Microbiology MCQ 2 - Biotechnology Engineering (BT) MCQ

Acid fast staining targets mycolic acid in the cell wall of Mycobacterium species. 

Dilution factor
- 1 ml original diluted to 10ml means 10 times dilution
- 1 ml of diluted culture further diluted to 100 ml means 100 times dilution 
Total dilution factor = 1000 times = 10^-3
Here. 0.5 ml of final culture contains 200 colonies

Maximum synthesis of antibiotics in a microbial culture occurs in stationary phase because in stationary phase, nutrition and space become limitation. So to prevent excess growth in limited resources  and in this stress condition, microbes starts producing antibiotics (as a survival mechanism).

Photolithoautotrophs are the organisms which use
    - CO₂ as carbon source (Autotrophs)
    - Inorganic ions / compounds as H⁺/e^– source (Litho)
    - Sunlight as energy source (Photo)

Aerotolerant anaerobes grow equally well in the presence or absence of oxygen, eg. Streptococcus pyrogenes.

Sequence of events that occur during lytic cycle of bacteriophage infection is,
(i)    Virus attaches on to the surface of the host bacterium.
(ii)    Penetration of viral DNA into the host
(iii)    Synthesis of viral nucleic acid and protein
(iv)    Assembly and packaging of new virus
(v)    Release of new virus by lysis of the host cell

Genome of retroviruses is single stranded RNA and not ds DNA.

Creutzfeldt Jacob disease in humans is caused by prions. Prions are infectious proteins with no nucleic acid.

Penicillin inhibits cell wall synthesis in bacteria by inhibiting the process of transpeptidation reaction, which is essential for cell wall synthesis.

Streptomycin inhibits translation in prokaryotes by preventing the formation of 70S ribosomes. It acts on the 30S subunit of prokaryotic ribosomes.

Gentamycin is an antibiotic produced by the bacteria belonging to Micromonospora sp. It inhibits translation by inhibiting 16s rRNA.

D-amino acids are most likely present in cross links of peptidioglycan layer as proteases easily cleave L-amino acids.

Exotoxins are produced by some species of gram positive and gram negative bacteria.
    - They are secreted out of the cell
    - They are heat labile, and get inactivated rapidly at 60 to 80ºC
    - They are polypeptides
    - They can be converted to toxoids and used as vaccines. 

Tetanus is caused by Clostridium tetani
    Anthrax is caused by Bacillus anthracis
    Whooping cough is caused by Bordetella pertusis    
    Meningococcal meningitis caused by Bordetella pertusis

Kuru disease is caused by prions in humans. Scrapie disease is caused by prions in sheep.  

HIV is an enveloped virus and contains a RNA dependent DNA polymerase for infection. DNA copy of HIV genome is integrated into host cell DNA.

All the characteristic present in options are correct regarding gram positive cells.

Cocci bacterium has spherical shape. 
Surface area of sphere = 4ar²
Volume of sphere = 4/3ar²