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Biochemistry - Metabolism 1

matic2's version from 2012-06-10 17:22

Metabolism Sites

Question Answer
FA oxidation (beta-oxidation)mitochondria
Acetyl-CoA productionmitochondria
TCA cycle locationmitochondria
HMP shunt locationcytoplasm
F.A. Synthesiscytoplasm
Protein synthesisRER
Steroid synthesisSER
Location of heme synthesisboth cyto/mito
Location of gluconeogenesiscyto/mito
Location of urea cyclecyto/mito

Rate Determining Enzymes of Metabolic Processes

Question Answer
Phosphorylaseadds phosphate without using ATP
Dehydrogenaseoxidizes substrate
Rate limiting step glycolysisPFK-1 (F6P-->F16BP)
Rate-limiting step gluconeogenesisF16-Bis-phosphatase (F16BP-->F6P)
Rate-limiting step TCA cycleisocitrate dehydrogenase (isocitrate-->alpha ketoglut.)
Rate-limiting step for glycogen synthesisglycogen synthase (UDP-glucose-->storage from of glycogen)
Rate-limiting step for glycogenolysisglycogen phosphorylase (glycogen-->limit dextran)
Rate-limiting step in HMP shuntG6PD (glucose 6P --> 6 phosphogluconate)
Rate-limiting step in de novo pyrimidine synthesiscarbamoyl phosphate synthase 2, cyto only
Rate-limiting step in de novo purine synthesisglutamine PRPP amidotransferase
Rate-limiting step in urea cyclecarbamoyl phosphate synthase 1 (ATP+HCO3+ammonia-->carbamoyl phosphate), mito only
Rate-limiting step in FA synthesisacetyl CoA carboxylase (ACC-->malonyl coA), requires biotin
Rate-limiting step in FA oxidationcarnitine acyltransferase 1 (palmitoylcarnitine-->palmitoyl CoA)
Rate-limiting step in ketogenesisHMG-CoA synthase (acetyl CoA-->hmg CoA)
Rate-limiting step in cholesterol synthesisHMG-CoA reductase (HMG CoA-->mevalonic acid)


Question Answer
Carriers of phosphate groupsATP
Electron carriersNADH, FADH2, NADPH
Acyl carrierscoenzyme A, lipoamide
Carriers of biotinCO2
Carriers of 1-carbon unitstetrahydrofolate
Carriers of CH3 groupsSAM
Carriers of aldehydesTPP
Use of NAD+ vs NADPHNAD+ used for catabolic processes to carry reducing equivalents away as NADH, NADPH used for anabolic processes like steroid/FA synthesis as supply of reducing equivalent
NADPH is product ofHMP shunt
Uses of NADPHanabolic processes, respiratory burst, p-450, glutathione reductase
Aerobic metabolism ATP yield32 from malate-aspartate shuttle (heart and liver) vs only 30 from glycerol-3P shuttle (muscle)
Shuttle systemsrequired to move NADH across impermeable inner mito membrane, malate-aspartate shuttle is in heart/liver and gives 2.5 ATP/NADH, glycerol-3P shuttle is in muscle and gives 1.5 ATP/NADH


Question Answer
1st step glycolysisconversion of glucose to G6P via hexokinase or glucokinase
Hexokinaseglucose-->G6P, found everywhere, high affinity (low Km), low capacity (low Vmax), un-induced by insulin, feedback inhibition via G6P
Glucokinaseglucose-->G6P, in liver and beta cells of pancreas, low affinity (high Km), high capacity (high Vmax), induced by insulin (GLUcokinase is a GLUtton- has high vmax b/c it can’t be satisfied), NO feedback inhibition (unlike hexokinase), phosphorylates excess glucose (after a meal) to sequester it in liver-->blood glucose buffer
Rate-limiting step of glycolysisPFK-1 converts F6P-->F16BP, ATP and citrate negatively feedback, AMP and F2,6BP positively regulate
Steps of glycolysis requiring ATPhexokinase (glucose-->G6P) and PFK1 (F6P-->F16BP)
PEP-->pyruvatevia pyruvate kinase, produces ATP, negative inhibition via alanine and ATP, positive feedback via F16BP
Steps of glycolysis producing ATP1,3 BPG-->3-PG via phosphoglycerate kinase, and PEP-->pyruvate via pyruvate kinase
FBPase 2used in fasting state to break down glucagon, F2,6BP-->F6P, activated by glucagon-->increased cAMP-->increase PKA-->increase FBPase-2 (decreased PFK2)
PFK2use in fed state, F6P-->F2,6BP (positive feedback to PFK1), insulin-->decreased cAMP-->decreased PKA-->decrease FBPase2 (so increase PFK2)
FBPase2 and PFK2part of same complex but respond in opposite ways to phosphorylation by PKA


