Exam 3 Flashcards
1
Q
Biochemical basis for megaloblastic anemia – explain how B12 deficiency leads to functional folate deficiency
A
- Vitamin B12 deficiency results in deficiency in methionine synthase deficiency and therefore accumulation of N5-methyl THF and concomitant decreased in concentrations of more oxidized forms of THF, therefore Vitamin B12 leads to a functional folate deficiency - N5 N10 methylene is one of these more oxidized forms that would decrease. This is required for DNA synthesis (thymidine) - N10 formyl THF is required for purine synthesis, it is however decreased now too - Therefore lack of THF in oxidation states blocks DNA replication - Result is production of megaloblastic anemia – RBCs with large cytoplasm, but unable to divide
1
Q
Describe how Phe, Tyr are degraded
A
1
Q
Role of glutathione-S-transferase enzyme family?
A
- catalyze transfer of glutathione to molecules with reactive electrophiles, generating thioether linkage bw compound and cysteine of glutathione, preventing interaction with other molecules
2
Q
How to decipher folate or vitamin B12 or combined deficiency in clinical setting?
A
- Megaloblastic anemia can occur when deficiency in both and can be treated with folate in either cases. Folate given to B12 pt with allow sufficient oxidized THF to be available for DNA synthesis and resolving of megaloblastic anemia - Folate alone will not resolve the neurologic symptoms that go along with vit B12 deficient patients – demyelination leading to brain and nerve damage. Methylmalonyl acidemia seen in vitamin B12 deficient pt, not in folate deficient pt - Combined deficiency seen in chronic malnourished (eg. Alcoholic pts)
3
Q
Describe how ammonium ions are transported and excreted within the blood
A
- Glutamine produced in peripheral tissues enters the bloodstream and is absorbed by the kidneys, liver and gut - Amide group is hydrolyzed by glutaminase and produces glutamate and ammonium ion - Kidney excretes NH4+ directly and liver produces urea in urea cycle. Glutamine is nutrient in gut, ammonium enters hepatic portal and metabolized by liver
3
Q
Synthesis of proline
A
3
Q
Describe reactions of urea cycle. Where is each reaction taking place?
A
3
Q
Describe degradation of GMP vs degradation of AMP to their constituent parts
A
- General theme is to remove phosphate, then ribose, leaving you with base a.) GMP: - GMP = Guanosine + Pi (ez: 5-nucleotidase) - Guanosine + Pi = Guanine + Ribose-1-P (ez: purine nucleoside phosphorylase) b.) AMP pathway 1: - AMP = IMP + NH4+ (ez: AMP deaminase) - IMP = Inosine + Pi (ez: 5-nucleotidase) - Insoine + Pi = hypoxanthine + Ribose-1-P (ez: purine nucleoside phosphorylase) c.) AMP pathway 2: - AMP = Adenosine + Pi (ez: 5-nucleotidase) - Adenosine = inosine + NH4+ (ez: adenosine deaminase) - Insoine + Pi = hypoxanthine + Ribose-1-P (ez: purine nucleoside phosphorylase)
4
Q
Asparagine synthesis
A
4
Q
Describe orotic aciduria
A
- Rare hereditary condition resulting in UMP synthase mutation - Crystalluria, hypochromic megaloblastic anemia, growth retardation, neurologic abnormalities - Anemia is unresponsive to B12 and folic acid - Treatment with uridine
5
Q
What molecule is the temporary ammonium ion carrier in the body?
A
- glutamine
6
Q
Describe synthesis of OAA from AAs
A
6
Q
Outline synthesis of catecholamines. Where does each reaction occur?
A
8
Q
What AAs are made from pyruvate and 3-PG?
A
- Ala, Ser
8
Q
Common alpha-ketoacid/aminoacid pairs in reactions with alpha-ketoglutarate/glutamate?
A
- pyruvate/alanine - oxaloacetate/aspartate
8
Q
What is meant by glucogenic AAs? Which are these? What is meant by ketogenic AAs? Which are these? Which are both?
A
- Glucogenic = These AAs can be converted into glucose via TCA intermediates (alpha-kg, succ coa, fumarate, OAA) and pyruvate – anything that generates OAA, an intermediate in gluconeogenesis - Ketogenic = These AAs can be converted into acetyl-CoA and acetoacetyl-CoA, can never become glucose - Gluco/ketogenic AAs = TIPhe mnemomic = all T AAs (thr, tyr, trp), iso, phe - Ketogenic AAs = all L AAs - Glucogenic AAs = all others
8
Q
Which AAs are converted into pyruvate?
A
- Mnemonic: Some Good Children are Pyrates - Serine, Glycine, Cysteine, Alanine = Pyruvate
8
Q
Explain the role of sorbitol in the pathology of diabetes
A
- In DM pts, there is more free glucose in the cells than in other pts. This is a result of many things, including the failure of phosphorylation by hexokinase/glucokinase. This turns on aldose reductase, which uses NADPH to general sorbitol, which is used by polyol DH to form fructose, consuming NAD. As a result, antioxidant defenses that rely on NADPH are weakened and NADH is high, so glycolytic capacity is reduced. - Sorbitol also is osmotically active and draws water into cells, distorting cellular/tissue structure
8
Q
What is meant by term ‘salvage pathways’? What are the sources of substrates for these pathways?
