1. 1 NUCLEIC ACIDS & PROTEIN SYNTHESIS Chapter 10 Topics:DNA RNA Protein Synthesis CPI Biology

2. 2 Understanding Heredity  Important discoveries: By 1940s, nucleic acid composition known; ribose & deoxyribose sugars known Avery Oswald (1943) determined that DNA carried genetic info Erwin Chargraff (1950) found that the amount of certain nitrogen bases occurred in 1:1 ratio Linus Pauling (1948) found many proteins coiled into an - helix (spiral, like a spring) Rosiland Franklin (late 1940s-early 50s) X-ray crystallography on DNA, captured structure Maurice Wilkins (1950s, Kings College) colleague of Franklin, worked on other aspects of DNA James Watson/Francis Crick (1950s) working on DNA structure as well  The race was on….

3. 3 Structural Components Nucleotide Structure consists of: Phosphate group Sugar – deoxyribose or ribose Nitrogen bases – adenine, guanine, cytosine, thymine, uracil  All nucleotides have same phosphate group, 2 sugar possibilities, and several base possibilities

4. 4 Nitrogen Bases  Purines – 2 rings of C & N atoms Adenine (A) Guanine (G)  Pyrimidines – 1 ring of C & N atoms Thymine (T) (in DNA only) Cytosine (C) Uracil (U) (in RNA only)

5. 5 DNA Structure  DNA components known, but how were they “put together” & how did it work?  Many scientists competed in the race to determine what this molecule looked like. Some worked to find the answer, others worked to find the answer first. Rosiland Franklin Maurice Wilkins James Watson & James Crick  Watson/Crick/Wilkins received Nobel Prize (1963) for determining DNA structure

6. 6 Double Helix of DNA  DNA molecule: Double stranded – each strand composed of alternating sugar & phosphate strands; 1 strand going “up”, the other “down” “Ladder rungs” connecting the strands are 2 nitrogen bases; always a purine + a pyrimidine; bonded by H Bond; pair combo same size Only possible base pair combos: AT, CG  See pictures, next 2 slides

7. 7 Nitrogen Base Pairs  A-T Purine + Pyrimidine  G-C Purine + Pyrimidine

8. 8 DNA Structure Left Strand 3’ to 5’ UP Right Strand 3’ to 5’ DOWN

9. 9 RNA Structure  Single helix structure Single strand of alternating phosphate & sugar (ribose) sugars Nitrogen base bonded to strand  Bases: adenine & guanine (purines), cytosine & uracil (pyrimidines) Uracil replaces thymine  Sugar is ribose Ribose replaces deoxyribose

10. 10 Purine/Pyrimidine Comparison GCATGCATPurinesPyrimidines 2 Rings1 Ring 3 H BondsGC 2 H bondsAT (U) DNA GCAT RNA GCAU

11. 11 DNA/RNA Comparison DNARNA StructureDouble HelixSingle Helix PhosphateSame SugarDeoxyriboseRibose Bases Purine Pyrimidine Adenine Thymine Guanine Cytosine Adenine Uracil Guanine Cytosine

12. 12 DNA Replication  Replication – process of copying DNA  DNA replication occurs during “S phase” of Interphase  Hydrogen bonds broken by helicases; DNA double helix “unzips”  DNA polymerases then move along single (opened) strands & attach nucleotides to “open” base; manufacturing a new strand H bonds join base pairs Covalent bonds join phosphate/sugar groups & base to strand

13. 13 DNA Replication -Helix unzips from bottom to top -New nucleotide groups bond to old strand -Two new DNA double helixes form, each having 1 old & 1 new strand ====================== -Mutations (change in nucleotide sequence) can occur during process; ~1/10,000 nucleotides -Enzymes proofread/repair errors in sequencing -Other “agents” may cause sequencing errors: chemicals, UV radiation

14. 14 DNA Replication  DNA replication important for mitosis and meiosis  Occurs during S phase of interphase  Yields 2 identical DNA molecules  For growth/repair of somatic cells  Encodes the genetic information of organism  Enables genetic info to be passed to subsequent generations

