• Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

Card Range To Study

through

image

Play button

image

Play button

image

Progress

1/40

Click to flip

Use LEFT and RIGHT arrow keys to navigate between flashcards;

Use UP and DOWN arrow keys to flip the card;

H to show hint;

A reads text to speech;

40 Cards in this Set

  • Front
  • Back
1C metabolism definition
Processes that move 1C via methylene/methyl/formyl
1C metabolism vitamins
- Folate compounds (carry the C)
- Vitamin B12
Folic acid sources
"Foliage" - green, leafy vegetables
Folate not used directly
Two separate reductions via dihydrofolate reductase (DHFR)
Folate -> DHF -> THF
DHFR reaction
Folate + NADPH + H+ (via DHFR) -> DHF
- 2H added each rxn
Methotrexate
Cancer drug, inhibits Folate -> THF reactions
- Slows DNA synthesis, bad for quickly dividing cells
1C binding site
on the N5 or N10 atoms
Main C-carrying forms of folate
N5-methyl THF (methyl on N5)
- N5,N10-methylene THF (CH2 shared by N5 and N10)
Major carbon donor
Serine - donates methyl
- Not essential acid - never rate limiting..
Serine C-donating rxn enzyme
Serine hydroxymethyl transferase
Serine C-donating rxn
Serine + THF (via Serine hydroxymethyl transferase) -> Glycine + N5,N10 methylene THF + H2O
Absortion of dietary folate
Naturally polyglutamated
- Glutamates removed by small intestine enzyme
- Transported into small intestine cell by reduced folate carrier
- Reduced by DHFR
- Converted to N5-methyl THF
- Transported in blood, taken up by cells
- Glutamate tail added once in cell - traps it
1C-THF functions
1) dUMP -> dTMP (Thymidylate synthase rxn)
2) Purine nucleotide synthesis
3) Methionine cycle
Thymidylate synthase rxn
dUMP + 5,10-Methylene THF (via Thymidylate synthase) -> dTMP + DHF
Thymidylate synthase rxn is weird b/c...
N5,10-methylene THF provides C and reducing equivalents
Methionine cycle purpose
Burn one ATP to create SAMe, a high-energy C-donating molecule
SAMe purpose
Besides THF variants, does almost ALL other 1C transfers
SAMe synthesis
Methionine + ATP (via methionine adenosyl transferase) -> SAMe + PPi + Pi
Methionine cycle rxns
Methionine + ATP -> SAMe + PPi + Pi
SAMe + something -> S-adenosyl homocysteine + methylated something
S-adenosyl homocysteine + H2O -> Adenosine + Homocysteine
Homocysteine + B12 + N5-methyl THF -> Methionine + THF
B12 deficiency
THF gets "trapped" as N5-CH3-THF
- methionine not regenerated
Alternate homocysteine destiny
Can become cysteine instead of regenerating methionine
B12 sources
Only synthesized by microorganisms - get from animal sources (liver, mollusks)
- No B12 in purely vegetarian diet!
B12 malabsorption
Some kind of GI disease/problem
B12 absorption process
B12 bound to R-proteins at ingestion
Intrinsic factors (IF) released in stomach
Pancreatic proteases remove R-proteins
IF binds B12 in duodenum
IF-B12 absorbed in ileum
Inside lumenal cell, IF removed, transcobalamine II (TCII) gets B12
TCII-B12 taken up by cells via TCII receptors
Atrophic gastritis
Autoimmune disease, parietal cells destroyed
- No stomach acid, no B12 absorption either
- Can lead to pernicious anemia...
Tapeworm
also competes for B12 uptake
Other B12-dependent process
Propionyl CoA (from odd # FA) -> Succinynl CoA
Elderly nutrition
Often marginal B12 shortages in nursing homes, etc.
High plasma N5-CH3-THF
B12 deficiency
Low plasma B12
B12 intake deficiency
Elevated plasma homocysteine
THF and/or B12 deficiency
Folate deficiency
Low serum folate, low red cell folate, normal B12
B12 deficiency
High serum folate, low RBC folate, low B12, high methylmalonate
Folate deficiency pathophysiology
Failure of purine/thymidylate synthesis
- Slowed DNA synthesis in marrow, Hb production normal
- Large RBC's - more Hb than normal inside
Macrocytic anemia
Large RBC's in circulation, lyse
Megaloblastic anemia
Cells in marrow have large nuclei, poorly condensed chromatin
- DNA synthesis not keeping up with Hb production
B12 deficiency pathophysiology
Folate trapped as N5-CH3-THF
- Functional shortage of folate
- Impaired DNA synthesis, low platelets, low WBC
- Neurological problems
Pernicious anemia
Degeneration of spinal cord, nervous system
- Dementia, other irreversible damage
- B12 supplements can stop damage, can't reverse it
Neural tube defects
Prenatal defect due to lack of folate
Elevated homocysteine levels
Result from lack of folate, B12
- Toxic to endothelium - increased heart attack, stroke
- Vitamin supplements reduce levels, don't reverse damage