A
- Conversion of free bases and nucleosides to nucleotides - Sources are: diet, purine/pyrmidine nt degradation products
9
Q
Three types of jaundice: Causes of each? Explain? What happens to color of urine and feces in each case?
A
- Pre-hepatic jaundice: hemolysis. More unconjugated bili in blood than liver can deal with. Moves into tissue membranes. No change to urine or feces color - Hepatic/hepatocellular jaundice: liver disease prevents conversion of unconjugatd bilirubin into bilirubin diglucuronide. Unconjugated bilirubin moves into other tissue membranes. Urine is pale, feces is pale - Post-hepatic/cholestatic jaundice: obstruction of liver exits allows for some processing of unconjugated to conjugated bilirubin, but prevents conjugated form from moving out (into gut). Conjugated form can move into blood and embed into tissue membranes with unconjugated. Also moves to kidney where it causes orange color in urine. Feces are pale
10
Q
Which AAs can be used to synthesize Oxaloacetate?
A
- Every AAs used to generate pyruvate, then pyruvate into OAA via pyruvate carboxylase - In addition, aspartate and asparagine – Ox with a big ASP (ass)
10
Q
What are the products of pyrimidine degradation? How are these secreted?
A
- Beta-alanine and beta-aminoisobutyrate - Water soluble and eliminated in urine
12
Q
Describe de novo synthesis of purines
A
- PRPP = 5 phosphoribosyl 1 pyrophosphate - Ribose 5 phosphate + ATP = PRPP (ez: PRPP synthetase) - PRPP + gln = PRA (phosphoribosylamine) + PPi (ez: amidophosphoribosyltransferase) - 9 step process to convert PRA to IMP (4 reactions require ATP, C and N donated from gly, gln, asp, CO2 and N10-formyl THF). IMP = inosine monophosphate - IMP precursor for AMP and GMP via following rxns: - IMP + Asp + GTP = adenylosuccinate + GDP + Pi (ez: adenylosuccinate synthetase) - Adenylosuccinate = AMP + fumarate (ez: adenylosuccinase) - IMP + NAD = xanthosine5monophosphate (ez: IMP dehydrogenase) - XMP + Gln + ATP = GMP + glu + AMP (ez: GMP synthase) - Specific Nucleoside monophosphate kinases (convert XMP to XDP) and diphosphate kinases (XDP to XTP)
12
Q
From what compound is PRPP synthesized? What enzyme catalyzes this reaction
A
- Ribose 5 phosphate - Ez: PRPP synthetase
13
Describe synthesis of succinyl-CoA from AAs.
14
What AAs are made from: alpha-ketoglutarate and oxaloacetate?
- Asp, Asn, Arg, Glu, Gln, Pro
15
Why does accumulation of uric acid lead to development of gout and kidney stones?
- Uric acid is normally excreted in urine - It and salts have limited solubility, they are typically close to saturation in normal healthy individuals. Common salt = sodium urate - Deposition of sodium urate in kidney = kidney stone - Deposition of sodium urate in joints = gout (triggers inflammatory response)
15
Which is the only purine nucleoside that can be salvaged to a nucleotide?
- Adenosine
16
What is Maple Syrup urine disease? Causes? Symptoms? Result? Treatment?
- Genetic defect in BCKDH that leads to accumulation of BC alpha-ketoacids in body - Symptoms: poor feeding, vomiting, slow/irregular breathing, ketoacidosis, hypoglycemia and neurological dysfunction - High incidence in old order menonite - Result: fatal in one week unless treatment - Treatment: reduced BCAA in diet and monitoring of serum BCAA levels
17
Synthesis of glycine
- PLP = active form of B6
17
Regulation of GDH
- High energy (high GTP, high NADH) = inhibition of enzyme = decreased formation of alpha-KG - Low energy (high ADP) = activation of enzyme = increased formation of alpha-KG
17
Which AAs can be used to synthesize alpha-ketoglutarate?
- Mnemonic: Greg’s Hot Girlfriends Are Pregnant Ovals - Glutamine, Histidine, Glutamate, Arginine and Proline (and ornithine)
17
Describe metabolism of early fast.
17
Describe heme degradation and excretion
- Heme is cleaved between A and B rings by heme oxygenase, yielding biliverdin - Biliverdin reductase used NADPH to form bilirubin, which is unconjugated (aka indirect) - Becomes bound to albumin and travels to liver where it is conjugated to two UGT molecules and becomes bilirubic diglucuronide. This is form that is excreted in bile - When in gut, BDG is modified into urobiliongen by gut and then spontaneously to urobilins / stercobilins which is found in feces - Some urobilinogen is absorbed back into blood and spontaneously converted into urobilin, which is urinated out.
