Molecular Biology Terms

Transcription and Translation

• Termination occurs when no tRNA can bind to a stop codon, leaving the tRNA holding the polypeptide in the P site.
• DNA gyrase is an enzyme that introduces negative supercoils into DNA, belonging to the type II topoisomerase family.

DNA Structure and Topology

• Supercoiling refers to the higher level coiling of DNA that is already complementary during transcription or recombination.
• Catenanes are circular molecules of DNA that may become interlocked during transcription or recombination.

Gene Expression

• An open reading frame is a sequence of bases in DNA or RNA that can be translated to give a protein.
• Constitutive genes often have -10 and -35 region promoter sequences close to consensus, but are repressed under rare conditions.
• Enhancers are regulatory sequences inside or far away from the promoter region that bind transcription factors.

mRNA Structure

• The 5'-UTR is the region of an mRNA between the 5' end and the translation start site.
• A primary transcript is the original RNA molecule obtained by transcription from a DNA template, before any processing or modification has occurred.

Gene Regulation

• Housekeeping genes are switched on some of the time because they are needed for essential life functions.
• The Pribnow box is a region of bacterial promoters, 10 bases back from the start of transcription, recognized by RNA polymerase.