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Biochemistry Flashcards

1
Q

Functions of B1 (thiamine)

A

Cofactor for…

  1. Pyruvate dehydrogenase (links glycolysis to TCA cycle)
  2. alpha-ketoglutarate dehydrogenase (TCA cycle)
  3. Transketolase (HMP shunt)
  4. Branched chain ketoacid dehydrogenase
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2
Q

Vitamin B1 (thiamine) deficiency (and diagnosis)

A

Impaired glucose breakdown, leading to ATP deletion
Worsened by glucose infusion (ALWAYS give thiamine infusion with glucose in someone you suspect with a deficiency)

Diagnosis made by an increase in RBC transketolase activity following B1 administration

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3
Q

Functions of Vitamin B2 (riboflavin)

A

Component of flavins FAD and FMN, used as cofactors in redox reactions (ie, succinate dehydrogenase reaction in TCA cycle)

FAD and FMN are derived from riboFlavin (B2 = 2 ATP)

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4
Q

Vitamin B2 (riboflavin)

A

Cheilosis (inflammation of lips, scaling and fissures at corner of mouth)
Corneal vascularization

(the 2 Cs of B2)

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5
Q

Functions of Vitamin B3 (niacin)

A

Constituent of NAD+ and NADP+ (used inredox rxns).
Derived from tryptophan.
Synthesis requires B2 and B6

NAD derived from Niacin (B3 = 3ATP)

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6
Q

Vitamin B3 deficiency

A

Glossitis

Three Ds:
Diarrhea, Dementia, Dermatitis (broad collar rash)

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7
Q

Function of Vitamin B5

A

Essential component of coenzyme A (a cofactor for acyl transfers) and fatty acid synthesis

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8
Q

Vitamin B5 deficiency

A

Dermatitis, eneritis, alopecia, adrenal insufficiency

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9
Q

Functions of B6 (pyridoxine)

A

Converted to pyridoxal phosphate (PLP), a cofactor used in transamination, decarboxylation reactions, glycogen phosporylase

Synthesis of cystathionine, HEME, NIACIN, histamine and neurotransmitters including serotonin, epinephrine, norepi, dopamine and GABA

Homocysteine to Cysteine
Succinyl-CoA to Heme

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10
Q

Vitamin B6 deficiency

A

Convulsions, hyper-irritability, peripheral neuropathy, sideroblastic anemias due to impaired hemoglobin synthesis

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11
Q

Functions of Vitamin B7 (biotin)

A

Cofactor for carboxylation enzymes:

Pyruvate carboxylase: pyruvate to oxaloacetate

Acetyl-CoA carboxylase: aceyle Co-A to malonyl CoA

Propionyl CoA carboxylase: propionyl CoA to methylmalonyl CoA

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12
Q

Vitamin B7 (biotin) deficiency

A

Relatively rare. Dermatitis, alopecia, enteritis. Caused by antibiotic use or excessive ingestion of raw egg whites

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13
Q

Functions of B9 (folate) deficiency

A

Converted to tetrahydrofolic acid (THF), a coenzyme for 1-carbon transfer/methylation reactions

Important for the synthesis of nitrogenous bases in DNA and RNA

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14
Q

Vitamin B9 (folate) deficiency

A

Small reserve pool stored primarily in the liver

Macrocytic, megaloblastic anemia; hypersegmented polymorphonuclear cells; glossitis; NO neuro symptoms

Can be caused by several drugs (phenytoin, sulfonamides, methotrexate)

Most common vitamin deficiency in the US. Seen in alcoholism and pregnancy

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15
Q

Labs to diagnos Vit. B9 (folate) deficiency

A

Increased homocysteine

Normal methylmalonic acid

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16
Q

Functions of Vitamin B12

A

Cofactor for methionine synthase and methylmalonyl-CoA mutase

Homocysteine to Methionine
Methylmalonyl-CoA to Succinyl-CoA

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17
Q

Vitamin B12 deficiency

A

Macrocytic, megaloblastic anemia
Hypersegmented PMNs
Parasthesias and subacute combined degeneration (degeneration of dorsal columns, lateral corticospinal tracts, and spinalcerebellar tracts)

Found in animal products. Synthesized only by microorganisms. Very large reserve pool

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18
Q

Labs to diagnose Vitamin B12 deficiency

A

Increased serum homocysteine AND increased methylmalonic acid

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19
Q

What does the drug Fomepizole inhibit?

A

It inhibits Alcohol dehydrogenase

Prevents Ethonal&raquo_space;> Acetaldehyde

Antidote for methanol or ethylene glycol poisoning

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20
Q

What does the drug Disulfiram inhibit?

