Amino Acid Metabolism I Flashcards
How many amino acids do we have
20
unneeded or damaged proteins are marked for destruction by the covalent attachment of chains of a small protein called _____. and then degraded by a large, ATP-dependent complex called the ______
Ubiquitin, proteasome
What is the primary use of amino acids provided through degradation or digestion
building blocks for the synthesis of proteins and other nitrogenous compounds such as nucleotide bases
Amino acids in excess of those needed for biosynthesis can neither be ____ or _____.
stored, excreted
Surplus amino acids are used as
metabolic fuel ( the alpha-amino group is removed, and the resulting carbon skeleton is converted into a major metabolic intermediate)
most amino groups harvested from surplus amino acids are converted into ____ through the ____. And their carbon skeletons are transformed into
urea through the urea cycle. Acetyl CoA, Acetoacetyl CoA, pyruvate, or one of the intermediates of the TCA cycle
Coenzyme that forms Schiff-base intermediates, that allow alpha amino groups to be shuttled between amino acids and ketoacids
pyridoxal phosphate
Protein digestion begins in the
stomach
Primary proteolytic enzyme of the stomach
pepsin
In the small intestine the low pH of the food as well as the polypeptide products for pepsin digestion stimulate the release of
Sodium bicarbonate and a variety of proteolytic enzymes are released from the pancreas
Pancreatic enzymes are secreted as _______. Name them
-Zymogens
Tyrpsinogen, chymotrypsinogen, proelastase, and procarboxypeptidase
What is the proteolytic enzyme on the plasma membrane of intestinal cells.
Aminopeptidase N
Aminopeptidases digest proteins form the ____ end
amino-terminal end
____ amino acids, as well as ___ and ____, are transported into the intestinal cells
Single amino acids, as well as Di and Tripeptides
At least ____ different amino acid transporters exist, each specific to a different group of amino acids. They transport amino acids into the intestinal cells
7
Amino acids in the intestinal cells are transported into the blood by a number of _______ antiporters for use by other tissues
Na+-amino acid
Protein digestion is primarily a result of the activity of enzymes secreted by the ____
pancreas
The half-lives of proteins range over ____ orders of magnitude
several (from minutes to days)
A small (76 amino acids) protein present in all eukaryotic cells, is a tag that marks proteins for destruction
Ubiquitin (Ub)
The first step in amino acid degradation is the
removal of nitrogen
what is the major site of amino acid degradation in mammals
the liver (although muscles readily degrade the branched chain amino acids)
______ catalyze the transfer of an alpha-amino group form an alpha amino acid to an alpha ketoacid
aminotransferases (also called transaminases)
Aminotransferases (also called transaminases) generally funnel alpha amino groups form a variety of amino acids to ______ for conversion into NH4+
alpha-ketoglutarate
The nitrogen atom in glutamate is converted into fee ammonium ion (NH4+) by oxidative deamination, a reaction catalyzed by
glutamate dehydrogenase
Glutamate dehydrogenase is unusual because it can utilize either ____ or _____
NAD+ or NADP+
glutamate dehydrogenase is allosterically inhibited by ____ and stimulated by ___
inhibited by GTP, stimulated by ADP
What is negative nitrogen balance? and when can it be seen
more nitrogen out than in. Commonly seen in Cancers because you are degrading proteins unnaturally fast
What is positive nitrogen balance? and when is it commonly seen
Postive nitrogen balance is seen in athletes, pregnancy, and newborns
all aminotransferases contain the prosthetic group _____, which is derived form ______
pyridoxyl phosphate (PLP), which is derived form pyridoxine (vitamin B6)
The production of Ammonia from amino acids has how many steps and what are they
- 2
- Step 1: Transamination: transfer of an alpha amino group form an alpha amino acid to an alpha-ketoacid
- Step 2: oxidative Deamination: Nitrogen atom in glutamate is converted into free ammonium ion
muscles lacks the enzymes of the ____ cycle
urea
Enzyme that catalyzes the coupling of free NH3 with HCO3 to make Carbamoyl phosphate
Carbamoyl phosphate synthetase I
What is the committed step in the urea cycle
the coupling of free NH3 with HCO3- to make Carbamoyl phosphate (catalyzed by carbamoyl phosphatase syntheses I)
Carbamoyl phosphate synthetase I requires how many ATP
2
Enzyme that catalyzes the transfer of Carbamoyl group (from carbamoyl phosphate) to Ornithine to form Citrulline
Ornithine transcarbamoylase
Enzyme that Catalyzes the condensation of Citrulline with Aspartate to form Argininosuccinate
Argininosuccinate synthetase
Enzyme that cleaves Argininosuccinate into Arginine and Fumarate
Argininosuccinase (Argininosuccinate lyase)
In the urea cycle the aspartate carbon skeleton is conserved in the production of
fumarate
Catalyzes Arginine hydrolysis to urea and ornithine
Arginase
Carbamoyl group has a high transfer potential because of its
anhydride linkage
