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  2. 3. INTODUCTION. <ul><li>The biosynthesis of RNA, called transcription . </li></ul><ul><li>RNA synthesis, or transcription, is the process of transcribing DNA nucleotide sequence information into RNA sequence information </li></ul>
  3. 4. WHAT IS RNA? <ul><li>RNA is a polymer composed of alternating units of ribonucleotides connected through a 3’-5’ phosphodiester bond. </li></ul><ul><li>It is a single stranded nucleic acid that involves in protein synthesis. </li></ul>
  4. 5. WHAT IS RNA.? <ul><li>In contrast with DNA, ribonucleotides contain: </li></ul><ul><li>Hydroxl group on the 2’ carbon of the ribose sugar. </li></ul><ul><li>The base uracil in place of thymine. </li></ul>
  5. 6. TYPES OF RNA. <ul><li>There are three major types of RNA: </li></ul><ul><li>Ribosomal RNA. </li></ul><ul><li>Transfer RNA. </li></ul><ul><li>Messenger RNA. </li></ul>
  6. 7. TYPES OF RNA. <ul><li>Minor types: </li></ul><ul><li>Small nuclear RNA. </li></ul><ul><li>Small interfering RNA. </li></ul><ul><li>Micro RNAS. </li></ul><ul><li>Other small RNAS. </li></ul>
  7. 8. RIBOSOMAL RNA. <ul><li>Ribosomal RNA (rRNA)-is the most abundant form of RNA, </li></ul><ul><li>nucleotides are in a globular form, </li></ul><ul><li>combine with proteins to make ribosomes. </li></ul><ul><li>Ribosomes- are organelles where proteins are made </li></ul>
  8. 9. TRANSFER RNA. <ul><li>Transfer RNA (tRNA)- consist of a single chain of about 80 RNA. </li></ul><ul><li>nucleotides folded into a hairpin shape that binds to specific aminoacids. </li></ul><ul><li>Adopter molecule that carry specific amino acid to the ribosome. </li></ul>
  9. 10. MESSENGER RNA. <ul><li>Messenger RNA (mRNA)- consists of RNA nucleotides in the form of a single uncoiled chain. </li></ul><ul><li>carries genetic information from the DNA </li></ul><ul><li>in the nucleus to the cytosol of a eukaryotic cell. </li></ul>
  10. 11. DNA TRANSCRIPTION <ul><li>DNA is transcribed into RNA by DNA-dependent RNA polymerase (usually just called RNA polymerase ). </li></ul><ul><li>After binding to its start site in DNA, a specific sequence of base called the promoter, RNA polymerase & its supporting accessory proteins synthesize RNA using the base sequence of one strand of double helix DNA. </li></ul>
  11. 12. Transcription requirements <ul><li>Transcription requires: </li></ul><ul><li>a promoter sequence on a DNA template. </li></ul><ul><li>RNA polymerase and accessory transcription factors. </li></ul><ul><li>Nucleotide triphosphates. </li></ul>
  12. 13. promoter sequence <ul><li>A region on the DNA that determines the specificity of transcription of a particular gene. </li></ul><ul><li>Promoters contain specific DNA sequences and response elements which provide a binding site for RNA polymerase and for proteins called transcription factors that recruit RNA polymerase. </li></ul>
  13. 14. RNA polymerase <ul><li>is a complex multisubunit enzyme, responsible for the transcription . </li></ul><ul><li>interacts with the promoter regions of genes as well as with a variety of elements and transcription factors to determine essentially all of the parameters that govern transcription. </li></ul>
  14. 15. Classess of RNA polymerase. <ul><li>RNA polymeraze 1 : synthesizes the precursor of rRNA named pre rRNA . </li></ul><ul><li>RNA polymerase 2: synthesizes pre mRNA. </li></ul><ul><li>RNA POLYMERASE 3: synthesizes pre Trna. </li></ul><ul><li>All these enzymes synthesize what is called primary transcript or immature RNAs (pre form) which by some modifications occur after transcription, will give the mature rRNA, mRNA and tRNA. </li></ul>