BIO273 Transcription PDF

BIO273 Biology Flow of Information: Transcription Gene Expression  Process by which information from a gene is used to synthesize a functional gene product, usually a Protein All cells have the same DNA, but not all genes are expressed Transcription...

BIO273 Biology Flow of Information: Transcription Gene Expression  Process by which information from a gene is used to synthesize a functional gene product, usually a Protein All cells have the same DNA, but not all genes are expressed Transcription Translation DNA mRNA PROTEIN Transcription  Sequence of nucleotides in DNA is converted into a sequence of nucleotides in RNA Translation  Sequence of nucleotides in RNA is converted into a sequence of amino acids in protein SCHOOL OF BIOLOGICAL SCIENCES 2 AND APPLIED CHEMISTRY Transcription  Assembly of an mRNA transcript by using DNA as a template  RNA Polymerase also only added to the 3’ end of RNA RNA nucleotides pair with complementary DNA in continuously Hydrogen bonding between the RNA & DNA nucleotides SCHOOL OF BIOLOGICAL SCIENCES 3 AND APPLIED CHEMISTRY Transcription  Only one DNA strand is used as the template by RNA Polymerase Antisense strand  Read by RNA Polymerase to create RNA transcript Coding (Sense) strand  DNA sequence will be same as new RNA transcript Usually used when presenting a DNA sequence Can be confusing as Coding strand is not used by RNA Polymerase SCHOOL OF BIOLOGICAL SCIENCES 4 AND APPLIED CHEMISTRY Transcription – Sequence of Events Initiation  RNA Polymerase binds to a DNA sequence called the Promoter  RNA Polymerase creates a Transcription Bubble  Only separates small amount of double stranded DNA Elongation  RNA Polymerase add RNA nucleotides, complementary to DNA  RNA Polymerase forms the Sugar – Phosphate backbone Termination  Hydrogen bonding of the RNA – DNA helix break  New RNA strand is released for further modifications  RNA may remain in the Nucleus or exit into the Cytoplasm SCHOOL OF BIOLOGICAL SCIENCES 5 AND APPLIED CHEMISTRY Transcription – Promoter Promoter  DNA sequence that is a start site for Transcription  Promoter is upstream from the coding gene sequence Transcription Factors  Proteins which bind to the Promoter  Proteins made by the cell to control gene expression (ON / OFF)  Specific sequences corresponding to the nucleotides in Promoter SCHOOL OF BIOLOGICAL SCIENCES 6 AND APPLIED CHEMISTRY Transcription – Transcription Factors Different effects when bound to Promoter  Activator increases gene expression  Repressor inhibits gene expression  RNA Polymerase will bind & start to unwind DNA strands  Promoters with Transcription Factors control which genes are expressed SCHOOL OF BIOLOGICAL SCIENCES 7 AND APPLIED CHEMISTRY Transcription Bubble  Only a short DNA sequence is unwound at Promoter site  Complementary RNA nucleotides added one at a time  RNA Polymerase creates Sugar – Phosphate backbone  As RNA Polymerase moves along the strand, bubble closes behind SCHOOL OF BIOLOGICAL SCIENCES 8 AND APPLIED CHEMISTRY Transcription - Termination  Hydrogen bonds break between RNA strand & the DNA template  RNA Polymerase will continue until it reaches a Terminator sequence in the DNA  Terminator Proteins release the RNA Polymerase & RNA strand Result  RNA copy of a gene coded in the DNA sequence SCHOOL OF BIOLOGICAL SCIENCES 9 AND APPLIED CHEMISTRY Transcription Promoter Transcription unit 5¢ 3¢ 3¢ 5¢ Start DNA RNA polymerase Initiation Unwound DNA Coding (Sense) DNA strand 5¢ 3¢ 3¢ 5¢ Template (Antisense) DNA strand RNA transcript Elongation Rewound DNA 5¢ 3¢ 3¢ 5¢ 5¢ RNA transcript Termination 5¢ 3¢ 3¢ 5¢ 5¢ 3¢ Completed RNA transcript SCHOOL OF BIOLOGICAL SCIENCES 10 AND APPLIED CHEMISTRY Summary  Transcription is the process of making an RNA copy from DNA  Transcription Factors bind to Promoter regions upstream from gene  My turn gene expression OFF or ON  RNA Polymerases just with Transcription Complex on DNA  RNA Polymerase unwinds & uses the Antisense DNA as template  RNA Polymerase reaches a stop sequence  RNA Polymerase & RNA released from DNA strand SCHOOL OF BIOLOGICAL SCIENCES 11 AND APPLIED CHEMISTRY