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Study Period Targeted Review > Biochem > Flashcards

Biochem Flashcards

1
Q

Causes of hyperammonemia

A

Most common = ornithine transcarbamylase deficiency (converts ornithine to citrulline in urea cycle): causes hyperammonemia and orotic aciduria.

Other causes: carbamoyl phosphate synthetase I deficiency (regulated by N-acetylglutamine). CPS I forms carbamoyl phosphate for the urea cycle

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2
Q

Causes of orotic aciduria

A

Ornithine transcarbamylase deficiency: hyperammonemia and orotic aciduria

UMPS deficiency (involved in de novo pyrimidine synthesis): hyperammonemia, megaloblastic anemia, mental retardation

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3
Q

RNA polymerases in euks

A

RNA pol I: makes rRNA, found only in nucleolus (Rampant - most common)

RNA pol II: makes mRNA (Massive - largest); opens DNA at promotor site. Inhibited by amanita mushrooms mRNA is read 5-3’

RNA pol III: makes 5S rRNA, tRNA (Tiny - smallest)

No proofreading function

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4
Q

RNA polymerase in proks

A

1 RNA polymerase (multisubunit complex) makes all 3 kinds of RNA. DNA-dependent RNA pol in proks is inhibited by Rifampin

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5
Q

Types of eukaryotic DNA pol

A

DNA pol alpha: replicates lAgging strand and makes RNA primer
DNA pol beta: repairs DNA
DNA pol gamma: replicates mtDNA (gamma = gaga = baby –> maternal…mtDNA)
DNA pol delta: replicates leaDing strand

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6
Q

DNA pol in proks

A

DNA pol I: excises RNA primer w/ 5-3’ exonuclease and replaces it with DNA
DNA pol III: elongates leading strand as well as lagging strand until it reaches primer of preceding fragment. 3-5’ exonuclease activity (proofread)

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7
Q

Hereditary fructose intolerance

A

AR deficiency in ALDOLASE B; causes accumulation of F1P and decrease in available phosphate –> reduced glycogenolysis/gluconeogenesis. Sx: hypoglc, jaundice, cirrhosis, vomiting. Decrease fructose & sucrose intake

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8
Q

Essential fructosuria

A

AR deficiency in FRUCTOKINASE; benign and asymptomatic. Hexokinase will take over and convert fructose to F6P. Sx: fructose in blood and urine

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9
Q

Galactosemia

A

AR deficiency in GALACTOSE-1-PHOSPHATE URIDYL TRANSFERASE (classic). galactose-1-P builds up. vom, feeding intolerance, jaundice, hepatomegaly soon after BF, and neonatal cataracts (galactose –> galactitol).

Milder form = GALACTOKINASE deficiency; neonatal cataracts which may p/w inability to track objects or lack of social smile, but otherwise asymptomatic. galactose builds up in blood, urine

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10
Q

PKU

A

Inability to convert Phe to Tyr d/t deficient Phe hydroxylase. Tyr becomes essential AA. Features: mental retardation, seizures, light pigmentation, musty body odor

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11
Q

Cystinuria

A

Defect of renal PCT & intestinal AA transporter prevents reabsorption of COLA (cystine, ornithine, lysine, arginine). Excess cystine in urine –> hexagonal cystine stones. Dx w/ cyanide-nitroprusside test; Tx: alkalinize urine (acetazolamide, potass citrate), chelate, hydrate

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12
Q

Homocystinuria

A

3 types:

  • cystathionine synthase (CS) deficiency: can’t form cysteine from homocysteine. tx w/ decreased methionine, increased cysteine, B6, B12, folate.
  • reduced affinity of CS for pyridoxal phosphate. Tx w/ lots of B6 and cysteine
  • Methionine synthase deficiency: can’t form methionine from homocysteine. tx w/ increased methionine

HOMOCYstinuria: high urine Homocysteine, Osteoporosis, Marfan habitus, Ocular changes (down/in sublux), CV effects (thrombosis/atherosclerosis), kYphosis + intellectual disability

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13
Q

Number of Cal/gram of various metabolic fuels (1 Cal = 1 kcal)

A

(# letters = # Cal)
1g CARB/protein (e.g. WHEY) = 4 Cal
1g ALCOHOL = 7 Cal
1g FATTY ACID = 9 Cal

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14
Q

Wernicke-Korsakoff syndrome

A

B1 (thiamine) deficiency causing confusion, ophthalmoplegia, ataxia [wernicke] + later IRREVERISBLE mem loss, confabulation, personality change [korsakoff]. Damage to medial dorsal nucleus of thalamus and mammillary bodies. Dx w/ low RBC transketolase (will increase after giving vit B1).

