Genetics Lecture 5 PDF

Genetics Transcription LECTURE (5) DR. El-Sawy 1  Genetics Transcription Def  Synthesis of prot...

Genetics Transcription LECTURE (5) DR. El-Sawy 1  Genetics Transcription Def  Synthesis of protein from gene. 1. Transcription = DNA → RNA Steps 2. Translation = RNA → protein 1. Exons  Protein coding sequence Structure 2. Introns  Intervening sequence (non-protein coding sequences).  Synthesis of RNA from a DNA template by RNA polymerase. Def  Primary RNA transcript is synthesized from 5` to 3` and complementary to 3’ –5’ strand of DNA. 1. Template DNA. 2. 4 Ribonucleotide triphosphate (ATP, GTP UTP & CTP). 3. RNA polymerase enzymes. 4. Transcription factors. Required materials DR. El-Sawy 2  Genetics Transcription  DNA serves as template for RNA synthesis : 1. Template strand: The strand of DNA that is transcribed into RNA. DNA 2. Coding strand: because its base sequence is identical to that of the RNA synthesized except for the change of T for U. RNA structure (Ribonucleic acid)  It is generally single stranded.  Nitrogenous bases: Uracil (U) replace Thymine (T) in the pyrimidine bases.  Pentose sugar: ribose RNA polymerase RNA polymerase RNA polymerase RNA polymerase Types I II III Transcript rRNA Transcript mRNA Transcript tRNA DR. El-Sawy 3  Genetics Transcription  RNA polymerase II starts transcription when it finds a promotor  Binding of RNA polymerase II to promotor on DNA.  Several sequences are common to RNA polymerase II promoter & include : Initiation CAAT box (CCAATC) & TATA BOX (TATAAA box) : GC box (GGGCGG): 25 to 35 base pairs upstream 70 to 80 base pairs of start-point. upstream of start point. Binds several proteins "TFIID" Determine frequency of which is 1st step in transcription. transcription events.  Addition of more ribonucleotide triphosphates (UTP, ATP, GTP, and CTP) according to complementary base pairing with template DNA strand, in 5′ to 3′ direction.  The RNAP release pyrophosphate and incorporate nucleoside Elongation monophosphate (AMP, GMP, CMP and UMP).  Started when RNA polymerase meets terminator (termination signal is reached). Termination DR. El-Sawy 4  Genetics Transcription Inhibitors of eukaryotic transcription : Actinomycin D which inhibit : 1. Initiation of replication by binding DNA template interfering Acts on DNA: with action of DNA polymerases. 2. Initiation of transcription by binding DNA template interfering with action of transcription enzymes & proteins. Bind to RNA- α- amanitin (eukaryotic RNA Polymerase II inhibitor) polymerase Replication Transcription  Both strands  Single strand Template  Whole genome  Small portion of genome Primer  Yes  No Enzyme  DNA polymerase  RNA polymerase Product  dsDNA  ssRNA  A-T  A-U Base pair  G-C  T-A  G-C DR. El-Sawy 5  Genetics Transcription DR. El-Sawy 6