Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Metabolic Pathways > Lecture 2 (1B) - The Urea Cycle > Flashcards

Lecture 2 (1B) - The Urea Cycle Flashcards

1
Q

Ammmonium

A

NH4+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Ammonia

A

NH3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Active nitrogen

A

NH3 (ammonia)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Nitrogen from… microbes and plants

A
  • NO2-
  • NO32-
  • NH3
  • N2
  • involves the enzyme nitrogenase
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Nitrogen from… animals

A

from diet, mainly amino acids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Nitrogen uses

A
  • amino acids
  • purines and pyrimidines (DNA bases)
  • haems
  • chlorophylls (for rings)
  • corrins
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

The urea cycle in animals

A

• nitrogen formed from amino acid breakdown

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Animals excrete nitrogen in 3 ways

A
  • ammonia in aquatic animals (ammonotelic)
  • uric acid in birds and reptiles (uricotelic)
  • urea in humans (ureotelic)
  • try to convert ammonia (active, dangerous, toxic) into urea
  • ammonia –> urea UREA IS NOT URINE
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

The urea cycle - history

A
  • outlined in 1932 by Krebs and Henselieit
  • more detail by Ratner and Cohen (identified components in cycle and details)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Urea cycle - overall process

A

ammonia + bicarbonate + aspartate

–>

urea + fumarate

• uses 3ATP –> 2 ADP + AMP + 2 Pi + PPi (requires energy)

CO2 + NH4+ + 3ATP + aspartate + 2H2O

–>

urea + 2ADP + 2Pi + AMP + PPi + fumarate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Urea cycle uses

A

3 ATP

–>

2ADP + AMP + 2 Pi + PPi

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Aquatic animals excrete nitrogen as

A

ammonia

• ammonotelic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Ammonotelic

A

• aquatic animals excrete nitrogen as ammonia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Birds and reptiles excrete nitrogen as

A

uric acid

• uricotelic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Uricotelic

A

• birds and reptiles excrete nitrogen as uric acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Humans excrete nitrogen as

A

urea

• ureotelic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Ureotelic

A

humans excrete nitrogen as urea

  • try to convert ammonia (active, dangerous, toxic) into urea
  • urea is NOT urine
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Urea cycle - basics

A
  • occurs in the liver - NOT KIDNEYS - GENERATED IN THE LIVER
  • urea into blood
  • kidneys extract urea (kidney filters, eg like dialysis)
  • excreted in urine
19
Q

Urea =

A

2 nitrogens from NH3 (ammonia) and from aspartate

20
Q

Urea cycle - mechanics

A

• requires 5 enzymes

  • 2 mitochondrial
  • 3 cytosolic

• specific components therefore transported across mitochondrial membrane (ornithine and citrulline transporters)

21
Q

The priming step

• not strictly part of the urea cycle

A

• carbamoyl phosphate synthetase

(CPS I) (-etase = uses energy)

• CPS I = mitochondrial,

regulated by N-acetylglutamate

2 ATP + Bicarbonate + ammonia

–>

carbamoyl phosphate + 2 ADP + Pi

• 1 phosphate attached to carbamoyl phosphate to activate it

22
Q

The rate-limiting step of the urea cycle

(controls cycle/speed)

A

generally the first step controls/regulates the cycle/process

  • FIRST NITROGEN INCLUDED
  • CPS I reaction in mitochondria
  • 3 step process
23
Q
  1. 3 steps of the rate-limiting step
A

1.

ATP + HCO3-

–>

carboxyphosphate + ADP

2.

NH3 + carboxyphosphate

–>

carbamate + Pi

3.

