1. Molecular Biology of the Gene DNA Structure and Function

2. History of DNA 1869 Johann Friedrich Miescher 1924 Microscope studies using stains for DNA and protein show that both substances are present in chromosomes. 1952 Alfred Hershey and Martha Chase

3. SCIENTIFIC DISCOVERY: DNA is a double-stranded helix  Erwin Chargaff  Rosalind Franklin / Maurice Wilkins  James Watson and Francis Crick  In 1962, the Nobel Prize

4. SCIENTIFIC DISCOVERY: Experiments showed that DNA is the genetic material  Until the 1940s, the case for proteins serving as the genetic material was stronger than the case for DNA. –Proteins are made from ____different amino acids. –DNA was known to be made from just ____ kinds of nucleotides.  Studies of bacteria and viruses –ushered in the field of molecular biology, the study of heredity at the molecular level, and –revealed the role of DNA in heredity.

5. DNA and RNA are polymers of nucleotides  DNA and RNA are nucleic acids.  The building blocks or monomers of nucleic acids are ____________________  A nucleotide is composed of a –_________________ –__________________  The nucleotides are joined to one another by a bond creating the sugar-phosphate backbone.

7. A A A A A A A C T T T T T T C C C C G G G G G C CG A T A DNA double helix T DNA nucleotide Covalent bond joining nucleotides A C T Two representations of a DNA polynucleotide G G G G C T Phosphate group Sugar (deoxyribose) DNA nucleotide Thymine (T) Nitrogenous base (can be A, G, C, or T) Sugar Nitrogenous base Phosphate group Sugar-phosphate backbone

8. 4 Different Types of Nucleotides Found in DNA

9. Base pair Hydrogen bond Partial chemical structure Computer model Ribbon model

10. 3’ and 5’ ends of nucleotide strand

11. Purine or pyrimidine ? Hydrogen bonds hold the 2 strands together

12. 2 General Functions for DNA 1. 2.

13. DNA replication depends on specific base pairing  In their description of the structure of DNA, Watson and Crick noted that the structure of DNA suggests a possible copying mechanism.  DNA replication follows a semiconservative model.

14. DNA Replication SEMICONSERVATIVE 1. Helix unwinds 2. 2 strands separate 3. Free nucleotides bind to open bases according to pairing rules (parent strand acts as template) 4. 2 identical strands consist of one parent strand and one newly formed strand.

15.  DNA replication begins at the origins of replication where –DNA unwinds at the origin to produce a “bubble,” –replication proceeds in both directions from the origin, and –replication ends when products from the bubbles merge with each other.  DNA replication occurs in the 5 to 3 direction. –Replication is continuous on the 3 to 5 template. –Replication is discontinuous on the 5 to 3 template, forming short segments. DNA replication proceeds in two directions at many sites simultaneously

16. Leading and Lagging strands Why? DNA polymerases can only assemble new strands in the 5’-> 3’ direction, need a 3’ end (-OH) provided by RNA primer.

18. Overall direction of replication DNA ligase Replication fork Parental DNA DNA polymerase molecule This daughter strand is synthesized continuously This daughter strand is synthesized in pieces 3 5 3 5 3 5 3 5

19. DNA replication proceeds in two directions at many sites simultaneously  Key proteins are involved in DNA replication. –Helicase –DNA Polymerases- –Primase –Proofreader –DNA ligase

20. Parental DNA molecule Origin of replication “Bubble” Parental strand Daughter strand Two daughter DNA molecules

21. http://207.207.4.198/pub/flash/24/menu.swf ANIMATION…Replication http://highered.mcgraw-hill.com/olc/dl/120076/bio23.swf http://www.phschool.com/science/biology_place/biocoach/dnarep/intro.html

22. DNA Repair

23. DNA processes Replication Protein Synthesis –Transcription –Translation

24. Protein Functions…. Metabolism (enzymes are proteins) Structural (build form) Transport (ex- hemoglobin) Protection (antibodies are proteins) Cell communication (hormones)

25. Review of Protein Structure… Only 20 different common amino acids Structure determines function ! Hundreds of thousands of different proteins !

26. The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits  DNA specifies traits by dictating protein synthesis.  The molecular chain of command is from –DNA in the nucleus to RNA and –RNA in the cytoplasm to protein.  __________________ is the synthesis of RNA under the direction of DNA.  __________________ is the synthesis of proteins under the direction of RNA.

