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The Central Dogma and Transcription

The Central Dogma and Transcription. Chapter 17: Sections 17.1-17.3. Today’s Exit Ticket. The bonds creating the primary structure of a protein are called 1) peptide bonds and form between a 2) C atom in one amino acid and a 3) N atom in another amino acid.

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The Central Dogma and Transcription

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  1. The Central Dogma andTranscription Chapter 17: Sections 17.1-17.3

  2. Today’s Exit Ticket The bonds creating the primary structure of a protein are called 1) peptide bonds and form between a 2) C atom in one amino acid and a 3) N atom in another amino acid. The bonds creating the secondary structure of a protein are called 4) hydrogen bonds and form between 5) the backbone molecules of amino acids (NOT R-groups). The bonds creating the tertiary structure of a protein can be covalent, ionic, or hydrogen bonds, and form between 6) R-groups. 7) Describe the quaternary structure of a protein. Quaternary structure is the interaction of different polypeptide subunits to make a larger molecule. 2

  3. Unit 4 • Proteins • Transcription (DNA to mRNA) • Translation (mRNA to tRNA to proteins) • Gene expression/regulation (turning genes on and off) • Viruses 3

  4. The Central Dogma andTranscription Chapter 17: Sections 17.1-17.3

  5. How do we get from DNA to traits? • Gene expression= DNA directs the synthesis of proteins TWO STEPS: (1) transcription (2) translation All organisms do this!

  6. Outline Basic principles of transcription & translation Transcription in detail RNA processing in Eukaryotes The genetic code

  7. DNA 1 Synthesis of mRNA in the nucleus mRNA NUCLEUS CYTOPLASM mRNA 2 Movement of mRNA into cytoplasm via nuclear pore Information flow from genetic information encoded as DNA blueprint (genes) to RNAcopies Fig. 5.26

  8. DNA & RNA provide information to make proteins • DNA and RNA = bothnucleic acids • Both are made of nucleotide monomers What’s the difference between DNA and RNA?? • 3 Major Differences: DNARNA • Different sugars: deoxyribose ribose • Different bases: C & G, A & T C & G, A & U • Structure: double-stranded single-stranded (usually)

  9. DNA 1 Synthesis of mRNA in the nucleus mRNA NUCLEUS CYTOPLASM mRNA 2 Movement of mRNA into cytoplasm via nuclear pore Ribosome 3 Synthesis of protein Amino acids Polypeptide Information flow from genetic information encoded as DNA blueprint (genes) to RNAcopies and on to synthesis of proteins. Fig. 5.26

  10. Transcription vs. Translation DNA RNA Proteins Hello, friend Hullo, mate สวัสดีเพื่อน Transcription: • Like copying info from a book in the reserved section of the library • Using the same language Translation: • Literally translating between two different languages • Take the copied info from the library and translate it into French/Spanish/Mandarin

  11. Videos of Gene Expression: Hank’s Transcription and Translation Crash Course http://www.youtube.com/watch?v=itsb2SqR-R0 From DNA to Protein http://www.youtube.com/watch?v=D3fOXt4MrOM

  12. 1. Overview of transcription and translation Genes are nucleotide sequences, hundreds or thousands of nucleotides long

  13. 1. Overview of transcription and translation THE CENTRAL DOGMA: DNA  RNA  PROTEIN

  14. 1. Overview of transcription and translation PROTEIN

  15. 1. Overview of transcription and translation

  16. Outline Easing in: basic principles of transcription and translation Transcription in detail RNA processing in Eukaryotes The genetic “code”

  17. Transcription vs. Translation DNA RNA Proteins Hello สวัสดีครับ Hello Transcription: • Like copying info from a book in the reserved section of the library • Using the same language Translation: • Literally translating between two different languages • Take the copied info from the library and translate it into French/Spanish/Mandarin

  18. 2. Transcription in detail Fig. 17-4 Successful transcription requires 3 basic processes: • Initiation • Elongation • Termination

  19. 2. Transcription in detail Fig. 17-4 Successful transcription requires 3 basic processes: • Initiation • Find the location where we start reading DNA • Actually begin making mRNA  To achieve this, we need some kind of signal on or in the DNA that says “START TRANSCRIBING HERE”

  20. 2. Transcription in detail the “start here” signal where the gene is a) Initiation Transcription Unit: “Upstream” of the gene is a promoter • whole promoter = several dozen nucleotides  example of DNA that is essential but is not transcribed Now we know WHERE to initiate, but HOW do we initiate?

