Transcription and Translation PowerPoint


Published on

Published in: Education
No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Transcription and Translation PowerPoint

  1. 1. Transcription and Translation
  2. 2. Transcription and Translation <ul><li>What is transcription? Explain what happens during transcription. </li></ul><ul><li>What is translation? Explain what happens during translation. </li></ul><ul><li>Explain how transcription and translation are related to DNA replication. </li></ul><ul><li>If you begin with a parent DNA strand of A A T G C A G T, what will the complementary mRNA strand be? (Think about it before you answer.) </li></ul>
  3. 3. Compared structures of DNA and RNA <ul><li>DNA-Deoxyribonucleic acid </li></ul><ul><ul><li>Bases-cytosine, guanine, adenine and thymine </li></ul></ul><ul><ul><li>Double stranded </li></ul></ul><ul><ul><li>Function-store genetic information </li></ul></ul>
  4. 4. <ul><li>B. RNA-Ribonucleic acid </li></ul><ul><ul><li>Base-Cytosine, guanine, adenine and uracil </li></ul></ul><ul><ul><li>Single stranded </li></ul></ul><ul><ul><li>Functions- </li></ul></ul><ul><ul><ul><li>rRNA-ribosomal RNA (makes up about 60% of ribosomal structure </li></ul></ul></ul><ul><ul><ul><li>mRNA-messenger RNA (record information from DNA and carry it to ribosomes) </li></ul></ul></ul><ul><ul><ul><li>tRNA-transfer RNA (delivers amino acids to proteins at the ribosome to extend the chains) </li></ul></ul></ul>Compared structures of DNA and RNA
  5. 5. RNA nucleotide DNA nucleotide
  6. 6. Comparison of RNA and DNA sugars <ul><li>Deoxyribose </li></ul><ul><li>Ribose </li></ul>
  7. 7. Compared structures of DNA and RNA
  8. 8. RNA single strand with hairpin loop Although it looks like a double helix, it is one strand wrapped around itself. It is similar to a twisted bobby pin.
  9. 9. Reading Quiz (Orange book-Chapter 6) <ul><li>Transcription is the process of making: </li></ul><ul><li>a. RNA b. tRNA c. mRNA d. rRNA </li></ul><ul><li>2. An intron is found in: </li></ul><ul><li>a. DNA b. RNA c. mRNA d. tRNA </li></ul><ul><li>3. The enzyme used in transcription is: </li></ul><ul><li>a. RNA primase b. RNA polymerase </li></ul><ul><li>c. DNA polymerase d. a and b are both correct </li></ul><ul><li>4. How many bases make a codon? </li></ul><ul><li>a. 1 b. 2 c. 3 d. 4 </li></ul><ul><li>5. Translation occurs in the: </li></ul><ul><li>a. nucleus b. cytoplasm c. both </li></ul>
  10. 10. Transcription <ul><li>Transcription=the synthesis of mRNA from a DNA template </li></ul><ul><li>Occurs in the 5’ ->3’ direction (if you don’t know what this means go back and look it up!!) </li></ul><ul><li>Involves RNA polymerase </li></ul><ul><li>mRNA, tRNA and rRNA must all be transcribed for protein synthesis to take place </li></ul>
  11. 11. <ul><li>E. mRNA </li></ul><ul><li>-the sequence of mRNA nucleotides determine the primary sequence of the polypeptides </li></ul><ul><li>F. tRNA </li></ul><ul><li>-carries the amino acids to mRNA </li></ul><ul><li>-tRNA folds in on itself </li></ul><ul><li>-see p. 305 figure 17.12 </li></ul><ul><li>G. rRNA </li></ul><ul><li>-major components of ribosomes </li></ul>Transcription (three types of RNA)
