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Uworld_sitr > 5/3 Biochemistry > Flashcards

5/3 Biochemistry Flashcards

1
Q

Pyruvate Kinase Deficiency

A

Red Pulp Hyperplasia

Pyruvate kinase deficiency causes hemolytic anemia due to failure of glycolysis and resultant failure to generate sufficient ATP to maintain erythrocyte structure. Splenic hypertrophy results from increased work of the splenic parenchyma (hyperplasia of reticuloendothelial cells), which must remove these deformed erythrocytes from the circulation.

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2
Q

Lactic acidosis in septic shock

A

Due to tissue hypoxia > impairs oxidative phosphorylation

Causes shunting of pyruvate to lactate following glycolysis. Hepatic hypoperfusion also contributes to the buildup of lactic acid as the liver is the primary site of lactate clearance.

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3
Q

Risk factor and presentation for aspiration pneumonia

A

Risk factor: dementia and hemiparesis (vocal cord paralysis= soft, breathy voice)

Presentation: rhonchi, dense air space opacities in superior region of lower lobes or posterior region of upper lobes (dependent locations) on CXR

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4
Q

Cause of Ehlers-Danlos that is a result of a defect in the extracellular processing of collagen

A

N-terminal propeptide removal

Due to procollagen peptidase deficiency

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5
Q

Alkaptonuria

A

AR disorder of tyrosine metabolism (prevents conversion of tyrosine to fumarate)

Lack of homogentisic acid dioxygenase leads to accumulation of homogentisic acid

BLACK URINE when exposed to air, blue-black pigment on face (sclera, ear cartialge), ochronotic arthropathy, severe arthritis in adults

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6
Q

Mutation causing gout

A

X-linked mutation affecting the phosphoribosyl pyrophosphate (PRPP) synthetase gene - activating mutation causing increased production and degradation of purines

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7
Q

Cell type responsible for the intense inflammatory response seen in gout

A

Neutrophils

Rx with NSAIDs (or colchicine if NSAIDs are contraindication)

Acute gouty arthritis

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8
Q

Primary carnitine deficiency

A

Myopathy (high creatine kinase, weakness), cardiomyopahy (S3 gallop), hypoketotic hypoglycemia w/ decreased muscle carnitine content

Impaired fatty acid transport from cytoplasm into mitochondria, prevents B-oxidation of fatty acids in acetyl CoA

Cardiac and skeletal muscle injury, impaired ketone production during fasting

Deficient synthesis of acetoacetate

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9
Q

Fructokinase deficiency

A

‘Essential fructosuria’
Asymptomatic, AR, fructose is excreted unchanged in urine

Hexokinase takes over role of fructose metabolism (converts to fructose 6 phosphate which will enter glycolysis)

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10
Q

Niemann Pick disease

A

AR, sphingomyelinase deficiency

Sphingomyelin accumulation within lysosomes, lipid laden foam cells, hepatosplenomegaly

Hypotonia, neurologic degeneration, cherry red macular spot

NOTE: NO HEPATOSPLENOMEGALY seen in Tay-Sachs, otherwise very similar

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11
Q

Restrict this substance in diet to improve condition in patient with impaired transport of ornithine from cytosol to mitochondira

A

Protein

Urea cycle defect

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12
Q

Vitamin C deficiency (scurvy)

A

Vit C is necessary for hydroxylation of proline and lysine residues in pro-collagen

Most often seen in severely malnourished individuals

Capillary bleeding, poor wound healing, periodontal disease (bony deformities and subperiosteal hemorrhages in children)

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13
Q

G protein coupled receptors

A

Bind glycoprotein hormones (TSH, LH, FSH)

Transmembrane domain is composed of alpha helices with hydrophobic amino acids (alanine, valine, leucine, isoleucine, phenylalanine, tryptophan, methionine, proline, glycine)

Transmembrane domain anchors the protein to the phospholipid bilayer of cell membrane

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14
Q

Folate Deficiency: administration of which supplement would reduce erythroid precursor cell apoptosis?