17
Outline salvage of pyrimidine bases
- Orotate/uracil and thymine + PRPP = XMP + PPi (ez: pyrmidine phosphoribosyltransferase) - No cytosine salvage
18
From what are Asp, Asn, Arg, Glu, Gln and Pro made from?
- alpha-ketoglutarate and oxaloacetate
19
Synthesis of cysteine
- s-adenosylhomocysteine is acted on by adenosylhomocysteinase, which generates adenosine and homocysteine - cystathionine beta-synthase and cystathionase are both B6 requiring enzymes
19
Function of vitamin B12 – what reactions is it involved in?
- Only needed by two enzymes: 1.) methymalonyl-CoA mutase and 2.) methionine synthase - 1.) Converts L-methylmalony-CoA (intermediate in taking VOMIT AAs from propionyl-CoA) to succinyl-CoA - 2.) Converts N5 methyl THF to THF while converting homocysteine to methionine
19
Describe changes in mRNA levels that occur as a result of insulin binding
- Increase in acetyl-CoA carboxylase and FA synthase - Decrease in PEP carboxykinase
20
Which urea cycle product is a TCA intermediate? How is the TCA cycle connected to the urea cycle? Why is this important?
- Fumarate production in urea cycle links urea cycle to TCA cycle in what is known as urea-TCA bicycle - Urea cycle requires ATP energy. Fumarate generates energy in TCA cycle to offset ATP requirements by TCA cycle - OAA can be converted into aspartate and feed into urea cycle
20
How to distinguish between hepatic and post-hepatic jaundices?
- Hepatic: watch for other marker of liver disease, such as ALT and AST - Post-Hepatic: watch for other markets of blocked bile ducts such as presence of alk phos in serum
21
What two molecules are carriers of methyl groups?
- SAM and THF
22
Regulation of purine salvage?
- PRPP consumed by HGPRtase and APRtase - Less available for amidophosphoribosyltransfer, therefore less PRA formed therefore less de novo synthesis
23
Most oxidized form of THF and most reduced form of THF? Which form accumulates within the body? In context of THF, what is the one carbon pool and what are the major contributors? Which THF form accumulates in body?
- oxidized form: N10-formyl THF - reduced form: N5-methyl THF - THF can carry and move single carbon molecules around the body. - Major one carbon pool source = serine via 3-PG - Minor sources = formaldehyde (from methanol), formate (from tryptophan), histidine - Accumulated THF form: N5-methyl THF
23
Impact of diabetes on glucose and FA metabolism.
1.) Glucose: Insulin has no impact on liver, fat and muscles, as a result: - Glucose comes in, remains in serum - Liver receives AA from muscles and performs gluconeogenesis - Fat leaves adipose and enters liver, where ketone bodies are generated 2.) Lipids: insulin does not activate LPL and deactivate HSL, as a result: - Chylomicrons carrying dietary TAG stay in serum and cannot enter adipose via action of LPL - HSL is on and is performing lipolysis, TAGS are degraded into FAs, which enter circulation and travel to liver. FAs are generated in excess of what is needed to generate ketone bodies. As a result, TAGs are synthesized and packaged into VLDL, which become elevated in blood.
25
Synthesis of glutamine
26
What are the products, substrates, cofactors of phenylalanine hydroxylase?
- substrates: o2, THBtn, phenylalanine - products: tyrosine, H2o and DHBtn - cofactors: DHBtn reductase, which requires NADH
27
What enzyme catalyzes the committed step of purine synthesis and what is its product?
- Formation of PRA is committed step of purine synthesis - PRPP + gln = PRA + glu (ez: amidophosphoribosyltransferase)
29
Distinguish between carbomyl phosphate synthetase I and carbomyl phosphate synthetase II? Clarify what their substrates are and where each activity is found in the cell?
1.) CPS I: - Found in mitochondria of liver, synthesizes carbomyl phosphate for urea cycle - Substrates: bicarb, 2ATP, ammonium; Products: carbomyl phosphate, ADP, phosphate 2.) CPS II: - Found in cytosol of liver, synthesizes UMP - Substrates: bicarb, 2ATP, gln; Products: carbomyl phosphate, ADP, glu
30
Fuel preferences / energy needs of RBCs, muscles, brain, adipose and liver
- RBCs: glucose, anerobic metabolism - Non-cardiac muscle: glucose-anaerobic/aerobic, FFAs - Cardiac muscle: glucose aerobically only, FFAs - Brain: glucose aerobically, ketone bodies after serious period of starvation - Adipose: glucose, TAG – FAs - Liver: FAs, glucose, AAs and lactate
32
Outline salvage of purine bases
- Hypoxanthine + guanine + PRPP = IMP / GMP (ez: HGPRtase) - Adenine + PRPP = AMP (ez: APRtase)
33
What is THF? What is its function? Where is it derived from?
- THF = tetrahydrofolate - Serves as a carrier of one carbon groups - Derived from folate, vitamin B9, which is found in foliage, green leafy veg, liver, eggs and beans
34
Describe creatine synthesis.
34
Outline synthesis of T3/4. What precursor molecule is used?
