Section 5 - Intracellular Traffic and Energy Conversion Flashcards
How much total membrane does the ER take up?
50%
True or false: the ER is connected to the nuclear membrane
True: it extends from the nucleus into the cytosol
What are the functions of the ER?
Production of transmembrane proteins, secreted proteins, lipids, and calcium storage
What is the ER composed of?
Tubules and membranous sacs
Where is the ER the densest?
Near the nucleus
Where is the ER the least dense?
In the cytosol (away from the nucleus)
True or false: the ER in mammalian cells is the same as the ER in plant cells
False: they have very different structures
True or false: the entirety of the ER has the same function
False: different regions of the ER can be specialized for different functions
What is an example of a specific region of ER having a specialized function?
Rough ER
What is rough ER?
ER with attached ribosomes
What is smooth ER?
ER without ribosomes
What is co-translation?
When proteins are transported to the ER during translation
Is the rough ER constantly rough?
No. The ribosomes associate and dissociate from the ER, thus changing it to rough or smooth
True or false: ribosomes sit on the ER, waiting for mRNA to come
False: they are assembled in the cytosol and translocated to the ER
How does the rough ER become rough?
By the ribosome assembling in the cytosol, and then moving towards the ER
What is the function of smooth ER?
Transporting synthesized proteins / lipids to other regions of the cell (golgi)
Where is rough ER most likely to be found?
Closer to the nucleus
Why is rough ER found more commonly closer to the nucleus?
That is where mRNA is most likely to be found
What is the function of calcium in the cell?
Act as initiators for many biological functions
Why is calcium kept in the ER?
Keep cytosolic concentration low for proper function (proper cell signaling)
What is the specialized ER in muscle cells important for?
Contraction
How does the ER sequester calcium?
Through calcium binding proteins and calcium channels
What is needed on a polypeptide to direct it to the ER?
A signal sequence
Where are transmembrane proteins made?
Embedded in the ER