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Biochemistry 2.1
UWORLD + FA biochemistry review
| Question | Answer |
|---|---|
| Photosensitivity | manifests as a VESICLE AND BLISTER formation on sun-exposed areas, as well as edema, pruritus, pain and erythema |
| Photosensitivity is seen in _____________ steps of ______________ synthesis. | LATE; Porphyrin |
| Why is photosensitivity seen with late steps of porphyrin synthesis? | due to accumulation of porphyrinogens that react with oxygen excited by UV-light |
| What is a common porphyrin disorder associated with photosensitivity? | Porphyria Cutanea Tarda (PCT) |
| PCT is caused by deficiency of which enzyme? | Uroporphyrinogen decarboxylase (UROD) |
| PBG deaminase deficiency causes? | Acute intermittent porphyria (AIP) |
| Which is associated with photosensitivity, AIP or PCT? | PCT |
| Abdominal pain, neuropsychiatric symptoms and PBG accumulation? | AIP |
| What is the function of vWF? | bids to glycoprotein IB receptors on platelets to mediate platelet adherence after endothelial damage. |
| Deficiency of vWF can cause abnormal? | Ristocetin agglutination assay |
| In cases of vWF deficiency, the administration of ________________, causes a normal ristocetin agglutination on assay. | Desmopressin |
| Low levels of vWF cause | poor agglutination in the presence of ristocetin |
| What are key vignettes features of a woman with vWF deficiency? | Gingival bleeding and heavy menses |
| Bernard-Soulier syndrome: | Hereditary deficiency of GP Ib receptors |
| What is the clinical presentation of Bernard-Soulier syndrome? | Thrombocytopenia, enlarged platelets, and mucocutaneous bleeding |
| Why is there no agglutination of ristocetin in Bernard-Soulier syndrome, upon addition of normal serum (or desmopressin)? | There is a lack of GP Ib receptors and not vWF |
| Glanzmann thrombasthenia: | Hereditary deficiency of GP IIb/IIIa receptors |
| How is the risotein agglutination test in Glanzmann thrombasthenia? | Normal, since GP Ib receptor and vWF are normal. |
| What is the Hageman factor? | Factor XII (12) |
| Deficiency of Hageman factor causes? | Thrombotic events and not associated with bleeding. |
| What are the cofactors needed or used by Branched-chain alpha-ketoacid dehydrogenase? | Thiamine, Lipoate, Coenzyme A, FAD, and NAD |
| What illness is associated with mutated branched amino acid enzyme? | Maple Syrup Urine disease |
| Maple Syrup Urine disease requires of _____________ supplementation to improve symptoms, and lifelong restriction of ______________, __________, and ___________. | Thiamine; Restriction of : Valine, Leucine, and Isoleucine |
| What enzyme is responsible to initiate the cascade of Pyruvate to produce Energy? | Pyruvate dehydrogenase |
| Pyruvate + Pyruvate dehydrogenase -----> | Acetyl-CoA |
| In Pyruvate metabolism, an excess amount of Acetyl-CoA accumulation will cause? | 1. Inhibition of Pyruvate dehydrogenase (stop making energy) 2. Stimulate (increase/accelerate) Pyruvate carboxylase activity, in order to make more Oxaloacetate ---> Glucose |
| Pyruvate + CO2 + Pyruvate carboxylase ------> | Oxaloacetate |
| Gluconeogenesis produces ----> | Glucose |
| Increased amounts or concentration of Oxaloacetate causes: | Inhibition of and slowing of Pyruvate carboxylase activity. |
| G6PD: | is a rate limiting enzyme of the PPP |
| What is the major source of cellular NADPH synthesis? | Pentose Phosphate Pathway (PPP) |
| The PPP is the major source of intracellular _____________. | NADPH |
| NADPH is necessary for: | 1. Reducing agent (protects RBC from oxidative damage) 2. Biosynthesis of cholesterol, fatty acids, and steroids 3. Phagocytic cells generating a respiratory burst via NADPH oxidase. |
| G6PD deficiency: | It is seen with acute hemolytic anemia and jaundice. Usually after consumption of fava beans. |
| HbS: | aggregates in the deoxygenated state |
| HbS polymers: | form fibrous strands that reduce RBC membrane flexibility and promote RBC sickling |
| Sickling: | Occurs under circumstances that are associated with ANOXIA including low pH and high levels of 2,3-BPG |
| Sickle cells are predisposed to ________________ ____________ and _________________, especially in the __________ and ______, due to __________ blood flow. | Microvascular occlusion and Microinfarcts; Liver and Spleen due to slow blood flow. |
