Urea cycle

Urea cycle

1. UREA CYCLE
OPTOM FASLU MUHAMMED

2. Urea cycleUrea cycle
DefinitionDefinition

The The urea cycleurea cycle (also known as the (also known as the
ornithine cycleornithine cycle) is a cycle of ) is a cycle of
biochemicalbiochemical reactions occurring in reactions occurring in
many animals that produces many animals that produces ureaurea ( (NN
HH2)22)2CCOO from from ammoniaammonia (NH3) (NH3)

3. FunctionFunction
Organisms that cannot easily and Organisms that cannot easily and
quickly remove ammonia usually quickly remove ammonia usually
have to convert it to some other have to convert it to some other
substance, like urea or substance, like urea or uric acid,uric acid,
which are much less toxic.which are much less toxic.
 Insufficiency of the urea cycle Insufficiency of the urea cycle
occurs in some genetic disorders occurs in some genetic disorders
(inborn errors of metabolism), and in (inborn errors of metabolism), and in
liver failure. liver failure.

4. • Urea is less toxic than ammonia.Urea is less toxic than ammonia.
•The The Urea CycleUrea Cycle occurs mainly in occurs mainly in
liverliver. .
•The 2 nitrogen atoms of urea enter The 2 nitrogen atoms of urea enter
the Urea Cycle as the Urea Cycle as NHNH
33
(produced (produced
mainly via Glutamate mainly via Glutamate
Dehydrogenase) and as the aminoDehydrogenase) and as the amino NN
of aspartateof aspartate. .
•The NHThe NH
33 and HCO and HCO
33
--
(carbonyl C) that (carbonyl C) that
will be part of urea are incorporated will be part of urea are incorporated
first into first into carbamoyl phosphatecarbamoyl phosphate . .

H
2NC
O
NH
2
urea

5. Urea cycleUrea cycle
Ammonia is toxicAmmonia is toxic
Readily ionises to ammonium Readily ionises to ammonium
ion NHion NH
44
++
NHNH
44
+ +
converted to urea in liver converted to urea in liver
(urea cycle)(urea cycle)
Urea contains 2 x NHUrea contains 2 x NH
22
One from NHOne from NH
44
++
One from aspartate One from aspartate
Urea excreted in urineUrea excreted in urine

7. Urea CycleUrea Cycle
•Enzymes in Enzymes in
mitochondriamitochondria: :
1.1. Ornithine Ornithine
Trans-Trans-
carbamylasecarbamylase
Enzymes in Enzymes in
cytosolcytosol::
2.2. Arginino- Arginino-
SuccinateSuccinate
SynthaseSynthase
3.3. Arginino- Arginino-
succinasesuccinase
4.4. Arginase. Arginase.
H
2NCOPO
3
2-
O
CH
2
CH
2
CH
2
HC
COO
-
NH
3
+
NH
3
+
CH
2
CH
2
CH
2
HC
COO
-
NH
3
+
NH
CO NH
2
COO
-
CH
2
HC
COO
-
NH
2
CH
2
CH
2
CH
2
HC
COO
-
NH
3
+
NH
CNH
2
+
COO
-
CH
2
HC
COO
-
H
N
AMP + PP
i
ATP
CH
2
CH
2
CH
2
HC
COO
-
NH
3
+
NH
C
NH
2
+
H
2N
COO
-
HC
CH
COO
-
CNH
2H
2N
O H
2O
P
i

ornithine
urea
citrulline
aspartate
arginino-
succinate
fumarate
arginine
carbamoyl
phosphate
Urea Cycle
1
2
3
4

8. BY:BY:
Abdulrhman Mohammed Twhari.Abdulrhman Mohammed Twhari.
Ebrahim MohammedEbrahim Mohammed DaghririDaghriri