Vitamin B12 Flashcards
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| 8708244723 | Cobalamin | vitamin B12; cobalt in structure - forms planar ring | 0 | |
| 8708264568 | Vitamin B12 | generic descriptor for corrinoid compounds exhibiting the biological activity of vit b12 | 1 | |
| 8708273040 | Corrinoid compound | compound containing cobalt-centered corrin ring | 2 | |
| 8708281177 | Best corrinoid compound | methylcobalamin - because of role in MS | 3 | |
| 8708284684 | Synthesis of vit b12 | solely by bacteria; accumulates in animal tissues (liver) | 4 | |
| 8708291780 | Dietary sources of B12 | animal products; liver is highest bc storage | 5 | |
| 8708314838 | Food fortified with B12 | Almond milk - 1 cup, 50% DV Kashi cereal - 3/4 cup, 100% DV Tofu - 3 oz, 20% DV | 6 | |
| 8708349587 | Differences between naturally occurring and synthetic B12 | Natural - bound to protein, requires gastric acid for absorption; Synthetic - not bound to protein | 7 | |
| 8708367003 | Binding/transport proteins of B12 | R-protein; IF; transcobalamin 2 (main transport in plasma) | 8 | |
| 8708372246 | R-protein | aka haptocorrin/transcobalamin 1; glycoproteins secreted by salivary glands; binds to B12 to protect from stomach acid | 9 | |
| 8708379935 | Intrinsic factor (IF) | glycoproteins secreted by gastric parietal cells; binds to B12 in intestine; transports B12 to IF receptor | 10 | |
| 8708441454 | Transcobalamin 2 | main trasport protein for B12 in plasma | 11 | |
| 8708445513 | B12 active absorption occurs in 3 places | stomach; duodenum; ileum; only vitamin absorbed this way | 12 | |
| 8708447555 | Active absorption in the stomach | Food B12 - released from proteins by pepsin/HCL; Free B12 - binds to R, forming B12-R complex | 13 | |
| 8708458269 | Active absorption in the duodenum | B12-R acted upon by pancreatic protease - releases free B12; Free B12 binds to IF | 14 | |
| 8708467230 | Active absorption in the ileum | B12-IF binds to receptor (cubilin) on intestinal cell; internalized by endocytosis; released from IF-cubilin; free B12 binds to transcobalamin 2 in portal blood | 15 | |
| 8708479528 | Cubilin | IF receptor | 16 | |
| 8708491458 | B12 passive absorption | simple diffusion; occurs in small intestine; inefficient - 1%; used in therapy - 500 micrograms by mouth; also intranasally, sublingually | 17 | |
| 8708516268 | Routes of B12 therapy | by mouth; intranasally; sublingual tablets; can have shot; dose >500 micrograms | 18 | |
| 8708523073 | Atrophic gastritis | chronic inflammation of gastric mucosa with loss of parietal cell function; autoimmune disorder in which antibodies destroy parietal cells; loss of intrinsic factor and gastric acid; most common cause of pernicious anemia | 19 | |
| 8708686940 | Transcobalamin 3 | function unknown | 20 | |
| 8708694205 | Cellular uptake of B12 | enters through receptor-mediated endocytosis; endosome becomes acidified - B12 released; to methionine synthase in cytoplasm; to methylmalonyl CoA Mutase in mitochondrion | 21 | |
| 8708715187 | B12 RDA | 2.4 micrograms; because only a cofactor for 2 enzymes | 22 | |
| 8708729198 | Number of enzymes for which B12 is a cofactor | 2 | 23 | |
| 8708747080 | Storage of B12 | 2-4mg; 50% in liver; 70% stored as adenosylcobalamin; not actually stored - being used by enzymes | 24 | |
| 8708754659 | Excretion of B12 | Bile - 1.5 micrograms/day - 70% reabsorbed; pts with p anemia do not reabsorb (no IF) | 25 | |
| 8708764924 | Function of B12 in humans | 2 rxns: methyl group transfer reactions, mutases; remethylation of homocysteine and methylmalonyl CoA to succinyl CoA exchange 1 H and some other groups btwn 2 adj carbon atoms | 26 | |
| 8708768491 | Methionine synthase (MS) | uses methylcobalamin as an intermediate methyl carrier at one active site of MS enzyme; transfers methyl group from cobalamin to homocysteine at another active site; in cytoplasm | 27 | |
| 8708808358 | Methymalonyl CoA Mutase (MCM) | in mitochondira; enzyme that catalyzes the isomerization of methylmalonyl-CoA to succinyl-CoA; uses adenosylcobalamin in active site | 28 | |
| 8708820249 | Testing method for B12 deficiency | methylmalonic acid in blood stream - high levels indicate build up | 29 | |
| 8708830338 | Use of adenosylcobalamin | relatively weak Co-CH2 bond; easily broken to form free radical; FR abstracts a hydrogen from methylmalonyl CoA | 30 | |
| 8708858201 | Methyl trap hypothesis | methyl is trapped in N-5 methyl form; MTHFR reaction is irreversible; homocysteine increases; 5-methyl-THF increases | 31 | |
| 8708872838 | Implication of impaired DNA synthesis due to B12 deficiency | megaloblastic anemia | 32 | |
| 8708877948 | Remethylation of homocysteine vs. Methylmalonyl CoA to succinyl CoA | Remethylation - methylcobalabin, cytoplasm; Methylmalonyl - adenosylcobalamin, mitochondria | 33 | |
| 8708886653 | Implication of MMA (methylmalonic acid) accumulation | neurodegeneration | 34 | |
| 8708890188 | Masking B12 deficiency | folic acid can correct megaloblastic anemia, but not other effects; B12 deficiency causes "secondary folate deficiency" | 35 | |
| 8708905577 | B12 deficiency | megaloblastic anemia; degeneration of spinal cord; worsens without B12 therapy; hard to diagnose in early stages | 36 | |
| 8708911000 | B12 status indicators | Serum B12 (<300 pg/mL mild - <148pmol/L severe); functional indicator - homocysteine; specific indicator - MMA; holotranscobalamin - newer method reflects serum levels; megaloblastic anemia - not specific, severe deficiency | 37 | |
| 8709222249 | Pernicious anemia | caused by lack of functional IF in stomach; 2-3% of population >65 years (rare in younger pop); gastrectomy can cause; IM B12 injection monthly of 100-1000 micrograms cyanocobalamin; oral B12 supplement >1000 micrograms | 38 | |
| 8709233580 | Treatments for pernicious anemia | IM B12 injection monthly of 100-1000 micrograms cyanocobalamin; oral B12 supplement >1000 micrograms | 39 | |
| 8709238192 | Non - autoimmune gastritis | gastric atrophy - loss of stomach acid; can be caused by H. pylori; have IF so can absorb crystalline normally; may affect >30% of elderly | 40 | |
| 8709249041 | B12 and nitrous oxide | oxidizes cobalt in B12; results in B12 deficiency/spinal cord degeneration; dentists, dental assistants, ppl who use it as drug (whip-its) | 41 | |
| 8709259517 | Neurological abnormalities due to B12 deficiency | degeneration of peripheral nerves; impaired touch/pain sensation; ataxia; degeneration of spinal nerves; memory loss, altered mood, reaction to stress; abnormal reflexes and stamina | 42 | |
| 8709279270 | Proposed mechanism for demyelination of nervous system | decreased synthesis of S-adenosylmethionine; disrupted odd chain fatty acid metabolism - accumulation of MMA and proprionic acid | 43 |