Question

How is a given protein, like P53, characterized as a tumor suppressor gene vs a proto-oncogene? Explain the difference between the two gene categories.

With a protein in the ER, how does a secreted protein get to the plasma membrane via the golgi apparatus? Be sure to note the secretory pathway

please help me on these two questions

Answer 1

Ans 1- Proto oncogenes normally remain inactive in the genome, they constitute that part of genome which is known as junk DNA. But when these genes are mutated they enhance cell division and inhibits apoptosis.

In contrast Tumour suppressor genes are normally functional in cells. For example P53 performs function of activating DNA repair pathways on DNA damage, arrests the cell at G1/S phase and acts as cell cycle check points, induces senescence in cells with short telomeres and activates apoptotic pathways. But when they get mutated all these functions are altered and cells divide uncontrollably as well as apoptosis is prevented, hence cancerous growth results.

The major difference between these two genes is that proto oncogenes gets switched on upon mutation and Tumour suppressor genes gets switched off upon mutation.

Ans 2- after the synthesis of proteins in ER they get transported to Golgi by COPII vesicles and after getting processed in Golgi the proteins destined for ER are returned back by COPI vesicles. This pathway is known as secretory pathway.

Golgi apparatus adds oligosaccharides to the nascent polypeptides and then properly fold them with the help of Bip and calnexin proteins. This process is known as protein processing.

After this the processed proteins are packaged inside vesicles and the process are known as membrane protein targeting. These proteins contain signal peptides through which they are targeted to plasma membrane. After reaching plasma membrane these signal peptides binds to specific receptors and then get internalised by membrane fusion.