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Unformatted text preview: Chapter 8 Transcription and processing (DRAFT) Expression of genetic material By expression we mean the production of RNAs and proteins. Gene expression is accomplished by the processes: Transcription RNA processing translation The central dogma of molecular biology was enunciated by Francis Crick in 1958. The central dogma The flow of information from loci to proteins The flow is unidirectional Information here means the precise determination of sequence. Transcription Transcription is the production of an RNA molecule using a DNA molecule as a template. Define transcript : The RNA product of transcription. Note the linguistic analogy. When we transcribe our notes we rewrite them in the same language. The information in the nucleotide DNA is copied into a nucleotide chain of RNA. So the information flows from nucleotide polymer to nucleotide polymer. RNA is produced from the 5 to 3 because the 3OH is necessary for extension. Types of RNA : tRNA : transports amino acids to the translation complex and aligns them at the correct location along the mRNA. rRNA : Combine with proteins to make ribosomes. rRnas do most of the catalytic functions of the ribosomes. Recall the definition of ribozymes . snRNAs : small nuclear RNAs. combine with specific proteins to form ribonucleoprotein particles (snRNPs). These particles compose the spliceosome that removes introns and splices exons together. scRNA small cytoplasmic RNA. Direct protein traffic within the eukaryotic cell. Properties of RNA . Usually single stranded at production that can then assume many complex shapes for many functions. More complex shapes than double stranded DNA. It is this ability to assume complex shape that gives RNA its catalytic ability allowing some RNAs to be ribozymes . (Note: This catalytic ability of RNA is congruent with hypothesis that RNA may have preceded DNA as the genetic material.) RNA is produced from only one strand of the DNA molecule called the template strand . The other strand is called the non template strand. RNA polymerase is the enzyme that makes the bonds between the RNA monomers. It does not need a primer. The RNA product does not remain base-paired to the Template DNA, the enzyme displaces the growing chain only a few nucleotides behind where each nucleotide is added....
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