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35 terms

MCB 15: Week 7-2

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wht are three central functions of the pentose phosphate pathway
1) NADPH biosynthesis
2)ribose-5-phosphate
3) sugar-phosphate of varying lengths
where is the HMP active?
in tissues that routinely sunthesize fatty acids or steroids
synthesis of 1 palmitoyl-CoA (7 additinos of 2 C units)requires how mjuch NADPH
14
synthesis of 1 cholesterol requires how much NADPH?
14
what form of reducing power does RBC need and why does it need this?
NADPH to protect from ROS
hwo is hemoglobins Fe maintained in proper +2 configuration
methemoglobin reductase which uses NADH NOT NADPH
what is the main regulatory step in HMP
glucose6phosphate to 6p-gluconolactone.

this step is inhibited by NADPH
transketolases
transfer 2 carbon keto groups. they also require thiamin pyrophosphate (TPP) covalently bound to enyme via schiff base to the nh2 group of lysine residue
transaldolase
creates 4 and 6 c sugar from 7 and 3 sugar. this does not require TPP and transfers a 3 c fragment
fates of ribulose-5-phosphate
1)epimerization to xylulose 5 p
2)isomerization to ribose 5 p (nucleotides)

remaining xlulose5p can be reset by transketolase to sedoheptulose 7 p (7C)
Wernicke-Korsakoff syndrome
mutation reduces affinity for vit b1 in transketolase (TPP)

brain atrophy, amnesia, paralysis
ratio of NADP/NADPH
1:10

vs

nad/nadh ratio= 1000:1
how to make deoxyribonucleosides
reduction of ribonculeosides with NADPH

if this is defected.. NO DNA! WHA!!
what maintains rubonucleotide reductase in proper state?
thioredoxin reductase which requires NADPH
NADPH reducing power usage
indirectly via glutathione from sulfydryl groups of cysteine residues or folate derivatieves. these are ONLY reduced by NADPH
glutathione
major defense against oxidative stress. -SH groups sacrificed so that other essential proteins are in the reduced state.

it comes from non-ribosomal hepatic origin
what happens if glutathione cant protect -SH groups on proteins from being oxidized?
then globular proteins will lose ther 3 primed structure. this formes masses " HEINZ BODIES". this makes cells less pliable, RBC removal, and hemolysis of spleen
glutathione's role in reducing peroxides?
glutathione peroxidase requires Se as cofactor and reduces hydrogen peroxide to peroxide and water.

this reduces organiz peroxides to alcohols, and reverses lipid peroxidation

BUT if you have selenium deficiency- you are very likely to get damage by ROS
how does liver use glutathione-s-transferase
it attaches glutathione to toxic molcules which makes them more solule (resembles p450)
detoxificiation of acetaminophen (tylenol)
broken down first by cytochrome p450 enzyme which forms highly toxic intermediate NAPQI. BUT glutathione's action now creates that into a non-toxic product that is secreted

however, in an overdose. glutathione reserves are exhausted so buildup of NAPQI results in liver damage

MAYBE N-acetyl-cystein (precursor to GSH) can protect against NAPQIs effects
absorbic acid
vitamin C

when it is oxidized it turns into dehydroazcorbate which is recyceld by takign Hs from reduced glutathione which is recycled by NADPH from shunt
NADPH involvement in cytochrome p450
cytochrome p450 is nadph dependent mono-oxygenase. it requires NADPH in HYDROXYLATIONS of aromatic and aliphatic compounds (usually in eukaryotic ER, not mitocondria)

ex xenobiotics- after hydroxylation, they become more hydrophilic and easily excreted via urine

exception=tobacco smoke and aflatoxin become MORE DANGErous!
role of NO
formed by NADPH through reduction of l-arginine

indirectly an endogenous vasodilator

forms radical OH and mediates bacteriocidal activity

inhibits platelet aggregation so interferes with thrombus initiation
how do you form NO
from L-arginine and NADPH

NO synthase (CA DEPENDENT ENZYME)

side effects: NO diffuses to smooth muscles where it synthesizes cGMP which makes muscles contract

(conversion of cGMP- 5 GMP is done by guanylate phosphodiesterase)
Viagra
prolonging NOs action makes this work
done by inhibiting cGMP breakdown
g6p dehydrogenase deficiency
loss of reducing power since you get less NADPH
what are the three primary dangerous radicals
superoxide, hydrogen peroxide, hydroxyl radical
antioxidants other than NAPDH
fat soluble: Vit A, Vit E(alpha-tocopherol, lycopenes)

water soluble: vitamine C, Glutathione

Uric Acid (gout patients rarely get MS)

Bilirubin- against lipid peroxidation
superoxide
normal by product of oxidative metabolism at the level of CoQ

it is relatively non-toxic but when its radicals join with NO it forms dangerous peroxynitrate (OONO). this can cause peroxidation and nitration of tyrosyl hydroxide groups in proteins which is bad
Amyotrophic lateral sclerosis (Lou Gehrig's disease aka maladie de Charcot)
neurodegenerative: motor neurs affected

enzyme defect: cytosolic superoxide dismutase (inability to detoxify O2)
hydroxyl radical
damages membranes by lipid peroxidation

can damage nucleic acids causing breakage and alter structure of bases
what enzumes detoxify h2o2
catalase, h peroxidase, gsh peroxidase
cofactors for superoxide dismutase
in cytosol: uses Zn and Cu
in mito: uses Mn and Cu
catalase
contains Heme and Fe
in peroxisomes which is filled with hydrogen peroxides

1/4th of our alcohol is broken down in peroxisomes in this way (alcohol dehydrogenase)
superoxide/peroxide is not always bad- when is it useful?
phagocytes/macrophages: need it to destroy bacteria ect through a respiratory burst

htis uses rapid glucose metabolism by pentose shunt to produce NADPH ( respiratory burst uses NADPH oxidase to make NADPH turn into NADP) this helps o2 turn into o2- which goes into h2o2 then oh which is the killer (uses Fe+2 to Fe +3)