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Protein Synthesis

Protein Synthesis. 3 major processes: Replication → DNA copied to form 2 new DNA molecules Nucleus Transcription → DNA info copied to RNA Nucleus Translation → building a protein according to RNA instructions Cytoplasm. RNA & Transcription. From Gene to Protein

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Protein Synthesis

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  1. Protein Synthesis • 3 major processes: • Replication→ DNA copied to form 2 new DNA molecules • Nucleus • Transcription → DNA info copied to RNA • Nucleus • Translation → building a protein according to RNA instructions • Cytoplasm

  2. RNA & Transcription From Gene to Protein (DNA  RNA  Protein) Honors Biology Ms. Kim

  3. The Flow of Genetic Information • DNA • information in a specific sequence (order) of nucleotides along 2 DNA strands • Leads to specific traits by controlling the synthesis of proteins • Gene expression includes two stages • Transcription: DNA  RNA • “transcribe” = to copy into another form • Translation: RNA polypeptide (proteins) • “translate” = to change into another language

  4. What is transcription? • Process of copying DNA (the template strand) into a complementary RNA strand • Occurs in the nucleus • Similar to DNA replication, but Uracil (U) replaces Thymine (T)

  5. Why RNA? • RNA – Ribonucleic Acid • How does DNA get out of the nucleus and go to the ribosomes where the proteins are made? • It can’t! DNA cannot leave the nucleus! • So, it copies itself into RNA and that leaves and goes to the ribosomes • EXAMPLE – library book, photocopy

  6. What are the characteristics of RNA? • Ribose Nucleic Acid • Single stranded • Made of sugars (called ribose), phosphate groups and nitrogen bases • Backbone= alternating ribose sugar/phosphates held together by PHOSPHODIESTER BONDS • Made of RNA nucleotides • Contains bases: • (A) Adenine • (G)Guanine • (C) Cytosine • (U) Uracil (replaces Thymine)

  7. DNA vs. RNA: • Sugars = • DNA – deoxyribose • RNA – ribose • Nitrogen bases = • DNA – A, C, G and thymine (T) • RNA – A, C, G and uracil (U) • Location = • DNA – inside nucleus only • RNA – in and out of nucleus • Stranded = • DNA – Double stranded • RNA – Single stranded

  8. Messenger RNA • mRNA copies the DNA code and carries it into the cytoplasm where protein synthesis happens • Notice how the bases of mRNA are organized into codons • A codon consists of 3 consecutive bases  code for a specific amino acid • Remember a chain of amino acids = a protein • So….DNA codes for proteins!

  9. The Ribosome • Part of cell where translation (protein synthesis) occurs • Where proteins are actually made

  10. Basic Principles of Transcription and Translation • Transcription • the synthesis of RNA from DNA (DNA  mRNA) • Produces messenger RNA (mRNA) • Occurs in the nucleus of eukaryotes and nucleoidregion of prokaryotes • Translation (happens later) • actual synthesis of a polypeptide • mRNA  polypeptide  protein • Occurs on ribosomes

  11. DNA TRANSCRIPTION mRNA Ribosome TRANSLATION Polypeptide Prokaryotic cell. In a cell lacking a nucleus, mRNAproduced by transcription is immediately translatedwithout additional processing. In prokaryotes, transcription and translation occur together

  12. Nuclear envelope DNA TRANSCRIPTION Pre-mRNA RNA PROCESSING mRNA Ribosome TRANSLATION Eukaryotic cell. The nucleus provides a Separate compartment for transcription. The original RNA transcript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA. Polypeptide (b) In eukaryotes, pre mRNA transcriptsare modified (changed) before becoming true “mature” mRNA “Transcript” is a fancy word for “message”

  13. How is Protein Made? • Cells are controlled by a cellular chain of command • DNA RNA protein • Called the “Central dogma of biology” • What are proteins made out of? • Amino acids • There are 20 different amino acids • building blocks of proteins • All living things use the same 20 amino acids to make proteins!!!

