Exam 4 Flashcards
The majority of transaminases exhibit a specificity for L-glutamate and alpha-ketoglutarate.
True.
Urea is synthesized in mammalian kidneys.
False.
Nitrogen fixation, catalyzed by the enzyme nitrogenase, is a process that requires energy.
True.
Nitrogen fixation via nitrogenase produces hydrogen gas as well as ammonia.
True.
Glutamine is a nitrogen donor in several biosynthetic reactions and represents a means of carry nitrogen between tissues.
True.
Each of the 20 common amino acids can be described as being either glucogenic or ketogenic.
False.
Arginase is an enzyme found at high activity levels in nearly all mammalian organs and tissues.
False.
Because of the importance of their function, regulatory proteins have long half-lives.
False.
Like most catabolic processes, the protein hydrolysis that occurs during turnover is not energy consuming.
False.
The urea cycle requires 4 ATP equivalents per molecule of urea that is produced.
True.
A transaminase enzyme would convert alanine to _________ while converting ___________ to glutamate.
pyruvate
alpha ketoglutarate
When there is excess ammonia and little aspartate available for the urea cycle, ammonia combines with ___________ to produce glutamate, which then undergoes transamination with _____________ to produce the necessary oxaloacetate.
alpha ketoglutarate
oxaloacetate
Amino acids whose carbon chains are catabolized to form acetyl CoA are said to be _____________. Those that form intermediates of glycolysis or the citric acid cycle are said to be ___________.
ketogenic
glucogenic
In the biosphere, the two major sources of nitrogen ultimately used for amino acid synthesis are ____________ and _____________.
atmosphere N2
soil NO3-
The sources of the two nitrogen atoms and the carbon atom of urea are ___________, __________, and __________, respectively.
NH4+
aspartate
HCO3-
One of the nitrogen atoms and the carbon atom of urea enter the urea cycle as a single molecule, namely ________________.
carbamoyl phosphate
The urea cycle requires energy to form urea. The equivalent of ________ ATP molecules is required.
4
The exchange of glucose and alanine between muscle and liver is called the __________.
glucose-alanine cycle
Several molecules of the protein ____________ are attached to proteins targeted for degradation.
ubiquitin
The multiprotein complex that hydrolyzes targeted proteins to peptides during the turnover process is called the _______________.
proteasome
The nitrogenous bases of nucleotides and nucleosides are of two types - the purines, which are heterocycles containing six atoms, and the pyrimidines, which are heterobicycles containing nine atoms.
False.
Nucleotide biosynthesis occurs only in cells that undergo replication.
False.
To synthesize the purine ring, liver cells require metabolic sources of glycine, formate, glutamine, CO2, and aspartate.
True.
In purine nucleotide synthesis, the purine ring is synthesized and then attached to ribose-5-phosphate to make nucleotides. In pyrimidine nucleotide synthesis, the components of the pyrimidine ring are assembled on ribose-5-phosphate.
False.
Inosine 5’-monophosphate (IMP) is an intermediate from which both 5’-AMP and 5’-GMP are synthesized.
True.
To synthesize GMP from IMP, ATP is required, whereas to synthesize AMP from IMP, GTP is required.
True.
To synthesize the pyrimidine ring, liver cells require asparagine, glutamate and bicarbonate.
False.
The first step in the pyrimidine ring biosynthesis involves formation of carbamoyl phosphate, catalyzed by carbamoyl phosphate synthetase. This is the same enzyme that operates in the urea cycle.
False.
Uric acid, an avian excretion product, is a pyrimidine.
False
Orotate is the end product of the pyrimidine biosynthetic pathway and is the derivative from which the pyrimidine nucleosides and nucleotides are made.
False.
The disease gout is the result of excess amounts of uric acid.
True.
dTMP is formed by the reduction of the ribose moiety of ribothymidylate.
False.
Most free purine and pyrimidine molecules are salvaged, but some are catabolized. Catabolism of both purine and pyrimidine molecules leads to the excretory product uric acid.
False.
The components of a nucleotide are a/an _____________, a/an ______________, and _____________.
purine or pyrimidine base
ribose or deoxyribose
1 or more phosphate groups
The active form of ribose 5-phosphate required for nucleotide biosynthesis is ____________.
PRPP
In liver cells, the location of purine biosynthesis is ____________.
the cytosol
During purine nucleotide synthesis, the first reaction of 5-phosphoribosyl 1-pyrophosphate is the addition of nitrogen to the ribose residue. The source of nitrogen is ___________.
glutamine
Carbamoyl phosphate is involved in the biosynthesis of which type of nucleotides, the pyrimidines or the purines.
pyrimidines
The recycling of products from the normal cellular breakdown of nuclei acids is an energy-conserving process called ____________.
salvage
A common treatment for gout, allopurinol works by inhibiting xanthine oxidase. Instead of producing ______________, the two more soluble products of purine metabolism _____________ and _____________.
uric acid
xanthine
hypoxathine
CTP is formed from UTP by transformation of the keto group at C-4 of the pyrimidine ring to an amino group. The source of the nitrogen for this amino group is __________ that is converted to __________.
glutamine
glutamate
Anticancer drugs such as 5-fluorouracil and methotrexate prevent the synthesis of ____________.
dTMP
Nucleotides are molecules that contain only a sugar and a nitrogenous base.
False.
Nucleosides are obtained as breakdown products of nucleic acids and contain a pentose and a nitrogenous base bonded to the pentose by a beta-N-glycosidic bond.
True.
Uracil and thymine are members of the pyrimidine family and are typically found as components of DNA.
False.
The nucleoside moieties of nucleic acids exist predominantly in the anticonformations due to steric hindrance present in the syn conformation.
True.
