2Molecular . Purine salvage deficiencies Genetic code features Dna Replication Flashcards
What is the end product of guanosine and adenosine degradation?
Uric acid, which is renally excreted eventually
What enzyme catalyzes the conversions of both guanine to guanylic acid (GMP) and hypoxanthine to inosinic acid (IMP)?
Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
What enzyme in the purine salvage pathway catalyzes both the conversions of hypoxanthine into xanthine and of xanthine into uric acid?
Xanthine oxidase
Lesch-Nyhan syndrome is the result of an absence of what enzyme?
Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) (He’s Got Purine Recovery Trouble)
What enzyme catalyzes the formation of adenylic acid from adenine?
• Adenine phosphoribosyltransferase (APRT)
What type of inheritance does phosphoribosyltransferase demonstrate?
X-linked recessive
To a deficiency of which purine salvage enzyme may severe combined immunodeficiency (SCID) be due? What is the inheritance pattern?
Adenosine deaminase (ADA), which converts adenosine into inosine; autosomal recessive
A child with intellectual disability, gout, and choreoathetosis self-mutilates. How would you treat him?
This is Lesch-Nyhan syndrome, treated with allopurinol or (second line) febuxostat
A child with intellectual disability, gout, and choreoathetosis self-mutilates. Activity of which two enzymatic pathways is increased?
Uric acid production (xanthine oxidase) and de novo purine synthesis (phosphoribosyl-pyrophosphate)
What is the classic presentation of Lesch-Nyhan syndrome?
HGPRT: Hyperuricemia, Gout Pissed off (e.g., aggression), Retardation (intellectual disability), dysTonia
Through which mechanism does the drug allopurinol act?
Blocks xanthine oxidase (XO), thereby inhibiting conversion of hypoxanthine to xanthine
What are the only codons that code for tryptophan and methionine?
UGG (tryptophan) and AUG (methionine)
How is the genetic code unambiguous and yet redundant?
Whereas each codon specifies a single amino acid (unambiguous), an amino acid can be coded for by multiple codons (redundant
Feedback inhibition of which enzyme occurs because of ATP and dATP accumulation in severe combined immunodeficiency?
Ribonucleotide reductase
What does a commaless, nonoverlapping genetic code entail?
The entire genome is read from a fixed starting point as a continuous string of bases
exeption some viruses
Typically the genetic code is considered universal (i.e., conserved throughout evolution). What is one noteworthy exception to this rule?
Human mitochondrial DNA, which is not conserved
What is the purpose of DNA topoisomerase’s creation of a break in the DNA helix?
Relaxes supercoils; helps unwind DNA for proper replication
In DNA replication, prokaryotes have ____ (multiple/one) origin(s) of replication, whereas eukaryotes have ____ (multiple/one) origin(s).
One; multiple
What enzyme has 3′-to-5′ exonuclease activity in prokaryotic DNA replication?
DNA polymerase III has 3′–to–5′ exonuclease activity for proofreading
What enzyme elongates the leading strand of DNA synthesis by building on an RNA primer?
DNA polymerase III
What does DNA polymerase III require to initiate replication?
An RNA primer, created by primase
What enzyme degrades the RNA primer and replaces it with DNA during prokaryotic DNA replication?
DNA polymerase I
To which end of the newly synthesized DNA molecule does DNA polymerase III add the next deoxynucleotide?
The 3′ end—this is 5′–to–3′ synthesis
When does DNA polymerase III stop adding deoxynucleotides to the 3′ end?
When it reaches the primer of the preceding fragment
