1. 1 Nucleic acids are made of nucleotides similar to how proteins are made of amino acids each nucleotide consists of 3 parts –a 5 carbon sugar (deoxyribose or ribose) –a phosphate group –a nitrogenous base (adenine, thymine, cytosine, guanine, and uracil)

2. 2 Nucleotides are derived from Nucleosides each nucleoside consists of 3 parts –a 5 carbon sugar (deoxyribose or ribose) –a nitrogenous base (adenine, thymine, cytosine, guanine, and uracil) –three phosphate group –The energy from releasing the two phosphate groups to form the nucleotide is used for the process of DNA/RNA synthesis

3. 3 Nucleotide AMP Sugar 3’ end Phosphate Group Nitrogen Base (Adenine) 5’ end

4. 4 Nucleoside NTP Sugar 3’ end Phosphate Group Nitrogen Base (Adenine)

5. 5 DNA structure 2 strands twisted into a helix sugar -phosphate backbone nitrogenous bases form steps in ladder –constancy of base pairing –A binds to T with 2 hydrogen bonds –G binds to C with 3 hydrogen bonds antiparallel strands 3’to 5’ and 5’to 3’ each strand provides a template for the exact copying of a new strand order of bases constitutes the DNA code

6. 6 Significance of DNA structure 1.Maintenance of code during reproduction. Constancy of base pairing guarantees that the code will be retained. 2.Providing variety. Order of bases responsible for unique qualities of each organism.

7. 7

8. 8 Genetics – the study of heredity 1.transmission of biological traits from parent to offspring 2.expression & variation of those traits 3.structure & function of genetic material 4.how this material changes

9. 9 Levels of genetic study

10. 10 Levels of structure & function of the genome genome – sum total of genetic material of an organism (chromosomes + mitochondria/chloroplasts and/or plasmids) –genome of cells – DNA –genome of viruses – DNA or RNA chromosome – length of DNA containing genes gene- fundamental unit of heredity responsible for a given trait –site on the chromosome that provides information for a certain cell function –segment of DNA that contains the necessary code to make a protein or RNA molecule

11. 11 Genomes vary in size smallest virus – 4-5 genes E. coli – single chromosome containing 4,288 genes; 1 mm; 1,000X longer than cell Human cell – 46 chromosomes containing 31,000 genes; 6 feet; 180,000X longer than cell

12. 12

13. DNA replication is semiconservative because each chromosome ends up with one new strand of DNA and one old strand.

14. 14 Semi-conservative replication of DNA

15. 15 DNA replication Begins at an origin of replication Helicase unwinds and unzips the DNA double helix An RNA primer is synthesized DNA polymerase III adds nucleotides in a 5’ to 3’ direction Leading strand – synthesized continuously in 5’ to 3’ direction Lagging strand – synthesized 5’ to 3’ in short segments; overall direction is 3’ to 5’

16. 16 Bacterial replicon

17. 17 Flow of genetic information

18. 18 What are the products that genes encode? –RNAs and proteins How are genes expressed? –transcription and translation

19. 19 Gene expression Transcription – DNA is used to synthesize RNA –RNA polymerase is the enzyme responsible Translation –making a protein using the information provided by messenger RNA –occurs on ribosomes

20. 20 Genotype - genes encoding all the potential characteristics of an individual Phenotype -actual expressed genes of an individual (its collection of proteins)

21. 21 DNA-protein relationship 1.Each triplet of nucleotides (codon) specifies a particular amino acid. 2.A protein’s primary structure determines its shape & function. 3.Proteins determine phenotype. Living things are what their proteins make them. 4.DNA is mainly a blueprint that tells the cell which kinds of proteins to make and how to make them.

22. 22 DNA-protein relationship

23. 23 3 types of RNA messenger RNA (mRNA) transfer RNA (tRNA) ribosomal RNA (rRNA)

24. 24

25. 25 DNA RNA PROTEINS Transcription RNA polymerase Translation ribosomes

26. 26 Transcription 1.RNA polymerase binds to promoter region upstream of the gene 2.RNA polymerase adds nucleotides complementary to the template strand of a segment of DNA in the 5’ to 3’ direction 3.Uracil is placed as adenine’s complement 4.At termination, RNA polymerase recognizes signals and releases the transcript 100-1,200 bases long

27. 27 Transcription

28. 28 Translation Ribosomes assemble on the 5’ end of a mRNA transcript Ribosome scans the mRNA until it reaches the start codon, usually AUG A tRNA molecule with the complementary anticodon and methionine amino acid enters the P site of the ribosome & binds to the mRNA

29. 29 Translation

30. 30

31. 31 Interpreting the DNA code

32. 32 Translation elongation A second tRNA with the complementary anticodon fills the A site A peptide bond is formed The first tRNA is released and the ribosome slides down to the next codon. Another tRNA fills the A site & a peptide bond is formed. This process continues until a stop codon is encountered.