- Synthesized from tyrosine residue on thyroglobulin, after synthesis of the molecules, proteolysis releases them as free T3/4
34
How does thymine nucleotide synthesis differ from the other pyrimidines?
- Only make deoxyribose nucleotide forms
36
Molecular action of insulin
- Binds to IR in PM of target cells - IR = kinase, phosphorylates itself then IRS - Phosphorylation cascade ensues, but at level of enzymes, dephosphorylation occurs via phosphatase - Cell undergoes dramatic changes in protein activation, protein localization and gene transcription
37
What is meant by term essential AAs. List them. Special case
- AAs that cannot be synthesized - Pvt Tim Hall = mnemonic - Phe, Val, Thr, Try, Iso, Met, His, Arg, Leu, Lyc - Special case = Arg – can be synthesized, not sufficiently to keep up with needs
37
Synthesis of methionine
37
What is the clinical correlation of deficiency in uridine nucleotide synthesis?
- UMP synthase mutation = orotic aciduria - Crystalluria, hypochromic megaloblastic anemia, growth retardation, neurologic abnormalities - Anemia is unresponsive to B12 and folic acid - Treatment with uridine
38
What is Hartnup disease? Symptoms? Treatment?
- Rare genetic disorder affecting transporter of large, neutral amino acid resulting in no absorption of these amino acids across intestinal epithelial cells, also in prox tubule of kidney causing elimination issue - Symptoms? Similar to pellagra, which is niacin deficiency – 4 D’s – diarrhea, dermatitis, dementia, death. - Treatment? Dietary supplementation with niacin
38
What molecules accumulate with a vitamin B12 deficiency? Explain which reactions these are implicated in?
- 1.) D & L methylmalonyl-CoA (D and L methylmalonate) and 2.) N5-methyl THF - 1.) In process of converting VOMIT AAs to succinyl-CoA - 2.) In converting homocysteine and N5 methyl THF into methionine and THF respectively
39
What enzyme is defective in tyrosinemia-II? Symptoms?
- tyrosine aminotransferase - Symptoms: keratitis, photophobia, skin lesions on palms and soles, intellectual disability
40
Cofactor requirement(s) for aminotransferases.
- Vitamin B6 (pyridoxal 5’-phosphate)
41
Main source of glutamate is the diet. How else is it synthesized in the body?
- Transamination via aminotransferase enzyme (ALT / AST) - Deamidation of glutamine via glutaminase
43
What enzyme is involved in regulating AA catabolism? How does regulation occur?
- Primarily regulated by liver glutamate dehydrogenase (in mitochondria) - Regulation of glutamate DH is by cellular energy charge - High energy (high GTP, high NADH) = inhibition of enzyme - Low energy (high ADP) = activation of enzyme
44
Function of glutathione
- Intracellular reducing agent: scavenging free radicals and destroying peroxides - Drug detoxification
45
What is Lesch-Nyan syndrome?
- Hereditary syndrome with severe or complete deficiency of HGPRtase activity - Hyperuricemia, uric acid stones, intellectual disability and self-injurious behavior
46
Describe the synthesis of pyruvate from AAs.
47
Why does an inability to generate THBtn decrease production of tyrosine, catecholamines and serotonin?
- Tyrosine: synthesized by phenylalanine hydroxylase - Catecholamines: synthesized in part by tyrosine hydroxylase - Serotonin: synthesized by tryptophan hydroxylase - These hydroxylase enzymes require o2, NADH and THBtn
47
What enzyme inserts iron into heme molecule? Where in cell?
- Ferrochelatase inserts Fe2+ into protoporphyrinogen IX molecule causing formation of heme B
48
Precursor to GABA, how is it derived? What are cofactor requirements? Use?
- Glutamate - Decarboxylation of glutamate forms GABA - Requires pyridoxal phosphate - Neurotransmitter
48
Why do T1 diabetic pts often present with DKA whereas type 2 don’t?
- Function of insulin in addition to glucose metabolism is to repress ketone body production and inhibit lipolysis. - In absence as is case with T1 diabetics, large amounts of FFAs are released, ketogenesis ensues and ketoacidosis results. - Lipolysis is seen in T2 diabetics, but not as much as insulin is still available in large amounts and does have somewhat of an effect of repressing lipolysis.
50
Describe vitamin B12 absorption into body and storage
- R-binders in salivary enzymes bind B12 and pass it onto intrinsic factor, produced by stomach parietal cells - Absorbed in ileum through receptor mediated endocytosis - Binds to transcobalamin and is transported to tissues - Preferentially distributed to liver as vit-B12:transcobalamin complex and stored there. Kidney has some B12 stores
51
In what cells does insulin have a function? What response?
- Muscle: uptake of glucose, production of glycogen - Liver: production of glycogen, production of TAG - Adipose: uptake of glucose
53
What enzyme is defective in tyrosinemia-I? Symptoms? Treatment
- fumarylacetoacetate hydrolase - symptoms: severe condition affecting liver, kidney and peripheral nerves, fatal at young age if untreated (liver failure) - Dietary management and nitisinone (inhibits coversion of p-hydroxyphenylpyruvate to homogentisate)
54
What is ALT?