  12. 12. Transcription (Initiation) <ul><li>RNA polymerase binds to the promoter site </li></ul><ul><li>Promoter =region of DNA where RNA polymerase attaches and initiates transcription </li></ul><ul><ul><li>-Determines which strand of DNA will serve as the template </li></ul></ul><ul><li>RNA polymerase -hooks together RNA nucleotides as they base pair along the DNA template </li></ul><ul><li>Transcription unit -area of DNA that will be transcribed </li></ul>
  13. 13. <ul><li>E. Transcription initiation complex -the area where transcription factors and RNA polymerase are bound to the promoter </li></ul><ul><li>F. TATA box -promoter DNA sequence </li></ul><ul><li>-the actual sequence is 5'-TATAAA-3' </li></ul><ul><li>-RNA polymerase binding site </li></ul><ul><li>G. After polymerase is bound to the promoter DNA, the two DNA strands unwind and the enzyme starts transcribing the template strand </li></ul>Transcription (Initiation)
  14. 14. Transcription (RNA strand elongation) <ul><li>RNA polymerase moves along DNA template </li></ul><ul><li>It unwinds 10-20 DNA bases at a time </li></ul><ul><li>RNA polymerase adds nucleotides in the 5’ ->3’ direction </li></ul><ul><li>As RNA polymerase moves along, the DNA double helix reforms </li></ul><ul><li>The new section of RNA ‘peels away’ as the double helix reforms </li></ul>
  15. 15. Transcription (termination) <ul><li>Transcription stops when RNA polymerase reaches a section of DNA called the terminator </li></ul><ul><li>Terminator sequence = AAUAAA </li></ul><ul><li>Next, the RNA strand is released and RNA polymerase dissociates from the DNA </li></ul><ul><li>The RNA strand will go through more processing </li></ul>
  16. 16. Sense vs. Antisense DNA strands <ul><li>The DNA double helix has two strands </li></ul><ul><li>Only one of them is transcribed </li></ul><ul><li>The transcribed strand is the antisense strand </li></ul><ul><li>The non transcribed strand is the sense strand </li></ul><ul><li>mRNA is complementary to the anitsense strand </li></ul>
  17. 17. <ul><li>F. The 5’ end of the RNA nucleotides are added to the 3’ end of the growing chain </li></ul><ul><li>G. RNA nucleotides are linked together in the same fashion as DNA molecules </li></ul>Sense vs. Antisense DNA strands
  18. 18. RNA splicing (in eukaryotes) <ul><li>In eukaryotes RNA transcripts have long non-coding stretches of nucleotides </li></ul><ul><ul><li>-these regions will not be translated </li></ul></ul><ul><li>B. The non-coding sections are dispersed between coding sections </li></ul><ul><li>C. Introns-non-coding sections of nucleic acid found between coding regions </li></ul><ul><li>D. Exons -coding regions of nucleic acids </li></ul><ul><li>(eventually these are expressed as amino acids) </li></ul>
  19. 19. <ul><li>E. RNA polymerase transcribes introns and exons, </li></ul><ul><li>-this is pre-mRNA </li></ul><ul><li>F. Pre-mRNA never leaves the cell’s nucleus </li></ul><ul><li>G. The introns are excised and exons are joined together to form mRNA </li></ul><ul><li>H. pre-mRNA </li></ul><ul><li>I. Mature mRNA </li></ul>RNA splicing (in eukaryotes)
  20. 21. Translation <ul><li>Translation-forming of a polypeptide </li></ul><ul><li>-uses mRNA as a template for a.a. sequence </li></ul><ul><li>-4 steps (initiation, elongation, translocation and termination) </li></ul><ul><li>-begins after mRNA enters cytoplasm </li></ul><ul><li>-uses tRNA (the interpreter of mRNA) </li></ul>
