Talaro. Chapter 9: Microbial Genetics

Transcription

1 Talaro Chapter 9: Microbial Genetics

2

3 3

4 Figure 9.2 4

5

6 James Watson and Francis Crick

7 Rosalind Frank: DNA is a double helix!!!

8 DNA Composition Nitrogenouse base Adenine (A) Thymine (T) Guanine (G) Cytosine (C) Phosphate Deoxyribose Genes Nitrogenouse base combinations

9 Genetics the study of heredity The science of genetics explores: 1. Transmission of biological traits from parent to offspring 2. Expression and variation of those traits 3. Structure and function of genetic material 4. How this material changes 9

10 Genome sum total of genetic material of a cell (chromosomes + mitochondria/chloroplasts and/or plasmids) Genome of prokaryotes and eukaryotes DNA Genome of viruses DNA or RNA DNA complexed with protein constitutes the genetic material as chromosomes Eukaryotic chromosomes Multiple and linear Stored in the nucleus Bacterial chromosomes single circular loop 10

11 Chromosome is subdivided into genes, the 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 Three basic categories of genes: 1. Genes that code for proteins structural genes 2. Genes that code for RNA (rrna and trna) 3. Genes that control gene expression regulatory genes 11

12 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

13 Eukaryotes = histones, nucleosomes, supercoiling Prokaryotes = topoisomerase (DNA gyrase) 13

14 14

15 15

16 Identical Cells. Or are they? Daughter cells with DNA copies 16

17 Mutations Mutations genotypic alteration results in phenotypic change. Spontaneous random change Induced due to exposure to mutagens UV Chemicals

18 Mutation Categories THE BIG BAD DOG ATE THE FAT RED CAT. (original a.k.a. wild type) THE BIG BAD DOG ATE THE FIT RED CAT. (missense) THE BIG BAD. (nonsense) B THE BIG BAB DDO GAT ETH EFA TRE DCA T. (insertion) THE BIG BDD OGA TET HEF ATR EDC AT. (deletion) A

19 Genetic recombination occurs when an organism acquires and expresses genes that originated in another organism 19

20 20

21 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 to recipient through pilus 21

22 Figure 9.23 (1) 22

23 Figure 9.23 (2) 23

24 High-frequency recombination donor s fertility plasmid has been integrated into the bacterial chromosome When conjugation occurs, a portion of the chromosome and a portion of the fertility plasmid are transferred to the recipient 24

25 Figure 9.23 (3) 25

26 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 DNA acquired from environment (i.e. dead cells) 26

27 Figure 9.24 Fredrick Griffith s experiment. Insert figure 9.23 transformation Smooth (S) = virulent S. pneumoniae Rough (R) = non-virulent S. pneumoniae 27

28

29 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 Lytic cycle Specialized transduction a highly specific part of the host genome is regularly incorporated into the virus Lysogenic cycle 29

30 Figure 9.25 Generalized transduction 30

31 Figure 9.26 Specialized transduction 31

32 32

33 Special DNA segments that have the capability of moving from one location in the genome to another jumping genes Cause rearrangement of the genetic material Can move from one chromosome site to another, from a chromosome to a plasmid, or from a plasmid to a chromosome May be beneficial or harmful 33

34 Figure 9.27 Transposons 34

35 Vancomycin-resistant S. aureus Methicillin-resistant S. aureus Vancomycin-resistant Enterococcus Extended spectrum beta-lactamases