Polvi lec #9

Question 1

What are the two basic steps of transport of materials from rough ER to golgi?

Answer 1

Vesicle budding and then vesicle targeting and fusion

Question 2

If something is wrong with the protein that plays a role in the formation of vesicles at the ER what happens?

Answer 2

The ER just grows bigger and bigger and we don’t have a golgi

Question 3

If something is wrong in the ability of vesicles to fuse to golgi what happens?

Answer 3

we have no golgi and over abundance of vesicles

Question 4

What is the definition of the endoplasmic reticulum?

Answer 4

is a system of membranes and vesicles that encloses the ER lumen (inside of the ER)

Question 5

What are the two types of ER?

Answer 5

rough ER
smooth ER

Question 6

What is the structure of the rough ER?

Answer 6

Has ribosomes bound to the cytosolic side of the membrane, is composed of a network of cisternae, and is attached to the outer membrane of the nucelus

Question 7

What is the structure of the smooth ER?

Answer 7

lacks ribosomes, is composed of interconnected curvy tubular membranes and is connected to the RER

Question 8

What is the function of the smooth ER? Where do we find it?

Answer 8

The smooth ER is found in cell types such as skeletal muscles, kidney tubules, and steroid producing endocrine glands
It’s functions are: synthesizing steroid hormones, synthesizing membrane lipids, detoxifying organic compounds in the liver, and sequestering calcium ions in skeletal and cardiac muscle

Question 9

What is the function of rough ER? Where do we find it?

Answer 9

Is extensive in cells with roles in protein secretion (pancreatic acinar cells, intestinal cells, and endocrine cells)

Functions include protein synthesis and initiation of the addition of sugars

Question 10

What portion of all proteins are synthesize din the RER ribosomes? In the free ribosomes?

Answer 10

1/3 in RER ribosomes
2/3 in free ribosomes

Question 11

What is co-translational translocation?

Answer 11

is peptides (proteins) that move into the lumen of the ER as they are being synthesized by the ribosome

Question 12

What proteins undergo co-translational translocation?

Answer 12

secreted proteins
integral membrane proteins and soluble proteins (that reside in compartments of the endomembrane system)

Question 13

Where are proteins made by free ribosomes released?

Answer 13

into the cytosol

Question 14

What kinds of proteins are being translated by free ribosomes?

Answer 14

proteins that remain in the cytosol such as peripheral proteins on the cytosolic surfaces of a membrane
Proteins transported to the nucleus, mitochondria, and chloroplast

Question 15

Are free ribosomes and rough ER ribosomes structurally and functionally different?

Answer 15

No! the only thing that differs is where the synthesized protein is going

Question 16

How are secreted and soluble proteins synthesized by the RER ribosomes?

Answer 16

1. Protein synthesis begins on a free ribosome forming a peptide as translation happens
2. A signal sequence (a sequence at the peptide N end which is 6-15 hydrophobic amino acids) gets recognized by the signal recognition particle and the SRP binds to both the signal sequence and ribosome
3. After binding of SRP to signal sequence and ribosome, polypeptide synthesis is halted temporarliy
4. The complex of SRP, signal sequence, and ribosome is directed to the ER membrane by interacting with the SRP receptor
5. The ribosome and polypeptide get transferred from the SRP receptor to the translocon (a protein pore in the ER membrane) , the signal sequences removes the plug and opens up the protein pore), and the SRP leaves the SRP receptor
6. Polypeptide continue to grow through pore and into RER lumen, when the peptide grows into the lumen the signal sequence is cut off by singal peptidase
7. The ribosome is released, and protein chaperones fold the peptide into a proper protein

Question 17

How are integral membrane proteins synthesized by co-translation translocation?

Answer 17

the SRP recognizes the hydrophobic transmembrane domain of the integral protein as the signal sequence and brings it to the ER
The peptide passes through the translocon and gates on either side of the translocon open and allows the protein to enter the lipid bilayer directly based on their solubility properties

Question 18

What determines the direction of the transmembrane protein insertion?

Answer 18

It’s charge, the cytosol side of the lipid bilayer is negative, so the more postively charged side of the protein should be facing that end (can be C end or N end, whatever is more + will be oriented that way