ATP + carbamate

–>

carbamoyl phosphate + ADP

(once again phosphate added as activation)

24
Q

CPS I and CPS II

A

CPS I relevant - in mitochondrion

CPS II not relevant - in cytosol

25
Q

Urea cycle steps after rate-limiting

A

in mito

  1. ORNITHINE TRANSCARBAMOYLASE

ornithine + carbamoyl phosphate

–>

citrulline + Pi

cytosolic

  1. ARGININOSUCCINATE SYNTHETASE

ATP + citrulline

–>

citrulline-AMP + PPi

citrulline-AMP + Aspartate

–>

argininosuccinate + AMP

(second N added from aspartate, urea created)

  1. ARGININOSUCCINASE

argininosuccinate

–>

arginine + fumarate

  1. ARGINASE

arginine

–>

urea + ornithine

26
Q
  1. Ornithine transcarbamoylase
A

ornithine + carbamoyl phosphate

–>

citrulline + Pi

  • carbamoyl transferred to ornithine to get citrulline
  • ornithine is out in the cytosol but then transported to mitochondrial membrane
  • reaction in the mitochondrion, ornithine brought in from cytosol
  • next reaction cytosolic, citrulline transported out
27
Q
  1. Argininosuccinate synthetase
A

ATP + citrulline

–>

citrulline-AMP + PPi

citrulline-AMP + Aspartate

–>

argininosuccinate + AMP

  • in cytosol
  • bonds AMP to citrulline shown by 18-O labelling
  • SECOND NITROGEN (amino) INCLUDED (from aspartate)
  • urea now fully assembled
  • in creation of argininosuccinate urea has been created
28
Q
  1. Argininosuccinase
A

argininosuccinate

–>

arginine + fumarate

  • arginine = amino acid precursor to urea
  • fumarate can be used for aspartate cleaves argininosuccinate into arginine and fumarate
  • carbon skeleton of aspartate is preserved in the form of fumarate
29
Q
  1. Arginase
A

arginine

–>

urea + ornithine

  • ornithine recreated = cycle (originally put in to make citrulline)
  • passed to mitochondrion
  • hydrolysis
  • ornithine goes to mitochondrion
  • urea is excreted
30
Q

Regulation of the Urea Cycle

A
  • N-acetylglutamate
  • glutamate
  • all other enzymes controlled by substrate concentration
31
Q

Regulation of the Urea Cycle

N-acetylglutamate

A

allosteric activation of carbamoyl phosphate synthetase I (priming step)

32
Q

Regulation of the Urea Cycle

Glutamate

A
  • glutamate increase in amino acid breakdown
  • hence increased in N-acetylglutamate
  • hence urea cycle upregulated in turnover
33
Q

Regulation of the Urea Cycle

All other enzymes controlled by

A

substrate concentration

34
Q

Urea cycle diseases

A
  • hyperammonemia
  • ornithine transcarbamoylase deficiency (OTCD)
  • argininosuccinase deficiency
35
Q

Urea cycle disease

Hyperammonemia

A
  • major problems with the brain (makes brain switch off, lethargic)
  • probably interferes with production of - glutamate - GABA
  • hence neurological defects result - brain starts to switch off - morbidity
36
Q

Urea cycle disease

Ornithine transcarbamoylase deficiency (OTCD)

A

ornithine + transcarbamoyl phosphate

–>

citrulline + Pi

• elevated levels of

  • glutamate
  • orotic acid
  • ammonia

• low levels of citrulline

37
Q

Urea cycle disease

OTCD treatment

A

diet supplement

  • benzoate, phenylacetate

• take up ammonia in different ways of excretion, different products excreted

38
Q

Urea cycle disease

argininosuccinase deficiency

A

argininosuccinate

–>

arginine + fumarate

  • usually severe hyperammonemia
  • very few other levels altered
39
Q

Urea cycle disease

arginninosuccinase deficiency treatment

A

diet supplement

  • arginine to help with the cycle
  • limited protein intake
40
Q

The urea cycle begins with the coupling of

A

free NH3 (ammonia) with HCO3 - (bicarbonate) to form carbamoyl phsophate

41
Q

NH3 is a strong base that normally exists as

A

NH4 + in aqueous solution

but carbamoyl phosphate synthetase only uses NH3 as a substrate

42
Q

Parts of the urea cycle that happen in the mitochondrial matrix

A
  • formation of NH4 + by glutamate dehydrogenase
  • its incorporation into carbamoyl phosphate as NH3
  • synthesis of citrulline next 3 reactions of the urea cycle in the cytoplasm
43
Q

Urea cycle - picture

A
44
Q

Recreating aspartate from fumarate

A

Metabolic Pathways (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions