Microbial Genetics

1. Microbial Genetics Microbiology 2314

2. Genetics • The Study of 1. Heredity 2. What Genes Are 3. How Genes Function 4. How Genes Carry Information 5. How Genetic Information is Expressed 6. How Genes are Replicated and Passed

3. Genome and DNA • Genome is the genetic information of the cell. • Genome is composed of chromosomes containing genes. • DNA is a double stranded helix. • Hydrogen bonds exist between nitrogenous base pairs

4. Nitrogenous Bases • a. Adenine • b. Thymine • c. Cytosine • d. Guanine • 2. Deoxyribose Sugar • 3. Phosphate

5. Genes • Are Short Sections of DNA • Code for Proteins • 1000’s of Bases • 41000 Possibilities

6. The Genetic Code • The sequence of nucleotides in DNA or RNA that determines the specific amino acid sequence in the synthesis of proteins. • It is the biochemical basis of heredity and nearly universal in all organisms. • An Operon is a unit made up of linked genes that is thought to regulate other genes responsible for protein synthesis. 

7. Genetic Expression • DNA Transcribed to RNA • RNA Translated to Protein

8. How Does DNA Serve as Genetic Information • DNA is transcribed to RNA • RNA is translated to Protein • Proteins can then act as enzymes, structural units, etc to carry on the biochemical processes of life. • Therefore Protein carries on life. Easy as pie.

9. Genotype and Phenotype • Genotype 1. Genetic Composition of an Organism 2. Represents the Potential Properties • Phenotype 1. The Expression of the Genes 2. What You See

11. Replication • The duplication of DNA which occurs during the S phase of Interphase. • 1 Strand  2 Complementary Strands • DNA Polymerase

15. Transcription • The process by which a molecule of DNA is copied into a complementary strand of RNA. • 1 Strand DNA  2 Strands RNA • RNA Polymerase

18. Translation • The process in which the information in the nucleotide base sequence of mRNA is used to dictate the amino acid sequence of a protein. • 1 Strand RNA  Amino Acid Chain  Protein

19. RNA and Protein Synthesis • RNA is a Single Stranded Nucleic Acid • RNA Acts as a Messenger between DNA and Ribosomes • Process Takes Amino Acids and Forms Proteins

20. Why Is It Necessary? • DNA / Nucleus • Ribosomes / Cytoplasm • Need a Messenger

21. Composition • Nitrogenous Bases a. Guanine b. Cytosine c. Adenine d. Urasil • Ribose Sugar • Phosphate

22. Definitions • Codon 1. Three-base segment of mRNA that specifies amino acids. 2. Sense Codons 3. Nonsense Codons (AUG / Methionine) • Anticodon 1. Three-base segment of tRNA that docks with a codon. 2. Docking results in deposition of amino acid.

23. Protein Synthesis in Prokaryotes and Eukaryotes • The basic plan of protein synthesis in Eukaryotes and Archaea is similar to that in bacteria. • The major structural and mechanistic themes recur in all domains of life. However, eukaryotic protein synthesis entails more protein components than does prokaryotic protein synthesis, and some steps are more intricate.

24. Noteworthy Similarities and Differences Between the Two • Ribosomes. Eukaryotic ribosomes are larger. The differences between eukaryotic and prokaryotic ribosomes can be exploited for the development of antibiotics • Initiator tRNA. In eukaryotes, the initiating amino acid is methionine rather than N-formylmethionine.

25. Noteworthy Similarities and Differences Between the Two • Initiation. The initiating codon in eukaryotes is always AUG. In almost all cases, eukaryotic mRNA has only one start site and hence is the template for a single protein. . In contrast, a prokaryotic mRNA can have multiple start sites, and serve as a template for several proteins. • Termination. Termination in eukaryotes is carried out by a single release factor, eRF1, compared with two in prokaryotes.

