In Run-on transcription- the RNA polymerase that has already initiated transcription in vivo simply “runs on” or continues to elongate the same RNA chains. 

TLS Online TPP Program

#Id: 3649

#Unit 3. Fundamental Processes

Valine cannot coordinate the Zn2+ in this way and hence does not undergo adenylation by ThrRS. A separate editing site deal with misacylated Ser–tRNAThr.

TLS Online TPP Program

#Id: 3650

#Unit 3. Fundamental Processes

TyrRS distinguishes between tyrosine and phenylalanine through hydrogen bonding with tyrosine’s OH group. Since no other amino acid resembles tyrosine, the enzyme can do without an editing function.

TLS Online TPP Program

#Id: 3651

#Unit 3. Fundamental Processes

GlnRS is absent in gram-positive bacteria, archaebacteria, cyanobacteria, mitochondria, and chloroplasts.

TLS Online TPP Program

#Id: 3652

#Unit 3. Fundamental Processes

In many bacteria glutamate is linked to tRNAGln by the same GluRS that synthesizes Glu–tRNAGlu. The resulting Glu–tRNAGln is then converted to Gln–tRNAGln by Glu–tRNAGln amidotransferase in an ATP-requiring reaction in which glutamine is the amide donor.

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#Id: 3653

#Unit 3. Fundamental Processes

Some microorganisms that lack AsnRS use a similar transamidation pathway for the synthesis of Asn–tRNAAsn from Asp–tRNAAsn.

TLS Online TPP Program

#Id: 3654

#Unit 3. Fundamental Processes

The translation machinery relies on the high fidelity of the aminoacyl-tRNA synthetases to ensure the accurate decoding of each mRNA.