Microbial Genetics

1. Microbial Genetics

2. Microbial Genetics Genetics is the study of heredity which is concerned with how: • information in nucleic acids is expressed • nucleic acids are duplicated and transmitted to progeny • these processes account for the characteristics of progeny

3. Nucleic Acids • The heredity material found in cells • Large molecules that are acidic in nature • Associated with the nuclear material of cells

4. Nucleic Acids Two types Deoxyribonucleic Acid Ribonucleic Acid

5. Deoxyribonucleic Acid Is responsible for all cellular activity. Directs the production of proteins. Is double stranded and helical. Is maintained by hydrogen bonds (weak bonds) Is very stable and can survive • Temperatures as high as 70 C • High salt concentrations • Acid environments

6. Ribonucleic Acid • Ribonucleic acid (RNA) is a biologically important type of molecule that consists of a long chain of nucleotide units. • Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate. RNA is very similar to DNA, but differs in a few important structural details: in the cell, RNA is usually single-stranded.

7. Ribonucleic Acid Three types of RNA • mRNA messenger • tRNA transfer • rRNA ribosomal

8. Ribonucleic Acid mRNA messenger Is complementary to one strand of DNA and functions to carry the genetic material from the chromosome to the ribosome. Transcription

9. Ribonucleic Acid tRNA transfer Is responsible to transfer information from mRNA to rRNA. Translation

10. Ribonucleic Acid rRNA ribosomal Is associated with the ribosome and accepts information from tRNA and correlates the information to synthesize proteins. Protein Synthesis

11. Nucleic Acids Are constructed from a string of small molecules called Nucleotides. Nucleotides consist of a 5-carbon sugar (pentose), one or more phosphate groups, and a base containing nitrogenous rings.

12. Base Types Purines Contain 2 nitrogenous rings Adenine and Guanine

13. Base Types Pyrimidines Contain 1 nitrogenous ring Cytosine and Thymine in DNA Uracil replaces Thymine in RNA

14. Rules for Base Pairings Adenine always pairs with Thymine in DNA (A-T) Uracil replaces Thymine in RNA Guanine always pairs with Cytosine (G-C) and are stronger bonds.

15. Central Dogma Theory The central dogma theory of molecular biology is represented by a simple pathway: DNA— >RNA-->protein, which demonstrates the flow of genetic information in a living cell. The major processes involved in this pathway are replication, transcription, and translation.

16. Central Dogma Theory In DNA replication, the DNA polymerase enzyme replicates all the DNA in the nuclear genome in a semi-conservative manner, meaning that the double stranded DNA is separated into two and a template is made by DNA polymerase. This allows genomic material to be duplicated so it can be evenly partitioned between two somatic cells (daughter cells) upon division.

17. Central Dogma Theory The process in which DNA is copied into RNA by RNA Polymerase is called transcription. Three forms of RNA are produced here: messenger RNA (mRNA), ribosomal RNA (rRNA), and t ransfer RNA (tRNA).

18. Central Dogma Theory Summary 1. DNA guides the synthesis of mRNA which in turn directs the order in which amino acids are assembled into proteins. 2. DNA directs its own replication by giving rise to two complete, identical DNA molecules. This replication is necessary because each cell must inherit a complete set of all genes in order to carry out the cell’s life processes.

19. Reverse Transcriptase Another process in this pathway is reverse transcription, which involves copying RNA information into DNA using reverse transcriptase.

20. Reverse Transcriptase Recently, this processes has been defined and may expand the central dogma. For example, retroviruses use the enzyme "reverse transcriptase" to transcribe DNA from a RNA template. The viral DNA then integrates into the nucleus of the host cell. Then it is transcribed, and further translated into proteins. This biological process effectively adds another pathway to the central dogma of molecular biology.

21. DNA Replication in Bacteria Bacteria contain 1 chromosome Many contain plasmids When bacterial chromosomes replicate both strands are duplicated. Each strand functions as a template. During replication, enzymes known as polymerases transport nucleotides from the cytoplasm that are complimentary to the template and fit them into place, resulting in two strands, one parental and one new one

22. DNA Replication in Bacteria During replication, enzymes known as polymerases transport nucleotides from the cytoplasm that are complimentary to the template and fit them into place, resulting in two strands, one parental and one new one. The replication is said to be semi- conservative because the parental strand is conserved (remains the same ).

