In the absence of ATP, the myosin head is firmly attached to the actin filament. 

TLS Online TPP Program

#Id: 7069

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 7070

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 7071

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 7072

#Unit 3. Fundamental Processes

The charging of a tRNA with its cognate amino acid is a remarkably accurate process.

Experimental measurements indicate, for example, that at equal concentrations of isoleucine and valine, IleRS transfers ∼40,000 isoleucines to tRNAIle for every valine it so transfers.

TLS Online TPP Program

#Id: 7073

#Unit 3. Fundamental Processes

This rejection of noncognate tRNAs at a stage of the reaction that precedes the synthesis of misacylated tRNA is sometimes referred to as kinetic proofreading.

TLS Online TPP Program

#Id: 7074

#Unit 3. Fundamental Processes

 Valyl-tRNA synthetase can sterically exclude isoleucine from its catalytic pocket because isoleucine is larger than valine. In contrast, valine should slip easily into the catalytic pocket of the isoleucyl-tRNA synthetase. Although both amino acids will fit into the isoleucyl-tRNA synthetase amino acid–binding site, interactions with the extra bonding with tyrosine’s OH group. Since no other amino acid resembles tyrosine, the enzyme can do without an editing function