1. Chapter 10 Nucleic Acids & Protein Synthesis

2. After completing the chapter on Genetics, we discussed the passing on of genes, but how are genes produced?

3. Brief history of DNA Frederick Griffith Frederick Griffith – 1928 Experimented with pneumonia bacteria called Streptococcus pneumoniae. There were two strains of the bacteria: 1 formed smooth colonies and caused pneumonia The other formed rough colonies and was harmless. Heat kills disease causing strain - mice don’t get pneumonia. Adds heat killed strain to the harmless strain injected into mice. The mice die. He cultures the bacteria. Finds that the harmless rough bacteria had been “transformed” or changed into the lethal strain.

4. Griffith’s Transformation Experiment

6. Conclusion The harmless bacteria were transformed by some factor from the harmful bacteria = this is called transformation Did not know what that factor was though

7. Oswald Avery 1944 Repeated Griffith’s work but used enzymes to destroy proteins in the heat killed bacteria. Pneumonia and transformation still occurred. Then used an enzyme to destroy RNA. Still transformed occurred. Finally, used an enzyme to break apart DNA. This stopped transformation!!!

9. Conclusion DNA is the nucleic acid that stores and transmits genetic information.

10. Hershey and Chase – 1952 Used T4 bacteriophage virus that infects E. coli bacteria A virus is a non-living pathogenic particle that can’t replicate on its own Capsid (protein)

11. The Lytic Cycle of Virus infectionLytic Cycle Attaches onto host cell Injects DNA into host cell Replication of Viral parts Reassembly of virons Lysis – bursting out

12. What part of a virus actually infects & causes the host cell to become a viral factory? Used radioactive isotopes of phosphorus and sulfur P 32 and S 35 Proteins do not have Phosphorus DNA doesn’t contain Sulfur

13. Used S 35 Used P 32 Found that the S 35 stayed outside the cell & P 32 ended up in new virons Animation

14. Conclusion The genetic material of the bacteriophage is located in the DNA, not the protein coat

15. Structure of DNA Structure of DNA Deoxyribonucleic acid Polymer of the monomer – Nucleotides Single nucleotide 5 carbon sugar –deoxyribose A phosphate group A nitrogen base S P N-base Nucleotide Sugar & phosphate alternate to make up the sides of the strand Found only in nucleus

16. Erwin Chargaff – 1940’s Noticed a pattern in the amounts of the four bases: Adenine, Guanine, Cytosine, and Thymine Found the number of Guanine & Cytosine nitrogen bases is always equal in DNA & the number of Thymine and Adenine is always equal. Didn’t know why though!

17. 4 nitrogen bases Guanine - Purine Cytosine - Pyrimidine Adenine - Purine Thymine - Pyrimidine Follow base pairing rule Adenine with Thymine Guanine with Cytosine Bases are held together by weak hydrogen bonds N-bases connect to sugars by a covalent bond

18. 5 Carbon sugar Phosphate group Nitrogen base Weak H bond Covalent bond

19. History of DNA History of DNA: Rosalind Franklin Rosalind Franklin took X-Ray diffraction photo of DNA.

20. Watson and Crick Watson and Crick (1953) Using Franklin’s photo, came up with the double helix form of DNA. Won Nobel Price w/ Maurice Wilkins (1962). Original DNA model.

23. So, how does DNA replicate? Occurs during S phase of interphase – DNA makes two exact copies of the original; if not, a mutation occurs. STEPS: 1.The double helix unwinds and flattens out (like a zipper) 2.An enzyme called DNA helicase (like the zipper slide) unzips the strand at the weak hydrogen bonds. This exposes the nitrogen bases (each tooth of the zipper). 3.Another enzyme called DNA polymerase will be responsible for rezipping the strands. It will take free nucleotides in the nucleus and bond them to the exposed bases, following the base pair ruling – G – C and A – T. EACH SIDE OF THE MOLECULE ACTS AS A TEMPLATE FOR A NEW STRAND. 4.The base pairing continues until the entire strand has their complement. 5.Now there are two identical strands of DNA http://highered.mcgraw- hill.com/sites/0072943696/student_view0/chapter3/animation__dna_replication__q uiz_1_.html

24. SUMMARY: * DNA helicase unzips the double strand * Original (old) strands of DNA are on the outside of the new strands – THESE ARE THE TEMPLATES * Replicates takes place in opposite directions with the help of DNA polymerase * Semi-conservative model

25. How good is DNA at replicating ? Accurate to about 1 error for every 1,000,000,000 base pairs. Why? Two reasons: complementarity and DNA polymerase, the “proofreader!” Gene Mutation – error resulting from misreading of DNA or problem in the transcription/translation process (We’ll revisit this later) Mutations in genes that control cell division or repair enzymes may cause cancer

26. The Flow of Genetic Information DNA cannot leave the nucleus – it uses a helper molecule called RNA DNA is the template for RNA = transcription RNA then directs the synthesis of proteins on ribosomes = translation DNA  RNA  protein

27. Ribonucleic acid RNA Ribonucleic acid The other Nucleic Acid Acts as a messenger between DNA and the ribosomes and carries out protein synthesis DNA is too large to get out of the nucleus; it is also protected in the nucleus from DNases. The cell uses RNA to bring its message to the rest of the cell for protein synthesis

28. How DNA & RNA Differ: * RNA is a single stranded molecule *RNA has ribose sugar instead of deoxyribose *RNA contains Uracil in place of Thymine so Adenine bonds with Uracil *RNA can be found in the nucleus, cytoplasm or at the ribosomes

29. Let’s Review!!! Ribosomes are small organelles that are involved with making proteins They are made up of proteins and rRNA They consist of two subunits – large and small Ribosomes are found both in the cytoplasm and on the endoplasmic reticulum

30. There are three different kinds of RNA Messenger RNA (mRNA) Formed in the nucleus and goes to the ribosomes; carries genetic code from DNA through the cytoplasm to the ribosomes Transfer RNA (tRNA) Shaped like T; carries amino acids to the mRNA on the ribosomes Ribosomal RNA (rRNA) Most abundant; found in globular form (like a big glob) and makes up the ribosomes

31. The Process of Protein Synthesis * Process by which DNA codes for the production of proteins (polypeptide chains) and protein assembly - Polypeptide chains are polymers of the 20 different amino acids. - Uses a genetic code – chemical letters in RNA that make up words which code for particular amino acids - Check your understanding: what happens if the letters change?