27. 3 parts of RNA (the other nucleic acid) nucleotide sugar = _________ phosphate group nitrogenous base (A,U,C,G) U=Uracil Nucleotides: 2 types DNA & RNA

28. 3 Types of RNA Required for Protein Synthesis mRNA= messenger RNA tRNA= transfer RNA rRNA= ribosomal RNA

29. DNA NUCLEUS CYTOPLASM RNA Transcription Translation Protein

30. T Strand to be transcribed A C T TC A A A A A T DNA AA T C T T T T GAG G RNA Transcription AAAA U U U U U G G G Translation Polypeptide MetLysPhe Stop codon Start codon

31. The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits The connections between genes and proteins –The initial one gene–one enzyme hypothesis was based on studies of inherited metabolic diseases. –The one gene–one enzyme hypothesis was expanded to include all proteins. –Most recently, the one gene–one polypeptide hypothesis recognizes that some proteins are composed of multiple polypeptides.

32. Transcription- overview  Transcribing (writing) information from DNA  Takes place in the nucleus  Promoter region is recognized by RNA polymerase as a start location  Assembles mRNA strand mRNA

33. RNA polymerase Free RNA nucleotides Template strand of DNA Newly made RNA Direction of transcription T G A G G A A U C CA C T T A A C C G G U T U T A ACC T A T C TRANSCRIPTION

34. RNA polymerase DNA of gene Promoter DNA Initiation 1 2 Terminator DNA 3 Elongation Area shown in Figure 10.9A Termination Growing RNA RNA polymerase Completed RNA

35. Genetic information written in codons is translated into amino acid sequences  The sequence of nucleotides in DNA provides a code for constructing a protein.

36. Transcription produces genetic messages in the form of RNA  Overview of transcription –An RNA molecule is transcribed from a DNA template by a process that resembles the synthesis of a DNA strand during DNA replication. –RNA nucleotides are linked by the transcription enzyme RNA polymerase. –Specific sequences of nucleotides along the DNA mark where transcription begins and ends. –The “start transcribing” signal is a nucleotide sequence called a promoter.

37. Transcription produces genetic messages in the form of RNA –Transcription begins with initiation, as the RNA polymerase attaches to the promoter. –During the second phase, elongation, the RNA grows longer. –As the RNA peels away, the DNA strands rejoin. –Finally, in the third phase, termination, the RNA polymerase reaches a sequence of bases in the DNA template called a terminator, which signals the end of the gene. –The polymerase molecule now detaches from the RNA molecule and the gene.

38. DNA Cap Exon IntronExon RNA transcript with cap and tail ExonIntron Transcription Addition of cap and tail Introns removed Tail Exons spliced together Coding sequence NUCLEUS CYTOPLASM mRNA POST-TRANSCRIPTIONAL MODIFICATION

39.  Eukaryotic mRNA –RNA splicing –Additions- cap and tail Post-Transcriptional Modification: Eukaryotic RNA is processed before leaving the nucleus as mRNA

40. Post-Transcriptional Modification: Eukaryotic RNA is processed before leaving the nucleus as mRNA  Messenger RNA (mRNA) –encodes amino acid sequences and –conveys genetic messages from DNA to the translation machinery of the cell, which in –prokaryotes, occurs in the same place that mRNA is made, but in –eukaryotes, mRNA must exit the nucleus via nuclear pores to enter the cytoplasm. –Eukaryotic mRNA has –introns, interrupting sequences that separate –exons, the coding regions.

41. Genetic information written in codons is translated into amino acid sequences The flow of information from gene to protein is based on a triplet code: the genetic instructions for the amino acid sequence of a polypeptide chain are written in DNA and RNA as a series of nonoverlapping three-base “words” called codons. Each amino acid is specified by a codon. –64 codons are possible. –Some amino acids have more than one possible codon.

42. Transfer RNA molecules serve as interpreters during translation  Transfer RNA (tRNA)

43. Ribosomes build polypeptides  rRNA and proteins make up the ribosome.  Translation occurs on the surface of the ribosome

44. The genetic code dictates how codons are translated into amino acids  Characteristics of the genetic code –_______ nucleotides specify one amino acid. –61 codons correspond to amino acids. –AUG is the start codon; codes for methionine and signals the start of transcription. –3 “stop” codons signal the end of translation; _____, ____, ____ –__________- with more than one codon for some amino acids –_______________- the genetic code is shared by organisms from the simplest bacteria to the most complex plants and animals

45. GENETIC CODE

46. Practice DNA is TACAGGCGATGGATT mRNA is ____________________ Divide into codons (reading frames) Amino acids coded for are:

47. An initiation codon marks the start of an mRNA message (Initiation)  Translation can be divided into the same three phases as transcription: 1.initiation, 2.elongation, and 3.termination.  Initiation brings together…

48. An initiation codon marks the start of an mRNA message (Initiation)  Initiation establishes where translation will begin.  Initiation occurs in two steps. 1.An mRNA molecule binds to a small ribosomal subunit and the first tRNA binds to mRNA at the start codon. –The start codon reads AUG and codes for methionine. –The first tRNA has the anticodon UAC. 2.A large ribosomal subunit joins the small subunit, allowing the ribosome to function. –The first tRNA occupies the P site, which will hold the growing peptide chain. –The A site is available to receive the next tRNA.