  21. 22. <ul><li>B. Ribosomes </li></ul><ul><li>-made of proteins and rRNA </li></ul><ul><li>-each has a large and small subunit </li></ul><ul><li>-each has three binding sites for tRNA on its surface </li></ul><ul><li>-each has one binding site for mRNA </li></ul><ul><li>-facilitates codon and anticodon bonding </li></ul><ul><li>-components of ribosomes are made in the nucleus and exported to the cytoplasm where they join to form one functional unit </li></ul>Translation
  22. 23. <ul><li>B. Ribosomes (continued) </li></ul><ul><li>-the three tRNA binding sites are: </li></ul><ul><li>1. A site=holds tRNA that is carrying the next amino acid to be added </li></ul><ul><li>2. P site= holds tRNA that is carrying the growing polypeptide chain </li></ul><ul><li>3. E site= where discharged tRNAs leave the ribosome </li></ul>#8. Translation
  23. 24. Ribosomal structure Large subunit Peptidyl-tRNA binding site Aminoacyl-tRNA binding site mRNA 5’ Exit site Small subunit 3’ E P A
  24. 25. <ul><li>C. The genetic code </li></ul><ul><ul><li>Four RNA nucleotides are arranged 20 different ways to make 20 different amino acids </li></ul></ul><ul><ul><li>Nucleotide bases exist in triplets </li></ul></ul><ul><ul><li>Triplets of bases are the smallest units that can code for an a.a. </li></ul></ul><ul><ul><li>3 bases = 1 codon = 1 a.a. </li></ul></ul><ul><ul><li>There are 64 possible codes (64=4 3 ) </li></ul></ul>Translation
  25. 26. <ul><li>C. The genetic code </li></ul><ul><ul><li>Most of the 20 a.a. have between 2 and 4 possible codes </li></ul></ul><ul><ul><li>The mRNA base triplets are codons </li></ul></ul><ul><ul><li>In translation the codons are decoded into amino acids that make a polypeptide chain </li></ul></ul><ul><ul><li>It takes 300 nucleotides to code for a polypeptide made of 100 amino acids (Why?) </li></ul></ul>Translation
  26. 27. <ul><li>C. The genetic code (continued) </li></ul><ul><ul><li>61 of 64 codons code for a.a. </li></ul></ul><ul><ul><li>Codon AUG has two functions </li></ul></ul><ul><ul><li>-codes for amino acid methionine (Met) </li></ul></ul><ul><ul><li>-functions as a start codon </li></ul></ul><ul><ul><li>mRNA codon AUG starts translation </li></ul></ul><ul><ul><li>The three ‘unaccounted for’ codons act as stop codons (end translation) </li></ul></ul>Translation
  27. 28. <ul><li>D. How it works </li></ul><ul><li>DNA (antisense) </li></ul><ul><li>A C C A A A C C G </li></ul><ul><li>mRNA (transcription) </li></ul><ul><li>U G G U U U G G C </li></ul><ul><li>polypeptide (translation) </li></ul><ul><li>Trp - Phe - Gly- </li></ul>Translation
  28. 29. <ul><li>E. More on tRNA </li></ul><ul><ul><li>tRNA is transcribed in the nucleus and must enter the cytoplasm </li></ul></ul><ul><ul><li>tRNA molecules are used repeatedly </li></ul></ul><ul><ul><li>Each tRNA molecule links to a particular mRNA codon with a particular amino acid </li></ul></ul><ul><ul><li>When tRNA arrives at the ribosome it has a specific amino acid on one end and an anticodon on the other </li></ul></ul><ul><ul><li>Anticodons (tRNA) bond to codons (mRNA) </li></ul></ul><ul><ul><li>p. 304 (red book) </li></ul></ul>Translation
  29. 30. Where the a.a. attaches Hydrogen bonds Anticodon = tRNA diagrams Although we draw tRNA in a clover shape it’s true 3-D conformation is L-shaped.
