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Chapter 8 Microbial Genetics

Structure and Function of Genetic Material. DNA

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Chapter 8 Microbial Genetics

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    1. Chapter 8 Microbial Genetics Biology 1009 Microbiology Johnson-Summer 2003

    2. Structure and Function of Genetic Material DNA & RNA DNA=deoxyribonucleic acid RNA=ribonucleic acid Basic building blocks: Nucleotides Phosphate group Pentose sugar Nitrogenous base DNA and RNA-polymers Nucleotides-monomersDNA and RNA-polymers Nucleotides-monomers

    3. Structure of DNA Double stranded (double helix) Chains of nucleotides 5 to 3 (strands are anti-parallel) Complimentary base pairing A-T G-C A-adenine T-thymine G-guanine C-cytosineA-adenine T-thymine G-guanine C-cytosine

    4. DNA Structure Hydrogen bonds-hold base pairs together 5 end-means P comes off 5 carbon of deoxyribose sugar 3means P comes of 3 end of deoxyribose sugarHydrogen bonds-hold base pairs together 5 end-means P comes off 5 carbon of deoxyribose sugar 3means P comes of 3 end of deoxyribose sugar

    5. DNA Replication Bacteria have closed, circular DNA Genome: genetic material in an organism E. coli 4 million base pairs 1 mm long (over 1000 times larger that actual bacterial cell) DNA takes up around 10% of cell volume

    6. DNA Replication-occurs at the replication fork 5 to 3 DNA helicase-unzips + parental DNA strand that is used as a template Leading stand (5 to 3-continuous) *DNA polymerase-joins growing DNA strand after nucleotides are aligned (complimentary) Lagging strand (5 to 3-not continuous) *RNA polymerase (makes short RNA primer) *DNA polymerase (extends RNA primer then digests RNA primer and replaces it with DNA) *DNA ligase (seals Okazaki fragments-the newly formed DNA fragments) During replication, on parental ds DNA is converted into 2 identical ds daughter molecules After DNA helicase unzips DNA strand, free nucleotides present in cytoplasm are matched up to exposed bases on the single stranded parental DNA Dna polymerase can add nucleotides only to the 3 end Okazaki fragments-1000 nucleotidesDuring replication, on parental ds DNA is converted into 2 identical ds daughter molecules After DNA helicase unzips DNA strand, free nucleotides present in cytoplasm are matched up to exposed bases on the single stranded parental DNA Dna polymerase can add nucleotides only to the 3 end Okazaki fragments-1000 nucleotides

    7. Replication Fork

    8. Protein Synthesis DNA-------? mRNA------? protein transcription translation Central Dogma of Molecular Genetics

    9. Transcription One strand of DNA used as a template to make a complimentary strand of mRNA Promoter/RNA polymerase/termination site/5 to 3 Ways in which RNA & DNA differ: RNA is ss RNA sugar is ribose Base pairing-A-U mRNA-messenger RNAmRNA-messenger RNA

    10. Transcription

    11. Types of RNA Three types: mRNA: messenger RNA Contains 3 bases ( codon) rRNA: ribosomal RNA Comprises the 70 S ribosome tRNA: transfer RNA Transfers amino acids to ribosomes for protein synthesis Contains the anticodon (3 base sequence that is complimentary to codon on mRNA) mRNA-messengermRNA-messenger

    12. Genetic Code DNA: triplet code mRNA: codon (complimentary to triplet code of DNA) tRNA: anticodon (complimentary to codon)

    13. Genetic Code Codons: code for the production of a specific amino acid 20 amino acids 3 base code Degenerative: more than 1 codon codes for an amino acid Universal: in all living organisms 64 total codons 3 STOP codons uaa,uga,uag 1 start codon (for protein synthesis) aug (also a sense codon that forms aa)64 total codons 3 STOP codons uaa,uga,uag 1 start codon (for protein synthesis) aug (also a sense codon that forms aa)

    14. Genetic Code

    15. Translation Three parts: Initiation-start codon (AUG) Elongation-ribosome moves along mRNA Termination: stop codon reached/polypeptide released and new protein forms rRNA=subunits that form the 70 S ribosomes (protein synthesis occurs here) tRNA=transfers amino acids to ribosomes for protein synthesis)

    20. Mutations Changes in base sequence of DNA/lethal and inheritable Can be: Harmful Lethal Helpful Silent Silent-neutralSilent-neutral

    21. Normal DNA/Missense Mutation Missense-just one different amino acid formed-caused from a base substitution, single base is replaced with a different oneMissense-just one different amino acid formed-caused from a base substitution, single base is replaced with a different one

    22. Nonsense Mutation/Frameshift Mutation Nonsense mutation-base substitution in the middle of the mRNA results in the formation of the stop codon/protein synthesis stopped Frameshift-1 or a few nucleotides are deleted or inserted-alters 3by3 transitional reading frame/produces inactive protein Base substitutions and frameshift mutations occur spontaneously or by chemicals in the environmentNonsense mutation-base substitution in the middle of the mRNA results in the formation of the stop codon/protein synthesis stopped Frameshift-1 or a few nucleotides are deleted or inserted-alters 3by3 transitional reading frame/produces inactive protein Base substitutions and frameshift mutations occur spontaneously or by chemicals in the environment

    23. Genetic Transfer in Bacteria Genetic transfer-results in genetic variation Genetic variation-needed for evolution Three ways: Transformation: genes transferred from one bacterium to another as naked DNA Conjugation: plasmids transferred 1 bacteria to another via a pilus Transduction: DNA transferred from 1 bacteria to another by a virus Transduction-DNA passed from 1 bacteria to another in a bacteriophage (virus) and then incorporated into the host DNATransduction-DNA passed from 1 bacteria to another in a bacteriophage (virus) and then incorporated into the host DNA

    24. Transduction by a Bacteriophage

    25. Transformation

    26. Conjugation in E. coli F factor-plasmid F+ cell donor/f- is recipient Hfr-when plasmid becomes incorporated into chromosome of bacteria, that cell is called a high frequency of recombination cell During conjugation, hfr cell can transfer chromosomal dna to f-cellF factor-plasmid F+ cell donor/f- is recipient Hfr-when plasmid becomes incorporated into chromosome of bacteria, that cell is called a high frequency of recombination cell During conjugation, hfr cell can transfer chromosomal dna to f-cell

    27. Conjugation continued

    28. Conjugation continued

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