  21. 2. Transcription in detail Promoter sequence HOW: With an enzyme, as usual! a) Initiation RNA polymerase • Reads one strand of DNA and builds the mRNA • Can’t bind to the promoter on its own (in eukaryotes) • Only binds when specific transcription factors are present

  22. Promoter sequence Once RNA polymerase binds, it can only synthesize RNA in a 5’ to 3’ direction. Which of the two DNA strands shown here will it “read” as it makes RNA? • Top one • Bottom one • Both strands

  23. 2. Transcription in detail a) Initiation With transcription factors in place, RNA polymerase can now bind DNA at the right place to begin transcription of the gene

  24. 2. Transcription in detail Fig. 17-4 Successful transcription requires 3 basic processes: • Initiation • Bind transcription factors, then RNA polymerase to promoter region 2) Elongation • Make the full length mRNA transcript

  25. 2. Transcription in detail b) Elongation RNA Polymerase untwists DNA, makes mRNA

  26. 2. Transcription in detail b) Elongation Summary of elongation in transcription: • RNA polymerase untwists and separates 10-20 base pairs of DNA at a time • RNA nucleotides enter and pair with the DNA template (U, not T, pairs with A) • RNA polymerase bonds nucleotides onto the 3’ end of the RNA molecule • RNA polymerase moves along, the new RNA molecule peels away from the DNA, and the helix re-twists

  27. 2. Transcription in detail Fig. 17-4 Successful transcription requires 3 basic processes: • Initiation • Elongation make the full length mRNA transcript • Termination stop transcribing; mRNA completed

  28. 2. Transcription in detail c) Termination But how does it stop? Bacteria: termination sequence in the DNA Eukaryotes: a bit more complicated • enzymes cut the transcript free…among other things!

  29. Outline Easing in: basic principles of transcription and translation Transcription in detail RNA processing in Eukaryotes The genetic code

  30. 3. RNA processing in eukaryotes Observations: • Average human pre-mRNA transcript length: 27,000 nucleotides • Each amino acid is coded by 3 nucleotides • Average human protein: 400 amino acids  requires only 1200 nucleotides How does that work?

  31. 3. RNA processing in eukaryotes Before RNA transcripts leave the nucleus, they are modified.

  32. 3. RNA processing in eukaryotes Before RNA transcripts leave the nucleus, they are modified. Modified how? • Alteration of ends • Cutting out some of the middle  offers cell a way of controlling when and where proteins are produced

  33. 3. RNA processing in eukaryotes 1. Alteration of ends

  34. 3. RNA processing in eukaryotes 2. Cutting out some of the middle: RNA splicing

  35. 3. RNA processing in eukaryotes The sequence of DNA that codes for a eukaryotic protein is NOT a continuous sequence Some introns are “self-splicing”  catalyze their own excision!

  36. Ribozymes! Thomas Cech • CU Professor • 1989 Nobel Prize winner, along with Sidney Altman • Discovered that RNA can sometimes splice itself!

  37. 3. RNA processing in eukaryotes • Cutting out some of the middle: RNA splicing Why do introns exist? • Alternative splicing  alternative mRNA  multiple proteins from a single DNA sequence

  38. Outline Easing in: basic principles of transcription and translation Transcription in detail RNA processing in Eukaryotes The genetic code

  39. 4. The genetic code Nucleotides: A, T, G, and C in DNA (A, U, G, and C in RNA) Amino Acids 20 are commonly used by most organisms The genetic code consists of 3-letter codons: • Sequence of 3 nucleotides = specification of amino acid • Each triplet of mRNA nucleotides is called a codon

  40. 4. The genetic code Fig. 17-4 G C U G G U U G U C A U Protein Amino acid Gene 2 DNA molecule Gene 1 note: either strand may serve as the template depending upon the particular gene Gene 3 DNA template strand TRANSCRIPTION mRNA Codons TRANSLATION

  41. Math check: WAIT a second! • 4 nucleotides...in sets of 3... • Shouldn’t there be 43 codons?? YES! • Using just 4 nucleotides, DNA can make 64 different codons BUT... You just said there are only 20 amino acids!?! • Yes, friends, there are only 20.

  42. C U G A U C U A G U C C A G U C A A G U C G A G

  43. 4. The genetic code Fig. 17-4 Some notes on codons: • When we say “codon”, we are referring to RNA triplets • Codons are read in the 5’ to 3’ direction, because that is how they are read by the translation machinery • Codons don’t overlap (300 nucleotides encode 100 codons) 1 2 3 ACUUCCAAG

  44. Today’s Exit Ticket The final product of transcription is _(1)_. The template used for transcription is _(2)_. The first step of the process is called _(3)_ and involves the _(4)_ binding to the _(5)_ region. This allows _(6)_ to bind to the DNA and begin transcribing, in a process called _(7)_. During that process, the enzyme reads from the _(8)_’ to _(9)_’ direction and builds the new strand from _(10)_’ to _(11)_’. The last step of transcription is called _(12)_. In _(13)_, there is another step before translation. This is called _(14)_, and involves removing _(15)_ and adding a 5’ cap and 3’ poly-A tail. WORD BANK (not all will be used, some are used more than once): 3 5 DNA elongation eukaryotes exons initiation introns mRNA prokaryotes promoter RNA polymerase RNA processing termination transcription factors

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