Question Answer
Glycolytic enzyme deficiencyassociated with hemolytic anemia- can’t maintain Na/K ATPase-->RBC swelling/lysis, due to deficiencies in pyruvate kinase usually- RBCs metabolize glucose only anaerobically and depend solely on glycolysis
RBC metabolismmetabolize glucose anaerobically only and depends on glycolysis 100%
Pyruvate dehydrogenase inhibited by?ATP/NADH/acetyl Coa
Pyruvate dehydrogenasepyruvate + CoA + NAD+ --> acetyl CoA + NADH + CO2- requires 5 cofactors of pyrophosphate (B1 thiamine/TPP), FAD (b2 flavin), NAD (B3 niacin), CoA (B5 pantothenate), lipoic acid
Pyruvate dehydrogenase activated by?increased NAD+/NADH ratio, increased AMP, increased Ca
What inhibits lipoic acid?arsenic- will get vomiting, rice water stools, garlic breath
Pyruvate dehydrogenase deficiencycauses backup of substrates (pyruvate and alanine) resulting in lactic acidosis, can be congenital or acquired (alcoholics from b1 def.), will get neurologic defects, tx with intake of ketogenic nutrients only (high fat content or high lysine/leucine) to replace glucose as an E source
Pyruvate dehydrogenase is very similar to what other enzyme complex?alpha-ketoglutarate dehydrog. Complex (converts alpha keto.-->succinyl coA) in krebs
Pyruvate metabolism1. goes to OAA (which replenishes TCA or goes to gluconeo)
2. goes to acetyl CoA for TCA
3. goes to alanine via ALT
4. goes to lactate
Alanine and pyruvate metabolismalanine carries amino groups to the liver from m. (pyruvate --> alanine via ALT)
Cori cycleallows lactate from anaerobic metabolism to go to liver for gluconeogenesis to be glucose source for m./RBCs, shifts metabolic burden to the liver and requires 4 ATP/cycle

TCA Cycle

Question Answer
Pyruvate-->acetyl CoA produces what else1CO2, and 1 NADH, via pyruvate dehydrog.
TCA cycle overall3 NADH (x3ATP) , 1 FADH2 (x 2ATP), 1 GTP, 2 CO2- 12 ATP per acetyl CoA (so 24 for 1 glucose)
TCA cycle occurs where?in mito
TCA intermediatesCitrate Is Krebs’ Starting Substrate For Making Oxaloacetate- citrae-->isocitrate-->alph-Ketoglut-->Succinyl CoA-->Succinate-->fumarate-->malate-->OAA
Rate limiting step of TCA cycleisocitrate dehydrogenase
Alpha-ketoglutarate dehydrogenaserequires same cofactors as pyruvate dehydrog.- B1, B2, B3, B5, lipoic acid (TPP/flavin/niacin/pantothenate respectively)- converts alpha-keto -->succinyl coA
NADH vs FADH2 in ETCNADh electrons enter mito via malate/aspartate or glycerol 3P shuttles, FADH2 electrons are transferred to complex 2 (at lower E level than NADH), NADH produces 3 ATP, FADH2 produces 2 ATP
e- transport inhibitorsrotenone, cyanide, antimycin A, carbon monoxide- all directly inhibits e- transport causing a decreased H+ gradient and less ATP synthesis
ATPsynthase inhibitorsoligomycin- directly inhibit mitochondrial ATPsynthase causing an increased H+ gradient, no ATP b/c e- transport stops
Uncoupling agents2,4-DNP, aspirin (fevers often occur after asa overdose), thermogenin in brown fat- cause increase permeability of membrane-->decreased H+ gradient and increased O2 consumption, ATP synth stops but e- transport continues-->produces heat


Question Answer
Gluconeogenesis enzymesPathway Produces Fresh Glucose- Pyruvate Carboxylase (pyruvate-->OAA), PEP carboxykinase (OAA-->PEP), F1,6BPase (F16BP-->F6P), glucose-6phosphatase (G6P-->glucose)
Def. in gluconeogenic enzymeshypoglycemia
Gluconeogenesis locationoccurs in liver mostly, different enzymes work in either mito or cyto- pyruvate-->OAA (pyruvate carboxylase) is in mito, everything else in cyto
Muscle and gluconeogenesis?can’t participate b/c it doesn’t have glucose 6-phosphatase (G6P-->glucose)
Odd vs even chain FAs for gluconeogenesisodd chain FA yield 1 propionyl CoA during metabolism which can enter TCA (as succinyl coA) and go thru gluconeo to serve as glucose source- even chain FA can’t produce new glucose b/c only yield acetyl CoA equivalents

HMP Shunt (pentose phosphate pathway)

