4th hour


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4th hour

  1. 1. 4.3 Protein Synthesis <ul><li>4.3.1 TRANSCRIPTION (Nucleus) </li></ul><ul><li> - DNA mRNA </li></ul>4.3.2 TRANSLATION (Cytoplasm) - mRNA protein
  2. 2. Overview the roles of transcription and translation in the flow of genetic information
  3. 3. Importance of Protein Synthesis <ul><li>Production of hormones </li></ul><ul><li>Production of enzymes </li></ul>
  4. 4. <ul><li>4.3.1Transcription </li></ul><ul><li>Definition : </li></ul><ul><li>the synthesis of mRNA on a DNA template </li></ul><ul><li>which is take place in nucleus </li></ul><ul><li>information that has been transcribed from DNA to mRNA can then be translated and thereby expressed by the formation of specific protein. </li></ul><ul><li>(DNA mRNA protein) </li></ul>
  5. 5. Transcription <ul><li>RNA polymerase enzyme involved </li></ul><ul><li>Specific sequences of nucleotides along the DNA mark where the transcription begin ( promoter site ) and ends ( terminator site ) </li></ul><ul><li>The stretch of DNA that is transcribed into mRNA is called a transcription unit </li></ul><ul><li>mRNA elongates in its 5’ to 3’ direction </li></ul>
  6. 7. <ul><li>3 steps involves in transcription </li></ul><ul><ul><li>RNA POLYMERASE BINDING AND INITIATION </li></ul></ul><ul><ul><li>ELONGATION OF RNA STRAND </li></ul></ul><ul><ul><li>TERMINATION </li></ul></ul>THE PROCESS OF TRANSCRIPTION
  7. 8. <ul><li>RNA polymerase binding and initiation </li></ul><ul><li>RNA polymerase recognize and attaches to promoter site on DNA. </li></ul><ul><li>Enzyme begins to separate the DNA strand . </li></ul><ul><li>Segment of DNA strand unwind. </li></ul>
  8. 9. <ul><li>2. Elongation Of RNA strand </li></ul><ul><li>As RNA polymerase moves along the template of DNA, complementary RNA nucleotides pair with DNA nucleotides of the strand </li></ul><ul><li>RNA polymerase joins the RNA nucleotides together in the 5’ to 3’ direction </li></ul>
  9. 10. <ul><li>3. Termination </li></ul><ul><li>Elongation of mRNA continues until RNA polymerase reaches a terminator site on the DNA </li></ul><ul><li>Terminator site causes the RNA polymerase to stop transcribing DNA and release the mRNA </li></ul><ul><li>mRNA will leave the nucleus through the nucleus pore to the cytoplasm </li></ul>
  10. 11. RNA Splicing (RNA Processing) <ul><li>Exon : A nucleotide sequence in a gene that codes for parts or all of the gene </li></ul><ul><li>product and is therefore expressed in </li></ul><ul><li> mature mRNA. </li></ul><ul><li>Intron : A nucleotide sequence in a gene that does not code for gene product. </li></ul><ul><li> : It usually transcribed in eukaryotes into </li></ul><ul><li> mRNA but subsequently removed from </li></ul><ul><li> transcript before translation. </li></ul>
  11. 13. <ul><li>Genetic code </li></ul><ul><li>Genetic code: Base triplet in DNA provides a template for ordering the complementary triplet in mRNA molecule. </li></ul><ul><li>Every base triplet is amino acid. </li></ul><ul><li>Three bases of an mRNA codon are designated as first, second and third bases . </li></ul>
  12. 14. Genetic code <ul><li>There are only four nucleotide to specify 20 amino acids; A-adenine, C-cytosine, G-guanine, T-thymine (unique to DNA), U-uracil (unique to RNA) [pyrimidine, very similar to thymine]. </li></ul><ul><li>Flow of information from gene to protein is based on triplet code. </li></ul><ul><li>A cell cannot directly translate a gene’s base triplets into amino acids. </li></ul>
  13. 16. <ul><li>An mRNA molecule is complementary rather than identical to its DNA template according to base-pairing rules. </li></ul><ul><li>A-U, T-A, C-G, G-C </li></ul><ul><li>mRNA base triplets are called codons. </li></ul><ul><li>Noticed that U only can be found on mRNA strand, substitute for T (only on DNA strand). </li></ul><ul><li>U on mRNA pairs with A on DNA strand, while T on DNA strand pairs with A on mRNA. </li></ul><ul><li>Two important codons in protein synthesis are initiation codon (start signal) and termination codon or stop signal. </li></ul>
  14. 17. <ul><li>Initiation codon </li></ul><ul><li>Codon AUG is a starter to the process of translation. </li></ul><ul><li>Codon AUG has dual function, as a start signal / initiation codon and it also code for amino acid methionine (Met). </li></ul><ul><li>Polypeptide chains begin with methionine </li></ul><ul><li>An enzyme may subsequently remove starter amino acid from chain. </li></ul>
  15. 18. <ul><li>2. Termination codon </li></ul><ul><li>Three triplet bases of stop signal: UAA, UAG, UGA . </li></ul><ul><li>marking the end of a genetic code. </li></ul><ul><li>Genetic massages begin with the mRNA codon AUG, which signals the protein- synthesizing machinery to begin translating the mRNA at the location. </li></ul><ul><li>Three of 64 codons function as stop signal or termination codon. They are UAA, UAG and UGA . Any one of these termination codons marks the end of a genetic massage, and the completed polypeptide chain is released from the ribosome. </li></ul>