Protein Metabolism (Lab) Flashcards
T/F - Amino acids are not stored by the body (unlike fats and carbohydrates)
T
T/F - Amino acids must be obtained from the diet, synthesized de novo or produced from normal protein degradation
T
1st phase of AA catabolism
Removal of α-amino groups
Formation of ammonia and corresponding α-keto acid
Ammonia excreted in the urine or used to synthesize urea
2nd phase of AA catabolism
α-keto acids
common intermediates of energy producing metabolic pathways
(can be metabolized to CO2 and water, glucose, fatty acids, or ketone bodies)
Protein digestion starts in the ___
stomach
Dietary protein present in the stomach
stimulates the release of ___
gastrin
promotes secretion of pepsinogen and HCl/hydrochloric acid (has 3 functions)
Gastrin
FUNCTIONS OF HCL
- Antiseptic properties kill most bacteria
- Denaturing action “unwinds” globular
proteins - Acidic property leads to activation of
pepsinogen
affects the hydrolysis of 10% peptide bonds
Pepsin
Production of ____ is stimulated by the passage
of small amounts of acidic protein content into the
small intestine
secretin
Secretin stimulates ____ production, which in turn helps neutralize acidified gastric content
bicarbonate (HCO3-)
Promotes secretion of pancreatic digestive
enzymes trypsin, chymotrypsin, and
carboxypeptidase in their inactive forms
secretin
also have their zymogen forms
Proteolytic Enzymes
Specific to N- and C-terminal cleavage of Phe and Leu
Pepsin (pH 1.3)
Specific to C-terminal cleavage of Lys and Arg
Trypsin
Specific to C-terminal cleavage of aromatic amino acids
Chymotrypsin
T/F - N terminal side - <amino> - C-terminal side</amino>
T
are transported into the bloodstream via active transport process
Liberated amino acids
The passage of polypeptides and small proteins across the ____ is uncommon in adults
intestinal wall
In _____, the transport of polypeptides allows the passage of proteins such as antibodies in
colostrum milk from a mother to a nursing infant to build up immunologic protection in the
infant
infants
Protein Digestion and Absorption Pathway
- Mouth - Saliva (No effect on digestion)
- Stomach - HCl (denatures protein; Pepsin (Hydrolyzes peptide bonds)
–> Large Polypeptides - Small Intestine - Trypsin, Chymotrypsin, Carboxypeptidase, Aminopeptidase (all hydrolyzes peptide bonds)
- Intestinal Lining - Active transport
total supply of free amino acids available for use in
the human body
The Amino Acid Pool
Amino Acid Utilization
SOURCES
- Amino acid degraded of body
proteins - Amino acids derived from dietary
protein - Synthesis of non-essential AA from
intermediates of metabolism
Amino Acid Utilization
ROUTES OF DEPLETION
- Synthesis of body protein
- AA consumed for the synthesis of
essential nitrogen-containing
molecules - Conversion of AA to glucose,
glycogen, fatty acids, ketone
bodies, or H2O + CO2
The 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 each day)
Biosynthesis of non-essential amino acids in the liver
the 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
Protein degradation exceeds protein synthesis; Amount of nitrogen in urine exceeds consumed amount; Results in tissue wasting
Negative nitrogen imbalance
Rate of protein synthesis (anabolism) is more than
protein degradation (catabolism); Indicated by the synthesis of large amounts of tissue
Positive nitrogen imbalance
Uses for Amino Acids (4)
Protein synthesis
Synthesis of non-protein nitrogen-containing compounds
Synthesis of non-essential amino acids
Production of energy
Uses approximately 75% of free amino acids
Protein synthesis
Synthesis of purines and pyrimidines; Synthesis of heme for
hemoglobin
Synthesis of non-protein nitrogen-containing compounds
Essential amino acids
cannot be synthesized
due to the lack of an
appropriate carbon
chain
Synthesis of
non-essential amino
acids
Amino acids are not
stored in the body
(excess are degraded)
Production of energy
T/F - Each amino acid has a unique degradation pathway
T
T/F - The amino nitrogen atom is removed and excreted from the body as urea
T
T/F - The remaining carbon skeleton is converted to pyruvate, acetyl CoA, or a citric acid cycle intermediate
T
Two stages of amino acid degradation:
- Removal of the α-amino group
- Degradation of the remaining carbon skeleton
produced through transamination when α-ketoglutarate is
the amino group acceptor
Glutamate (Glutamate Production via Transamination)
always utilized glutamine in its amino
transfers, as many amino acids have their respective keto-acid
equivalent which are derived from or are themselves Krebs cycle
intermediates
Aminotransferase
Aminotransferase reaction uses
_____ as the amino group
acceptor.
