MICR1A_7_Bacterial Genetics

• Nucleoid

- bacterial DNA

• Plasmid

- chromosomal material

- may contain specific genes that may cause specific changes in the gene of bacteria (related to how a microbes have higher mutation rates)

Methicillin-Resistant Staphylococcus aureus

- before, S. aureus mutations have resistance to beta lactam antibodies such as Penicillin. so they used Methicillin as alternative then, some strains became Methicillin resistant too

• Trimethoprim resistance

• Penicillin family resistance

• Vancomycin resistance

• Genes to help the plasmid spread

• Disinfectant resistance

• Streptomycin family resistance

• Theory by Francis Crick in 1956

• he first proposed that the sequence of nucleotides in DNA determines the sequence of amino acids in a protein

• Expression

- genetic information is used within a cell to produce the proteins needed for the cell to function

• Recombination

- genetic information can be transferred horizontally between cells of the same generation

• Replication

- genetic information can be transferred vertically to the next generation of cells

• DNA Gyrase

- relaxes supercoiling

• DNA Ligase

- makes covalent bonds to join DNA strands

- important for Okazaki fragments

• DNA Polymerases

- synthesize DNA

- proofread to check for wrong bases

• Endonucleases

- cut DNA backbone in a strand of DNA

• Exonucleases

- cut DNA from an exposed end of DNA

• Helicase

- unwinds double-stranded DNA

• Methylase

- adds methyl group

• Photolyase

- separate UV-induced pyrimidine dimers

• Primase

- makes RNA primers

• Ribozyme

- RNA enzyme

- removes introns

- splices exons

• RNA Polymerase

- copies RNA from a DNA template

• snRNP

- RNA-protein complex that have the same function as Ribozyme

• Topoisomerase/ Gyrase

- relaxes supercoiling

- separates DNA circles

• Transposase

- cuts DNA backbone

Transcription in Prokaryotes

- the synthesis of a complementary strand of RNA from a DNA template

• rRNA

- integral part of ribosomes

- the cellular machinery for protein synthesis

• mRNA

- carries the coded information for making specific proteins from DNA to ribosomes

- where proteins are synthesized

- during transcription, there is the synthesis of strand mRNA

Missense Mutation

• when the change of a single base pair causes the substitution of a different amino acid in the resulting protein

Nonsense

• base substitutions that create a stop (nonsense) codon that prevents the synthesis of a complete functional protein

Frameshift Mutation

• one or a few nucleotide pairs are deleted or inserted in the DNA

• this can shift the “translation reading frame”

Silent Mutation

• occur when one nucleotide is substituted for another in the DNA which results to new codon that might still code for the same amino acid

• if the amino acid is changed, the function of the protein may not change if the amino acid is in a nonvital portion of the protein

Spontaneous mutations

• mutations that arise in the absence of known mutagens

Induced mutations

• mutations that occur following treatment with a mutagen

Mutagenesis

• the process by which a mutation is produced

Mutagens

• agents that increase the frequency of mutation

Nitrous Acid

• Action:

1. Convert the base adenine to a form that pairs with cytosine instead of the usual thymine

2. Alters DNA at different location

• Result:

• Base substitution

Nucleoside Analog

- e.g. 2-aminopurine and 5-bromouracil

• Action:

1. They are randomly incorporated in DNA

• Result:

• Causes mistakes in base pairing during DNA replication

• Subsequently, base pair substitutions in the progeny cells

Intercalating agents

- e.g. Ethidium bromide and Acridine orange

• Action:

1. Inserts between base pairs

• Result:

• Addition of base pairs

X rays and Gamma rays

• Action:

1. Forms of radiation that are potent mutagens

2. Ionize atoms and molecules

3. Penetrating rays cause electrons to pop out of their usual shells which will cause more damage and some ions oxidized bases in DNA

• Result:

• Errors in DNA replication to mutations

• Breakage of covalent bonds

• Causes physical breaks in chromosome

Ultraviolet (UV)

• Action:

1. Formation of harmful covalent bonds between pyrimidine bases

2. Thymine dimer formation

• Result:

• Thymine dimers causes problem in transcription or replication of the DNA

Genetic Recombination

• Refers to exchange of genes between two DNA molecules to form new combinations of genes on a chromosome

Vertical Gene Transfer

• occurs when genes are passed from an organism to its offspring

Horizontal Gene Transfer

• pass their genes laterally to other microbes

• ex.: between normal microbiota and pathogens in spread of antibiotic resistance

• Donor cell

• - gives a portion of its total DNA

  • Recipient cell

  Recombinant

  • the recipient cell that incorporated donor DNA into its own DNA

    Transformation

    • process where in genes are transferred from one bacterium to another as “naked” DNA in solution

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Conjugation

• requires direct cell-to-cell contact

• conjugating cells must generally be of opposite mating type

• Gram-negative

- sex pili

• Gram-positive

- sticky surface molecules

Transduction

• bacterial DNA is transferred from a donor cell to recipient inside a virus that infects bacteria called bacteriophage or phage