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46 Cards in this Set

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1. What pterin based cofactor is involved in adding or subtracting 1-carbon units?

2. Which co-enzyme, THF or THB is seen in rxns that transfer oxygen (hydroxylations), e.g., pehenylalanine hydroxylation associated with PKU.

3. which THB or THF contain pterin rings?
1. THF

2. THB

3. both
Give 3 sources for 1-carbon units.
a) glycine cleavage system: breaks down glycine (2-carbons) into CO2, NH4 and a 1C unit… b) Histidine(6-C) to glutamine (5-C)… c) Serine/Threonine Hydroxymethyltransferase: converts serine (3-C) to glycine (2-C)
What are the three parts of THF? Where do the 1-C units attach?
glutamate residues (n=1-6), PABA, pterin ring. b) N-5 on pterin ring and N-10 on PABA
Which THF with residues (n=1-6) can enter the cell membrane?

What part of the THF do the 1-C unit attach to?

the N-5 or N-10
What organism makes folate?

In what form can bacteria absorb THF?
by bacteria

It can't, I must make all of it's own THF
Where does Folate come from?
What is the name of the process where PABA is attached to the pterin ring?
What enzyme do humans lack that render them unable to conjugate PABA to the pterin ring?
dihydropteroate synthase
Can humans make the pterin ring, such as those found on biopterin?
Since bacteria makes PABA, it cannot absorb it. Thus it is essential that bacteria absorb the enzyme critical for the conjugation of PABA. What drugs inhibit bacterial growth and what related mechanism do these drugs use?
Sulfa drugs… they mimic PABA and thus competitively inhibit PABA from binding dihydropteroate
What are the 5 sources of 1-C units?
serine, glycine, histadine, formaldehyde, Tryptophane (formate)
1. What accept the 1-C units?

2. Besides THF and THB, which other coenzyme is based on the pterin ring?
1. THF

2. folate
What are the products of the 1-carbon units?
dTMP, Serine, Purines, B12•CH3
a) What are the 5 forms of folate, including folate that accept a 1-C unit. b) and which one isn't reversible?
a) Folate, formyl-FH4, methenyl-FH4, Methylene-FH4 and Methyl-FH4… b) methyl-FH4
Place the folate based carriers in order from least reduced to most reduced.

What is partly responsible for spina bifida?
formyl-FH4 < methenyl-FH4 < Methylene-FH4 < Methyl-FH4

maternal folate deficiency
Trace the pathway for the origin of 1-C unit entering into Formyl-FH4.
Tryptophan -> formate + FH4 + ATP -> Formyl-FH4
Trace the pathway for the origin of 1-C unit entering into Methenyl-FH4.
Histidine -> forminino + FH4 -> glutamate + methenyl-FH4
Trace the pathway for the origin of 1-C unit entering into Methylene-THF.
(Glycine OR Serine OR Formaldehyde) + FH4
What is the source of the Methyl-THF?
reduction of methylene-FH4 by NADH
Which folate based carriers are the most proximal to purine rings?
formyl-FH4 and Methenyl-FH4
1. which folate based carrier converts dUMP to dTMP?

2. Which Folate based carriers contribute 1-C units to DNA/RNA bases?
1. Methylene-FH4

2. Formyl-FH4 and methylene-FH4
What role does methyl-THF play in Homocystein degradation?
it serves has a cofactor and contributes a methyl group in the methionine synthase rxn.
What is required to convert homocystein to methionine?
methyl-THF, B12
What is another name for B12
What is the path of the 1-carbon unit from the methyl-THF to S-Adenosylmethionine (SAM = Ado-Met)
methyl-THF + Homocystein -(Methionine synthetase = homocysteine methyltransferase + B12 -> Methionine + free THF (to recycle) -> Methionine + ATP to form -> SAM
What makes AdoMet (SAM) an effective methyl donor?
The positive charge on the Sulfur to release -CH3
1. Give the complete "Activated Methyl Cycle" starting with methyl-THF and ending with Homocystein.

2. which of the intermediates of the above cycle acts as the methyl handle?
FH4-CH3 -> B12 -> homocystein -> methionine + ATP -> SAM (loss of CH3 to give) -> SAH (loss of adenosine to give) -> homocystein

2. which of the intermediates of the above cycle acts as the methyl handle? Homocysteine
1. What is the most important metyl donor in the body?

2. a) What is the most common use of SAM as a methyl donor? b)Where does this occur?
1. SAM (AdoMet)

a) Guanidinoacetate + SAM -> creatine… b) in the liver
1. What is the product of the following rxn: Norepinephrine + SAM -> ?

2. What did SAM do in the above rxn?
1. epinephrine

2. donated a methyl group to NE
Which enzyme catalyzes the methylization of homocystein?
methionine synthase (=homocysteine transferase)
Besides THF-CH3, how can homocysteine become methylated?
degradation of choline (phosphatidylcholine) produces Betaine, which serves as a 1-carbon donor to homocysteine
Where else can choline degradation contribute a 1-carbon unit?
a product of choline degradation (dimethylglycine) can contribute
On B12, what does the 1-carbon unit attach to? What does B12 resemble?
cobalt… a heme... where the cobalt is analogous to Fe
How do we absorb B12?
In the stomach R-binders and intrinsic factor are produced. R-binders bind B12 so it does not denature with HCl. Intestinal proteases release B12 from R-binders, while affinity of intrinsic factor for B12 increases. Specialized receptor in the Ileum binds intrinsic factor and B12 is shuttled across the membrane... then to the liver
What is pernicious anemia?
malabsroption of B12
Where do R-binders come from?
Gastric mucosa
Where does intrinsic factor come from?
parietal cells
What happens as people age that impairs B12 absorption?
lack of HCl (failure to breakdown meat products to capture B12)

poor intrinsic factor production, thus B12 does not bind to intestinal receptors and is excreted
What does B12 deficiency lead to?
megaloblastic anemia, because folate is not recycled… thus without purines and dTMP cells arrest in S-phase
Besides methionine synthetase (homocysteine methyltransferase), which enzymes require B12
methylmalonyl CoA Mutase
1. What are the consequences of B12 deficiency with respect to methylmalonyl CoA Mutase?

2. what are the consequences of B12 deficiency with respect to homocysteine methyltransferase?
1. neurologic which overtime may be irreversible (due to methylmalonyl CoA accumulation, demyelinization of nervous tissue, altered fatty acid synthesis

2. megaloblastic anemia and functional folate deficiency (which leads to loss of purine and thymidine base needed for DNA synthesis (stuck in S-phase)
What is thought to be the cause of neurological symptoms in methylmalonyl CoA Mutase/B12 deficiency? (3 causes)
1. Accumulation methylmalonyl CoA… 2. Demyelinization of nervous tissue… 3. Fatty acid biosynthesis affecting myelin synthesis: methylmalonyl CoA used instead of malonyl CoA… Priopionyl CoA used instead of acetyl CoA
What supplies the sulfur for the production of cysteine?

Which cofactor is needed in the rxn that produces cysteine?
homecysteine (or methionine)

Give the pathway for cysteine synthesis from homocysteine.
Homocysteine + (serine, PLP, cystathionine synthase also called CBS) --> cystathionine (cystathionase + PLP) --> cysteine
Since homocysteine is linked with cardiovascular disease, which 5 deficiencies can lead to this condition?
cytathionine synthase (CBS), vitamin B6 (PLP), homocysteine methyltransferase (methionine synthase), Methylene-THF reductase, choline