Unit 3c. Microbial Gene0cs

Size: px
Start display at page:

Download "Unit 3c. Microbial Gene0cs"


1 Unit 3c Microbial Gene0cs

2 Microbial Genetics! Gene0cs: the science of heredity Genome: the gene0c informa0on in the cell Genomics: the sequencing and molecular characteriza0on of genomes Gregor Mendel Grew pea plants from Gene0cs: the science of heredity Genome: the gene0c informa0on in the cell Genomics: the sequencing and molecular characteriza0on of genomes

3 A cell s genome includes! Chromosomes and! Chromosomes are structures containing the DNA!

4 A bacterium has a single circular chromosome consisting of a single circular molecule of DNA!

5 Plasmids (review)! small loops of extrachromosomal DNA in bacteria! often carry genes for virulence, bacteriocins (toxic proteins that kill other bacteria) or drug resistance (codes for enzymes that inactivate certain drugs or toxic substances)! can recombine into new combinations! transmitted from organism to organism!

6 Eukaryotic DNA sites!

7 DNA! Fig. 2.16! Nucleo0des

8 Genes! Segments of DNA (except in some viruses, in which they are made of RNA) that code for functional products! DNA

9 each gene could be several thousand or more base pairs long.! E. coli approximately 4,300 genes (4.6 million base pairs! Humans have approximately 20,000 to 25,000 genes.! Based on Human Genome Project!

10 Nucleic Acids! DNA and RNA! DNA: deoxyribonucleic acid! RNA: ribonucleic acid! Messenger RNA (mrna)! Ribosomal RNA (rrna)! Transfer RNA (trna)! Nucleotides are the structural units of nucleic acids!

11 Nucleotides (Review)! a nucleic acid is a long chain of nucleotides! each nucleotide has 3 parts:! a 5-carbon! ribose in RNA! deoxyribose in DNA! A group! a base!

12 One nucleotide!

13 RNA nucleotide with uracil!

14 Nucleic acids! RNA: usually a single chain of nucleotides (may be double in viruses)!

15 DNA: usually a double chain of nucleotides (may be single in viruses)! 2 kinds of base pairs:!

16 Nucleotides Complementary Base Pair! Nucleotide bases bind to each other in a specific manner = complementary base pairing.! Specific purines complementary base pair with specific pyrimidines.! Complementary base pairing in DNA

17 DNA! Double helix of James Watson and Frances Crick!

18 Review of Proteins:! long chains of amino acids: hundreds of amino acids in complex three-dimensional arrangements! there are 20 naturally occurring kinds of amino acids! each amino acid in a protein must be exactly the right kind of amino acid or it will be a different protein!

19 the function of a gene is to determine the sequence of the amino acids to make a specific protein!

20 The genetic code! The set of rules that determine how a nucleotide sequence is converted into the amino acid sequence! along a mrna, groups of 3 consecutive nucleotides is a codon, the genetic code for one amino acid! e. g. P R P R P R l l l U A C! 64 possible mrna codons for 20 amino acids! there can be up to 6 codons that specify the same amino acid! a few codons specify NO amino acid (start or stop codons), signal the end of the protein molecule s synthesis!

21 The genetic code!

22 An overview of genetic flow.figure 8.2!

23 1) DNA replication! reproduction of a molecule! basis of continuity of life! molecule unzips along the hydrogen bonds! each half attracts the nucleotides needed to recreate the other half! if successful, both new molecules are identical to the original and to each other!

24 DNA Replication 5 3 DNA Ligase Enzyme that connects sections of DNA together Leading Strand Lagging Strand 5 3

25 Figure 8.6!

26 DNA replication precedes cell division!

27 2) Transcription! = production of RNA by DNA! DNA produces several kinds of RNA! messenger-rna (m-rna) carries the genetic code for a protein out from the chromosome to the ribosomes! transfer-rna (t-rna) carries individual amino acids to the messenger RNA which puts them in the proper sequence! ribosomal-rna (r-rna) links up the amino acids to form a protein!

28 Translation! = protein synthesis, translating the genetic code into a specific protein! chain of amino acids

29 Simultaneous transcription and translation in bacteria! Fig. 8.10!


31 Connects RNA nucleotides together (like DNA polymerase) Becomes mrna (messenger RNA) this has the code for how to build a protein

32 Codon- A section of three nucleotides in a row that code for an amino acid


34 Polypeptide Chain all the amino acids who together



37 Mutations! Can be negative, neutral, or positive!! defined as a change in the base sequence of DNA! can involve one or more nucleotides! the source of new genes (such as virulence or drug resistance)! about one mutation per million replicated genes! causes:! errors in DNA replication! radiation! mutagenic chemicals!

38 The electromagnetic spectrum: effective wave lengths:! a. ultraviolet radiation! damages DNA! optimum wave length: 260 nm! poor penetrating ability!

39 Ames Test uses bacteria as carcinogen indicators (figure 8.22)! Many known mutagens have been found to be carcinogens!

40 Genetic Recombination! The exchange of genes between 2 DNA molecules to form new combinations of genes on a chromosome.! Vertical gene transfer! Genes are passed from an organism to its offspring! Horizontal gene transfer! Between bacteria of the same generation!! Donor cell to recipient cell = recombinant!

41 An overview of genetic flow.figure 8.2!

42 Bacterial gene transfers! Bacteria have a number of forms of recombination:!!!!

43 Bacterial conjugation (DNA transferred through a mating process)! 2 bacteria connected by a tube called the sex pilus! F = fertility factor (ability to mate)! F+ is equal to being male (one that grows the sex pilus)! F is equal to being a female! DNA passes through the sex pilus from the F+ to the F! usually just the F factor, but sometimes other genes are carried along! F becomes F+!

44 Figure 8.24: Griffith s Transformation Experiment!

45 Transduction:! Transduction: host DNA carried from cell to cell by virus! Figure 8.28!

46 Biotechnology

47 Cotton Plants with Bacillus gene inserted (left)

48 Bioremediation

49 Pharmaceuticals!

50 Figure 9.1!

51 DNA in diagnosis! 4. Nucleic acid hybridization! Basis of DNA probes! Short segments of ssdna that are complementary to the desired gene! Complementary strands of known DNA separated by heat! One side marked with fluorescent dye! DNA of unknown bacteria separated by heat! Will hybridize with fluorescent strand of known DNA if same kind. After rinsing away unbound DNA, a fluorescent DNA double strand will remain! Can hunt for complementary DNA within a massive amount of material, such as food!

52 DNA-DNA hybridization (fig )!

53 DNA probe to detect Salmonella! Why use E. coli?! Easily grown & researchers are familiar with its genetics! Figure 10.16!

54 DNA probe, continued!

55 DNA probe, continued!

56 DNA Chips (figure 10.17) An array of DNA probes arranged in a DNA chip can be used to identify pathogens!

57 BUT should we?