33. 33

34. 34 Translation termination Termination codons – UAA, UAG, and UGA – are codons for which there is no corresponding tRNA. When this codon is reached, the ribosome falls off and the last tRNA is removed from the polypeptide.

35. 35 Polyribosomal complex

36. 36 Eucaryotic transcription & translation differs from procaryotic 1.Do not occur simultaneously. Transcription occurs in the nucleus and translation occurs in the cytoplasm. 2.Eucaryotic start codon is AUG, but it does not use formyl-methionine. 3.Eucaryotic mRNA encodes a single protein, unlike bacterial mRNA which encodes many. 4.Eucaryotic DNA contains introns – intervening sequences of noncoding DNA- which have to be spliced out of the final mRNA transcript. 5.A 5’ cap and polyA tail are added to eucaryotic RNA.

37. 37 Split gene of eucaryotes

38. Regulation of protein synthesis & metabolism

39. 39 Operons a coordinated set of genes, all of which are regulated as a single unit. 2 types –inducible – operon is turned ON by substrate: catabolic operons- enzymes needed to metabolize a nutrient are produced when needed –repressible – genes in a series are turned OFF by the product synthesized; anabolic operon – enzymes used to synthesize an amino acid stop being produced when they are not needed

40. 40 Lactose operon: inducible operon Made of 2 segments: 1.Control locus- composed of promoter and operator 2.Structural locus- made of 3 genes each coding for an enzyme needed to catabolize lactose –  -galactosidase – hydolyzes lactose permease - brings lactose across cell membrane  -galactosidase transacetylase – uncertain function Regulator- gene that codes for repressor Not part of the operon

41. 41 Lac operon Normally off –In the absence of lactose the repressor binds with the operator locus and blocks transcription of downstream structural genes Lactose turns the operon on –Binding of allolactose to the repressor protein changes its shape and causes it to fall off the operator. RNA polymerase can bind to the promoter. Structural genes are transcribed.

42. 42 Lactose operon

43. 43 Tryptophan operon: repressible Normally on and will be turned off when nutrient is no longer needed. When excess tryptophan is present, it binds to the repressor and changes it. Then the repressor binds to the operator and blocks tryptophan synthesis.

44. 44 Repressible operon (a) Operon On. A repressible operon remains on when its nutrient products (here tryptophan) are in great demand by the cell because the repressor is unable to bind to the operator at low nutrient levels. (a) Operon Off. The operon is repressed when (1) tryptophan builds up and, serving as a corepressor, activates the repressor. (2) The repressor complex binds to the operator and blocks RNA polymerase from transcribing the genes for tryptophan biosynthesis Enzymes synthesize tryptophan Tryptophan immediately used in metabolism Tryptophan accumulates Tryptophan synthesis inhibited

45. 45 www.ndsu.nodak.edu/.../ prokaryo/prokaryo3.htm

46. 46 Antibiotics that affect gene expression Rifamycin – binds to RNA polymerase Actinomycin D - binds to DNA & halts mRNA chain elongation Erythromycin & spectinomycin – interfere with attachment of mRNA to ribosomes Chloramphenicol, linomycin & tetracycline-bind to ribosome and block elongation Streptomycin – inhibits peptide initiation & elongation

47. 47 Mutations – changes in the DNA Point mutation – addition, deletion or substitution of a few bases Missense mutation – causes change in a single amino acid Nonsense mutation – changes a normal codon into a stop codon Silent mutation – alters a base but does not change the amino acid

48. 48 Excision repair

49. 49 Ames Test

50. 50 Types of intermicrobial exchange conjugationrequires the attachment of two related species & formation of a bridge that can transport DNA transformationtransfer of naked DNA transductionDNA transfer mediated by bacterial virus

51. 51 conjugation

52. 52 transformation

53. 53 Generalized transduction

54. 54 Specialized transduction

55. 55 Transposons –DNA segments that shift from one part of the genome to another

56. 56 Applications of mechanisms of genetic variation Whether it is conjugation, transduction or transformation, scientists have used these or modification of these methods for research. Scientists have also used transposons and chemicals and radiation for inducing mutations in many different organisms (incuding bacteria) to study the effect of those mutations on those organisms. The field of molecular biology/genetic engineering and biotechnology have been made possible by using these mechanisms as tools.