23. Steps of DNA Replication • DNA unwound with enzyme (replication fork) • Complementary bases added to template (parent strand) using enzyme • Replication fork moves down strand • Newly replicated DNA rewinds • Process called Semiconservative Replication

24. Steps of DNA Replication Copied in 5’ to 3’ direction Polymerase can only add nucleotides to 3’ end In Prokaryotes, replication begins at specific site in chromosome called the origin of replication Replication of DNA begins a specific site on the DNA template termed the origin and proceeds in both directions from the origin until nuclear division and cytokinesis take place. Replication speed = 1000 nucleotides/sec

25. RNA Synthesis in Bacteria Transcription is the synthesis of RNA and involves the assembly of nucleotides by an enzyme, RNA polymerase. 1. RNA polymerase binds to DNA at a promoter site near the gene to be transcribed. 2. RNA polymerase travels the length of the DNA using it as a template to duplicate. 3. The RNA polymerase continues until it reaches a termination site at which time the transcription is complete.

26. Protein Synthesis in Bacteria Protein synthesis is carried out in the cytoplasm. It begins with DNA duplication by mRNA (Transcription) mRNA then migrates to the ribosome where tRNA transfers information from mRNA to rRNA (Translation).

27. Protein Synthesis in Bacteria Protein synthesis is continuous and takes place in three stages: 1. Initiation 2. Elongation 3. Termination

28. Protein Synthesis in Bacteria Initiation The beginning of protein synthesis starts methionine which is the start codon. Start codon is know as formylmethoinine (f-met). It is coded as AUG.

29. Protein Synthesis in Bacteria Elongation By a complex that begins with f-met, amino acids attach to form a chain (amino acids joined repeatedly to form proteins)

30. Protein Synthesis in Bacteria Termination Ends when the synthesis comes to a termination codon. Termination codons are codes as UAA, UAG, and UGA).

31. Codon A codon is a group of three nucleotides in DNA which acts as a code in the placing of an amino acid in a protein molecule.

32. Codon A codon is a group of three nucleotides in DNA which acts as a code in the placing of an amino acid in a protein molecule.

33. Codons are the Code for Amino Acids A codon is a group of three nucleotides in DNA which acts as a code in the placing of an amino acid in a protein molecule. AUG begins protein synthesis UAA, UAG, UGA are termination codons.

34. Changes in the DNA molecules can Cause Mutations One base pair is exchanged for another in the DNA molecule One or more base pairs are inserted in the DNA molecule. One or more base pairs are deleted in the DNA molecule There is a rearrangement of sections in the DNA molecule. There is an exchange of DNA region with another DNA molecule (Recombination). Some mutations harmful, some beneficial, some neutral

35. Plasmids Some plasmids encode for genes that enhance pathogenicity of a bacterium E-coli, plasmid encodes toxins produced and bacterial attachment to intestinal cells

36. Transposons Transposons: are small pieces of DNA (2,000 – 20,000 base pairs) fond in chromosomes and plasmids. They are able to direct synthesis of copies of themselves and become incorporated into the chromosome. Called “jumping genes” because of their ability to insert themselves into a chromosome or change their locations.

37. Mutagens Chemical and physical agents that cause mutations. UV light is absorbed by pyrimidines (cytosine and thymine). UV causes adjacent thymines in the same strand to react and bond with each other. Thymine dimers are replication errors in transcription; if not correct , can lead to cellular death. • Agents in environment that directly or indirectly cause mutation

38. Mutagens Nitrous acid alters the chemical structures of adenine, cytosine, and guanine so that they change the base pairing which introduces mutation during DNA replication. There are many agents in environment that directly or indirectly cause mutation Most mutations are harmful but some are beneficial because they introduce variability into the progeny which promotes survival.

39. Genetic Transfer and Recombination Recombination: exchange of homologous genes on a chromosome Transformation: genes transferred from one bacterium to Another. After cell death, some bacteria are lysed and release cellular contents into surrounding environment. The recipient cell is in a physiological state that will allow it to take up DNA. Transformation occurs naturally among a few organisms..

40. Genetic Transfer and Recombination

41. Conjugation Another form of transfer of DNA from one cell to another. Requires cell to cell contact and transfer of plasmids through f-factor pili. • Donor cells carry plasmid • Recipient cells usually do not have plasmid Streptococcus pneumoniae: S form encapsulated, R form non-encapsulated • Experiment which placed heat killed S form with live R form. • Resulted in live S form.

42. Transduction Transfer of genes from a donor to a recipient by a bacteriophage