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Protein Synthesis

Protein Synthesis. The whole point of all of this is to make proteins. DNA (gene)  RNA amino acid sequence Protein ***Why are proteins so important?***. Protein Synthesis. Proteins Synthesis: Transcription. What kind of RNA is DNA transcribed into?. mRNA Why?

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Protein Synthesis

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  1. Protein Synthesis • The whole point of all of this is to make proteins. • DNA (gene) RNA amino acid sequence Protein ***Why are proteins so important?***

  2. Protein Synthesis

  3. Proteins Synthesis: Transcription • What kind of RNA is DNA transcribed into? • mRNA • Why? • Because mRNA can leave the nucleus.

  4. A little more detail • Initiation: begins with Promoter DNA • Identifies which strand will be transcribed • Gives a spot for RNA polymerase to bind • Elongation : • RNA polymerase adds nucleotides 5’ to 3’ (about 40nts/sec) • Termination: • Terminator sequence on DNA codes for polymerase to detach and mRNA to leave nucleus and go to ribosome

  5. Fig. 17-3b-3 Nuclear envelope DNA TRANSCRIPTION Pre-mRNA RNA PROCESSING mRNA TRANSLATION Ribosome Polypeptide (b) Eukaryotic cell

  6. mRNA modification • mRNA receives a “cap” and a “tail” to protect it while in transit to the ribosome • The mRNA includes introns and exons . • Introns are removed before it leaves nucleus

  7. Protein Synthesis: Transcription

  8. Fig. 17-10 Exon Exon Intron 5 Exon Intron 3 Pre-mRNA Poly-A tail 5 Cap 146 31 104 1 105 30 Introns cut out and exons spliced together Coding segment mRNA 5 Cap Poly-A tail 1 146 5 UTR 3 UTR

  9. So what’s the purpose of exons and introns? • One gene can code for different proteins.. • Depending on which sections of the mRNA template are considered exons during processing. • This would explain our low number of genes for such a complex organism as a human

  10. Humans have only 1.5x as many genes as a fruit fly

  11. 0 DNA molecule Gene 1 Gene 2 Gene 3 DNA strand Transcription RNA Codon Translation Polypeptide Amino acid

  12. Proteins Synthesis: Transcription • Nucleotides are arranged into triplets called codons. • Example: AAC CG T TAC T TG GCA ATG • Each codon specifies (codes for) a particular amino acid. • The sequence of the codons in the DNA will be transferred to the RNA, which will then determine the sequence of amino acids.

  13. 0 DNA strand Transcription RNA Codon Translation Polypeptide Amino acid

  14. Protein Synthesis: Transcription • When RNA is being synthesized by enzymes, they pair the bases just like they would during DNA replication. • There is one BIG difference, though. • RNA does not have the base Thymine. • Instead, if the enzymes come across an Adenine base, they pair it with Uracil. • Can you transcribe the following DNA strand? DNA: ATC GGA TAC GGG CCA mRNA:

  15. Protein Synthesis: Transcription • But let’s remember the goal here… Proteins! Proteins! Proteins! • Now that we have our mRNA with the DNA code, the mRNA can leave the nucleus and head to the ribosome!

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