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12-3

12-3. Genes are coded DNA instructions that control the production of proteins within the cell. 1- Decoding the genetic messages by copying part of the nucleotide 2- RNA molecules contain coded information for making proteins. RNA consist of a long chain of nucleotides. Sugar in RNA is rebose

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12-3

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  1. 12-3

  2. Genes are coded DNA instructions that control the production of proteins within the cell. 1- Decoding the genetic messages by copying part of the nucleotide 2- RNA molecules contain coded information for making proteins.

  3. RNA consist of a long chain of nucleotides • Sugar in RNA is rebose • Generally is single- stranded • Contains Uracil in place of thymine.

  4. RNA Molecules • Is a disposable copy of a segment of DNA. • Is a working copy of a single gene • The ability to copy a single DNA sequence into RNA makes it possible for a single gene to produce hundreds of RNA molecules.

  5. Types of RNA • They have a lot of functions but most of them are in charge of protein synthesis. • It controls the assembly of amino acids into proteins. • There are 3 main types: • Messenger RNA • Ribosomal RNA • Transfer RNA

  6. 3 types of RNA

  7. Messenger RNA They serve as a messenger from DNA (inside the nucleus) to the rest of the cell.

  8. Ribosomal RNA Proteins are assembled on ribosomes. They are made up of several dozen proteins.

  9. Transfer RNA RNA molecule transfers each amino acid to the ribosome as it is specified by coded messages in mRNA.

  10. Transcription Copying part of the nucleotide sequence of DNA into complementary sequence in RNA.

  11. RNA polymerase Enzyme required to open DNA

  12. During transcription, RNA polymerase binds DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA.

  13. How does RNA polymerase “knows” where to start and stop making an RNA copy of DNA? RNA polymerase does not bind to DNA just anywhere.

  14. Promoter – region of DNA that indicates to the enzyme where to bind to make RNA. (Where to start and where to stop) Promoters STOP A A A C C C G G G Section of DNA

  15. RNA Editing DNA of eukaryotic genes contains sequence of nucleotides called: Introns –there are not involves in coding for proteins. Exons – Sequence that codes the synthesis of proteins. Exon Intron Exon Intron Exon

  16. RNA Editing When RNA molecules are formed, both introns and exons are copied from DNA. Introns are cut out of RNA molecules while in nucleus. The remaining exons spliced back together. Exon Intron Exon Intron Exon Exon Exon Exon Intron Intron Exon Exon Exon

  17. Scientist don’t know yet why RNA molecules have to throw away information? • Evolution???

  18. The Genetic Code Proteins are made by joining amino acids into long chains called polypeptides Polypeptides contain a combination of some or all 20 amino acids. The properties of proteins are determine by the order in which amino acids are joined.

  19. 19 10 5 11 5 4 16 12 5 14 17 7!!!! 7 22 25 18 16!!!

  20. RNA contains 4 different bases: The genetic code reads 3 letters at a time. So each 3 bases represents a “word” A U G C

  21. CODON Consists of 3 consecutive nucleotides that specify a single amino acid that is added to the polypeptide.

  22. RNA sequence: UCGCACGGU Sequence in three bases UCG – CAC - GGU Codon represents the different amino acids: UCG – CAC - GGU Serine – Histidenie- Glycine

  23. GAUACCCAG UUACCUACU

  24. There are 4 different bases, there are 64 possible three- base codons. (4 X 4 X 4 = 64)- Some amino acids are specified by more than one codon.

  25. Important • AUG – Codon that specifies on Methionine and serves as the initiation or “start” codon for protein synthesis. • There are also three stops: • UAA • UAG • UGA Promoters STOP A A A C C C G G G UAA UAG UGA Methionine AUG

  26. Translation The sequence of nucleotides bases in an mRNA molecule serves as instructions for the order in which amino acids should be joined together to produce polypeptides.

  27. Translation The cell uses information from messenger RNA to produce proteins.

  28. mRNA is transcribed from DNA in the nucleus and then leaves.

  29. Translation starts when an mRNA attaches to a ribosomal and then moves through it.

  30. The amino acid is them brought into the ribosome by tRNA and then transfer it to the polypeptide.

  31. tRNA • Each tRNA carries only one kind of amino acid • Methionine, serine, etc • Each one has three unpaired bases called anticodon that are complementary to one mRNA codon.

  32. Codons and Anticodons tRNA A U C A U G mRNA

  33. It assembles codon by codon.A peptide bond forms between the amino acids.

  34. The ribosomes release the first tRNA and continue with the next.

  35. The polypeptide continues to grow until the stop codon, on the mRNA. Then releases the polypeptide

  36. The Roles of RNA and DNA DNA – Master plan RNA – Blue prints

  37. Genes and Proteins Most genes contains more than instructions for assembling proteins. Proteins have to do with: color of a flower, shape of a leaf, human blood type, or sex of a new born baby. Proteins are enzymes that catalyze and regulates chemical reactions. There are genes for every characteristic.

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