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Microbiology

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Clinical/Applied Microbiology

Question
18 out of 45
 

A bacteria acquires a gene for restriction endonuclease by horizontal transfer. (AIIMS Nov 2010)



A Bacteria will be able to destroy host DNA more efficiently

B Bacteria will die due to methylase deficiency

C Bacteria will multiply faster

D Proof reading improved

Ans. B Bacteria will die due to methylase deficiency

a. A restriction enzyme (or restriction endonuclease) is an enzyme that cuts double stranded or single stranded DNA at specific recognition nucleotide sequences known as restriction sites. Such enzymes, found in bacteria, are thought to have evolved to provide a defense mechanism against invading viruses.

b. Inside a bacterial host, the restriction enzymes selectively cut up foreign DNA in a process called restriction; host (bacterial) DNA is methylated by a modification enzyme (a methylase) to protect it from the restriction enzyme’s activity.

c. By placing a methyl group on a base of the recognition site of a restriction endonuclease, methylases prevent the enzyme from cleaving the bacterial DNA and thereby protecting it. Collectively, these two processes form the restriction modification system.

d. Each restriction enzyme gene would be associated with another gene encoding the ability to produce a corresponding protective methylase enzyme.

e. In this question, the bacteria is acquiring a gene for restriction endonuclease by horizontal transfer.

f. It is not producing the protective methylase enzyme. Hence the restriction enzyme will cleave the bacterial DNA and it will die.

g. Each enzyme is named after the bacterium from which it was isolated using a naming system based on bacterial genus, species and strain. The 1st restriction endonuclease isolated was HindII from H. influenzae

h. While recognition sequences vary between 4 and 8 nucleotides, many of them are palindromic, which correspond to nitrogenous base sequences that read the same backwards and forwards.

i. Over 3000 restriction enzymes have been studied in detail, and more than 600 of these are available commercially and are routinely used for DNA modification and manipulation in laboratories, i. e genetic engineering.

j. Restriction enzymes are used to cut DNA into smaller strands followed by agarose gel electrophoresis in order to study fragment length differences among individuals (Restriction Fragment Length Polymophism – RFLP).

k. RFLP techniques have been used to determine that individuals or groups of individuals have distinctive differences in gene sequences and restriction cleavage patterns in certain areas of the genome. Knowledge of these unique areas is the basis for DNA fingerprinting.

Extra Edge

Some Important Negative Points In Microbiology Questions

a. Viremia does NOT occur in rabies

b. Conjugation does NOT involve Bacteriophage

c. In Chlamydial infection -Ureteritis+, cervicitis+, salpingitis+, proctitis +, Epididymitis+. But no orchitis, vulvitis

d. In Gonococcal infection-------------- Epididymitis+ But no orchitis

e. In TB------------------------------------ Epididymitis+ But rarely orchitis

f. In Syphilis------------------------------ Orchitis+ But no epididymitis, oophoritis

g. In Mumps ------------------------------ Orchitis+, Oophoritis+ But no epididymitis

h. Vertigo NOT occur in – Diphtheria

i. Diarrhea NOT occur in -- Botulism

j. Fever is NOT seen in - Botulism, staph food poisoning.

k. Transovarian transmission is NOT seen with - Louse, Flea.

l. NOT a components of Dane particle - Delta antigen

m. EBV is NOT associated with - Laennec's cirrhosis

n. (EBV is associated with IM, Burkitt's lymphoma & nasopharyngeal carcinoma).

o. Enterotoxins are NOT produced by – Streptococcus

p. Mycoplasma - is NOT an acid fast organism

q. Cl. sporogenes - is NOT a saccharolytic clostridia

r. Monocytes - are NOT useful in DNA analysis

s. Cryptococcus - is NOT a Di-morphic fungi.

t. Kidney - is NOT involved in cryptococcus infection

u. Anemia - is NOT commonly seen in Ascariasis

v. Candida - is NOT a causative agent of Madura foot

w. Sputum examination is NOT useful in - Trichiura, Babesia.

x. Pulmonary eosinophilia is NOT seen – babesiosis

y. Mycobacterial species are NOT differentiated by oxidase test.

z. Anti tubercular drug susceptibility can NOT be done by disc diffusion method.

aa. Infant botulism is NOT caused by preformed toxin.

· All botulinum toxins are neurotoxic except C2 (cytotoxic)

POINTS OF SPECIAL MENTION

a. Usually rickettsiae are not culturable, only rickettsia which is culturable - R. Quintana

b. Among Hepatitis viruses only HAV can be cultured.

c. Among various strains of Rota virus type-A strain can be cultured.

d. All Shigella ferment mannitol except Sh. dysentery.

e. Lactose is not fermented by Shigella except Sh. sonnei and paracolons which are late lactose fermenting.

f. E-coli toxins

g. - LT Cholera like (acts via c-AMP) - ST Poorly antigenic (acts via c-GMP)

h. VT Shiga like toxin (SLT, cytotoxic in vero or HeLa cells)

i. IL-I is produced by macrophage & monocytes, IL-2 by Tcells .

j. In Kala-azar

k. Hyper gamma-globulinemia occurs (with pancytopenia and relative lymphocytosis /monocytosis and

l. reversal of albumin: globulin ratio). globulin gives +ve Aldehyde test.

m. Cl/f of infectious mononucleosis with Monospot test positive - EBV

n. Infectious mononucleosis like syndrome with Monospot test negative - CMV.

o. Most rapid (fastest) & most sensitive method in TB diagnosis : Auramine rhodamine fluorescent dyes

Amebic meningoencephalitis is caused by : Naegleria fowleri, Acanthamoeba

Eosinophilic meningoencephalitis is caused by : Angiostrongyloides, Gnathostoma

Pneumocystitis Carinii is now k/as Pneumocystitis jiroveci

Clinical/Applied Microbiology Flashcard List

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