32. Transcription Translation Polypeptide forming Amino Acid

33. Part I. Transcription of DNA into mRNA (the message) DNA flattens and is unzipped exposing its bases (template) – sound familiar? RNA polymerase binds free RNA nucleotides to exposed DNA bases starting at a promoter – a specific DNA nucleotide pattern Complementary base pairing occurs, EXCEPT THERE IS NO THYMINE IN RNA. Instead, Adenine bonds with Uracil just as Thymine from DNA would bond with Adenine. Transcription continues until a termination signal is given (punctuation) to stop the transcription process If DNA reads: ATC GTC GAT TGG C AA mRNA: UAG CAG CUA ACC GUU mRNA leaves the nucleus through a pore to go out into the cytosol to locate a ribosome FYI – any of the three types of RNA are made this way http://www- class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2. html http://www- class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2. html

34. The Genetic Code: Where a group of 3 nucleotide bases translates into a particular amino acid This 3 “letter word” is called a codon Codons are groups of 3 adjacent bases on mRNA (AAA, CCC GGG) Each codon will specify a specific amino acid. When the codon is recognized by the anticodon, this is called Translation There are 64 different codons with punctuation as well for start and stop

35. Start codon Stop Codons

36. About the genetic code… Codons are code words found in mRNA Codons code for particular amino acids Three of the 64 codons are stop, one is start – AUG = methionine The code is degenerate – more than one codon can code for an amino acid – why is this important? The code is UNIVERSAL!!!

37. The questions are: what is an anticodon and how does the amino acid get selected?

38. Part II. Translation of mRNA into protein * At the ribosome, the process of translation occurs. Several ribosomes may undergo this process at one time mRNA will temporarily bind with the two ribosomal subunits tRNA is waiting in the cytoplasm with its corresponding amino acid Starting with the start codon (AUG), in groups of 3, mRNA will determine which amino acid tRNA must bring to the ribosome. Animation – Virtual CellVirtual Cell

39. Transcription Translation Polypeptide forming

40. Once tRNA brings the correct amino acid to mRNA at the ribosome, it releases and goes back to the cytoplasm to pick up it corresponding amino acid Adjacent amino acids bond together, making a peptide bond to form a polypeptide. Chain could be up to 10,000 amino acids long This continues until the entire message is translated. The chain of amino acids is formed called a polypeptide (protein). The translation ends when a STOP codon is reached (UAA, UAG, UGA).

41. When things go wrong: Does this process ever make a mistake? Have you ever had to copy a large amount of information? What is the likelihood of you making a mistake or more? What could cause these changes?

42. Changes in genetic material Gene Mutations: alters one or more genes Chromosomal Mutations: alter the entire chromosome or a portion of it.

43. Gene Mutations Point Mutations Point Mutations – affect only one amino acid Frameshift mutations Frameshift mutations – May affect an entire amino acid sequence.

44. Point mutation involves a change in one or a few nucleotides. Influences a single amino acid in the polypeptide change; caused by a substitution of a nitrogen base. Sickle cell anemia is an example of this – GUG instead of GAG Valine instead of glutamic acid

45. THE FAT CAT ATE THE RAT Take out “C” in Cat & substitute a “B” THE FAT BAT ATE THE RAT In this case, it does not really change the meaning to the sentence or the protein formed

46. If DNA reads: A T G G T C G A T T G G CAA mRNA: U A C C A G C U A AC C GUU Amino Acid: Tyrosine - Glutamine – Leucine -Threonine – Valine But if mRNA: U A C C A G C A A AC C GUU The AA: Tyrosine – Glutamine – Glutamine – Threonine – Valine

47. Frameshift mutation involves a change in the entire protein formed or a large portion of it. Caused by insertions (additions) or deletions of nitrogen bases. Tay-Sachs is a disease caused by a frameshift mutation

48. THE FAT CAT ATE THE RAT Take out “E” in THE & group into 3’s THF ATC ATA TET HER AT_ This makes no sense at all!!

49. If DNA reads: A T G G T C G A T T G G CAA mRNA: U A C C A G C U A AC C GUU AA: Tyrosine - Glutamine – Leucine -Threonine – Valine BUT if mRNA: U A C C A G U A A C C G U U _ THEN Amino Acid: Tyrosine - Glutamine – STOP!!!! The entire sentence makes no sense. The protein formed would be totally different

50. So which form of a mutation would be more severe? Frameshift mutation … Frameshift mutation … since an entirely new protein would be formed

51. CHROMOSOMAL MUTATIONS involve changes in number and structure of the chromosomes. Could change location of genes on the chromosomes or the number of copies of some of the genes.

52. Deletions – part of a chromosome is missing Duplications – Extra copies of genes are inserted Inversions – Reverse direction of parts of the chromosome Chromosomal Mutations animation

53. Parts of one non-homologous chromosome breaks off and attached onto another non-homologous chromosome Translocations