188+ quick-fire dental facts • tap a card to flip
Methylmalonyl-CoA mutase requires vitamin B12. Deficiency causes methylmalonic acid accumulation.
Which vitamin deficiency causes elevated methylmalonic acid?
1) Vitamin B6
2) Vitamin B1
3) Vitamin B12
4) Folate
Tangier disease results from ABCA1 deficiency causing defective cholesterol efflux and extremely low HDL.
Orange-yellow tonsils are characteristic of deficiency of which transporter?
1). NPC1
2). ApoE
3). ABCA1
4). LDL receptor
Methionine synthase converts homocysteine to methionine using methylcobalamin (vitamin B12), making it essential for DNA synthesis and normal neurological function.
Which enzyme requires vitamin B12 as a cofactor?
1) Phenylalanine hydroxylase
2) Methionine synthase
3) Tyrosine hydroxylase
4) Alanine aminotransferase
Vitamin B12 is required by methionine synthase, which converts homocysteine into methionine.
Vitamin B12 deficiency causes elevated homocysteine levels because of decreased synthesis of:
1). Glutamate
2). Methionine
3). Tyrosine
4). Cysteine
Parathyroid hormone (PTH) acts on the kidneys to increase calcium reabsorption and decrease phosphate reabsorption, which lowers plasma phosphate concentration.
Function of PTH?
1. decreases plasma phosphate concentration (PTH:? serum Ca², serum PO)
2. increases calcium absorption of bones
3. decreases calcium reabsorption in kidneys
4. none
Vitamin B12 participates in two reactions in the body-conversion of homocysteine to methionine and conversion ofmethylmalonyl-CoA to succinyl-CoA.
Methylmalonyl-CoA is produced via various amino acid degradation pathways, and from oddcarbon chain fatty acid oxidation. In the absence of B12, succinyl-CoA would only be produced as an intermediate of the TCA cycle, and if it were removed from the cycle for heme synthesis, energy production may suffer.
Glycine is usually obtained from the diet, although in a B12 deficiency a functional folate deficiency may also develop, leading to an inhibition of serine hydroxymethyltransferase, the enzyme that converts serine to glycine, and requires free tetrahydrofolate.
Succinyl-CoA and glycine are the precursors for heme synthesis. A B12 deficiency would not inhibit the production of acetyl-CoA, succinate, or alanine.
A vitamin B12 deficiency may affect heme synthesis by reducing the concentration of which of the following? Choose the one best answer.
1) Acetyl-CoA
2) Succinyl-CoA
3) Glycine
4) Alanine
Glucose is the primary and most common respiratory substrate utilized by almost all living organisms to undergo glycolysis and subsequent pathways to generate cellular energy (ATP).
Common substrate for respiration:
1. Glucose
2. Fats
3. Amino acids
4. Sucrose
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