Bacterial Genetics and Recombination

Bacterial recombination and Bacterial genetics

MRSA (methicillin-resistant Staphylococcus aureus

caused by a type of staphylococcus bacteria that has become resistant to antibiotics used to treat ordinary staph infections

genetic mutation causes drug resistance

1. non-resistant bacteria exists

2. bacteria multiply by the billions (a few bacteria will mutate) 

3. some mutations make the bacterium drug resistant (presence of drugs, only drug resistant bacteria can survive) 

4. drug resistant bacteria multiply and thrive

pLW1043 plasmid

• trimethoprim resistance

• penicillin family resistance

• vancomycin resistance

• genes to help the plasmid spread

• disinfectant resistance 

• streptomycin family resistance 

True

a single plasmid can carry the genes to resist many different antibiotics 

genetics

the study of what genes are and how they carry information, how their information is expressed, and how they are replicated and passed to subsequent generations or other organisms

genome

the genetic information in the cell

chromosomes

structures containing DNA that physically carry hereditary information; contains the genes 

genes

segments of DNA (except in some viruses which are made of RNA) the code of functional products that are usually proteins (rRNA, tRNA, microRNA)

nucleotides

repeating units consists of a nucleobase, (adenine, thymine, cytosine, guanine), deoxyribose, and phosphate group

base pairs

• adenine - thymine

• cytosine - guanine 

genetic code

the set of rules that determines how a nucleotide sequence is converted into the amino acid sequence of a protein

central dogma

• theory by Francis Crick in 1956

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

the flow of genetic information

• expression

• recombination

• replication 

what happens in the flow of genetic information

• DNA is the blueprint of a cell’s proteins, including enzymes

• DNA is obtained either from another cell in the same generation or from a parent cell during cell division

• DNA can be expressed within a cell or transferred to another cell through recombination and replication 

expression

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

• the cell metabolize and grows

recombination

genetic information can be transferred horizontally between cells of the generation

replication

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

DNA gyrase

relaxes supercoiling ahead of the replication fork

DNA ligase

makes covalent bonds to join DNA strands; Okazaki fragments, and new segments in excision repair

DNA polymerase

synthesize DNA; proofreads and facilitate repair of DNA

endonucleases

cuts DNA’s backbone in a strand of DNA; facilitate repair and insertions

exonucleases

cut DNA from an exposed end of DNA; facilitate repair

helicase

unwinds double-stranded DNA

methylase

adds methyl group to selected bases in newly-made DNAp

photolyase

uses visible light energy to separate UV-induced pyrimidine dimers

primase

an RNA polymerase that makes RNA primers from a DNA template

ribozyme

RNA enzyme that removes introns and splices exons together

RNA polymerase

copies RNA from a DNA template

snRNP

RNA-protein complex that removes introns and splices exons together

topoisomerase/gyrase

relaxes supercoiling ahead of the replication fork; separates DNA circles at the end of DNA replication

transposase

cuts DNA backbone, leaving single-stranded “sticky ends”

transcription in prokaryotes

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

• during transcription, there us the synthesis of strand of mRNA

• take note that an adenine in the DNA template dictates a uracil (U) in the mRNA, because RNA contains uracil instead of thymine (T) 

• the process of transcription requires RNA polymerase

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

translation

• process in which the mRNA serves as the source of information for the synthesis of proteins

• the language of mRNA is in the form of codons (group of 3 nucleotides)

translation process

• components needed to begin translation come together

• on the assembled ribosome, the tRNA carrying the first amino acid is paired with the start codon on the mRNA.

  • the place where this first tRNA sits is called the P site.

  • a tRNA carrying the second amino acid approaches 

• the second codon of the mRNA pairs with a tRNA carrying the second amino acid at the A site. 

  • the first amino acid joins to the second by a peptide bond

  • this attaches the polypeptide to the tRNA in the P site

• the ribosome moves along the mRNA until the second tRNA is in the P site

  • the next codon to be translated is brough into the A site.

  • the first tRNA now occupies the E site

• the second amino acid joins the third by another peptide bone, and the first tRNA is released from the E site

• the ribosome continues to move along the mRNA, and a new amino acid are added to the polypeptide

• when the ribosome reaches a stop codon, the polypeptide is released

• finally, the last tRNA is released, and the ribosome comes apart. 

  • the released polypeptide forms a new protein

mutations

• a permanent change in the base sequence of DNA

• such change can cause a change in the product encoded by the gene

types of mutation

• base substitution/point mutation

• silent mutation

• spontaneous mutations

• induced mutations

base substitution/point mutation

• most common type of mutation involving single base pairs

• a single base at one point in the DNA sequence is replaces with a different base 

normal DNA molecule

missense mutation

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

nonsense mutation

• 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 time

silent mutation

• occurs 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:

• converts the base adenine to a form that pairs with cytosine instead of the usual thymine

result: base substitution

nucleoside analog

action: 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

action: inserts between base pairs

result: addition of base pairs

x-rays and gamma rays

action: 

• forms of radiation that are potent mutagens

• ionize atoms and molecules

• penetrating rays cause electrons to pop out of their usual shells which will cause more damage and some ions oxidizes bases in the DNA

result:

• errors in DNA replication —> mutations

• breakage of covalent bonds

ultraviolet (UV)

action:

• formation of harmful covalent bonds between pyrimidine bases

• 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 trasnfer

occurs when genes are passed from an organism to its offspring

horizontal gene trasnfer

• pass their genes laterally to other microbes

  • between normal microbiota and pathogens in spread of antibiotic resistance

• donor and recipient cell

donor cell

gives a portion of its total DNA

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

conjugation

• required direct cell-to-cell contact

• conjugating cells must generally be of opposite mating type

sex pili

gram negative

sticky surfaced molecules

gram positive

trasnduction

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