Question Answer
Pentose pathwayprovides NADPH from abundant glucose-6P, also yields ribose for nucleotide synthesis and glycolytic intermediates
2 phase (ox is irreversible and non-ox is reversible) which both happen in cytoplasm, no ATP used/made
Sites of pentose pathwaylactating mammary glands, RBCs, liver, adrenal cortex
Glucose 6P dehydrogenaseglucose 6P-->NADPH + ribulose 5P + CO2, rate-limiting step in oxidative irreversible part of pentose pathway
Non-oxidative part of pentose pathwayribulose 5P-->ribose 5P + G3P + F6P via transketolases (requires B1)
Respiratory burstactivation of membrane-bound NADPH-oxidase (neutros and macros), rapid release of reactive oxygen intermediates for immune response
NADPH oxidase deficiencychronic granulomatous disease- these pts use H202 generated by invading organisms and convert it to reactive oxygen species- pts are at risk for infxn by catalase + orgs (S. aureus/aspergillus) b/c they neutralize their own H202 leaving WBCs w/o ROIs for fighting infxn
Glucose 6P dehydrogenase deficiencyXR disorder, more in blacks, increased malarial resistance, no NADPH oxidase to keep glutathione reduced which detoxs free radicals and peroxides, decreased NADPH can cause hemolytic anemia (poor RBC defense)
G6PD deficiency histologybite cells & Heinz bodies
Heinz bodiesoxidized Hb ppt w/in RBC
Bite cellphagocytic removal of Heinz bodies by macros
NADPHused for keeping glutathione reduced which detoxifies free radicals/peroxides, decreased NADPH leads to hemolytic anemia (poor RBC defense)

Fructose, Galactose, & Lactose Metabolism

Question Answer
Fructose intoleranceAR deficiency of aldolase B - Fructose1P accumulates causing decreased available phosphate-->inhibition of gluconeogenesis and glycogenolysis, tx is to reduce fructose/sucrose (glucose+fructose) intake
Sxs of fructose intolerancehypoglycemia, jaundice, cirrhosis, vomiting
Essential fructosuriaAR defect in fructokinase (fructose-->F1P), benign condition since fructose doesn’t enter cells- sxs only involve fructose appearing in blood/urine
Which is worse fructose intolerance or essential fructosuria?fructose intolerance (deficient aldolase B ties up all phosphate) gives jaundice/cirrhosis/vomiting/hypoglycemia, essential fructosuria will give fructose in urine/blood (defective fructokinase)
Classic galactosemiaAR absent of galactose-1P-uridyltransferase
accumulation of toxic substances (like galactitol in lens of eye), can cause failure to thrive, jaundice, hepatomegaly, juvenile cataracts, mental retardation
tx is to exclude galactose and lactose (galactose+glucose) from diet
Galactokinase deficiencyAR deficiency where galactitol accumulates if galactose is present in diet, galactokinase converts galactose-->galactose 1P
mild condition, sxs are galactose in blood/urine and infantile cataracts, may present as failure to track objects or to develop a social smile
Which is worse classic galactosemia or galactokinase deficiency?classic galactosemia- galacititol accumulates and can cause cause failure to thrive, jaundice, hepatomegaly, juvenile cataracts, mental retardation , galactokinase deficiency is more mild (infantile cataracts, galactose in blood/urine)
Which is worse defects of fructose metabolism or galactose?galactose metabolism (more severe sxs)
Aldose reductaseglucose-->sorbitol, used for trapping glucose in cell; sorbitol can then go to fructose by sorbitol dehydrogenase
Sorbitol dehydrogenasesorbitol-->fructose, tissue lacking this enzyme (schwann cells, retina, lens, kidney) are at risk of sorbitol accumulation-->peripheral neuropathy, retinopathy, and cataracts (all in chronic diabetes)
Sorbitol accumulationoccurs in tissues w/o sorbitol dehydrogenase (lens, kidney, schwann cells)- sorbitol is osmotically active and can’t cross membrane freely like glucose, prolonged hyperglycemic states (diabetes) causes sorbitol accumulation-->increased osmotic pressure-->water enters cell-->osmotic damage
Lactase deficiencyage-dependent and/or hereditary lactose intolerance (blacks/asians), due to loss of brush-border enzyme, may follow gastroenteritis, sxs of bloating, cramps, osmotic diarrhea, tx is avoiding dairy or adding lactase pills to diet
Essential amino acidsonly L-form aa’s in proteins- Met/Val/Arg/His are glucogenic, Leu/lys are ketogenic, Ile/Phe/Thr/Trp are keto/glucogenic
Acidic amino acidsaspartate and glutamate- both – charge at body pH
Basic amino acidsarginine, lysine, histidine- arg is most basic, his has no charge at body pH, arg/lys in histones which bind to – DNA

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