Giving dextrose alone to a thiamine-deficient pt (e.g. an alcoholic) can precipitate Wernicke encephalopathy d/t increased thiamine demand

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15
Q

Gluconeogenesis irreversible enzymes

A
  • Pyruvate carboxylase (pyruvate –> oxaloacetate). Requires biotin, activated by acetylCoA
  • PEP carboxykinase (oxaloacetate –> PEP). Requires GTP
  • F-1,6-bisphosphatase (F16BP –> F6P). Activated by ATP, glucagon; inhibited by AMP, F26BP
  • Glucose-6-phosphatase (G6P –> glc)
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16
Q

Rate limiting enzymes for:

  • de novo pyrimidine synthesis
  • de novo purine synthesis
  • glycolysis
  • gluconeogenesis
  • glycogenesis
  • glycogenolysis
  • TCA
  • HMP shunt (PPP)
  • urea cycle
A
  • pyrimidine: CPS2 (in cytosol, gets N from glutamine)
  • purine: glutamine PRPP amidotransferase
  • glycolysis: PFK1
  • gluconeogenesis: F-1,6-bisphosphatase
  • glycogenesis: glycogen synthase
  • glycogenolysis: glycogen phosphorylase
  • TCA: isocitrate dehydrogenase
  • HMP: G6PD
  • urea cycle: CPS1 (in mitoch, gets N from ammonium)
17
Q

Cofactors for pyruvate dehydrogenase and a-KG dehydrogenase complexes

A 
Help convert pyruvate to AcetylCoA for TCA, and isocitrate to a-KG in TCA. "The Lovely Co-enzymes For Nerds":
Thiamine pyrophosphate (B1)
Lipoic acid
CoA (B5, pantothenic acid)
FAD (B2, riboflavin)
NAD (B3, niacin)
18
Q

4 fates of pyruvate

A
  • AcetylCoA (TCA)
  • Lactate (Cori cycle)
  • Oxaloacetate (gluconeogenesis or replenish for TCA)
  • Alanine (Cahill cycle)
19
Q

Mnemonic for each step in TCA

A

“Citrate Is Krebs’ Starting Substrate For Making Oxaloacetate”: citrate, isocitrate, a-KG, Succinyl-CoA, Succinate, Fumarate, Malate, Oxaloacetate

20
Q

Steps of TCA inhibited by alcoholism/thiamine deficiency

A

Steps requiring NAD+ will be inhibited, as aldehyde dehydrogenase consumes NAD+ and increases the NADH/NAD+ ratio. These steps are malate –> oxaloacetate by malate dehydrogenase, isocitrate to a-KG by isocitrate dehydrogenase, and a-KG to succinyl-CoA by a-KG dehydrogenase.

a-KG –> succinyl-CoA will be particularly affected bc it also requires thiamine (B1) as a cofactor. Conversion of pyruvate to Acetyl-CoA by pyruvate dehydrogenase (to enter TCA) is also thiamine-dependent

21
Q

4 consequences of increased NADH/NAD+ ratio caused by alcohol metabolism

A
  1. pyruvate gets shunted to lactate, causing lactic acidosis
  2. oxaloacetate –> malate (backwards TCA): prevents gluconeogenesis, causing fasting hypoglc
  3. DHAP –> G3P (combines w/ FA’s to make TAGs) –> hepatosteatosis
  4. TCA slowed down to prevent making more NADH, so acetyl-CoA gets shunted to ketogenesis and lipogenesis, causing ketoacidosis and hepatosteatosis
22
Q

Hartnup disease

A

Deficiency of neutral AA (e.g. Tryptophan) transporters in PCT & enterocytes –> neutral aminoaciduria and pellagra-like sx (don’t have Tryp and can’t convert it to Niacin). Tx: high protein diet, nicotinic acid

Pellagra sx: diarrhea, dermatitis, dementia

23
Q

Alkaptonuria

A

Deficiency in homogentisinate oxidase, which is required to degrade Tyr to Fumarate to enter TCA. Homogentisic acid builds up –> pigment (bluish-black connective tissue, ear cartilage, sclerae); turns urine black on prolonged exposure to air; severe arthralgias (toxic to cartilage)

24
Q

AA precursors of:

  • porphyrin and heme
  • NO
  • GABA
  • histamine
  • SAM
  • creatine
A
  • porphyrin and heme: glycine
  • NO: arginine
  • GABA: glutamate
  • histamine: histidine
  • SAM: methionine
  • creatine: arginine
25
Q

FPBase2/PFK2 bifunctional enzyme complex, and activity in fed vs. fasting state

A
  • Fed state: increased insulin stimulates glycolysis, increasing the activity of PFK2 to convert F6P to F2,6BP. Increased F2,6BP stimulates PFK1 to continue glycolysis/inhibits gluconeogenesis
  • Fasting state: high glucagon stimulates gluconeogenesis, increasing the activity of FBPase2 to convert F2,6BP to F6P to make glucose/inhibits glycolysis
26
Q

Medium-chain acyl-CoA dehydrogenase deficiency

A

Reduced ability to break down FA’s into acetyl-CoA, resulting in hypoketotic hypoglycemia after prolonged fasting. Will also have low carnitine; lethargy, vom, seizures, coma, liver dysfxn, hyperammonemia, sudden death in infants/kids. Tx by avoiding fasting

27
Q

Systemic primary carnitine deficiency

A

Inherited defect in transport of LCFAs into mitoch –> toxic accumulation. Causes weakness, hypotonia, hypoketotic hypoglc

28
Q

Cyanide toxicity causes, presentation and treatment

A

Cyanide binds cytochrome c oxidase in ETC, preventing ATP prodxn. Toxicity can occur in pts treated w/ nitroprusside for HTN crisis (releases cyanide), or inhaling burning fumes of polyurethane or vinyl. P/w AMS, seizure, CV collapse, lactic acidosis, bright red venous blood. Tx: hydroxycobalamin (directly binds cyanide ions), induce methemoglobinemia (binds up cyanide) with a nitrite, and detoxifying sulfur donors (thiosulfate)

Study Period Targeted Review (17 decks)

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