  14. The Genetic Code • It’s a table used that TRANSLATES RNA nucleotides (or mRNA “letters”) into one of the 20 amino acids • 3 letter mRNA “word” = 1 amino acid • There are 4 different RNA “letters” that can be used • A, U, C, and G

  15. Codons: Triplets of Bases • Genetic information is coded as a sequence ofbase triplets, or codons • 3 letter mRNA “words” = codon • FOUND ONLY ON mRNA • Codons must be read in the correct order • For specified polypeptide to be produced • Always read in the 5’  3’ direction

  16. THE GENETIC CODE

  17. Evolution of the Genetic Code • The genetic code is nearly universal • Shared by organisms from the simplest bacteria to the most complex animals • All organisms have SAME DNA “letters” and SAME RNA “letters”

  18. Gene 2 DNA molecule Gene 1 Gene 3 DNA strand (template) 5 3 A C C T A A A C C G A G TRANSCRIPTION A U G G G G C U C U U U mRNA 5 3 Codon TRANSLATION Protein Gly Phe Ser Trp Amino acid Figure 17.4 During transcription, a gene determines the sequence of bases along length of mRNA.

  19. Transcription • DNA  RNA • RNA synthesis is done by RNA polymerase • Forces DNA strands apart (breaks H bonds btw bases) and hooks together RNA nucleotides • Follows same DNA base-pairing rules, except in RNA, uracil substitutes for thymine • A = U (T on DNA = A in RNA) • C = G

  20. Synthesis of an RNA Transcript • Initiation • DNA strands unwind • RNA polymerase initiates mRNA synthesis at start point on templates called promoters • RNA polymerase binds to promoter • Elongation • RNA polymerase moves downstream, unwinding DNA & elongating mRNA transcript 5 3 direction • In wake of transcription, DNA strands re-form a double helix. • Termination • mRNA transcript is released at terminator signal • RNA polymerase detaches from the DNA

  21. RNA Polymerase Binding and Initiation of Transcription • Promoters (on DNA) starts RNA synthesis (BOTH prokaryotes & eukaryotes) • RNA polymerase binds here then unwinds DNA • RNA Polymerase adds new FREE RNA nucleotides to DNA template strand in 5’ 3’ direction • “TATA box” = start signal on DNA promoter • Determines which strand is used as template  only 1 side is used at a time!

  22. Transcription Animation • http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

  23. Elongation Non-template strand of DNA RNA nucleotides RNA polymerase T A C C A T A T U 3 C 3 end T G U A G G A G E A C A C C 5 A A T A G G T T Direction of transcription (“downstream”) 5 Template strand of DNA Newly made RNA

  24. Intron 5 3 5 Cap Poly-A tail TRANSCRIPTION DNA Exon Pre-mRNA RNA PROCESSING Introns cut out and exons spliced together Coding segment mRNA Ribosome TRANSLATION mRNA 5 Cap Poly-A tail Polypeptide 1 146 3 UTR 5 UTR Split Genes and RNA Splicing • RNA splicing and RNA Modification • Removes introns and joins exons • Introns = non-coding regions • Exons = coding regions that EXIT nucleus Intron Pre-mRNA Exon Exon Mature mRNA Figure 17.10

  25. 3 1 2 RNA transcript (pre-mRNA) 5 Intron Exon 1 Exon 2 Protein Other proteins snRNA snRNPs Spliceosome 5 Spliceosome components Cut-out intron Mature mRNA 5 Exon 1 Exon 2 RNA splicing is carried out by spliceosomesin some cases Called small nuclear RNA + proteins (ribonucleoproteins)

  26. mRNA CodonsLets Practice:CCAAGAGUGUGAAUG

  27. Practice Coding • DNA Complementary – A T C • DNA Template - A G A • mRNA - U A G • Amino Acid Seq- Ile-Ser-Stop T C T TAG ATC T A G A U C U C U

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