15. 15 Is that all DNA does?  No, besides enabling genetic info to be passed to subsequent generations  DNA holds the code for all processes that the organism is able to perform  DNA codes for all the proteins that the organism can make So how does DNA “make” these proteins? Answer  RNA

16. 16 RNA Types  Messenger RNA – mRNA Single uncoiled chain  Transfer RNA – tRNA Single chain, folded into “cloverleaf” shape  Ribosomal RNA – rRNA RNA nucleotides in globular form, rRNA + proteins compose ribosomes

17. 17 mRNA  Single, uncoiled chain  Codon – set of 3 nucleotides

18. 18 tRNA -Cloverleaf structure -Anticodon sequence at bottom, matches up to codon sequence on mRNA -Amino Acid attached to 3’end

19. 19 rRNA -Ribosomes composed of nucleotides + proteins in globular form -Ribosomes are site of protein synthesis

20. 20 Transcription  Process of copying information on DNA to RNA & occurs in nucleus, 1 st step in protein synthesis  Steps:  1. Specific sections of DNA (genes) code for specific proteins, the beginning of a gene is marked by Promoters  2. RNA polymerase (primary transcription enzyme) recognizes the promoter and binds to it, DNA begins to “unzip” at that site

21. 21 Transcription steps, con’t.  3. RNA polymerase attaches to DNA nucleotide (promoter first) & begins adding complementary RNA nucleotides that match up  4. RNA polymerase moves from 5’ to 3’ direction, adding nucleotides and elongating the RNA strand  5. RNA polymerase reaches the termination signal, it breaks free from DNA strand  6. DNA zips up, mRNA moves from nucleus

22. 22 Transcription  Making of mRNA from DNA

23. 23 Translation  Process of assembling polypeptides (proteins) from info encoded on mRNA; 2 nd step in protein synthesis  Occurs at the ribosome in the cytoplasm  mRNA exits nucleus, joins to ribosome (which is composed of rRNA + proteins)

24. 24 Translation steps  1. mRNA to ribosome where it binds to ribosome  2. START codon is AUG Codes for methionine, signal to start  3. Some codons code for nothing – this signals process to start or stop  4. Ribosome moves along the mRNA strand to ‘read’ the codons  5. tRNA contains an anticodon that codes for an amino acid

25. 25 Translation, cont.  6. tRNA finds & attaches to a specific amino acid & brings it to the ribosome from cytoplasm  7. At the ribosome, matching mRNA codons to the tRNA anticodons occurs  8. As more tRNAs bring amino acids, peptide bonds form between them  9. As peptide bonds form, tRNAs drop away, tRNAs go find more amino acids  10. Ribosome continues to move along the mRNA strand and the protein is built

26. 26 Translation, cont.  11. When a STOP codon is encountered, the process stops, the protein is complete  12. Protein then collected for use in cell or export from cell  13. Protein undergoes refinement (structure & function) remove AUG folding (3D structure)  14. STOP codons are UAA, UAG, UGA

27. 27 Transcription: steps 1, 2 Translation: steps 3, 4

28. 28 CODONS in mRNA -Codon-group of 3 bases, code for An amino acid -Note 3 STOP Codons, UAA, UAG, UGA -Start codon is AUG -There are 64 codons -Codons are almost universal for all organisms

29. 29 Amino Acids Phenylalanine ProlineGlutamine Tryptophan LeucineThreonine Asparagine Arginine IsoleucineAlanineLysineSerine ValineTyrosineAspartic Acid Glutamic Acid SerineHistidineCysteineGlycine

30. 30 Overview  Understand similarities/differences of DNA & RNA  Understand DNA replication  Understand transcription  Understand translation

31. 31 Quiz #1  1. Name the components of DNA.  2. What are the names of the bases in DNA?  3. Name the base pair possibilities in DNA.  4. What type of bond joins the base pairs?  5. What is the result of DNA replication?

32. 32 Quiz Answers  1. nucleotides Sugar + phosphate + base pairs  2. thymine, adenine, guanine, cytosine  3. A-T, G-C  4. hydrogen  5. 2 identical DNA strands