There are 4 genes (I, Z, Y, A), 2 Promoters and 3 lac operators in Lac operon

The major O1 lac operator lies adjacent to promoter

Two auxiliary O2 and O3 lac operators 

All three operators are required for optimum repression 

TLS Online TPP Program

#Id: 3665

#Unit 3. Fundamental Processes

Size comparisons show that the ribosome is large enough to bind tRNAs and mRNA.

TLS Online TPP Program

#Id: 3666

#Unit 3. Fundamental Processes

Aminoacyl-tRNA Formation Is Very Accurate, the frequency of mischarging is very low; typically, less than 1 in 1000 tRNAs is charged with the incorrect amino acid.

TLS Online TPP Program

#Id: 3667

#Unit 3. Fundamental Processes

Valyl-tRNA synthetase can sterically exclude isoleucine from its catalytic pocket because isoleucine is larger than valine.

TLS Online TPP Program

#Id: 3668

#Unit 3. Fundamental Processes

The protein-coding region(s) of each mRNA is composed of a contiguous, non-overlapping string of codons called an open reading frame (commonly known as an ORF).

TLS Online TPP Program

#Id: 3669

#Unit 3. Fundamental Processes

Translation starts at the 5’end of the ORF and proceeds one codon at a time to the 3’end. The first and last codons of an ORF are known as the start and stop codons.

TLS Online TPP Program

#Id: 3670

#Unit 3. Fundamental Processes

mRNAs containing multiple ORFs are known as polycistronic mRNAs, and those encoding a single ORF are known as monocistronic mRNAs.