1.2.2 the synthesis and transport of proteins Flashcards
what sort of system do eukaryotic cells have
a system of internal membranes, which increases the total area of the membrane
why do eukaryotes have a relatively small surface area to volume ratio
because of their size
how does the small surface area to volume ratio of eukaryotic cells create problems for them?
the plasma membrane is too small an area to carry out all the vital functions carried out by membranes
what does the endoplasmic reticulum do
it forms a network of membrane tubules continuous with the nuclear membrane
what is the golgi apparatus
a series of flattened membrane discs
what are lyosomes
membrane bound organelles containing a variety of hydrolases that digest proteins, lipids, nucleic acids and carbohydrates
what does a vesicle do
transport materials between membrane compartments
what is the difference between rough endoplasmic reticulum and smooth
RER has ribsomes on its cytosolic face, while SER lacks ribosomes
where are lipids synthesised
in the SER, and inserted into its membrane
where does the synthesis of all proteins begin
in cytosolic ribosomes
where is the synthesis of cytosolic proteins completed, and where do they go upon completion
cytosolic ribosomes, and they just remain there once they have been synthesised
what do transmembrane proteins do
they carry a signal sequence, which halts translation and directs the ribosome synthesizing the protein to dock with the ER, forming the RER.
what is a signal sequence
a short stretch of amino acids at one end of the polypeptide that determines the eventual location of a protein in a cell
does translation continue after docking
yes
what happens after docking
translation continues, and the protein is inserted into the membrane of the ER
what happens once the proteins are in the ER
they are transported by vesicles that bud off from the ER and fuse with the golgi apparatus
what happens while the proteins move through the golgi apparatus
the proteins undergo post translational modification
how do molecules move through the golgi discs
in vesicles that bud off from one disc and fuse to the next one in the stack
what role do enzymes play in post translational modification
they catalyse the addition of various sugars in multiple steps to form the carbohydrates
what is the major modification in the post translational modificiation
the addition of carbohydrates
what happens to the vesicles that leave the golgi apparatus
they take the proteins to the plasma membrane and lyosomes
what is the relationship between vesicles and microtubules
the vesicles move along the microtubules to other membranes and fuse with them within the cell
where are secreted proteins translated
in ribosomes on the RER
where do the secreted proteins that are translated in ribosomes enter following their translation
the lumen of the RER
what are examples of secreted proteins
- peptide hormones
- digestive enzymes
what happens to the secreted proteins once they have entered the lumen of the RER
they move through the golgi apparatus and are then packaged into secretory vesicles
how are the secreted proteins released from the cell
the secretory vesicles move to and fuse with the plasma membrane
what are many secreted proteins released as
inactive precursors
what do the inactive precursor secreted proteins require
proteolytic cleavage
why do inactive precursors require proteolytic cleavage
to produce active proteins
what is proteolytic cleavage
another type of post translational modification
what is an example of a secreted protein that requires proteolytic cleavage to become active
digestive enzymes