26. Duh What? • Protein synthesis is essentially the same in both types of cells. However, in prokaryotes the ribosomes can attach directly to the mRNA molecule while the mRNA is being synthesized. In eukaryotes, the nuclear membrane separates transcription from translation. This separation allows for the RNA to be processed

27. Regulation of Bacterial Gene Expression • Efficient Process • Performed as Needed • Determined by Structural Genes • Example: E. coli / Lactose

28. Operon Model of Gene Expression • The formation of enzymes is determined by structural genes • E. coli digests lactose • No lactose / No need for enzymes • No Inducer / Repressor binds to DNA • Repressor blocks Transcription • Inducer Present / Inducer binds to Repressor

29. Why Does This Occur? • Bacteria do not make all the proteins that they are capable of making all of the time. Rather, they can adapt to their environment and make only those gene products that are essential for them to survive in a particular environment. For example, bacteria do not synthesize the enzymes needed to make tryptophan when there is an abundant supply of tryptophan in the environment. However, when tryptophan is absent from the environment the enzymes are made

30. Similarly, just because a bacterium has a gene for resistance to an antibiotic does not mean that that gene will be expressed. • The resistance gene may only be expressed when the antibiotic is present in the environment. A Typical Operon

31. What is an Operon? • In genetics, an operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single regulatory signal or promoter. • The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo trans-splicing to create monocistronic mRNAs that are translated separately

32. Structure of an Operon • This is the general structure of an operon: • Promoter – a nucleotide sequence that enables a gene to be transcribed. The promoter is recognized by RNA polymerase, which then initiates transcription. In RNA synthesis, promoters indicate which genes should be used for messenger RNA creation – and, by extension, control which proteins the cell manufactures.

33. Operator – a segment of DNA that a regulator binds to. It is classically defined in the lac operon as a segment between the promoter and the genes of the operon. In the case of a repressor, the repressor protein physically obstructs the RNA polymerase from transcribing the genes. • Structural genes – the genes that are co-regulated by the operon.

34. Lac Operon Model • In the case of the lac operon, the bacterial cell does not need lactose metabolizing proteins expressed if there is no lactose present to act as a substrate. • It makes sense, therefore, that the regulatory protein - the repressor - blocks transcription unless lactose is present.

35. In this situation, the repressor is unable to bind to the operator by itself. Hence, structural genes will be expressed at a level that is determined by the strength of the promoter.

36. When, the supply of a molecule is sufficient, or when it builds up to sufficient levels, it can bind to the repressor, alter its conformation, and render it unable to bind to its operator. • A molecule that acts in this way is called an effector.

37. TrpOperon Model • The trp operon is an example of a biosynthetic operon whose expression is regulated by an effector:

38. Induction and Repression • Induction The process that initiating transcription with an inducer. • Repression The repressing of transcription with a repressor.

39. Originally operons were thought to exist solely in prokaryotes, but since the discovery of the first operons in eukaryotes in the early 1990smore evidence has arisen to suggest they are more common than previously assumed.

40. Mutation • A change in the nitrogenous base sequence of DNA; that change causes a change in the product coded for by the mutated gene. • Neutral • Hazardous • Beneficial

41. Base Substitution - One base pair in DNA is replaced with a different base pair • Deletion - A piece of DNA breaks off and is lost • Duplication and Translocation - A piece of DNA breaks off and is incorporated into another strand of DNA • Frameshift - Deletion or Addition results in a shift in the DNA frame

42. Types of Mutations • Single Base Substitution - Also called Point Mutation - Two Kinds 1. Transition Purine Replaced by a Purine Pyrimidine Replaced by Pyrimidine 2. Transversion Purine Replaced by a Pyrimidine or Vice Versa

43. Purines 1. Adenine 2. Guanine • Pyrimidines 1. Thymine 2. Cytosine • Example Transition? • Example Transversion?

44. Types of Mutations • Missence Mutation - Codon is Altered Producing Altered Amino Acid - Example: Sickle Cell Disease GAG  GTG • Nonsense Mutation (Example Thalidomide) - Sense Codon is Altered to Stop Codon - TGG  TAA - TGG  TAG - TCA  TGA

45. Types of Mutations • Silent Mutation - Codon Changed but Still Codes for Same - Serine is TCT and TCG and TCA and TCC • Deletion (Results in Frameshift) - GAGCCGCAACTTC Deletion Occurs - GAGCCGCATTC Altered State Results • Insertion (Results in Frameshift) - GAGCCGCAACTTC Insertion Occurs - ACGAGCCGCAACTTC Altered State Results

46. Types of Mutations • Frameshift GAG CCG CAA CTT C… ACGAGCCGCAACTTC GAG CCG CAA CTT C… ACG AGC CGC AAC TTC

47. Mutagens • Tobacco products • Nitrous Acid • Mold Toxins • X-rays • Gamma Rays • UV Radiation • Some Artificial Sweeteners

48. UV Light • Skin cancer is the most commonly occurring cancer in the United States.

50. Tobacco Products • All forms of tobacco products have been shown to cause cancer.