1. Chapter 9 Microbial Genetics
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2. Crash course bio #10
Dna structure and replication

3. Genetics and Genes Genetics – the study of heredity
The science of genetics explores:
Transmission of biological traits from parent to offspring
Expression and variation of those traits
Structure and function of genetic material
How this material changes

4. Levels of Structure and Function of the Genome
Genome – sum total of genetic material of a cell
Genome of cells – DNA
Genome of viruses – DNA or RNA
DNA complexed with protein constitutes the genetic material as chromosomes

5. Microbial Genomes Bacterial chromosomes are a single circular loop
Eukaryotic chromosomes are multiple and linear

6. DNA Two strands twisted into a double helix
strands run in opposite directions...
Antiparallel
Basic unit (monomer) of DNA structure is a…
nucleotide
Each nucleotide consists of 3 parts:
A 5 carbon sugar – deoxyribose
A phosphate group
A nitrogenous base – adenine, guanine, thymine, cytosine

8. PROCESS BOX 9-1 If I had ONE HALF of a DNA strand that read:
5’ ATTAGCATAGC 3’
What would the OTHER HALF be? How do you know?
2 LINE MINIMUM

9. The Overall Replication Process
Replication occurs on both strands simultaneously
Creates complementary strands
Semiconservative replication process

10. DNA Replication
Making an exact duplicate of the DNA involves 30 different enzymes
Begins at an origin of replication (ORI)
Helicase unwinds and unzips the DNA double helix
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(b)
Replication forks

11. DNA Replication
An RNA primer is synthesized at the origin of replication by Primase
DNA polymerase III adds nucleotides in a 5′ to 3′ direction
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(b)
Replication forks 11 11

12. DNA Replication
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′
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(b)
Replication forks 12 12

13. PROCESS BOX 9-2 Why do lagging strands even have to exist?
2 LINE MINIMUM

14. DNA Replication
DNA polymerase I removes the RNA primers and replaces them with DNA
When replication forks meet, ligases link the DNA fragments along the lagging strand
Separation of the daughter molecules is complete
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(b)
Replication forks 14 14

16. Crash course bio #11
Transcription and Translation

17. RNAs Single-stranded molecule made of nucleotides
5 carbon sugar is ribose
4 nitrogen bases – adenine, uracil, guanine, cytosine
Phosphate

18. RNA
3 types of RNA:
Messenger RNA (mRNA) – carries DNA message through complementary copy; message is in triplets called codons
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)

19. RNA 3 types of RNA: Messenger RNA (mRNA)
Transfer RNA (tRNA) – made from DNA; secondary structure creates loops; bottom loop exposes a triplet of nucleotides called anticodon which designates specificity and complements mRNA; carries specific amino acids to ribosomes
Ribosomal RNA (rRNA) 19 19

20. RNA 3 types of RNA: Messenger RNA (mRNA) Transfer RNA (tRNA)
Ribosomal RNA (rRNA) – component of ribosomes where protein synthesis occurs 20 20

21. PROCESS BOX 9-3
What similarities exist between the three types of RNA? What differences exist?
3 LINE MINIMUM

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

24. PROCESS BOX 9-4
In your own words, sum up the goal of transcription. Be sure to include the cell structures involved
3 LINE MINIMUM

25. The Master Genetic Code
Represented by the mRNA codons and the amino acids they specify
Code is universal among organisms
Code is redundant

26. Translation: The Second Stage of Gene Expression
All the elements needed to synthesize protein are brought together on the ribosomes
The process occurs in five stages: initiation, elongation, termination, and protein folding and processing

27. Translation Ribosomes assemble on the 5′ end of an 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 and binds to the mRNA

28. Translation
A second tRNA with the complementary anticodon fills the A site

29. Translation
A peptide bond is formed is formed between the amino acids on the neighboring tRNAs 29 29

30. Translation
The first tRNA is released and the ribosome slides down to the next codon 30 30

31. Translation Another tRNA fills the A site and a peptide bond is formed31 31

32. Translation
This process continues until a stop codon is reached 32

33. 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

34. PROCESS BOX 9-5
In your own words, sum up the goal of translation. Be sure to include the cell structures involved
4 LINE MINIMUM

35. Regulation of Protein Synthesis and Metabolism
Prokaryote regulation
operons, a set of genes, all of which are regulated as a single unit

36. Operons 2 types of operons: Inducible –
operon is turned ON by substrate: catabolic operons - enzymes needed to metabolize a nutrient are produced when needed

37. Lac Operon Normally off
In the absence of lactose, the repressor binds with the operator locus and blocks transcription of downstream structural genes

38. Lac Operon Lactose turns the operon on by acting as the inducer
Binding of lactose 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. 38 38

39. Operons 2 types of operons: 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. Arginine Operon: Repressible
Normally on and will be turned off when the product of the pathway is no longer required

41. Arginine Operon: Repressible
When excess arginine is present, it binds to the repressor and changes it.
Then the repressor binds to the operator and blocks arginine synthesis.
Arginine is the corepressor. 41 41

42. PROCESS BOX 9-6 How do inducible and repressible operons compare?
4 LINE MINIMUM

43. Causes of Mutations
Spontaneous mutations – random change in the DNA due to errors in replication that occur without known cause
Induced mutations – result from exposure to known mutagens, physical (primarily radiation) or chemical agents that interact with DNA in a disruptive manner

44. DNA Recombination Events
Genetic recombination – occurs when an organism acquires and expresses genes that originated in another organism
3 means for genetic recombination in bacteria:
Conjugation
Transformation
Transduction

45. Conjugation
Conjugation – transfer of a plasmid or chromosomal fragment from a donor cell to a recipient cell via a direct connection
Gram-negative cell donor has a fertility plasmid (F plasmid, F′ factor) that allows the synthesis of a conjugative pilus
Recipient cell is a related species or genus without a fertility plasmid
Donor transfers fertility plasmid through pilus

46. Transformation
Transformation – chromosome fragments from a lysed cell are accepted by a recipient cell; the genetic code of the DNA fragment is acquired by the recipient
Donor and recipient cells can be unrelated
Useful tool in recombinant DNA technology

47. Griffith’s Work on Transformation

49. Transduction
Transduction – bacteriophage serves as a carrier of DNA from a donor cell to a recipient cell
Two types:
Generalized transduction – random fragments of disintegrating host DNA are picked up by the phage during assembly; any gene can be transmitted this way
Specialized transduction – a highly specific part of the host genome is regularly incorporated into the virus

50. Transduction
Specialized transduction
Generalized transduction

51. PROCESS BOX 9-7
What is a key difference between transformation and transduction? How does this affect the “outcome”?
3 LINE MINIMUM

52. Intermicrobial DNA Exchange