| Which organs tend to produce the highest rate of RBC sickling and why? | The organs that have increased and heavy blood flow such as the brain, muscles and placenta, due to increase extraction of oxygen from the blood (Oxygen unloading) |
| Oxygen unloading is: | Extraction of oxygen by tissue from the blood |
| What enzyme is inhibited by Isoniazid? | Pyridoxal phosphokinase |
| An inhibition of Pyridoxal phosphokinase leads to: | Vitamin B6 (Pyridoxine) deficiency |
| Pyridoxine active form: | is a cofactor for s-aminolevulinate synthase, the enzyme that catalyzes the rate-limiting step of heme synthesis |
| What inhibition is responsible for causing Sideroblastic anemia? | Inhibition of limiting step of heme synthesis (s-aminolevulinate synthase) |
| PBS shows an RBC with a "ring" formation around nucleus of "blue" granules. Dx? | Sideroblastic anemia |
| What are the steps (in order) of Base Excision repair? | 1. Glycosylase 2. Endonuclease 3. Lyase 4. DNA polymerase 5. Ligase |
| Mnemonic for remembering steps of Base excision repair process? | GEL-PL |
| In what organelle does the hydroxylation of Lysine and Proline residues occur during collagen synthesis? | Rough Endoplasmic Reticulum |
| Collagen gets it maximum tensile strength from which part of its synthesis process? | Hydroxylation of Proline and Lysine residues in the RER |
| Hydroxylation of Proline and Lysine in collagen synthesis uses ________________ as a cofactor. | Vitamin C |
| Vitamin C deficiency is known as _____________________. | Scurvy |
| Scurvy: | Vitamin C deficiency that produces fragile vessels, predisposing to gingival bleeding, ecchymosis, and petechiae |
| Thiamine is a cofactor for which 4 enzymes: | 1. Pyruvate dehydrogenase (pyruvate ---> Acetyl-CoA --> Kreb) 2. alpha-KG dehydrogenase (enzyme of Citric cycle) 3. Transketolase (enzyme in PPP) 4. Branched-chain a-ketoacid dehydrogenase (catabolism of branched amino acids) |
| Vitamin B12 deficiency: | - Elevated levels of Methylmalonic acid and Homocysteine - Neurological symptoms and megaloblastic anemia - Subacute combined degeneration: * Dorsal columns -- loss of prioception/vibration, and (+) Romberg sign * Lateral corticospinal tract -- Spastic muscle weakness, hyperreflexia |
| Vitamin B9 (Folate) deficiency: | Only has elevated level of Homocysteine and with no neurological deficits. |
| Niacin | Precursor for NAD and NADP |
| NAD is used for: | Catabolic reactions (glycolysis and B-oxidation) Citric cycle for: - Isocitrate dehydrogenase - a-KG dehydrogenase - Malate dehydrogenase |
| Fabry disease pathophysiology? | X-R disorder; due to alpha-galactosidase A deficiency resulting in the accumulation of sphingolipid globotriaosylceramide |
| What are some clinical features of Fabry disease? | Neuropathic pain, Angiokeratomas Telangiectasias Glomerular disease (Proteinuria) Cerebrovascular disease (TIA, stroke) Cardiac disease (LVH) |
| Metachromatic leukodystrophy: | due to arylsulfatase A deficiency resulting in accumulation of cerebroside sulfate |
| Clinical manifestation of Metachromatic leukodystrophy: | Progressive demyelination leading to ataxia, peripheral neuropathy, seizures and hypotonia |
| Niemann-Pick Disease: | accumulation of Sphingomyelin due to deficiency of Sphingomyelinase. |
| What are some clinical characteristics seen in Niemann-Pick disease? | Progressive neurodegeneration, cherry-spot in macula and hepatosplenomegaly. Associated with chromosome 11 |
| Which Lysosomal enzyme condition is associated with chromosome 15? | Tay-Sachs disease |
| What is the distinguishing feature between Niemann - Pick disease and Tay-Sachs disease? | Niemann-Pick disease presents with Hepatosplenomegaly. |
| What lysosomal conditions present with hepatosplenomegaly? | Niemann-Pick disease, Hunter disease, and Hurler disease |
| Krabbe disease is due: | Galactocerebrosidase deficiency resulting in accumulation of Galactocerebroside and psychosine. |
| How is Krabbe disease presented: | Peripheral neuropathy, destruction of oligodendrocytes, developmental delay , optic atrophy, adn globoid cells. |
| Gaucher's disease: | AR; "crumpled tissue paper"; Deficiency glucocerebrosidase and accumulation of glucocerebroside. Associated with chromosome 1. |
| "Whorled membrane" | Tay-Sachs disease |
| Galactosemia is due to deficiency in which two enzymes: | 1. GALK (Galactokinase) 2. GALT (Galactose-1-phosphate uridyl transferase) |