A

Folate deficiency inhibits formation of dTMP, limiting DNA synthesis and promoting megaloblastosis and erythroid precursor cell apoptosis

Thymidine supplementation can moderately increase dTMP levels and reduce erythroid precursor cell apoptosis

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15
Q

Biotin (vit B7) as a cofactor for enzymes, Biotin deficiency

A
  • can be due to consumption of raw egg whites
  • mental changes, myalgias, anorexia, macular dermatitis, lactic acidosis
  • Pyruvate carboxylase (pyruvate to oxaloacetate w/ gluconeogenesis)
  • acetyl-CoA carboxylase (acetyl-coA to malonyl-CoA in fatty acid synthesis)
  • Propionyl-CoA carboxylase (propionyl-CoA to methylmalonyl-CoA in fatty acid oxidation)
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16
Q

Binding of oxygen to hemoglobin drives the release of….

A

H+ and CO2 from hemoglobin (Haldane effect)- lungs

vs. in peripheral tissues, high concentrations of CO2 and H+ facilitate oxygen unloading from hemoglobin (Bohr effect)

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17
Q

Which enzyme has 5’ to 3’ exonuclease activity in addition to 3’ to 5’ exonuclease activity and 5’ to 3’ polymerase activity

A

DNA pol I in prokaryotes

5’ to 3’ exonuclease activity removes RNA primer and repairs damaged DNA sequences

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18
Q

Homocystinuria

A
  • defect in cystathionine synthase
  • inability to form cysteine from homocysteine
  • Cysteine is essential in the diet
  • Homocysteine builds up and is prothrombotic, resulting in premature thrombolic events (atherosclerosis, acute coronary syndrome)
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19
Q

Hemoglobin C

A

Missense mutation (glutamate for lysine) in beta globin cahin
Overall decrease in negative change for hemoglobin molecule
Speed of hemoglobin movement:
Hemo A > hemo S > hemo C

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20
Q

Congenital deficiency of propionyl CoA carboxylase

A

Enzyme responsible for conversion of propionyl CoA to methylmalonyl CoA

Leads to development of propionic acidemia

Propionyl CoA is derived from amino acids (Val, Ile, Met, Thr), odd-numbered fatty acids, cholesterol side chains

Poor feeding, vomiting, hypotonia, lethargy, dehydration, anion gap acidosis

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21
Q

PKU

A

Tyrosine is ESSENTIAL, restrict phenlalanine

Deficiency in phenylalanine hydroxylase (phenlalanine to tyrosine)

Fair complexion (lack of melanin), seizures, eczema, MUSTY ODOR

22
Q

Amatoxins (poisonous mushrooms, death cap)

A

Potent inhibitors of RNA polymerase II (halts mRNA synthesis)

Symptoms start 6-24 hours after ingestion: abd pain, vomiting, severe cholera-like diarrhea (with blood and mucus, acute hepatic and renal failure

urine testing for a-amanitin can confirm suspected poisoning

23
Q

How does insulin promote glycogen synthesis

A

Acts via receptor tyrokine kinase, stimulates phosphatidylinositol-3-kinase which activates protein phosphatase, which dephosphorylates/activates glycogen synthase

Increases synthesis of glycogen, proteins, fatty acids, nucleic acids

24
Q

Process of forming cataracts due to long term hyperglycemia

A

Glucose is converted to sorbitol by aldose reductase
Sorbitol is converted to Fructose by Sorbitol dehydrogenase

The lens contains high levels of sorbitol dehydrogenase, but this becomes overwhelmed with hyperglycemia

Sorbitol is trapped in the cells, increases osmotic pressure, facilitates influx of water into lens cells, hydropic lens fibers that degenerate , len opacification and cataract formation

25
Q

Mitochondrial DNA (mtDNA)

A

Most common non-nuclear DNA found in eukaryotic cells

Resembles prokaryotic DNA (small circular DNA molecules)

Maternally derived

Mutations involving mtDNA can cause mitochondrial disorders (ex. Leigh syndrome, MELAS)

26
Q

Thiamine (Vit B1) Deficiency

A

Beriberi
Dry: symmetrical peripheral neuropathy of distal ext. with sensory and motor impairments

Wet: + cardiac involvement (cardiomyopathy, high-output CHF, peripheral edema, tachycardia)

If neuro symptoms (esp w/ alcoholic, think Wernicke-Korsakoff)

27
Q

Primary myelofibrosis

A

Chronic myeloproliferative disorder

Caused by atypical megakaryotic hyperplasia, stimulates fibroplast proliferation, replacement of marrow space with collagen

Severe fatigue, splenomegaly, , early satiety/abdominal discomfort, hepatomegaly, anemia, bone marrow fibrosis

Mutation in JAK2, a cytoplasmic TK, leads to cytokine independent activation of signal transducers and activators of transcription (STAT proteins)

