (glycoproteins) out of the cell or delivers it to the cell surface
what is exocytosis?
- out of the cell - releases stuff we just made and tagged
- Transports material (glycoproteins) out of the cell or delivers it to the cell surface
what are the two different types of exocytosis?
- constitutive exocytosis
- regulated exocytosis
what is constitutive exocytosis?
releases extracellular matrix proteins
what is regulated exocytosis?
releases hormones and neurotransmitters
- signal saying what to do (will make it a short period of time then it’ll stop)
what is endocytosis?
- The cell takes in molecules and the particulate matter in 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 macrophages
- opens and closes to bring food inside the cell in a vacuole
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 the aid of a coat protein
- up-take is non-selective
what is receptor-mediated endocytosis?
- a specialized form of pinocytosis
- allows the cell to take up the 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?
- lysosomes are membrane-bound organelles made by the rER and Golgi body containing hydrolytic enzymes
- The interior of a lysosome is acidic which is required for the enzymes to be active
- They degrade proteins, lipids, carbohydrates, and nucleic acids and release breakdown products into the cell
how do we use lysosomes to break down products inside the cell?
- Lysosomes digest and recycle unwanted cellular materials this process is called autophagy and is important for cell health
- Lysosomal digestion is also important in programmed cell
death in which whole cells “intentionally” die.
what happens when there is defects in lysosomal enzymes?
- Defects in lysosomal enzymes can result in lysosomal
storage diseases
why are vacuoles important in plants?
- can perform lysosome-like functions
- large central vacuole absorbs water allowing plant cells to grow without a large increase in cytoplasm
- Usually largest compartment in a plant cell
food vacuoles are involved in…
phagocytosis
what are the different types of endocytosis?
- phagocytosis
- pinocytosis
- receptor-mediated endocytosis
for vesicles to form in pinocytosis what do we need?
coated protein pit
what is pinocytosis?
- Cell “drinking”
- uptake 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 are receptors in terms of proteins?
Receptors are proteins that will detect and bind to molecule/solute of interest
what fuses with lysosomes?
Phagocytic vacuoles fuse with lysosomes
what is autophagy?
Lysosomes digest and recycle unwanted cellular materials this process is called autophagy and is important for cell health
what are vacuoles?
large vesicles derived from the rER and the golgi
