UREA CYCLE AND ITS IMPORTANT, Schemes and Mind Maps of Microbial Physiology

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UREA CYCLE AND ITS

IMPORTANCE

Presented By :- MISS. GLORIYA

M.Sc. Microbiology

2nd Semester

UREA CYCLE

HISTORY

• In 1932, Hans Krebs––Nobel laureate of 1953––and his assistant Kurt Henseleit

discovered the steps of urea synthesis in mammals. This was the first metabolic cycle that

was elucidated (while the idea of metabolic cycles had been around for some time

already).

• It takes place primarialiy in the liver.

Properties of Urea

Cycle



Non toxic



Water soluble



Combines with two waste products into:-

• Co

UREA CYCLE

STEPS in the Urea Cycle

The third step is catalyzed by an enzyme called

argininosuccinate synthetase, which uses citrulline and

ATP to form a citrullyl-AMP intermediate, which reacts

with an amino group from aspartate to produce

argininosuccinate.

Citrulline + ATP + aspartate → argininosuccinate + AMP

• Ppi

The fourth step involves the cleavage of

argininosuccinate to form fumarate and arginine.

Argininosuccinate lyase is the enzyme catalyzing

this reaction

Argininosuccinate → arginine + fumarate

In the fifth and last step of the urea cycle, arginine is

UREA SYNTHESIS

Figure 19.14 Reactions of the urea cycle.

[Note: An antiporter transports

citrulline and ornithine across the inner

mitochondrial membrane.] ADP =

adenosine diphosphate; AMP =

adenosine monophosphate; PPi =

pyrophosphate; Pi = inorganic

phosphate; NAD(H) = nicotinamide

adenine dinucleotide

Significance of the Urea Cycle

The main purpose of the urea cycle is to eliminate toxic

ammonia from the body.

A dysfunctional urea cycle would mean excess amount

of ammonia in the body which may lead to

hyperammonemia diseases etc.

Defects in the urea cycle can cause vomiting, coma and

convulsions in new born babies.

Diagnosis of Urea Cycle Defects

• The concentration of the nitrogen-carrying amino acids, glutamine

and alanine, in plasma is elevated in the case of OTC deficiency.

• blood ammonia and urinary orotic acid monitoring and quantitation

are crucial in patients with unexplained neurological symptoms.

• OROTIC ACID = a precursor in biosynthesis of pyrimidines in

mammals, which is released from the mitochondrial dihydroorotate

dehydrogenase (DHODH) for UMP(cytoplasmic) synthase enzyme.

References

Microbial physiology (

th

Edition); Alebert G. Moet

Textbook of biochemistry; U. Satyanarayana , U.

Chakrapani

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