Transcription Packet #20 5/31/2016 2:49 AM1

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

RNA  Ribonucleic Acid  Composed of RNA nucleotides  Phosphate  Sugar  Ribose  Nitrogenous Bases  Purines  Adenine  Guanine  Pyrimidines  Cytosine  Uracil 5/31/2016 2:49 AM3

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

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

Types of Eukaryotic RNA 5/31/2016 2:49 AM6

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

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

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

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

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

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

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

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

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

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

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

mRNA Transcription & Translation 5/31/2016 2:49 AM18