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Transcription Packet #20 5/31/2016 2:49 AM1
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Introduction The process by which information encoded in DNA specifies the sequences of amino acids in proteins involves two steps – Transcription – RNA molecule, complementary to the DNA template strand, is synthesized – Translation – More to come later 5/31/2016 2:49 AM2
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RNA Ribonucleic Acid Composed of RNA nucleotides Phosphate Sugar Ribose Nitrogenous Bases Purines Adenine Guanine Pyrimidines Cytosine Uracil 5/31/2016 2:49 AM3
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Types of RNA Messenger RNA Contains information that specifies the amino acid sequence of polypeptide chains Serves as the template for protein synthesis 5/31/2016 2:49 AM4
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Types of RNA Transfer RNA – Class of RNA molecules that transport amino acids to ribosomes for incorporation into a polypeptide undergoing synthesis. – “Transporter” – Ribosomal RNA – RNA that make up ribosomes. – Provides a mechanism for decoding mRNA into amino acids and to interact with the tRNA during translation by providing peptidyl transferase activity. 5/31/2016 2:49 AM5
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Types of Eukaryotic RNA 5/31/2016 2:49 AM6
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Genes The Review 7 Where are genes located? On the chromosome What is the name of the location on the chromosome where genes are located? The Locus What are genes composed of? DNA 5/31/2016 2:49 AM
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Regions of the Gene I 8 Regulatory Region Receives signals from other genes or cellular environment This is where RNA Polymerase, the only enzyme used during transcription, binds on the DNA strand The Regulatory Region Has a region known as the Promoter Region The TATA Box is found in the Promoter Region The Coding Region Area where RNA nucleotides are joined together to make an RNA strand. 5/31/2016 2:49 AM
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Transcription Factors Transcription Factors Term loosely applied to any protein required to initiate or regulate transcription in eukaryotes. Includes gene regulatory proteins as well as the general transcription factors. General Transcription Factors In eukaryotes, if the transcription factor is involved in initiation of transcription, the protein will bind to RNA polymerase to form a preinitiation complex that is necessary to begin transcription. 5/31/2016 2:49 AM9
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Transcription Factors II Regulation of Transcription Activators Proteins bind to genes at sites known as enhancers and speed up the rate of transcription Repressors Proteins that bind to selected sets of genes at sites known as silencers and slow down transcription 5/31/2016 2:49 AM10
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Transcription Factors Basal Transcription Factors* In response to injunctions (command) from activators, these factors position RNA polymerase at the start of transcription and initiate the transcription process Coactivators Adapter molecules that integrate signals from activators and perhaps repressors. Allows communication between activators (and possibly repressors) basal transcription factors. 5/31/2016 2:49 AM11
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RNA Polymerase Only enzyme used during transcription. However, there are three variations of the enzyme— depending on the type of RNA being produced RNA Polymerase I Transcribes rRNA genes RNA Polymerase II Transcribes protein coding (mRNA) genes RNA Polymerase III Transcribes other functional RNA genes tRNA 5/31/2016 2:49 AM12
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Transcription Step by Step 13 Location Nucleus RNA Polymerase binds at the promoter region (sequence) and unzips the DNA strand Recall from the previous slide the transcription factors binding at the TATA box 5/31/2016 2:49 AM
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Transcription Step by Step 14 RNA Polymerase works downstream adding RNA nucleotides to the 3’ end of the newly formed RNA strand New RNA strand grows in the 5’ to 3’ direction The first 20 – 40 bases make up the 5’ cap In the cap, guanine exists in a modified format. 5/31/2016 2:49 AM
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Transcription Step by Step RNA Polymerase hits the “Terminator” sequence that signals the end of transcription Newly made RNA is released The New RNA strand is called pre-mRNA Why? Because the pre- mRNA needs to be “groomed” for the moment of Translation 5/31/2016 2:49 AM15
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Sections of pre-mRNA 16 Contains introns and exons. Introns The “Junk in the Trunk” Regions of the RNA strand that must be removed, via splicing, and will not be used during Translation Exons Regions of RNA that WILL be used and translated into amino acids during TRANSLATION 5/31/2016 2:49 AM
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Splicing Eukaryotic Cells 17 Removal of introns Location Nucleus of the Cell Enzyme used is Spliceosome Removes the introns via “cut & paste” After splicing, the pre- mRNA will be officially known as mRNA mRNA leaves the nucleus, through the nuclear pores, and enters the cytoplasm 5/31/2016 2:49 AM
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mRNA Transcription & Translation 5/31/2016 2:49 AM18
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