49. Elongation adds amino acids to the polypeptide chain  Once initiation is complete, amino acids are added one by one to the first amino acid.  Elongation is the addition of amino acids to the polypeptide chain.

50.  Each cycle of elongation has three steps. 1.Codon recognition: The anticodon of an incoming tRNA molecule, carrying its amino acid, pairs with the mRNA codon in the A site of the ribosome. 2.Peptide bond formation: The new amino acid is joined to the chain. 3.Translocation: tRNA is released from the P site and the ribosome moves tRNA from the A site into the P site. Elongation adds amino acids to the polypeptide chain

51. Polypeptide mRNA Codon recognition Anticodon Amino acid Codons P site A site 1 Peptide bond 2 formation Translocation 3 New peptide bond Stop codon mRNA movement Elongation

52.  Termination stage of translation, when –the ribosome reaches a stop codon, –the completed polypeptide is freed from the last tRNA, and –the ribosome splits back into its separate subunits. Elongation adds amino acids to the polypeptide chain until a stop codon; Termination

53. Other Helpful Animations….  http://highered.mcgraw-hill.com/sites (there are selections at this site that will help with replication, transcription and translation) http://highered.mcgraw-hill.com/sites

54. DNA Transcription mRNA RNA polymerase Transcription Translation Amino acid Enzyme CYTOPLASM Amino acid attachment 2 1 3 4 tRNA ATP Anticodon Initiation of polypeptide synthesis Elongation Large ribosomal subunit Initiator tRNA Start Codon mRNA Growing polypeptide Small ribosomal subunit New peptide bond forming Codons mRNA Polypeptide Termination 5 Stop codon Review: The flow of Genetic information in the cell is DNA RNA Protein

55. Mutations can change the meaning of genes  A mutation is any change in the nucleotide sequence of DNA.  Mutations can involve –large chromosomal regions or –just a single nucleotide pair.  Mutations can be spontaneous (mistakes during replication) or caused by mutagens. Examples- UV light, chemicals

56. . A mutation can be: –Harmful, giving rise to cancers. –Cause genetic disorders (if in sperm or egg) –Create new traits/variation in the species Mutations can change the meaning of genes

57. Normal hemoglobin DNAMutant hemoglobin DNA mRNA Sickle-cell hemoglobin Normal hemoglobin Glu Val C T T G A A CT GA A U

58. Normal gene Nucleotide substitution Nucleotide deletion Nucleotide insertion Inserted Deleted mRNA Protein Met Lys Phe Lys Phe Ala Gly Ser AUGAAGUUU GGC G CA GC G CA A G UUU AUGAA Met Lys Ala His Leu GUU AUGAA GGC G CA U U Met Lys Ala His Leu GUU AUGAA G G C UG G C

59. 1.Compare the structures of DNA and RNA. 2.State the contributions of Chargaff, Franklin, Wilkins, Watson and Crick to our understanding of DNA. 3.Describe the process of DNA replication. State the role of helicase, DNA polymerases, primase, and DNA ligase 4.Describe the general purpose of protein synthesis; relate DNA sequence to the specific protein produced. You should now be able to

60. 5.State the general flow of genetic information as genes are expressed. 6.Explain transcription and how mRNA is produced using DNA. 7.Explain how eukaryotic RNA is processed before leaving the nucleus. 8.Discuss the role of mRNA, tRNA and rRNA in translation. 9.Explain translation; initiation, elongation, translocation and termination. You should now be able to

61. 10.Describe the structure and function of ribosomes 11..Define mutation, causes of mutations, and potential consequences. 12. State the amino acid sequence in a polypeptide given the mRNA. You should now be able to © 2012 Pearson Education, Inc.

62. DNA (b) is a polymer made from monomers called is performed by an enzyme called (c) (a) (d) (e) (f) comes in three kinds called use amino-acid-bearing molecules called is performed by structures called (h) molecules are components of RNA Protein (g) (i) one or more polymers made from monomers called