Bacterial genetics

Question 1

Explain DNA replication on the direction and conservation

Answer 1

Bidirectional and semiconservative

Question 2

differentiate the replication in of the strands

Answer 2

1. leading strand
   
   1. continiuous
2. lagging strand
   
   1. discontinuous
   2. RNA primers, from primase
   3. DNA pol (one type)

Question 3

How does trascription begin for bacteria?

Answer 3

1. When RNA polymerase recognizes and binds to a promoter region on the DNA
   
   1. the particular subunit assists RNApolymerase bind to DNA is sigma factor
   2. after the RNA pol binds, sigma factor dissociates

Question 5

what are the structure at the termination site of bacterial RNA?

Answer 5

Hairpin loop forms and the RNA is pulled out

Question 6

What are the bacterial ribosomal units?

Describe the function of these units

Answer 6

rRNA

30S +50S= 70S

tRNA- Segments (3’ end) carry the amino acid to the rRNA and read the codon with the anticodon on the tRNA

Question 7

Describe the methods of genetic transfer in bacteria-3

Answer 7

1. horizontal gene transfer - from one bacterium to another
   
   1. mechanisms
      
      1. DNA mediated transformation
         
         1. ​DNA is transferred as “naked DNA”
      2. transduction
         
         1. ​bacterial DNA is transferred by a virus
      3. Conjugation
         
         1. ​DNA is transferred from one cell to another by direct contact

Question 8

Jenny is studying E. coli. Her sample shows that the genome is different from samples before and after log phase. Her sample tested negative for viruses. What is most likely happening?

How could she go about recreating this event and what is it called?

Answer 8

Transformation of her sample occured from competent cells taking up enviornmental DNA

Under certain growth conditinos some cells are competent

• competent - able to take in “naked DNA” throug hthe cell wall and membrane
• occurs near the end of log phaseof growth

She can artificially induce competency by a process called electroporation

Question 9

After collecting samples from a lake, the bacteria showed progress in the media of growth but then rapidly died from lysing. What is the method of gene transfer in this sample and explain the process.

Answer 9

Transuction

bacteriophage transfer bacterial genes from one cell to another. Sometime the released phage may carry part of the bacterial genes and be useful for future infected bacteria.

The bacteria become full of the phages and “pop” or lyse from the viruses.

1. types of transduction
   
   1. generalized
      
      1. replication leads to the degredation of the host c’some.
      2. part of the host C’some is incorporated into the phage, instead of viral genome.
      3. Infection of next bacteria may lead to an incorporation of a different bacterial gene in place of the new hosts
   2. specialized
      
      1. temperate phages ONLY
      2. the phage incorporates part of the viral and part of the virus DNA.
      3. upon infecting new host, it cannot replicate. But this injected DNA may be incorporated into the new hosts genome

Question 10

A sample from the wild does not have penicillin resistance, but when grown in a sample that is penicillin resistant, the wild sample become resistant. What happened with the genetic component?

Answer 10

conjugation- most likely

Fplasmid

1. codes for synthesis of a sex pilus and contained genes for penicillin resistance
   
   1. sex pilus is the protein appendage that attaches the donor to the recipient cell

Question 11

describe the following terms with reference to antimicrobial drugs

1. selective toxicity
2. antimicroial action
3. spetrum of activity
4. tissue distribution, metabolism and excretion
5. adverse effects
6. resistance

Answer 11

1. selective toxicity
   
   1. interfere with prokaryote lifesystem, not eukaryotes
      
      1. consider the mitochondria in humans
2. antimicroial action
   
   1. bacteriostatic
      
      1. ​inhits the growth allowing the host defense system to kill of eliminate the pathogen
   2. bactericidal
      
      1. kills microorganisms
3. spectrum of activity
   
   1. narrow spectrum
      
      1. affects one or a few types of bacteria
   2. broad spectrum
      
      1. affects many types of bacteria
4. tissue distribution, metabolism and excretion
   
   1. what happens to the drug when you introduce it to your body
      
      1. urinated, metabolized,
   2. what is the half life- the time it takes for the concentration of the drug to rach 50% of dosage
5. adverse effects
   
   1. allergic reactions
   2. toxic effets (therapeutic index)
   3. suppression of normal flora
6. resistance

Question 12

Doctor sam prescribed a drug that stop the addition of peptidoglycan in a gram + bacteria. What are 2 examples Sam can give and what does it act against?

Answer 12

Penicillins and cephalosporins

1. called beta lactam drugs
2. have a lactam ring that opens up to disrupt the cell wall.

bacteriocidal

Question 13

Dr.Sam needs to give a antibiotic that targets proteins synthesis for a patient.

1. What are the subunits being targeted and list the examples 1 and 4

Answer 13

Prokaryotes have a 70s ribosome (50s +30s)

exmaples

1. bactericidal
   
   1. aminoglycosides
2. bacteriostatic
   
   1. tetracyclines
   2. macrolides
   3. licosamides
   4. cholramphenicol

Question 14

Patient x has a gram negative and gram positive bacterial infection. Dr.Sam want to target the DNA replication cycle. What can he target, why and what can he use?

Answer 14

Target the topoisomerases, these are the same in gram- and gram+

1. topisomerases
   
   1. maintain supercoiling during DNA replication

fluoroquinolones- target topoisomerase

1. exmaples
   
   1. ciprofloxacin
2. bactericidal

Question 15

Dr.Sam needs to prescribe an antibiotic that targets the RNA pol.

What is he targeting, what diseases/strains are susceptible. Why does he stress to take the whole treatement?

Answer 15

Rifampicin-bactericidal

1. Targeting the RNA polymerase will block prokaryotic transcription
2. works against gram + and gram-
   
   1. useful against
      
      1. tuberculosis
      2. Hanses disese(leprosy)
3. treatement completment is stressed because resistance develops quickly dur to mutation in gene which codes for RNA polymerase

Question 16

After scrapping my knee on a hike, Dr.Sam puts some antibiotic ointment on before applying the banaid.

what was in the ointment, bactericidal or bacteriostatic, function against microbe, side affects

Answer 16

polymixin-B

bactericidal

binds to membrane of gram - bacteria which alters their permablity causing leakage of cellular contents

• not effective against gram +?

can affect eukaryotic cells, limiting it to topic application ONLY!!!

Question 17

Jane is testing a bacteria against some antibiotic strains.

What is this method, how can you interpret the results?

Answer 17

Kirby-Bauer disc diffusion method

discs have Ab on them that diffuse in to the medium.

• reading
  
  • growth up to disc
    
    • no suscebtibility = resistant
  • clear zone
    
    • zone of inhibition develops if the bacterium is susceptible to any degree
      
      • zone of inhibition size is dependent on characteristics of the drug and the susceptibility of the bacteria to that drug