How are proteins renewed?

Answer 1

Every protein molecule sooner or later reaches the end of its lifetime. This might be for example when oxidative damage has degraded it to the point where it cannot fulfill its function.

The only option left to the cell in this case is to somehow get rid of the damaged protein. A typical mechanism for this is called ubiquitinylation. This means that several ubiquitin residues are attached to the damaged protein. These residues will result in the protein being transported to the proteasome, where it is broken down into amino acids.

To maintain the function that the protein was performing, the cell has to create new protein molecules of the same type. This happens through the common pathway of gene expression:

1. The gene which encodes the protein is transcribed from the genomic DNA in the nucleus. This produces mRNA encoding the protein, which is shuttled to the cytoplasm.
2. Ribosomes in the cytoplasm attach to the mRNA and start translating the protein, coupling amino acids to each other in the sequence defined by the mRNA.
3. The resulting amino acid chain will then fold into the finished protein (either on its own, or with some help from chaperones).

Answer 2

I hope your question is all about how proteins are replenished? THere are Proteins synthesis machinery in cells that will produce them from the amino acids. The synthesis of a particular protein is directed by the gene which is in the DNA or genome.

Answer 3

Regulatory mechanisms in the cell trigger the transcription of DNA encoding a gene for a given protein or enzyme. That mRNA is translated at ribosomes outside the nucleus to polymerize amino acids in that sequence, encoded by codons, to form proteins.