Molecular Genetics

1. Molecular Genetics

2. DNA: The Genetic Material MAIN IDEA: The discovery that DNA is the genetic code involved many experiments.

3. Rosalind Franklin • Used X-ray crystallography to study DNA (pattern made when x-rays bombard them) • Franklin concluded: DNA is a double helix

4. Watson and Crick • Heard of Franklin’s work before she published it • Used her X-ray diffraction pictures and other mathematical data • Designed the 3-D model of DNA

5. DNA Structure • Double helix (twisted ladder) • Outside: sugar (deoxyribose) and phosphate • Rungs: nitrogenous bases • Adenine, guanine, cytosine, and thymine • A-T, G-C

9. Do Now • One strand of DNA has the following sequence of nitrogen bases: • ATTCGTAGCTAGCTAAC • What is the sequence of nitrogenous bases on the complementary strand of DNA? • How did scientists depend on each other to discover DNA?

10. Answer • ATTCGTAGCTAGCTAAC • The complementary strand is: • TAAGCATCGATCGATTG

11. 12.2: Replication of DNA MAIN IDEA: DNA replicates by making a strand that is complementary to each original strand.

12. DNA Replication • Occurs during S phase of mitosis/meiosis • DNA must make an exact duplicate of itself • “mistakes” (changes in the genetic code) = mutations

13. Semiconservative Replication • Process proposed by Watson and Crick • Original strands of DNA separate, serve as templates (patterns), and produce new DNA with one old strand and one new strand

15. Step 1: Unwinding • DNA helix must first untwist and “unzip” (H-bonds break between nitrogen bases)

16. Step 2: Base Pairing • Add new, complementary nucleotides to either side

18. Step 3: Joining • DNA replication may start at many different places on one chromosome • These sections must then be joined together when complete

19. Result of Replication • 2 identical DNA molecules • Each molecule: one old strand and one complementary new strand • Semi-conservative

20. 12.3: DNA, RNA, and Protein MAIN IDEA: DNA codes for RNA, which guides protein synthesis.

21. Protein Synthesis • DNA codes for RNA, which codes for building proteins • One gene directs the synthesis of one protein

22. DNA Has two strands Has thymine, not uracil Cannot leave nucleus Bigger than RNA Only 1 type Has sugar deoxyribose RNA Has one strand Has uracil, not thymine Can leave nucleus Smaller than DNA 3 types Has sugar ribose DNA and RNA

23. BOTH DNA and RNA • Both… • Are made of nucleotides • Have adenine, cytosine, and guanine • Carry genetic code • Are nucleic acids

24. Types of RNA • 3 types: • Messenger RNA (mRNA) – takes DNA’s message from nucleus to ribosome • Ribosomal RNA (rRNA) – makes up the ribosome and helps make protein • Transfer RNA (tRNA) – brings amino acids (protein parts) to ribosome

25. Transcription • DNA cannot leave nucleus, but RNA can • DNA is first transcribed (copied) into mRNA in the nucleus • DNA unzips, and complementary mRNA strand is made • RNA nucleotides attached according to base-pairs

26. Transcription

27. Practice transcription • DNA code: TTTAGGCATCCG • What’s the complementary RNA code?

28. Translation • mRNA leaves nucleus through nuclear pores goes to cytoplasm • mRNA joins ribosomes, and is translated into a protein • tRNA brings over the appropriate amino acid • Each amino acid joins to make a chain  protein!

29. Reading the Code • Codon – 3-base code of DNA • Each codon = 1 amino acid of protein chain • 64 codons, but only 20 amino acids • Some codons are repetitive and code for the same amino acids • Some start and end the protein

31. Practice • mRNA code: AUGCGGAUUUGA • Separate into codons • Use the chart to translate • Write the amino acids in the chain

32. Summary • One gene codes for one protein • Transcription (in nucleus)– DNA copied to mRNA • Translation (in cytoplasm)– ribosomes translate mRNA, and tRNA attaches amino acids to make proteins

33. Checkpoint • What are the 3 types of RNA and what do they do? • How many proteins does one gene make? • What is transcription? • What is translation? • Draw a diagram, concept map, etc to explain how DNA and RNA work together to make proteins.

34. Gene Regulation and Mutations Chapter 12.4

35. Gene Regulation • Gene expression is regulated by the cell; mutations can affect this expression

36. Mutations • Change in DNA sequence, either a single base pair (point mutation) or a large segment of DNA • Can cause alternate phenotypes, diseases/disorders, non-functioning proteins • Caused by mutagens

37. Point Mutations • Substitution – one base pair exchanged for a different one • Can cause missense – wrong amino acid is used • Can cause nonsense – codes for a stop codon and ends protein synthesis early

38. Examples NORMAL: THE BIG FAT CAT ATE THE WET RAT MISSENSE SUBSTITUTION: THE BIZ FAT CAT ATE THE WET RAT NONSENSE SUBSTITUTION: THE BIG RAT

39. Point Mutations cont’d • Deletion – one base pair eliminated • Insertion – one base pair added • Both result in frameshift, which is a change in the groups of 3 bases making codons

40. Examples NORMAL: THE BIG FAT CAT ATE THE WET RAT DELETION (FRAMESHIFT): THB IGF ATC ATA TET HEW ETR AT INSERTION (FRAMESHIFT): THE BIG ZFA TCA TAT ETH EWE TRA

41. Large Section Mutations • Larger sections of DNA can be: • Deleted • Inserted • Inverted (made backwards) • Translocated (moved to a different section or chromosome) • Duplicated (copied again) • Tandem repeats (copied many times)

42. Think… • What would be the result of a missense substitution mutation to an intron? • What would most likely be the result of a mutation in the last base position of a codon?