28
Q

Riboflavin deficiency

A

Ribofalvin is precursor to coenzymes FMN and FAD

FAD participates in TCA cycle and electron transport chain as electron acceptor for succinate dehydrogenase (succinate into fumarate)

Low riboflavin excretion, seen in chronic alcoholics and severely malnourished

Angular stomatitis, cheilitis, glossitis, seborrheic dermatitis, eye changes, anemia

29
Q

Maple Syrup Urine Disease

A

Defect in a-keto acid dehydrogenase

Inability to degrade branched chain amino acids

Dystonia, poor feeding, “maple syrup scent” of patient’s urine w/n first few days of life

Rx: restrict intake of branched chain amino acids (leucine, isoleucine, valine)

30
Q

PI3K/Akt/mTOR pathway

A

Intracellular signaling pathway important for anti-apoptosis, cellular proliferation, angiogenesis

Mutations in growth factor receptors, Akt, mTOR or PTEN that enhance the activity of this pathway contribute to cancer pathogenesis

Causes translocation of mTOR to nucleus and gene transcription

31
Q

Maturity-onset diabetes of the young

A

Mild, nonprogressive hyperglycemia that often worsenes with pregnancy-indced insulin resistance

Heterozygous mutation of glucokinase gene > decrease in beta cell metabolism of glucose, less ATP formation, and less insulin release

Glucokinase functions as a glucose sensory

32
Q

Biochemical process defective n Parkinson’s

A

Ubiquitination

Impairment of the ubiquitin-proteasome system can contribute to the development of neurodegenerative disorders, including Parkinson’s and Alzheimer’s disease

33
Q

Signal transduction of phospholipase C

A

Ligand-receptor binding and Gq protein activation, activation of phopholipase C (PLC), PLC hydrolyzes PIP2 and forms DAG and IP3. IP3 activates protein kinase C via an increase in intracellular Ca

34
Q

What is the effect of insulin on gluconeogenesis/glycolysis?

A

Fructose 2,6-bisphosphate activates phosphofructokinase 1 (increasing glycolysis) and inhibits fructose 1,6-bisphosphatase (decreasing gluconeogenesis)

Fructose 2,6 bisphosphate concentration is decreased in the presence of insulin and decreases in response to glucagon

35
Q

What inhibits beta-oxidation of fatty acids?

A

Malonyl-CoA

Cytosolic acetyl-CoA carboxylase converts acetyl-CoA to malonyl-CoA during the rate limiting step of de novo fatty acid synthesis. Malonyl CoA inhibits the action of mitochondrial carnitine acyltransferase, thereby inhibiting beta-oxidation of newly formed fatty acids

36
Q

Synchronization of glycogen degradation with skeletal muscle contraction occurs due to…

A

Release of sarcoplasmic calcium following neuromuscular stimulation. Increased intracellular calcium causes activation of phosphorylase kinase, stimulating glycogen phosphorylase to increase glycogenolysis

37
Q

Arginase deficiency

A

Progressive development of spastic diplegia, abnormal movements, growth delay, elevated arginine levels

Arginase is a urea cycle enzyme that produces urea and ornithine

Rx: low protein diet devoid of arginine, admin of synthetic protein

Note: Patients have mild or no hyperammonemia (vs. other urea cycle disorders..)

38
Q

Lactate dehydrogenase deficiency

A

In anaerobic glycolysis, NAD+ is regenerated from NAHD when pyruvate is converted to lactate via lactate dehyrdrogenase.

In patients with lactate dehydrogenase deficiency, glycolysis is inhibited in strenuously exercising muscle as muscle cells cannot regenerate NAD+. Consequently, high intensity physical activity leads to muscle breakdown, pain, and fatigue as insufficient amounts of energy are being produced in th exercising muscle.

39
Q

Hemoglobin F

A

2 Alpha chains and 2 gamma chains (present for the first few weeks of post natal life)

Patients with homoxygotic B-thalassemia are asymptomatic at birth due to presence of gamma globins and HbF

40
Q

Renal acid excretion in chronic acidotic states

A

Acidosis stimulates renal ammoniagenesis: renal tubular epithelial cells metabolize glutamine to glutamate, generating ammonium that is excreted in the urine and bicarbonate that is absorbed into the blood.

Acute ischemic colitis (due to embolic disease from a fib). Ischemic bowel undergoes anaerobic metabolism, causing lactate accumulation in the blood, leads to an anion gap metabolic acidosis.

