Answer:
(C) Aminoacyl-tRNA synthetases have an additional active site that binds to non-cognate tRNAs. The tRNAs that bind to this second active are hydrolyzed and released from the enzyme.
Explanation:
In case of translation, proof reading is done by aminoacyl-tRNA synthetases only. Aminoacyl-tRNA synthetases have two mechanisms to avoid error during translation which are mentioned as under:
<u>(1) Chemical proof reading:</u> Incorrect amino acids rather than being hydrolyzed in catalytic pocket get hydrolyzed in editing pocket and thus they hardly get attached to tRNA.
For example: For distinguishing similar amino acids like isoleucine and valine, isoleucyl-tRNA synthetase uses a second active site which is meant for only valine not for isoleucine. In this particular site, valine which had entered the enzyme is cleaved away with the help of editing reaction after which the enzyme is well prepared to process isoleucine which is the correct amino acid for this enzyme.
<u>(2) Kinetic proof reading: </u>Even if an incorrect amino acid has entered a particular aminoacyl-tRNA synthetase, it does not cause appropriate conformational change in the enzyme because of which the incorrect amino acid loosens from the enzyme and does not get incorporated.
Note: In this example, only chemical proof reading is mentioned not kinetic proof reading.
Answer:
1. P120 is degraded in the 26S proteasome
2. The 26S proteasome has a major role in protein degradation and is critical for protein homeostasis
3. Cell cycle and DNA replication are cellular processes regulated by the Ras and NFkB pathways
Explanation:
The proliferation-associated nucleolar protein (p120) is a protein known to be expressed during the interphase of the cell cycle, specifically in G1 and early S phase, where any problem with DNA replication trigger a checkpoint, i.e., a molecular cascade of signaling events that suspend DNA replication until the problem is resolved. In mammalian cells, the 26S proteasome is responsible for catalyzing protein degradation of about 80% (or even more) of their proteins. The 26S proteasome acts to degrade rapidly misfolded and regulatory proteins involved in the cell cycle, thereby having a major role in protein homeostasis and in the control of cellular processes. It is for that reason that inhibitors that block 26S proteasome function have shown to be useful as therapeutic agents in diseases associated with the failure of protein degradation mechanisms (e.g., multiple myeloma). The NF-κB are highly conserved transcription factors capable of regulating different cellular processes including, among others, cellular growth, inflammatory responses and apoptosis. Moreover, the MAPK/ERK pathway is able to transduce different signals received on the cell surface to the nucleus. The MAPK/ERK pathway is activated when a singling molecule binds to a cell receptor which triggers a signaling cascade that ends when a transcription factor induces the expression of target genes, ultimately producing a response in the cell (for example, the progression through the cell cycle).
When charged particles from the sun strike atoms in earth's atmosphere, it causes electrons to move to a higher energy state. When the electrons drop back to a low energy state they release light photons. This is what causes the Aurora lights
