Exam 2 Flashcards
Cells acquire nucleotides through two processes:
de novo synthesis and
salvage pathways.
De novo synthesis of purines results in the synthesis of
inosine that can be
converted into adenosine and guanosine.
Atoms in a newly synthesized purine are derived from
several sources
including the amino acids aspartate, glutamine and glycine, methyl groups
supplied by folic acid and carbon dioxide.
ADP and GDP regulate de novo synthesis of
purines at multiple points in the
pathway.
Hypoxanthine and guanine can be recycled through
the salvage pathway
with Hypoxanthine guanine phosphoribosyl transferase (HGPRT).
Xanthine oxidase catalyzes a
hydroxylase type reaction leading to the
formation of uric acid that can be excreted.
Excess uric acid is the cause of
gout
Gout is most often caused by
low levels of secretion of uric acid, but can
also be caused by excess production.
Crystallization of Sodium urate in the joints leads to
a localized inflammatory
response.
Allopurinol, a purine analog, is used to treat
gout. It inhibits Xanthine
oxidase preventing the formation of uric acid.
A HGPRT deficiency causes
Lesch-Nyhan syndrome that results in severe
retardation, crippling gouty arthritis and self-mutilation.
Lesch-Nyhan occurs in males only because
the HGPRT gene is located on
the X chromosome.
The breakdown of purines can replenish TCA cycle intermediates through
the production of fumarate.
The atoms in a pyrimidine ring are derived from
aspartate and carbamoyl
phosphate.
The first 3 enzymes in the synthesis of pyrimidines are
located on the same
protein (CAD protein).
The pyrimidines U and C can be
interconverted
dUMP is converted to TMP by
thymidylate synthase, an enzyme requiring
the transfer of a methyl group from tetrahydrofolate.
Inhibitors of tetrahydrofolate production are used as
as therapeutic agents for
treating cancer and bacterial infections.
Fluro substituted pyrimidine analogs that inhibit thymidylate synthase are
used as anticancer agents.
Ribonucleotide reductase converts
ribonucleotides to deoxyribonucleotides
Base-pairing in DNA is
A-T and G-C. In RNA it’s A-U and G-C.
Homologous regions of DNA can be compared among different species to
determine
phylogenetic relationships
Closely related organisms contain
similar DNA compliments, however they
are often arranged differently on the chromosomes of each species
The living world is made up of 3 divisions, or domains
: bacteria, archaea and
eukaryotes.