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Biochem Exam 6
One-Carbon Metabolism
| Question | Answer |
|---|---|
| What can carry carbon groups and force them to go somewhere else | Folates and s-adenosylmethionine (SAM) |
| Pteridine ring + PABA + glutamate forms what molecule | Folate |
| Folates can have many chemical forms with a chain of what attached | Glutamates |
| Can folates be synthesized in the body | No |
| What synthesizes folates | Bacteria and higher plants |
| What must ingested folates have done to them | Activation |
| What form of folate is absorbed in the intestine using a specfic transporter | Monoglutamate |
| What form of folic acid is found in supplements | Monoglutamate |
| Folate is reduced to FH2 then FH4 and this is catalyzed by | Dhydrofolate reductase |
| Where does the reduction of folate primarily | Intestinal cells |
| Where is FH4 reconjuaged to the polyglutamate form | Liver |
| Conjugated FH4 can accept | On carbon groups |
| Where does FH4 usally accept one carbon groups | At N5 or N10 |
| What is the primary carbon source that donates a carbon group to FH4 | Serine |
| Folates with carbon groups attached are called the | One-carbon pool |
| What are three important reactions that folates are involved in | Purine synthesis, dTMP synthesis, Methylcobalamin synthesis, Serine syntehsis |
| What is the most reduced and stable form of folates | N5-methyl-FH4 |
| What is the only thing the carbon of N5-methyl-FH4 can do | Transfer to vitamin B12 |
| What is another name for Vitamin B12 | Cobalamin |
| Corrin ring + cobalt make what molecule | Vitamin B12 (cobalamin) |
| Cobalt can form bonds with | Carbons |
| B12 is only synthesized by | Bacteria |
| What form of vitamin B12 is fround in most supplements but does not occur in nature | Cyanocobalamin |
| After ingesting B12 is converted to | Methyl cobalamin or deoxyadenosylcobalamin |
| What does B12 generally enter the small intestine boudn to | Haptocorrin (Transcobalamin I, R-binders) |
| Proteases digest Haptocorrin and other proteins releasing | B12 |
| B12 binds what to enter enterocytes as a complex | Intrinsic factor |
| Within the enterocytes, B12 is released from IF and binds what to be secreted as a complex | Transcobalamin II |
| What takes up and stores B12 | Liver |
| B12 is secreted by the liver in | Bile |
| What two reaction require B12 | Transfer of methyl group from N5-methyl-FH4 to homocystein to form methionine, Conversion of methylmalonyl-CoA to Succinyl CoA |
| Methylmalonyl CoA --> Succinyl CoA | Adenosyl B12 |
| Methylene-FH4 --> N5-Ch3-Fh4 | Methylenetetrahydrofolate reductase (MTHFR) |
| Homocysteine --> Methionine | Met synthase |
| Homocystein --> Cystathionine | Cystathionine synthase and PLP |
| Met is essential because there are no good dietary sources of | Homocysteine |
| DNA methyltransferases and histone methyltransferases require what as the methyl donor | SAM |
| DNA methylation is important for | Gene silencing and regulating dynamic gene expression |
| What could cause hyperhomocysteinemia | B6, B12, or Folate deficiencyMet synthase, MTHFR or cystathionine synthase mutations |
| Mild hyperhomocysteinemia is associated with | Increased risk of coronary artery disease and thrombosis |
| How can homocysteine levels be reduced | B12, B6 or folate supplementation Betaine and Choline supplementation |
| B12 or folate deficiencies can lead to | Macrocytic anemia |
| Red blood cells are larger than normal but fewer in number | Macrocytic anemia |
| Caused by enlarged hematopoietic precursor cells in bone marrow; Slowed cell division but normal growth rate so cells are larger than normal | Macrocytic anemia |
| Neurological symptoms occurs in B12 deficiency due to | Hypomethylationin the nervous system |
| Anemia occurs in B12 deficiency due to | Inhibition of DNA replication |
| B12 causes macrocytic anemia because need folate to get methylcobalmin and need B12 to recycle N5-Ch3-FH4 If B12 or met synthases are deficient, N5-methyl-Fh4 will build up resulting in a functional folate deficiency folate in a form that can’t be used | Methyl trap hypothesis |
| Folate deficiency during pregnancy increases the risk of | Neural tube defects |
| Dietary insufficiency and Chronic alcoholism are associated with | Folate and B12 deficiency |
| Abdominal surgery can cause a decrease in IF production, GI Disease, Intestinal parasites, certain drugs, and IF deficiency are associated with | B12 deficiency |
| Intrinsic factor deficiency results in | Pernicious anemia |
Created by:
mhaynes
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