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The Info List - Deamination


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(i)

DEAMINATION is the removal of an amino group from a molecule . Enzymes that catalyse this reaction are called DEAMINASES.

In the human body , deamination takes place primarily in the liver , however glutamate is also deaminated in the kidneys . In situations of excess protein intake, deamination is used to break down amino acids for energy. The amino group is removed from the amino acid and converted to ammonia . The rest of the amino acid is made up of mostly carbon and hydrogen , and is recycled or oxidized for energy. Ammonia is toxic to the human system, and enzymes convert it to urea or uric acid by addition of carbon dioxide molecules (which is not considered a deamination process) in the urea cycle , which also takes place in the liver. Urea
Urea
and uric acid can safely diffuse into the blood and then be excreted in urine.

CONTENTS

* 1 Deamination
Deamination
reactions in DNA
DNA

* 1.1 Cytosine * 1.2 5-methylcytosine
5-methylcytosine
* 1.3 Guanine * 1.4 Adenine

* 2 Additional proteins performing this function * 3 References

DEAMINATION REACTIONS IN DNA

CYTOSINE

Spontaneous deamination is the hydrolysis reaction of cytosine into uracil , releasing ammonia in the process. This can occur in vitro through the use of bisulfite , which deaminates cytosine, but not 5-methylcytosine
5-methylcytosine
. This property has allowed researchers to sequence methylated DNA
DNA
to distinguish non-methylated cytosine (shown up as uracil ) and methylated cytosine (unaltered).

In DNA
DNA
, this spontaneous deamination is corrected for by the removal of uracil (product of cytosine deamination and not part of DNA) by uracil- DNA
DNA
glycosylase , generating an abasic (AP) site. The resulting abasic site is then recognised by enzymes (AP endonucleases ) that break a phosphodiester bond in the DNA, permitting the repair of the resulting lesion by replacement with another cytosine. A DNA polymerase may perform this replacement via nick translation , a terminal excision reaction by its 5'-->3' exonuclease activity, f