Endomembrane Flashcards
What is the function of the endomembranes?
to compartmentalize eukaryotic cells by dividing the cytoplasm
T or F: the endomembrane system is composed of multiple organelles that function as a coordinated unit
True
What are the 6 organelles that make up the endomembrane system?
endoplasmic reticulum Golgi complex endosomes lysosomes vacuoles secretory vesicles
Which 2 organelles are not included in the endomembrane system?
mitochondria
chloroplasts
T or F: the combined surface of endomembranes is always less than the surface area of the surrounding plasma membrane
False
the combined surface of endomembranes can be MUCH larger than the surface of the plasma membrane
T or F: cells with different functions can have vastly different proportions of each endomembrane
true
Approximately how much of an animal cell’s total membrane does the ER constitute? How much of its volume?
~half of its membrane
~10% of its volume
How is the ER divided?
into ‘smooth’ and ‘rough’ ER
T or F: the smooth and rough ER are discrete and enclose two luminal spaces
FALSe FALSE FALSE
They are continuous and enclose a single luminal space
What is the structure of the rough ER referred as?
flattened sheets
What is the structure of the smooth ER referred as?
tubules
Where do the rough and smooth ER extend?
throughout the cytoplasm
Give some examples of the functions of the smooth ER
calcium sequestration
membrane lipid synthesis
detoxification of the cell
steroid hormone synthesis
glycogen storage in liver
Which half of the smooth ER bilayer are newly synthesized phospholipids inserted?
into the half bilayer facing the cytosol
How does the insertion of the phospholipids into the smooth ER bilayer facing the cytosol affect the orientation of the enzyme that synthesizes these lipids?
they are bound to the smooth ER membrane with their active sites facing the cytosol
How are the phospholipids flipped into the opposite leaflet?
by flippases
What are functions of the rough ER?
biosynthesis and processing of proteins
What types of proteins are included in the rough ER?
secretory proteins
membrane-bound proteins
proteins for internal use that require modification (ex. glycosylation, disulfide bridges, etc.)
What is another word for the structure of Rough ER (Sheets)?
cisternae
T or F: almost all proteins are initially synthesized on ribosomes within the cytosol
true
Where are polypeptides that are fully synthesized on ‘free’ ribosomes located?
in the cytosol and they remain in the cytosol
What are 4 proteins that fully synthesize on ‘free’ ribosomes?
cytosolic proteins
peripheral membrane proteins
nuclear proteins
proteins incorporated into chloroplasts, mitochondria, and peroxisomes
Where does a polypeptide with an ER signal sequence move to? How does this movement usually occur?
into the ER cisternal space through a protein-lined pore
this usually occurs co-translationally
Describe post-translational translocation
proteins that are synthesized completely on cytosolic ribosomes and are THEN moved to an organelle (ex. nucleus or peroxisome) AFTER translation