- alanine aminotransferase - synthesizes alanine and alpha-ketoglutarate from pyruvate and glutamate
55
What enzyme is defective in phenylketonuria? Symptoms?
- phenylalanine hydroxylase - Symptoms: intellectual disability, recurrent seizures, hypopigmentation, eczematous skin rashes
55
Outline salvage of pyrimidine nucleosides.
- Uridine / cytidine + ATP = UMP / CMP + ADP (ez: uridine-cytidine kinase)
56
A defect in tyrosine hydroxylase would impact synthesis of all except? A.) dopamine B.) epinephrine C.) melanin
- C.) melanin
57
What are inborn errors of metabolism relating to synthesis of succinyl-CoA from AAs?
- AAs = VOMIT (valine, odd chain FAs, methionine, isoleucine, threonine) - 1.) deficiency in propionyl-CoA carboxylase resulting in propionic / propionyl acidemia - 2.) deficiency in racemase resulting in D-methylmalonyl aciduria - 3.) deficiency in mutase (or Vit B12, required as cofactor) resulting in methylmalonyl aciduria
58
Describe degradation of bases?
- Hypoxanthine + o2 = xanthine + H2o2 (ez: xanthine oxidase) - Guanine + H2o = xanthine + NH4+ (ez: guanine deaminase) - Xanthine + o2 = uric acid + H2o2 (ez: xanthine oxidase) - Uric acid eliminated in urine
60
An inability to generate THBtn would impact synthesis of which of the following molecules? A.) histamine B.) NE C.) Thyroid hormone
- B.) NE (remember, tyrosine in thyroglobulin molecule, not free tyrosine)
61
Describe defects in heme synthesis
- AIP: acute intermittent porphyria: deficiency in PBG deaminase, causes build up of PBG and ALA. Give urine a dark red color. Life threatening and causes episodes of confusion and sharp abdominal pain - PCT: porphyria cutanea tarda: deficiency in uroporphyrinogen decarboxylase, leads to buildup of porphyrins (detected in urine). Porphyrins able to absorb visible and UV light. As a result, light energy is builtup and discharged into tissue and generates ROS. As a consequence, PCT causes photosensitivity of skin and leads to blistering of sun-exposed areas.
63
Treatment of argininosuccinate synthetase deficiency
- As a result of this deficiency – citrullinemia - Treat with arginine and phenylbutyrate supplements - Cirtruline can be cleared directly, but only carries single nitrogen
65
Three amino acids used to synthesize glutathione? Where synthesized? Why is it such a stable molecule?
- Glu, Cys and Gly - Made in liver (not on ribosomes) - Contains non-regular peptide bond called gamma-glutamyl linkage that is stable and resistant against proteases
66
How is the urea cycle regulated? Explain
- Carbomyl phosphate synthetase I = rate-limiting step - Carbomyl phosphate synthetase I is activated by N-acetylglutamate synthetase, which is activated by arginine - High levels of arginine are indicative of elevated peripheral blood ammonia levels
66
How does glutathione act to detoxify peroxides?
- Forms GSSG with peroxide, then reconverted to glutathione via glutathione reductase, which uses NADPH
68
What are Tyr and Cys made from?
- From Phe and Met, which are both essential AAs
68
Which pyrimidine degradation product is unique to pyrimidine metabolism? How is this important?
- Beta-aminoisobutyrate - Found in urine of cancer pts undergoing radiation or chemotherapy
69
Synthesis of melatonin
69
Which molecules are allosteric effectors? What are their signals and affects?
71
Synthesis of aspartate
72
The blood concentration of alanine and glutamine are higher than the concentration of other AAs. How do these AAs help rid the body of toxic ammonia?
- Alanine and glutamine are released in greatest quantity from muscle - BCAAs transfer their nitrogens to alpha-ketoacids (forming alanine and glutamine) and they travel to the liver where urea is formed
73
What is SCID? Causes?
- Group of immune disorders impacting B and T cell proliferation - ~15% of cases due to adenosine deaminase (in degradation of AMP) where adenine metabolites build up - Model: accumulation of dATP inhibits ribonucleotide reductase blocking DNA replication and preventing proliferation OR adenine metabolites are toxic to lymphocytes
75
Precursor to histamine, how is it derived? What are cofactor requirements? Use?
- Histidine - Decarboxylation of histidine - Pyridoxal phosphate - Produced by mast cells, involved in allergic reactions and in control of acid secretion by stomach
77
List disorders of phenylalanine and tyrosine degradation. Name enzymes.
- Phenylketonuria: deficiency in phenylalanine hydroxylase - Tyrosinemia-II: deficiency in tyrosine aminotransferase - Alcaptonuria: deficiency in homogentisate oxidase - Tyrosinemia-I: deficiency in fumarylacetoacetate hydrolase
79
What molecules are derived from tryptophan?