| Which galactosemia is the mild form? | GALK deficiency |
| GALK deficiency Galactosemia is mostly asymptomatic except for: | Lenticular accumulation of galactitol in the lenses, causing osmotic damage and development of cataracts. |
| Excess in galactose and or fructose in urine yield: | Urine test positive for reducing agents |
| Which galactosemia enzyme deficiency develops into severe presentation of the disease? | GALT deficiency |
| What is the clinical presentation of GALT deficiency? | Severe galactosemia; Hepatic and renal failure; Usually presents n neonates with vomit, lethargy and failure to thrive. |
| Aldolase B deficiency | Hereditary FRUCTOSE intolerance |
| Inability to metabolize fructose, causing hypoglycemia, hypophosphatemia,and failure to thrive | Aldolase B deficiency |
| What determines the sequence of amino acids? | The interaction of the mRNA codons with the tRNA anticodon. |
| What happens with a mischarged tRNA with the wrong amino acid? | In case of failing correction by the aminoacyl(AA)-tRNA synthase proofreading, the wrong amino acid will be integrated to the growing polypeptide chain. |
| What kinds of agents are used to treat CN poisoning? | Nitrates |
| Why are nitrates used to treat CN toxicity? | ability to induce methemoglobinemia |
| Methemoglobinemia: | Binds tightly to CN; causes a dusky discoloration of the skin and cannot carry oxygen |
| Methemoglobin contains ______ (___) instead of _______ (__). | Ferric (Fe3+); Ferrous (2+) |
| Which type of iron state binds more tightly to mitochondrial enzymes, thus reducing the CN toxic effects? | Ferric iron (Fe 3+) |
| Clinical presentation of CN toxicity? | Reddish skin discoloration, tachypnea, headache and tachycardia. Seen with Lactic acidosis with a narrow venous-arterial O2 gradient |
| What enzyme is in charge of correcting wrong tRNA anticodon amino acid? | aminoacyl-tRNA synthetase |
| BH4: | tetrahydrobiopterin |
| MC disorder due to a BH4 deficiency? | Phenylketonuria |
| What are the two main causes of Phenylketonuria? | 1. PAH deficiency 2, BH4 deficiency |
| MCC of BH4 deficiency? | Deficiency of dihydrobiopterin reductase, which reduces BH2 tin GH4. |
| BH4 is an important cofactor for? | 1. Phenylalanine hydroxylase 2. Tyrosine hydroxylase |
| What are the 4 Dopaminergic pathways? | 1. Mesolimbic --(positive symptoms of schizophrenia) 2. Mesocortical --(negative symptoms) 3. Nigrostriatal pathway -- EPS 4. Tuberoinfundibular --- Hyperprolactinemia |
| Glycogen storage disease type V: | McArdle Disease |
| Enzyme deficient in McArdle disease? | Myophosphorylase |
| What is the clinical presentation of McArdle disease? | Muscle glycogenolysis, which resulted in decreased exercise tolerance, muscle pain and cramping, and myoglobinuria with physical activity |
| How are the lactic acid level in McArdle disease? | Normal |
| On which organ does McArdle disease occurs? | Muscle |
| Myophosphorylase: | - isoenzyme of glycogen phosphorylase - during glycolysis it shortens the chains by clavein a-1,4-glycosidic linkages, liberation Glucose-1-phosphate |
| At what point does the cleaving done by myophosphorylase stop? | At point of reaching the "limit dextrin" |
| What is the Limit dextrin? | Glycogen chain with only 4 residuels left |
| What is liberated during glycogenolysis by the action of myophosphorylase? | Glucose-1-phosphate |
| What it's the aerobic fate of Pyruvate? | Converts into Acetyl-CoA by using Pyruvate dehydrogenase, which then enters the TCA |
| What is the anaerobic fate of Pyruvate? | Becosmes Lactic acid, by the enzyme Lactate dehydrogenase |
| Pyruvate + CO2 + _____________-----> Oxaloacetate --> ___________. | Pyruvate carboxylase; Glucose |
| GTP is synthesized by __________ during the TCA cycle conversion of _____________ to _____. | Succinyl-CoA synthase; Succinyl-CoA into Succinate |
| Which reaction requires GTP as cofactor in GLUCONEOGENESIS? | PEP carboxykinase uses GTP to synthesis PEP form Oxaloacetate |
| What is splicing? | Performed by splicesosomes; Removal of introns |
| What introns are removed during splicing? | 1. GU at the 5' splice site 2. AG at the 3' splice site |
| Mutations to the splice sites cause? | inappropriate removal of exons, and retaining introns ---> dysfunctional proteins |
Created by:
rakomi
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