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560D CLINICAL BIOCHEMISTRY PPT REVIEW QUESTIONS AND ANSWERS -KAYLAS
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560D CLINICAL BIOCHEMISTRY PPT REVIEWQUESTIONS AND ANSWERS -KAYLAS
What natural constituent non-enzymatically oxidizes porphyrinogens into
porphyrins and what part of the porphyrinogen structure is oxidized?
Porphyrinogens are unstable and LIGHT oxidizes them into porphyrins by
oxidizing the FOUR METHYLENE BRIDGES
What is the only enzyme catalyzed oxidation reaction of porphyrinogen in
humans?
ONLY enzyme-catalyzed oxidation reaction of porphyrinogen in humans
= protoporphyrinogen IX to protoporphyrin IX by protoporphyrinogen IX
oxidase
What enzyme controls the rate-limiting step of heme synthesis? Where is it
active and what are the substrate and products in the reaction? What is the
required cofactor?
DELTA-Aminolevulinic acid synthase (ALA synthase)
How many ATP-dependent processes are necessary to activate Delta-
Aminolevulinic acid (ALA) synthase?
2 ATP dependent processes - one cytosolic chaperone protein keeps it in
unfolded state in cytosol, then metal dependent protease cleaves off N- in mito
matrix to make ALA synthase, then 2nd ATP dependent chaperone folds it.
Short ½ life (~60 min)
What does the red blood cell (RBC) mRNA isoform of ALA synthase contain?
Why is this element important? (see sideroblastic anemia slide)
RBC ALA synthase mRNA contains an IRE (iron response element). IRE
regulates iron homeostasis at the translational level of ALA synthase by sitting
at 5' UTR mRNA thereby inhibiting translation when there is not enough iron
present to create heme.
, Does Protoporphyrinogen Oxidase create a porphyrinogen or a porphyrin? What
is the difference between porphyrinogen and porphyrin?
Creates a porphyrin called Protoporphyrin IX.
Difference = porphyrin = oxidized form that is water insoluble.
Where does excess protoporphyrin IX go?
Excess protoporphyrin IX gets excreted by biliary system into GI tract.
What two reductants are needed by Ferrochelatase to insert ferrous iron into
protoporphyrin IX to form heme?
Needs ascorbic acid/C and cysteine as reductants
What constituents repress/inhibit the activity of ALA synthase?
Heme and hematin repress ALA synthase activity
How does Glucose affect heme biosynthesis?
Glucose and one of its proximal metabolites inhibits heme biosynthesis through
transcription factor inactivation (glucose inhibits ALA synthase), hence
porphyrias may first occur when pt placed in LOW caloric/glucose state (b/c
sugar not there to stop the creation of porphyrias).
What are the 3 distinct parts of folate?
pterin, PABA, glutamic acid
Why can't humans synthesize folate?
Do not have the enzyme that couples pterin to PABA in humans to form pteroic
acid so we must eat folate in the diet
GI conjugase enzymes hydrolyze folate in the gut to monoglutamate for
absorption. What cofactor is needed for this reaction? What kinds of beverages
can also inhibit conjugase activity?
Zinc is needed for this reaction. Alcohol and Zn deficiency impede folate
absorption by inhibiting conjugase activity.
How much folate is destroyed during the canning process?
50-95% of folate is destroyed during canning
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