- Serotonin - Melatonin - Niacin
80
Outline salvage of purine nucleosides
- Adenosine + ATP = AMP + ADP (ez: adenosine kinase) - No salvage of guanosine
83
What are the degradation products of Tryptophan?
- Acetoacetyl-CoA - Acetyl-CoA - Fumarate
84
What molecules are regulators of gene expression? Signals? Affects?
84
Effect of lead on heme synthesis
- Lead inhibits porphobilinogen synthase, causing accumulation of ALA - Lead inhibits ferrochelatase, causing accumulation of protoporphyrinogen IX - Causes symptoms similar to the porphyrias
85
Which AAs are degraded to acetyl-CoA and fumarate?
- To acetyl-CoA: Leucine, Lysine, Phe, Tyr, Trp, Iso - To fumarate: Trp, Tyr, Phe
86
Describe metabolism of glucose, AAs and FAs in well-fed state
88
Synthesis of alanine
90
Treatment of argininosuccinate lyase deficiency
- As a result of this deficiency -- argininosuccinicaciduria - Treat with arginine – supports continued citrulline synthesis and continuation of cycle. Argininosuccinate is water soluble and relatively non-toxic, gets eliminated from kidney as waste - Argininosuccinate carries both nitrogens
91
Describe how heme is synthesized
- In mito: Glycine and succinyl-CoA acted on by ALA synthase = aminolevulenic acid (ALA) - 2 x ALA molecules acted on by PBG synthase (aka ALA dehydratase) and produce porphobilinogen (PBG) out in cytoplasm - 4 x PBG acted on by PBG deaminase with product fed into UPG III synthase to produce uroporphyrinogen III (UPG III) - UPG III acted on by UPG III decarboxylase to produce coporphyrinogen III (CPG III) - CPG III enters mito again and becomes protoporphyrinogen IX, which is acted on by ferrochelatase which adds Fe2+ to structure causing formation of heme B
92
What contributes to color of feces? Urine? Why?
- BDG (conjugated bilirubin) moves into gut in bile. It is converted to bilirubin and urobilinogen by bacteria. - Urobilinogen can be further converted into urobilins and stercobilins in gut and gives color to feces - Urobilinogen can also be absorbed into blood and converted to urobilin in blood stream, being moved to and excreted from kidneys.
93
How does 5-fluorouracil function?
- Inhibits thymidylate synthase, which blocks de novo dTMP synthesis, ultimately blocking cell proliferation - It is converted into FUMP by phosphoribosyltransferase in the cell - FUMP is phosphorylated by a kinase and converted into FUDP/FUTP - Ribonucleotide reductase converts it into FdUDP, with kinase converting it into FdUTP - FdUTP can be incorporated into DNA - FUTP can be incorporated into RNA - Biggest effect is FdUDP is acted on by phosphatase and product, FdUMP, inhibits thymidylate synthase
95
Describe synthesis of alpha-ketoglutarate from AAs
97
What are branched-chain amino acids? Metabolism / Pathway of BCAA degradation? Products?
- BCAA = LIV mnemonic = leu, iso, val - Metabolism: muscle has high levels of BCAT (branched-chain AA aminotransferase), which forms branched-chain alpha-ketoacids that are released into blood. BCKDH (branched-chain alpha-ketoacid DH) complex decarboxylates these BCAA in liver - Valine (see picture) - Isoleucine produces acetyl-CoA and propionyl-CoA, it is ketogenic and glucogenic AA - Leucine produces acetyl-CoA and acetoacetate, it is ketogenic AA only
98
What enzyme is defective in alcaptonuria? Symptoms?
- homogentisate oxidase - Symptoms: urine black upon standing, black pigmentation of cartilage and collage, joint destruction and arthritis
99
Gluco-/ketogenic AAs?
TIPhe = try, trp, tyr, iso and phe
100
Why does the drug hydroxyurea block cell proliferation?
- Inhibits ribonucleotide reductase and prevents dNTP synthesis, blocking cell division
103
Which molecules are inducers of covalent modifications (aka phosphorylations)? Signals and affects?
104
What inhibits thymidylate synthase?
- 5-fluorouracil - Methotrexate
106
Describe familial hyperinsulinemic hypoglycemia type 6. Causes? Result?
- Mutations to glutamate dehydrogenase enzyme rendering it insensitive to inhibition by GTP. - As a result, increased AA catabolism occurs in environment that is high energy - Leads to elevated levels of ATP and hyperammonemia - Increased ATP in beta-cell promotes insulin releases, resulting in hypoglycemia - Less active urea cycle with more ammonia production = hyperammonemia
107
What pyrimidine bases cannot be salvaged?
- Cytosine
109
Glucogenic AAs?
- All AAs except for TIPhe and L AAs
111
How is gluconeogenesis in liver connected with muscle glycolysis?
- Glucose enters glycolysis with pyruvate as end product - Pyruvate is converted into alanine via ALT and sent into bloodstream - Alanine is taken up by liver and converted back into pyruvate by ALT - Pyruvate is converted into glucose via gluconeogenesis
113
Synthesis of serine
115
What is the clinical significance of ALT and AST?