α-ketoglutarate
Reactions catalyzed during
amino acid catabolism: (2)
A. Alanine aminotransferase
(ALT) – transfers an amino
group from alanine
B. Aspartate aminotransferase
(AST) – transfers an amino
group from aspartate
a biochemical reaction in which an
α-amino acid is converted to an α-keto acid with
release of an ammonium ion that occurs in the
mitochondria of the liver and kidney
Deamination
Oxidative Deamination (2):
a. Disposal of amino acids
b. Synthesis of amino acids
Transport of Ammonia to the Liver
- Tissues use ______ to combine ammonia with
glutamate to form glutamine
glutamine synthase
Transport of Ammonia to the Liver
- _____is then transported in the blood to the liver
Glutamine
Transport of Ammonia to the Liver
- Cleavage is then done by ______ to produce glutamate
and free ammonia
glutaminase
Transport of Ammonia to the Liver (In the muscle)
Alanine is transported by the blood to the liver where it is
converted to _____
pyruvate
the body’s only way to SAFELY remove ammonia
(NH3) from the body
Urea Cycle
can be toxic, hence the need for its
removal
Ammonia build up
mainly described as a series of biochemical reactions
in which urea is produced from ammonium ions and
aspartate as nitrogen sources
The Urea Cycle
produced in the liver is transported via blood to
the kidneys and eliminated from the body in urine
Urea
The Urea Cycle Processes (4):
- CARBOMOYL GROUP TRANSFER
- CITRULLINE-ASPARTATE CONDENSATION
- ARGININOSUCCINATE CLEAVAGE
- UREA FROM ARGININE HYDROLYSIS
- CARBOMOYL GROUP TRANSFER
one of the sources
of fuel for the urea cycle
Carbamoyl Phosphate
CARBOMOYL GROUP TRANSFER
How many ATP molecules are expended in
the formation of one carbamoyl
phosphate molecule?
2 (contains a
high-energy phosphate bond and is
formed in the mitochondrial matrix.)
CARBOMOYL GROUP TRANSFER
The carbamoyl group of carbamoyl
phosphate is transferred to ornithine to
form ____
citrulline
- CITRULLINE-ASPARTATE CONDENSATION
Citrulline is transported into the _____and reacts with _____to produce _______, utilizing ATP
cytosol, aspartate, argininosuccinate synthetase
- ARGININOSUCCINATE CLEAVAGE
Argininosuccinate is cleaved to arginine and fumarate by the enzyme _______
argininosuccinate lyase
- UREA FROM ARGININE HYDROLYSIS (3):
a) Hydrolysis of arginine produces urea
and regenerates ornithine under the
influence of arginase
b) The oxygen atom present in urea
comes from water
c) Ornithine is transported back to
mitochondria to be used in the urea
cycle
Net Reaction
How many ATP molecules used in
the production of one urea molecule
4
How many are consumed in the production of
carbamoyl phosphate
2
The equivalent of two ATP
molecules is consumed in step
two of the urea cycle to give ___ and the ___
AMP and the PPi
Relationship of the Urea Cycle and Krebs Cycle
Fumarate produced is
ultimately converted to
aspartate
- Aspartate re-enters the
urea cycle at step two
Glucogenic and Ketogenic Amino Acids
____ removes the amino group
from an amino acid
Transamination/oxidative deamination
An ______ that contains the skeleton of the amino acid is produced
α-keto acid
Products formed are among a group of ____
seven intermediates (Four products are intermediates in the citric acid cycle; Three products are pyruvate, acetyl CoA, and acetoacetyl CoA
Glucogenic and Ketogenic Amino Acids
The amino acids converted to citric acid cycle intermediates can serve as ______
glucose precursors
Glucogenic and Ketogenic Amino Acids
The amino acids converted to acetyl CoA or acetoacetyl-CoA can contribute to the formation of ______
fatty acids
An amino acid that has a
carbon-containing degradation product
that can be used to produce glucose via
gluconeogenesis
Glucogenic amino acids
An amino acid that has a
carbon-containing degradation product
that can be used to produce ketone
bodies (only Leu and Lys are purely
ketogenic)
Ketogenic amino acids
Glucogenic Nonessential Amino Acids (11):
Alanine
Arginine*
Asparagine
Aspartate
Cysteine
Glutamate
Glutamine
Glycine
Histidine*
Proline
Serine
Glucogenic Essential Amino Acids (3):
Methionine
Threonine
Valine
Glucogenic and ketogenic Nonessential amino acid (1):
Tyrosine
Glucogenic and ketogenic Essential amino acid (3):
Isoleucine
Phenylalanine
Tryptophan
Ketogenic Essential Amino Acids (2)
Leucine
Lysine
