1
Q
How do molecules enter the nucleus
A
- movement of proteins and other large molecules into and out of the nucleus is an energy-demanding process
- transport involves transport proteins called importins and exportins
- proteins transported into nucleus remain folded
- need the right tag: nuclear proteins contain a 17-aa long NLS
- NLS are sequences required for nuclear entry
- NES are sequences required for nuclear export
2
Q
What is the function of NLS
A
nuclear entry of proteins
3
Q
What is the function of NES
A
Nuclear export of proteins
4
Q
What is the function of signal peptide
A
- entry of proteins into secretory pathway
- insertion of proteins into membranes
5
Q
What is the function of endomembrane systems?
A
- Synthesis, modification, transport and secretion of proteins
- Synthesis of lipids and detoxification of toxins
- Transportation and breakdown (digesting) of large biomolecule-containing particles.
Summary: The Endomembrane System Manufactures, Ships, and Recycles Cargo
6
Q
What is the signal hypothesis?
A
– All proteins start to be synthesized on free ribosomes
– Proteins bound for the endomembrane system have a ‘postal code’ – It directs the growing polypeptide to the RER
▪ 20-amino-acid-long ER signal sequence
7
Q
What is the process of exocytosis?
A
- Proteins to be secreted from the cell are transported to the membrane in secretory vesicles which release their contents to the exterior by exocytosis.
8
Q
What is the process of endocytosis?
A
-Vesicles also form by the reverse process, endocytosis, which brings molecules into the cell from the exterior.
9
Q
How Do Proteins Reach Their Destinations?
A
- Each protein that comes out of the Golgi apparatus has a molecular tag – Places it in a particular type of transport vesicle
- Each type of transport vesicle also has a tag
– Allows it to be transported to the correct destination - For e.g., proteins are secreted out of a cell by exocytosis