- AST found at highest levels in liver, but also in other tissues including cardiac muscle - ALT abundant in liver - Both are normally low in serum - When tissues are damaged, these enzymes are released into the serum - Elevation of AST indicates liver disease, but also acute MI, kidney damage, pancreatitis etc. - Elevation of ALT is more specific indicator of liver damage
116
Describe protein digestion in the digestive tract
- Acidic pH of stomach denatures proteins - Pepsinogen is secreted by the stomach - It autoinhibits it’s active site, becomes altered in acidic environment and cleaves itself into pepsin - Pepsin’s active site contains aspartic acid residues. - It is a endopeptidase and cleaves internal peptide bonds, prefers bonds formed between AA groups of aromatic and hydrophobic amino acids - Chyme enters duodenum, stimulates release of secretin and CCK by intestinal mucosa - Secretin: stimulates acinar cells in pancreas = alkaline fluid released (bicarb rich), which neutralizes chym - CCK: stimulates release of bile and release of pancreatic digestive zymogens (trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidases) - Enteropeptidase present on wall of intestinal mucosa cleaves trypsinogen to trypsin - Trypsin cleaves remaining pancreatic zymogens into active forms (chymotrypsin, elastase, carboxypeptidases)
117
What is acute pancreatitis? Symptoms? Causes? Triggers? Treatment?
- Inflammatory disease of pancreas caused by premature activation of pancreatic digestive zymogens - Symptoms = abdominal pain, vomiting - Causes = pancreatic necrosis - Triggers = alcohol, infections, gallstones - Treatment = supportive via analgesics, fasting, elemental jejunal tube or TPN
118
Strategies used to lower ammonia levels in individuals with urea cycle defects
Protein restriction (not elimination d/t essential AA req or supply AA via alpha-ketoacids)
Hemodialysis (removes excess ammonia)
Phenylbutyrate (metabolite binds glutamine in water soluble form, which is excreted by kidneys) and benzoate (metabolite binds glycine in water soluble form, which is excreted by kidneys)
Mannitol (promotes diuresis)
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What is Gly made from?
- From serine, which is made from 3-PG
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What is phenylketonuria. Causes? Pathology? Symptoms? Treatment? Why avoid aspartame if phenylketonuric?
- Mutation in phenylalanine hydroxylase (more common) or DHBtn reductase leads to a elevation of phenylpyruvate, phenylalanine and other metabolites. - Pathology: not fully understood, but: accumulation of phenylalanine competitively inhibits the transport of other AAs across the BB barrier, which might interfere with NT synthesis. Also leads to reduced synthesis and increased degradation of myeline. Phe is also a competitive inhibitor of tyrosinase and intereferes with melanin synthesis - Symptoms: intellectual disability, recurrent seizures, hypopigmentation, eczematous skin rashes - Treatment: limiting dietary Phe (not eliminating, as it is essential), supplementation with tyrosine, treatment before child is 3 weeks of age, lifelong monitoring of plasma phenylalanine - Aspartame is a dipeptide of aspartic acid and methylated Phe derivative. Eating will cause formation of phenylalanine
123
How does methotrexate function to inhibit thymidylate synthase?
- Methotrexate is an antifolate medication - Remember, N5-N10-methylene THF is needed to convert dUMP to dTMP
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In what cells does glucagon have a function? What response?
- Liver: stimulates degradation of glycogen, stimulates gluconeogenesis from AA sources, stimulates energy production from AA sources - Adipose: stimulates lipolysis
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Synthesis of tyrosine
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Regulation of pyrimidine synthesis
1.) UTP and CTP - Carbomyl phosphate synthetase II (inhibited by UTP, activated by PRPP) - CTP synthase (inhibited by CTP, activated by UTP) 2.) dTTP - thymidylate synthase (unknown)
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Regulation of ribonucleotide reductase
- Allosteric: NTPs and dNTPs activate and inhibit (dATP inhibits) - Transcriptional
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Outline synthesis of melanin
- Tyrosinase converts tyrosine to DOPA and then to dopaquinone, which eventuall yields black/brown (eumelanin) or red/yellow (pheomelanin)
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Mechanism by which allopurinol reduces uric acid levels
- Allopurinol and its metabolite oxypurinol (made by xanthine oxidase) are analogs of hypoxanthine - They inhibit xanthine oxidase and reduce uric acid formation - Intermediates such as hypoxanthine and xanthine are more soluble than uric acid and are eliminated in urine
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What molecules (besides ketogenic/glucogenic) are derived from tyrosine?
- Catecholamines (dopamine, NE, epi) - Thyroid hormones – T3/4 - Melanin
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From what are Ala and Ser made from?
- Pyruvate and 3-PG
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What is pernicious anemia?
- Lack of intrinsic factor secreted by parietal cells of stomach
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What is purpose of vitamin B12 in THF metabolism and keeping functional folate pool?
