Amino Acid Metabolism (Lec) Flashcards
repetitive process in which proteins are degraded and resynthesized
protein turnover
T/F - The rate of protein synthesis is just sufficient to replace the protein being degraded
T (Leads to hydrolysis and resynthesis of 300-400 g of body protein eaach day
state that results when the amount of nitrogen taken into the human body as protein equals the amount of nitrogen excreted from the body in waste materials
nitrogen balance
amount of nitrogen in urine exceeds consumed amount, also results in tissue wasting
negative nitrogen imbalance
rate of protein synthesis (anabolism) is more than protein degradation (catabolism)
positive nitrogen imbalance
indicated by the synthesis of large amounts of tissue
positive nitrogen imbalance
T/F - Amino acids are not stored by the body, unlike fats and
carbohydrates.
T (must either be obtained from the diet,
synthesized de novo, or produced from normal protein
degradation)
T/F - Proteins can be used as an energy source, but is rarely
used as such.
T
directed towards conserving tissues to the
greatest extent possible
Metabolism
Digestion of protein compromises?
muscle
where the mechanical breakdown of the proteins begins
teeth
Protein digestion starts in the?
stomach
Dietary protein stimulates the release of?
gastrin (a hormone that stimulates the stomach to
release gastric acid (hydrochloric acid) and pepsinogen
(Recall: zymogens))
Functions of HCl:
Antiseptic - kill most bacteria
low pH will denature proteins
Acidic environment activates pepsinogen
Pepsin affects the hydrolysis of __ of peptide bonds
10%
stimulated by the passage of small
amounts of acidic content into the small intestine.
Secretin production
(promotes the secretion of pancreatic digestive
enzymes : trypsin, chymotrypsin, and carboxypeptidase in
their inactive forms)
secreted by enterocytes - cells in the intestinal lining - and
further breakdown the remaining polypeptides into amino
acids.
Dipeptidase, tripeptidase, and aminopeptidase
The pool of amino acids are then used to:
- synthesize proteins
- synthesize nitrogen-containing compounds (purines,
pyrimidines) - turned into glucose, glycogen, fatty acids, ketone bodies,
water, or carbon dioxide (energy source)
the state of which amino acids are especially catabolized
to yield the carbon skeleton and to form intermediates for
carbohydrate and lipid biosynthesis, which are then used as
an energy source.
In the starved state
degraded to form ketone bodies ,
which degrade to acetyl-CoA or acetoacetyl-CoA
Ketogenic amino acids
degraded to TCA intermediates,
which can then be used for glucose synthesis
(gluconeogenesis)
Gluocgenic amino acids
Body protein is catabolized primarily in?
muscle and liver
Amino acids released from proteins usually lose their amino
group through?
transamination or oxidative deamination
T/F - Each amino acid has a unique degradation pathway
T
two main mechanisms involved in the degradation
of amino acids:
transamination and oxidative deamination
A reversible process
transamination
Aminotransferase used as catalyst =, a-amino acids are converted to alpha Keto acid
Transamination
(Glutamate can be produced through
transamination, with a-ketoglutarate
as amino group acceptor)
An alpha-amino acid is converted to
an alpha-keto acid, releasing an
amoonium ion
Oxidative Deamination
Occurs in the liver and kidney
mitochondria
Oxidative Deamination
Summary of Oxidative Deamination and the Transport of Ammonia to the Liver
the amino acids are broken down, while passing along the amino group with the help of enzymes until it can finally be sent to the urea cycle.
Tissues use glutamine synthase to combine ammonia with glutamate to form glutamine.
Glutamine is then transported in the blood to the liver.
Cleavage is then done by glutaminase to produce glutamate and free ammonia.
Cahill Cycle
Alanine is transported by the blood to the liver
where it is converted to pyruvate
Connects with the Cori Cycle. Alanine serves as carrier of ammonia and of the carbons of pyruvate from skeletal muscle to liver (Cori)
__ ATP molecules are used to produce ONE urea molecule
4
Two molecules of ATP are used in the production of?
carbamoyl phosphate
The equivalent of 2 ATP molecules are consumed in the __ step to produce AMP
2nd
UREA CYLE
First Step : Carbomoyl
Group Transfer
Carbon dioxide and ammonia are
combined to form carbamoyl phosphate
with the help of carbamoyl phosphate
synthetase (formed in the
mitochondrial matrix)
The carbamoyl group of carbamoyl
phosphate is transferred to ornithine to
form citrulline
UREA CYLE
Second Step : Citrulline Aspartate Condensation
Citrulline is then transported into the
cytosol, reacting with aspartate to form
argininosuccinate synthetase, utilizing
ATP.
This step makes use of the enzyme
argininosuccinate synthetase, utilizing
ATP.
UREA CYLE
Third Step : Argininosuccinate
Cleavage
Argininosuccinate is cleaved to
arginine and fumarate by the enzyme
argininosuccinate lyase.
UREA CYLE
Urea From
Arginine Hydrolysis
Hydrolysis of arginine produces urea
and regenerates ornithine under the
influence of the enzyme arginase.
The oxygen atom present in urea
comes from water. Ornithine is transported back to the
mitochondria, to be reused in the urea
cycle.
PRODUCTS OF UREA CYCLE (8)
ORNITHINE
CARBAMOYL P.
CITRULLINE
ASPARTATE
ARGININOSUCCINATE
FUMARATE
ARGININE
UREA
The fumarate produced is ultimately
converted to aspartate.
Aspartate reenters the urea cycle at Step 2
Both the urea cycle and the Krebs cycle
were discovered by Hans Adolf Krebs