41
Q

Pigmented gallstones

A

Composed of calcium salts of unconjugated bilirubin and typically arise secondary to bacterial or helminthic infection of the biliary tract.

Beta-glucuronidase released by injured hepatocytes and bacteria hydrolyzes bilirubin glucuronides to unconjugated bilirubin.

The liver fluke Clonorchis sinensis has a high prevalence in East Asian countries and is a common cause of pigment stones.

42
Q

Cyanide poisoning

A

Toxicity of cyanide is dependent on its ability to binds ferric iron (Fe3) with high affinity, inhibiting cytochrome c oxidase in mitochondria (essential for oxidative phosphorylation). Inhibition results in severe lactic acidosis and death.

Redding skin, tachypnea, headache, tachycardia, N/V, confusion, weakness. Seizures, cardiovascular collapse.

Administration of inhaled amyl nitrite oxidizes ferrous iron (Fe2) present in hemoglobin to ferric iron (Fe3), generating methemoglobin. Methemoglobin is incapable of carrying O2 but has a high affinity for cyanide. It binds and sequesters cyanide in the blood, freeing it from cytochrome oxidase.

43
Q

Production of ribose from fructose-6-phosphate

A

Transketolase and transaldolase carry out the nonoxidative reactions of HMP shunt. Some cells do not use the oxidative phase reactions to produce cytosolic NADPH, but all cells can synthesize ribose from fructose-6 phosphate using the non-oxidative reactions.

44
Q

Lead toxicity

A

Young children, impoverished, who reside in homes built bedore 1978 are at significant risk for lead toxicity.

Lead directly inhibits ferrochelatase and delta-aminolevulinic acid (ALA) dehydratase, resulting in anemia, ALA accumulation, and elevated zinc protoporphyrin levels. Neurotoxicity is also a significant longterm complication.

45
Q

Fabry’s disease

A

galactosidase A deficiency

Neuropathic pain, angiokeratomas, decreased sweating, renal failure, cardiac/stroke

46
Q

Acute intermittent porphyria attacks

A

Due to accumulation of aminolevulinate (ALA) and porphobilinogen (PBG), resulting from inherited PBG deaminase deficiency combined with ALA synthase induction (typically due to certain medications, alcohol use, or a low calorie diet).

Management with glucose or hemin inhibits ALA synthase activity.

47
Q

Oxygen-hemoglobin dissociation curve

A 
Left curve:
Decreased H+
Decreased 2,3 DPG
Decreased temperature
Think LUNGS= Left shift
O2 is less available to tissues

Right curve:
Increased H+
Increased 2,3 DPG
Increased temperature

48
Q

Under normal circumstances, KRAS is only active when bound to….?

A

GTP
The regulation of the Ras-MAPK signal transduction pathway requires a balance between active (GTP-bound) and inactive (GDP-bound) Ras proteins.

RAS gene mutations, which result in constitutively activated Ras proteins, are implicated in the development of malignant tumors.

49
Q

Phenylketonuria (PKA)

A

Severe intellectual disability, history of seizures, abnormal pallor of catecholaminergic brain nuclei on autopsy, MUSTY/mousy odor

Inability to convert phenylalanine into tyrosine (phenylalanine hydroxylase or cofactor tetrahydrobiopterin deficiency)

50
Q

Tay-Sachs

A

AR, B-hexosaminidase A deficiency, accumulation of GM2 ganglioside

Progressive neurologic deterioration, weakness, hypotonia, developmental regression, seizures, blindness, spasticity, macrocephaly, abnormal startle reflex, cherry-red macula spot (with white macula halo)

NO HEPATOSPLENOMEGALY (vs. Niemann Pick)

51
Q

Heme oxygenase

A

Found in macrophages

Degrades heme into biliverdin (green) > which is further reduced into bilirubin (yellow) by biliverdin reductase

Causes bruises to turn green

52
Q

Diabetic ketoacidosis: what is the cause of increased glucose?

A

Increased triglyceride breakdown in adipose tissue due to insulin deficiency.

Glycerol is converted to glycerol-3-phosphate in the liver by glycerol kinase. Then DHAP is formed, which can produce ATP (through glycolysis) or glucose (through gluconeogenesis)

Glycerol produced by degradation of triglycerides in adipose tissue can be used by glycerol kinase in the liver and kidney to synthesize glucose during gluconeogenesis.

Uworld_sitr (42 decks)

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