What is the targeting pathway from translation until the protein reaches it's final functional destination for PFK and insulin?
Choose from the following choices for each:
a) golgi -> ER -> outside of cell
b) ER -> golgi -> cytoplasm
c) cytoplasm only
d) nucleus -> cytoplasm
e) cytoplasm -> ER -> outside of cell
f) cytoplasm -> golgi -> outside of cell
g) ER -> cytoplasm
h) ER -> golgi -> outside of cell
h) ER -> golgi -> outside of cell
Proteins that are destined for the membranes or compartments of the endomembrane system, as well as proteins that will be secreted from the cell (insulin, for example), are translated on ribosomes that are bound to the rough ER.
For proteins translated on rough ER, the proteins are found in one of two places at the end of translation. If a protein is targeted to a membrane of the endomembrane system, it will be in the ER membrane. If a protein is targeted to the interior of an organelle in the endomembrane system or to the exterior of the cell, it will be in the lumen of the rough ER. From the rough ER (membrane or lumen), these non-cytoplasmic proteins move to the Golgi apparatus for processing and sorting before being sent to their final destinations.
To determine the targeting pathway from translation until the protein reaches its final functional destination for PFK (phosphofructokinase) and insulin, we first need to understand the general process of protein targeting.
1. Translation: The process begins with translation, where the protein is synthesized by ribosomes in the cytoplasm. Ribosomes read the mRNA sequence to create a linear chain of amino acids, forming a polypeptide chain.
Now, let's look at the targeting pathway for each protein:
1. PFK (Phosphofructokinase):
- PFK is an enzyme involved in glycolysis, the metabolic pathway that breaks down glucose to produce energy.
- The correct targeting pathway for PFK is the "cytoplasm only" (c). Once synthesized in the cytoplasm, PFK remains in the cytoplasm to carry out its function in glycolysis.
2. Insulin:
- Insulin is a hormone produced by the pancreas and is involved in regulating blood sugar levels.
- The correct targeting pathway for insulin is "ER to golgi to outside of cell" (h). Here's how it happens:
- After translation, the newly synthesized insulin polypeptide enters the endoplasmic reticulum (ER).
- In the ER, post-translational modifications such as signal peptide cleavage and folding occur.
- The modified insulin protein then leaves the ER in transport vesicles and travels to the Golgi apparatus.
- Within the Golgi apparatus, further processing takes place, including additional modifications and packaging into secretory vesicles.
- The mature insulin vesicles are then transported to the plasma membrane for secretion outside of the cell.
In summary, PFK remains in the cytoplasm (c) after translation, while insulin follows the ER to golgi to outside of cell pathway (h).