Biochem Flashcards
How are proteins targeted for lysosomes modified differently in the golgi apparatus than those destined for extracellular secretion?
- Golgi body phosphotransferase enzyme catalyzes the phosphorylation of mannose residues allowing for proper transit through Golgi apparatus
- Deficient phosphorylation of these residues seen in I-cell disease
What takes over the role of fructokinase in fructokinase deficiency?
Hexokinase; converting fructose –> fructose-6-phosphate
What is the primay defect is familial dysbetalipoproteinemia (type III hyperlipoproteinemia); clinical features of this disease?
- AR; lack of ApoE3 and ApoE4 –> decreased clearance of chylomicrons and VLDL remnants by the liver
- Eruptive and palmar xanthomas and premature atherosclerosis
What is the function of the TATA and CAAT boxes found within the eukaryotic genome?
Promoters of transcription by serving as bindings sites for transcription factors and RNA polymerase II
What is found at the 3’ end of tRNA and what is its function?
- A 3’ CCA tail used as a recognition sequence by proteins
- The 3’ terminal hydroxyl group of CCA tail serves as AA binding site
Hereditary fructose intolerance is due to a deficiency of aldolase B which leads to a buildup of what; how does this cause toxicity?
Fructose-1-phosphate –> depletes intracellular phosphate and inhibits activation of hepatic phosphorylase and gluconeogenesis
What are presenting sx’s of hereditary orotic aciduria?
- Physical and mental retardation i.e., low height/weight, etc.
- Megaloblastic anemia
- Elevated urinary orotic acid levels
What is the primary function of the nucleolus?
- Synthesis and assembly of immature 60S and 40S ribosomal subunits
- Which are exported from the nucleus to fully mature in the cytoplasm
The rubber-like properties of elastin are due to what?
High content of nonpolar (hydrophobic) AA’s and extensive cross-linking btw elastic monomers facilitated by lysyl oxidase
What is the most common enzyme deficiency leading to impaired beta-oxidation; classic signs and sx’s include what?
- Medium chain acyl-CoA dehydrogenase
- Classic findings after a fast: hypoketotic hypoglycemia + mild hepatomegaly + liver dysfunction
Which lysosomal storage disease is associated with hepatosplenomegaly, pancytopenia, and severe bone pain?
Gaucher disease –> beta-glucocerebrosidase deficiency
Expression of which enzyme in the adrenal medulla is upregulated by cortisol and is responsible for converting NE –> epinephrine?
Phenylethanolamine-N-methyltransferase (PNMT)
The alteration of the hepatic NAD/NADH ratio in alcoholics induces fatty liver through inhibition of which 2 pathways?
- Gluconeogenesis and Fatty acid oxidation
- Also assoc. w/ impaired lipoprotein assembly and increased peripheral fat catabolism
What is responsible for the clinical variability of mitochondrial inherited diseases?
Heteroplasmy: during mitosis mitochondria are randomly distributed btw daughter cells; some cells contain damaged mtDNA and others are normal
What is the wobble hypothesis?
- Certain tRNA molecules can recognize multiple different codons coding for the same amino acid
- Stats the first 2 nucleotide positions on the mRNA codon require traditional (Watson-Crick) base pairing, whereas the third “wobble” nucleotide position may undergo less stringent (nontraditional) base pairing
- i.e., 1 tRNA molecule recognizes 2 codons (CUC and CUU) because only the first 2 nucleotide positions form traditional bonds
A child with severe intellectual disablility, history of seizures and abnormal pallor of catecholaminergic brain nuclei (substantia nigra, locus ceruleus, and vagal nucleus dorsalis) on autopsy is suggestive of what condition?
- Phenylketonuria
- Deficiency of phenylalanine hydroxylase (most common) or dihydropteridine reductase
What is a key distinguishing feature seen in the hepatocytes of patient with Cori Disease (Type III)?
Cytosolic accumulation of glycogen with abnormally short outer chains = limit dextrans
Hepatic steatosis is a cardinal manifestation of which glycgoen storarge disorder?
von Gierke disease –> glucose-6-phosphatase deficiency
Branched chain alpha-ketoacid dehydrogenase requires which 5 co-enzymes? (hint: mnemonic)
- Thiamine
- Lipoate
- Coenzyme A
- FAD
- NAD
* Tender Loving Care For Nancy*
What is the most abundant amino acid in collagen?
- Glycine
- Triple helical conformation of collagen occurs due to the simple and repetitive AA sequence within each alpha chain, in which glycine (Gly) occupies every 3rd AA position (Gly-X-Y)
Which labratory analysis method is used to measure the degree of methylation and determine the number of CGG repeats in Fragile X Syndrome?
Southern Blot
A 3-year old boy experiences progressive development of spastic diplegia, abnormal movement, growth delay w/ labs showing elevated arginine levels in the plasma and CSF; what is the diagnosis?
- Arginase deficiency
- Arginase catalzyes the breakdown of arginine –> urea + ornithine during the urea cycle
- Unlike other urea cycle disorders these pt’s have mild or no hyperammonemia
What is the major RNA product of RNA polymerase I, II, and III in eukaryotes?
- RNA polymerase I = Ribosomal RNA
- RNA polymerase II = Messenger RNA
- RNA polymerase III = Transfer RNA
What is the MOA of the toxin, Ricin (from the castor oil plant Ricinus communis)?
Inhibits protein synthesis by cleaving rRNA component of eukaryotic 60S subunit
Thiamine is a necessary co-factor for which enzymes?
- Pyruvate dehydrogenase
- α-ketoglutarate dehydrogenase
- Transketolase
What is the hallmark of tx for Maple Syrup Urine Disease?
Dietary restriction of BCAA’s = Leucine, Valine, and Isoleucine
Supplementation and restriction of what may help prevent adverse events in pt’s with homocystinuria due to deficiency of cystathione beta-synthase?
- High dose pyridoxine (B6) a cofactor for the deficient enzyme
- Restriction of methionine
