Amino Acid Metabolism & Urea Cycle
These two amino acids are classified as "purely ketogenic" because they can only be converted into Acetyl CoA or Acetoacetyl-CoA
DAILY DOUBLE!!!!
A deficiency in the enzyme Tyrosinase prevents the production of melanin, resulting in this clinical condition
Albinism
This term describes a situation where one functional copy of a gene is not sufficient to maintain a normal phenotype, often resulting in an autosomal dominant inheritance pattern
Haploinsufficiency
This molecule, synthesized from Ribose 5-phosphate by its namesake synthetase, serves as the "activated" sugar donor for both purine and pyrimidine synthesis
PRPP (5-Phosphoribosyl-1-pyrophosphate)
Maple Syrup Urine Disease is caused by a deficiency in a complex that breaks down these three specific branched-chain amino acids
TRIPLE POINTS!!!!
Leucine, Isoleucine, & Valine
In the first and rate-limiting step of the Urea Cycle, this mitochondrial enzyme requires N-acetylglutamate as an essential activator
Carbamoyl phosphate synthetase I (CPSI)
This autosomal recessive disorder is caused by a defect in the SLC6A19 gene, leading to impaired absorption of neutral amino acids, particularly tryptophan
Hartnup disease
Duchenne Muscular Dystrophy is usually caused by this specific type of mutation that shifts the triplet reading frame, leading to a total loss of dystrophin
Frameshift (or Out-of-frame) mutation
These three amino acids contribute specific atoms to the construction of the purine ring
TRIPLE POINTS!!!!
Aspartate, Glycine, Glutamine
This enzyme converts hypoxanthine to xanthine and xanthine to uric acid, and is the target of Allopurinol
Xanthine oxidase
This product of the Urea Cycle is also an intermediate of the TCA cycle, providing a metabolic link between the two pathways
Fumarate
This specific urea cycle enzyme deficiency is unique because it is X-linked recessive, whereas the others are typically autosomal recessive
Ornithine transcarbamylase (OTC) deficiency
This term describes the phenomenon where a single mutation causes multiple, seemingly unrelated phenotypic effects in different organ systems
Pleiotropy
This cytosolic enzyme catalyzes the rate-limiting step of pyrimidine synthesis and is inhibited by UTP
Carbamoyl Phosphate Synthetase II (CPSII)
Beyond the urea cycle, Arginine serves as the direct precursor for these two specialized signaling and energy molecules
DAILY DOUBLE!!!!
Nitric oxide & Creatine
This is the only amino acid that undergoes rapid oxidative deamination, a reaction catalyzed by its namesake dehydrogenase in the mitochondria
Glutamate
This syndrome is caused by a near-complete deficiency of HGPRT, leading to uric acid stones, spasticity, and characteristic self-mutilating behavior
Lesch-Nyhan Syndrome
Mutations in these regulatory elements, rather than the gene's coding sequence, can cause tissue-specific defects like polydactyly or lactase persistence
Enhancers
This enzyme converts dUMP to dTMP and is a major target for the chemotherapy drug 5-Fluorouracil
Thymidyl Synthase
This genetic concept explains why different mutations in the FGFR3 gene can cause either Achondroplasia or the more lethal Thanatophoric Dysplasia
Allelic Heterogeneity
In most transamination instances, this molecule acts as the universal acceptor of the amino group, subsequently becoming glutamate
alpha-Ketoglutarate
If a patient has hyperphenylalaninemia but normal Phenylalanine Hydroxylase activity, they likely have a deficiency in the synthesis or recycling of this essential cofactor
Tetrahydrobiopterin (BH4)
While deletions of 7q11.23 cause Williams Syndrome, duplications of the same region typically lead to this specific developmental symptom
Language delay
This chemotherapy agent inhibits Dihydrofolate Reductase, preventing the regeneration of THF needed for nucleotide synthesis
Methotrexate
This biological principle explains why "in-frame" deletions in the DMD gene lead to a less severe phenotype than "out-of-frame" deletions
Reading Frame Rule