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  1. 1. DNA and RNA relationship <ul><li>A gene is a genetic sequence that codes for an RNA . </li></ul><ul><li>In protein coding genes, RNA codes for a protein. </li></ul>
  2. 2. <ul><li>During protein synthesis a working copy of the code is made from RNA </li></ul><ul><li>Overall scheme: DNA -> RNA -> protein </li></ul>
  3. 3. <ul><li>HOW ? </li></ul>
  4. 4. Processes involving the two.. <ul><li>TRANSCRIPTION = The transfer of the coded information from the nucleus to the cytoplasm. </li></ul><ul><li>TRANSLATION = The conversion of that info into polypeptides on ribosomes. </li></ul><ul><li>Both these reaction involves DNA + RNA . </li></ul>
  5. 5. Transcription <ul><li>nucleus. </li></ul><ul><li>major components = DNA, RNA polymerase  </li></ul><ul><li>Importance = Gene is activated. </li></ul><ul><li> = A copy of the code is made from RNA (m-RNA) </li></ul><ul><li>= m-RNA leaves the nucleus, goes to cytoplasm.  </li></ul>
  6. 6. Transcription <ul><li>Formation of m-RNA molecule </li></ul><ul><li>RNA polymerases </li></ul><ul><li>Separate the 2 DNA strands and link RNA nucleotides as they base pair along the DNA template </li></ul><ul><li>Can only add nucleotides to the 3' end; thus mRNA goes in the 5' to 3' direction </li></ul>
  7. 7. Translation <ul><li>cytoplasm, on the ribosomes m-RNA </li></ul><ul><li>Major components = Ribosomes Peptidyl transferase enzyme Transfer RNAs  </li></ul><ul><li>Importance = Ribosome decodes the m-RNA and makes the correct protein. </li></ul>
  8. 8. Transcription <ul><ul><li>a Working Copy of the Code is Made From RNA </li></ul></ul><ul><li>The RNA copy of the code is complementary: </li></ul><ul><li>  DNA Base RNA Base  A U, C G, G C, T A </li></ul><ul><li>Note that U replaces T in RNA (U = uracil) </li></ul><ul><li>RNA leaves the nucleus and goes into the cytoplasm, attaches to a ribosome to make protein (translation) </li></ul>
  9. 9. Transcription… <ul><li>DNA acts as template for the synthesis of RNA </li></ul><ul><li>RNA polymerase attaches to the double helix. </li></ul><ul><li>H+ bonds are broken = DNA unwinds. </li></ul><ul><li>Coding strand acts as a template and is copied by base pairing of nucleotides. </li></ul><ul><li>A complementary polynucleotide strand of mRNA is built. </li></ul><ul><li>The mRNA detaches and leaves the nucleus through the nuclear membrane pore. </li></ul><ul><li>In the cytoplasm, mRNA becomes attached to ribosomes . </li></ul>
  10. 11. Close up… <ul><li>Eukaryotic genes contains 2 regions: “exons” and “introns”. </li></ul><ul><li>Exons – code for amino acids. </li></ul><ul><li>Introns - DO NOT . Fx? </li></ul><ul><li>During transcription, both E+I are copied from the DNA. </li></ul><ul><li>DNA sequence coding for proteins exons may be interrupted by non coding DNA i ntrons. </li></ul>
  11. 12. During RNA synthesis, non-coding sequences of base pairs needs to be subtracted from the coding sequences of a gene in order to transcribe DNA into (mRNA.) So that.. mRNA that leaves now consists of a continous coding region
  12. 13. <ul><li>Before mRNA leaves the nucleus, introns are removed </li></ul>
  13. 14. RNA splicing.. <ul><li>Process to remove unwanted materials. </li></ul><ul><li>i. In the nucleus, DNA that includes the E + I is first transcribed into a complementary nuclear RNA copy (nRNA) </li></ul><ul><li>ii. Introns are removed from nRNA by a process called RNA splicing. </li></ul><ul><li>The edited sequence is called mRNA </li></ul>
  14. 15. Vital steps <ul><li>Initiation </li></ul><ul><li>Elongation </li></ul><ul><li>Termination </li></ul>
  15. 16. Transcription <ul><li>Initiation </li></ul><ul><li>RNA polymerases bind to DNA at promoters (initiation site); </li></ul><ul><li>Enzyme separates the 2 DNA strands and transcription begins </li></ul><ul><li>Elongation </li></ul><ul><li>RNA polymerases move along the DNA </li></ul><ul><li>1- untwists and opens a short segment of DNA (DNA template) </li></ul><ul><li>2- links incoming RNA nucleotides to the 3' end the elongating strand </li></ul><ul><li>1 at a time in the 5' to 3' direction </li></ul><ul><li>the non-coding strand of DNA reforms a DNA-DNA double helix by pairing with the coding strand </li></ul>
  16. 17. Termination <ul><li>RNA polymerases reaches a termination site on the DNA </li></ul><ul><li>RNA molecule is then released </li></ul>