When amino acids from dietary proteins enter a cell, how are they able to enter the urea cycle? correct answers Through conversion to aspartate
The two mechanisms to regulate protein ubiquitination are biochemical changes to correct answers target proteins and E3 ligases
Why does it make sens...
when amino acids from dietary proteins enter a cel
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When amino acids from dietary proteins enter a cell, how are they able to enter the urea cycle?
correct answers Through conversion to aspartate
The two mechanisms to regulate protein ubiquitination are biochemical changes to correct
answers target proteins and E3 ligases
Why does it make sense that tadpoles (which live in water) have low levels of the enzyme
arginase, but after metamorphosis into frogs (which live on land), thier arginase levels increase?
correct answers Tadpoles living in water can excrete ammonia directly, but once on land, they
need to excrete urea.
A person who has alkaptonuria is easily diagnosed from his or her black urine. What causes the
black color? correct answers Urine of these individuals turns black when exposed to air as a
result of oxidation of homogentisate.
Which of the following is a starting material for the synthesis of heme? correct answers Glycine
What is the mechanism by which Roundup works? correct answers Glyphosate is a competitive
inhibitor to plant EPSP synthase.
Why do angina patients carry nitroglycerine with them? correct answers As a rapid source of NO
for blood vessel dilation.
Nitrogen in biochemical compounds ultimately comes from what source? correct answers
Nitrogen gas
Compare the function of pepsin with that of secretin. correct answers Pepsin cleaves polypeptide
bonds, whereas secretin neutralizes pH back to 7.
Undiagnosed phenylketonuria (PKU) can lead to severe neuronal damage and mental incapacity,
which is avoidable if the disease is diagnosed at birth. In contrast, albinism is easily diagnosed at
birth, but there is no treatment, which leads to an increased risk of skin cancer in these patients.
Choose the three statements that BEST explain the reasons for these differences. correct answers
PKU is the result of substrate accumulation, which can be avoided using a restricted diet.
However, albinism is due to a missing product, which cannot be replaced though injections or
dietary regimes.
Defects in the enzyme tyrosinase occur in every cell of the body and there is no way to replace
this enzyme without embryonic human gene therapy. IN contrast, defects in the enzyme
phenylalanine hydroxylase can be ameliorated by restricting certain amino acids in the diet.
Phenylalanine is found in many types of food, including aspartame, and therefore by avoiding
foods with high amounts of phenylalanine, the build-up of pyruvate metabolites can be
, controlled. In contrast, skin pigments must be made from tyrosine and there is no way to do this
is tyrosine metabolism is compromised.
Order the following steps involving the regeneration of ribonucleotide reductase that occurs in
most animals so that it may carry put the formation of deoxyribonucleotides. (Note that not all
steps are shown.)
1. Reduction of thioredoxin
2. Reduction of ribonucleotide reductase
3. Oxidation of thioredoxin reductase
4. Reduction of thioredoxin reductase correct answers None of these answers are correct
4, 3, 1, 2
Explain why cells with defects in thymidine kinase grow in media containning high amounts of
5-bromodeoxyuridine [BrdU], whereas cells with normal thymidine kinase will die when
exposed to BrdU? correct answers When thymidine kinase is lacking, BrdU does not become
phosphorylated and hence cannot be incorporated into DNA.
A mutation in the gene encoding which of the following enzymes would affect the synthesis of
both AMP and GMP? correct answers PRPP synthetase
Which of the following is a benefit of the nucleotide salvage pathways compared with de novo
synthesis? correct answers Reduced energy expenditure
If a mutation of the decarboxylase enzyme that functions in the biosynthetic pathway of UMP
causes the pathway to halt at that step, which of the following would no longer occur? correct
answers Generation of CO2
The transformation of ribose-5-phosphate to AIR in the first stage of purine biosynthesis in E.
coli consumes the equivalent of 5 ATP. The second stage consumes correct answers Less than 5
ATP
(3 ATP, making the total ATP consumption 8 ATP for both stages)
To determine the role of gluteredoxin in the generation of deoxyribonucleotides by
ribonucleotide reductase, which organisms would be the best to study? correct answers Bacteria
Defects in nucleotide metabolism that lead to a buildup of uric acid cause the disease gout. Select
the TWO true statements below regarding potential treatments for gout. correct answers An
inhibitor of xanthine oxidase, such as allopurinol, will limit the conversion of hypoxanthine to
uric acid, and could be effective in reducing uric acid levels.
Supplying humans with the enzyme urate oxidase theoretically could be effective in reducing
uric acid levels.
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