Genetics: DNA Sequences and Gene Expression

DNA Sequences and Gene Expression

• Genetic code is used to convert the base sequence in nucleic acids, read in groups of three, into the sequence of a tRNA.
• Termination occurs when no tRNA exists to bind to a stop codon, causing the tRNA holding the polypeptide to remain in the P site.
• DNA gyrase is an enzyme that introduces negative supercoils into DNA, and is a member of the type II topoisomerase family.
• Supercoiling refers to the higher-level coiling of DNA that is already a complementary strand.
• Catenanes are circular molecules of DNA that can become interlocked during transcription or recombination.

Gene Structure and Regulation

• An open reading frame is a sequence of bases (either in DNA or RNA) that can be translated to give a protein.
• Constitutive genes often have both their -10 and -35 region promoter sequences very close to consensus, which are repressed under rare conditions.
• Enhancers are regulatory sequences inside, and often far away from, the promoter region that bind transcription factors.
• The 5'-UTR region of an mRNA is located between the 5' end and the translation start site.
• Primary transcript is the original RNA molecule obtained by transcription from a DNA template, before any processing or modification has occurred.

Gene Expression and Regulation

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

True or False

• A: (F) - There is only one possible model for ordering cell-cycle events, the dependent pathway.