- Serves to take the most reduced form of THF = N5 methyl THF back to THF form and in the process converts homocysteine to methionine - THF has no other functions in most reduced form, only when in oxidized forms does it have specific functions, including in DNA synthesis
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Roles of nucleoside 5 monophosphate and nucleoside disphosphate kinases?
- Nucleoside 5 monophophate kinases: XMP + XTP = 2 XDP - Nucleoside disphosphate kinases: XDP + XTP = XTP + XDP
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What are the two causes of megaloblastic anemia?
- B12 deficiency - Folate deficiency
139
Describe homocystinuria. Causes? Symptoms? Treatment?
- Grossly evelated homocysteine (plus other metabolites of this) accumulat in body and are seen in urine - Most commonly due to cystathionine beta-synthase mutation - Symptoms: dislocation of optic lens, osteoporosis, lengthening and thinning of long bones, thromboembolism, intellectual disability - Treatment: low methionine diet with cysteine supplements, pyridoxine or betaine supplements
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How are ribonucleotides converted into deoxyribonucleotides?
- Ribonucleotides must be in diphosphate form - Enzymes needed : ribonucleotide reductase and thioredoxin reductase. - Cofactors: thioredoxin - Thioredoxin reductase uses NADPH to generate reduced thioredoxin for another rxn to occur
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Deficiency from niacin causes what diseases?
- Pellagra - Hartnup disease
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Implication of pyrimidine salvage pathway?
- PRPP consumptions means less PRPP available to stimulate CPS II, orotate phosphoribosyltransferase, therefore de novo pyrmidine synthesis is decreased
144
Which three AAs contribute to creatine synthesis? Where does the nitrogen in creatine come from? Where does the synthesis take place? Where does creatine come from in diet?
- glycine, arginine and methionine (s-adenosylmethionine) - nitrogen comes from arginine - liver (some in kidney) - meat and fish
145
Describe allosteric regulation of purine synthesis: what enzymes are regulated? Which allosteric modulators are responsible for this regulation?
- PRPP synthetase (inhibited by ADP and GDP) - Amidophosphoribosyltransferase (inhibited by AMP, GMP; activated by PRPP) - Adenylosuccinate synthetase (inhibited by AMP) - IMP dehydrogenase (inhibited by GMP)
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Synthesis of serotonin
147
Heme synthesis enzymes affected by lead
- Porphobilinogen synthase - Ferrochelatase
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Ketogenic AAs?
L starting AAs – leucine, lysine
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Symptoms of imborn errors of creatine metabolism. Treatment?
- Children present with hypotonia, little to no skeletal or cardiac muscle pathology - Neurological symptoms: epileptic seizures, intellectual disability - Treated by creatine administration
150
Describe problems associated with refeeding and causes of refeeding syndrome. Consider what starvation leads to? How to refeed?
- Starvation: 1.) leads to degradation of digestive enzymes, 2.) depletes intracellular phosphate pools and 3.) depletes potassium stores - Problems: 1.) digestion is impaired and feeding leads to diarrhea and dehydration, 2.) glycolysis starting soaks up phosphate from serum leading to life-threatening hypophosphatemia and 3.) sudden insulin release (insulin moves K into cells) lowers serum potassium further - Watch electrolytes (esp. phosphate and K)
151
Why do some porphyrias cause photosensitivity?
- Porphyrins are conjugated systems, which absorb UV and visible light. - The light energy must be discharged upon being absorbed, so it is discharged into the tissues and generates ROS. As a result photosensitivity of skin occurs
152
Describe de novo synthesis of pyrimidines
1.) Synthesis of uridine nucleotides (three\* enzymes below are part of CAD multifunctional protein) - Gln + bicarb + ATP = carbomyl phosphate + ADP + glu (ez: \*carbomyl phosphate synthetase II) - Carbomyl phosphate + Asp = N-carbamoyl aspartate + Pi (ez: \*asp transcarbamoylase) - N-carbamoyl aspartate = dihydroorotate (ez: \*dihydroorotase) - Dihydroorotate + NAD = orotate + NADH (ez: dihydroorotate DH) - Orotate + PRPP = OMP + Pi (ez: ^orotate phosphoribosyltransferase) - OMP = UMP + Co2 (ez: ^OMP decarboxylase) Notes: three beginning ezs are part of \*CAD multifunctional enzyme, last two are part of ^UMP synthase multifunctional enzyme 2.) Synthesis of cytosine nucleotides - UMP is converted to UTP via nucleoside-5-monophosphate kinases and nucleoside diphosphate kinases - UTP + glut + ATP = CTP + gln + ADP + Pi (ez: CTP synthase) 3.) Synthesis thymine nucleotides - Note: TMP, TDP or TTP are never synthesized (never get ribose forms), only make dTMP, dTDP and dTTP - dUMP + N5,N10-methylene THF = dTMP + THF
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Which AAs can be used to synthesize succinyl-CoA? How?
- Mnemonic: VOMIT - Valine, odd-chain fatty acids, methionine, isoleucine, threonine - These are converted into propionyl-CoA, which undergoes intermediates to become succinyl-CoA
