Microbial genetic and genetic engineering and Antimicrobial Therapy REVIEW

What does replication result in?

• produces two copies of the original DNA, each of which contains one of original strand, and one newly synthesized strand

• Always done in a semiconservative pattern

Where does replication begin?

• At the replication origin

• This will always be an A-T rich region because it requires less envy to break the hydrogen bonds between adenine and thymine (2 bonds) than guanine and cytosine (3 bonds)

What does Helicase do in replication?

• At the A-T rich region, Helicase will break the hydrogen bonds within the double stranded DNA molecule. Therefore, creating two single strands of DNA that can be replicated

• These single strands of DNA are then kept separate by Single Stranded Binding Proteins

Leading Strand (RNA primase, DNA Polymerase III, and I)

• Synthesized continuously in the 5’—>3’ direction

• RNA primase will lay down a short RNA primer, so DNA Polymerase III has a starting point

• DNA polymerase III will then continue from the primer to read the template strand of DNA and add the corresponding nucleotides via hydrogen bonding

• DNA polymerase I will then remove the RNA primer and replace it with nucleotides

Lagging strand (RNA primase, DNA Polymerase III and I, Okazaki Fragments)

• synthesized discontinuously backwards in the 5’—>3’ direction

• Multiple RNA Primers are laid down by RNA Primase

• DNA Polymerase III fill as in the spaces in between RNA primers with DNA nucleotides

• DNA Polymerase I removes the RNA nucleotides and replaces them with DNA

• Since the lagging strand is made in segments (Okazaki Fragments), these fragments must be fused together. This is done via the enzyme Ligase

Transcription

• DNA —> mRNA

• DNA is separated using helicase

• Strand in 3’—>5’ direction is used as template strand for transcription. (5’—>3’ strand is coding strand not used for transcription)

• RNA Polymerase composes a single strand of RNA that is complementary to the DNA code (A-U and G-C)

• This single strand is mRNA and contains the code for how to synthesize a specific protein

• mRNA will leave the DNA molecule and enter the cytoplasm where it will join ribosome for translation

Translation

• mRNA —> Protein

• rRNA forms ribsomal subunits that make up ribosome, which is site of protein synthesis

• Ribosome reads mRNA in three letter sequence (codons) which represents an Amino Acid

• tRNA transfers AAs from cytoplasm to ribosomes

  • Bottom is a specific AA bound

  • Top is a anticodon sequence. Always reverse of codon sequence

• tRNA uses anticodon as a codon matching proofreader to make sure sequence is correct

• There is no tRNA sequence that corresponds it the stop coons, so when it reaches stop codon translation ends

Broad spectrum antibiotics

• effective against more than one group of bacteria

  • Pro- best in emergencies when causing agent unknown and patient is critical

  • Con- they are prone to killing normal biota and can cause superinfection

Narrow spectrum antibiotics

• target a specific bacterial group

  • Pro- not as harmful to normal biota

  • Con- not useful in emergencies because you must know causative agent

Superinfections

• occur after taking a broad-spectrum antibiotic. Drug destroys your normal biota, allowing pathogens that were left behind to grow and cause a secondary infection

  • Lactobacilli in vagina are killed by antibiotics used to threat other bacterial infections. Once they are gone the acidic pH in vagina goes away, allowing overgrowth of Candida albicans, causing yeast infection/oral thrush

  • Can also kill biota writhing the colon allowing Clostrsidium difficile to overgrow and cause an antibiotic associated colitis infection

Probiotics

Preparation of live microorganisms fed to animals and humans to improve intestinal biota

Prebiotics

Nutrients that encourage the growth of beneficial microbes

Inhibition of cell wall synthesis and its drug?

• penicillin and vancomycin

• Beta lactation ring is used to destroy peptidoglycan in bacterial cell walls

Disruption of cell membrane function and its drug?

• polymyxin

• Destroys phospholipids in cell membrane of bacteria

Inhibition of protein synthesis (30s vs 50s) and the drug

• Streptomycin and tetracycline inhibits the 30s ribosomal subunit

• Erythromycin and chloramphenicol Inhibits the 50s ribosomal subunit

Inhibition of nucleic acid synthesis and the drug

• Rifampin binds to RNA polymerase and inhibits RNA synthesis

• Ciprofloxacin inhibits DNA replication in bacteria through inhibition of DNA Gyrase enzyme

Antimetabolite activity and the drug

• sulfa drugs and Trimethoprim

• Inhibits the production of folic acid

Horizontal gene transfer and the types

• bacterium would acquire genetic information from another source

  1. Transformation- bacterium incorporates naked DNA into its genome

  2. Transduction- bacterium acquires genetic information from another bacteriophage

  3. Conjugation- genetic information exchanged from one bacterium to another via the pili appendage