  30. 31. Translation (Initiation) <ul><li>A. Initiation </li></ul><ul><li>1. Brings together mRNA, tRNA (w/ 1 st a.a.) and ribosomal subunits </li></ul><ul><li>2. Small ribosomal subunit binds to mRNA and an initiator tRNA </li></ul><ul><li>-start codon= AUG </li></ul><ul><li>-start anticodon-UAC </li></ul><ul><li>-small ribosomal subunit attaches to 5’ end of mRNA </li></ul>
  31. 33. <ul><li>B. Initiation </li></ul><ul><li>2. (continued) </li></ul><ul><li>-downstream from the 5’ end is the start codon AUG (mRNA) </li></ul><ul><li>-the anticodon UAC carries the a.a. Methionine </li></ul><ul><li>3.After the union of mRNA, tRNA and small subunit, the large ribosomal subunit attaches </li></ul><ul><li>4. Initiation is complete </li></ul>#9. Translation (Initiation)
  32. 34. <ul><li>B. Initiation </li></ul><ul><li>5. The intitiator tRNA and a.a. will sit in the P site of the large ribosomal subunit </li></ul><ul><li>6. The A site will remain vacant and ready for the aminoacyl-tRNA </li></ul>Translation (Initiation)
  33. 35. Translation (Initiation)
  34. 36. Translation (Elongation) <ul><li>Amino acids are added one by one to the first amino acid (remember, the goal is to make a polypeptide) </li></ul><ul><li>Step 1- Codon recognition </li></ul><ul><ul><li>mRNA codon in the A site forms hydrogen bonds with the tRNA anitcodon </li></ul></ul><ul><li>Step 2- Peptide bond formation </li></ul><ul><ul><li>The ribosome catalyzes the formation of the peptide bonds between the amino acids (the one already in place and the one being added) </li></ul></ul><ul><ul><li>The polypeptide extending from the P site moves to the A site to attach to the new a.a. </li></ul></ul>
  35. 37. <ul><li>The tRNA w/ the polypeptide chain in the A site is translocated to the P site </li></ul><ul><li>tRNA at the P site moves to the E site and leaves the ribosome </li></ul><ul><li>The ribosome moves down the mRNA in the 5’ ->3’ direction </li></ul>Translation (Translocation)
  36. 38. <ul><li>Happens at the stop codon </li></ul><ul><li>Stop codons are UAA, UAG and UGA </li></ul><ul><ul><li>-they do not code for a.a. </li></ul></ul><ul><li>C. The polypeptide is freed from the ribosome and the rest of the translation assembly comes apart </li></ul><ul><li>D. Animation (you move it) </li></ul><ul><li>E. Animation (you watch it) </li></ul><ul><li>F. Animation (McGraw-Hill) </li></ul>Translation (Termination)
  37. 39. Gene expression <ul><li>Jacob and Monad (1961) </li></ul><ul><li>-studied control of protein synthesis in E. coli and lactose digesting enzymes </li></ul><ul><li>-found that E. coli do not produce lactose digesting enzymes when grown in a medium without lactose </li></ul><ul><li>-when bacteria were placed in a lactose environment, enzymes were found within minutes </li></ul>
  38. 40. <ul><li>B. Genes can be switched on or off as necessary </li></ul><ul><li>-a gene that is ‘on’ will be transcribed </li></ul><ul><li>-in E.coli , the enzyme lactase will be produced if the gene is ‘on’ </li></ul><ul><li>-if the gene is ‘off’ mRNA will not be created and translation can not occur </li></ul>Gene expression
  39. 41. <ul><li>C. The operon model </li></ul><ul><li>-proposed by Jacob and Monad </li></ul><ul><li>-explains how genes switch on and off </li></ul><ul><li>-operon=promoter, operator and structural genes </li></ul><ul><li>-lac operon is found in E.coli </li></ul>Gene expression
  40. 42. <ul><li>D. The lac operon </li></ul>Gene expression
  41. 43. <ul><li>D. The lac operon (no lactose) </li></ul><ul><li>-lactose is absent, repressor is active, operon is off, no mRNA is produced, RNA polyermase cannot bind because it is blocked by the repressor that has bound to the operator </li></ul>Gene expression
  42. 44. <ul><li>D. The lac operon (lactose is present) </li></ul><ul><li>-lactose is present, repressor is inactive, operon is on, mRNA is transcribed, RNA polymerase binds to operator </li></ul><ul><li>-an isomer of lactose binds to the repressor and changes its shape </li></ul><ul><li>-this prevents it from binding to the operator </li></ul><ul><li>-lactase is produced </li></ul>Gene expression
  43. 45. #11. Compare Transcription in Eukaryotes and Prokaryotes <ul><li>Link </li></ul>