A

It inhibits Acetaldehyde dehydrogenase

Prevents Acetldehyde&raquo_space; Acetate

Drug for alcohol abstinence, contributes to hangover symptoms

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21
Q

Ethanol metabolism increases the ____/_____ ratio in the liver, causing…

A

Increases the NADH/NAD+ ratio, causing…

  1. Pyruvate&raquo_space; Lactate
  2. Oxaloacetate&raquo_space; Malate (prevents gluconeogenesis and causing fasting hypoglycemia)
  3. Dihydroxyacetone phosphate&raquo_space; glycerol-3-phosphate (combines with fatty acids to make triglycerides, causing hepatosteatosis)
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22
Q

What is the rate determining enzyme in Glycolysis?

Regulators of that step?

A

Phosphofructokinase-1 (Fructose 6-P&raquo_space; Fructose 1,6-BP)

Down-regulated by: ATP and Citrate (TCA)
Up-regulated by AMP and Fructose-2,6-bisphosphate

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23
Q

What is the rate determining enzyme in Gluconeogenesis?

Regulators of that step?

A

Fructose 1,6-bisphosphatase (Fructose 1,6-BP to Fructose 6-BP)

Down-regulated by AMP and fructose-2,6-bisphosphate

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24
Q

What is the rate determining enzyme in the TCA cycle?

Regulators of that step?

A

Isocitrate dehydrogenase (Isocitrate&raquo_space; alpha-Ketoglutarate)

Down-regulated by: ATP, NADH
Up-regulated by: ADP

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25
What is the rate determining enzyme in Glycogenesis? | Regulators of that step?
Glycogen synthase Down-regulated by: Epinephrine, Glucagon Up-regulated by: Glucose-6-phosphate, insulin, cortisol
26
What is the rate determining step in HMP shunt? | Regulators of that step?
Glucose-6-phosphate dehydrogenase (G6PD) (Glucose-6-phosphate >> 6-phosphogluconolactone) Down-regulated by: NADPH Up-regulated by: NADP+
27
What is the rate determining step in De Novo Pyrimidine synthesis? Regulators of that step?
Carbomoyl phosphate synthetase II (Glutamine + CO2 >> Orotic acid) Down-regulated by: UTP Up-regulated by: ATP
28
What is the rate determining step in De Novo Purine synthesis? Regulators of that step?
Glutamine-phosphoriboslpyrophosphate (PRPP >> IMP) Down-regulated by: AMP, inosine monophosphate (IMP), and GMP
29
What is the rate determining step of the Urea Cycle? | Regulators of that step?
Carbomoyl phosphate synthetase I (CO2 + NH3 >> Carbamoyl phosphate) Up-regulated by: N-acetylglutamate
30
What is the rate determining step of Fatty Acid synthesis? | Regulators of that step?
Acetyl-CoA carboxylase (Acetyl-CoA >> Malonyl-CoA) Down-regulated by: Glucagon, palmitoyl-CoA Up-regulated by: Insulin, Citrate
31
What is the rate determining step of Fatty Acid oxidation? | Regulators of that step?
Carnitine acyltransferase I Down-regulated by Malonyl-CoA
32
What is the rate-determining step in Ketogenesis?
HMG-CoA synthase | (
33
What is the rate-determining step in Cholesterol synthesis? | Regulators of that step?
HMG-CoA reductase (HMG CoA >> Mevalonate) Down-regulated by: Glucagon, cholesterol Up-regulated by Insulin, thyroxine
34
The four fates of Pyruvate
1. Alanine via Alanine aminotransferase (B6 cofactor) 2. Oxaloacetate via Pyruvate carboxylase 3. Acetyl-CoA via Pyruvate dehydrogenase (B1, B2, B3, B5, lipoic acid cofactors) 4. Lactate via Lactic acid dehydrogenase (B3 cofactor)
35
Function of HMP shunt
Provides a source of NADPH from abundantly available glucose-6-P Makes ribose for nucleotide synthesis and glycolytic intermediates In lactating mammary glands, liver, adrenal cortex and RBCs
36
Essential fructosuria
Defect in fructokinase (Fructose >> Fructose 1-P) Autosomal recessive Fructose appears in blood and urine. Benign condition.
37
Fructose intolerance
Autosomal recessive Defect in aldolase B Fructose 1-P accumulates, inhibition of glycogenolysis and gluconeogenesis Hypoglycemia, jaundice, cirrhosis, vomiting. After eating fruit, juice or honey. Tx: decrease intake of both fructose and sucrose
38
Galactokinase deficiency
Autosomal recessive Galactitol accumulates if galactose is present in diet Galactose appears in blood and urine. Infantile cataracts. Failure to track objects or to develop a social smile
39
Classic galactosemia
Autosomal recessive Absence of galactose-1-phosphate uridyltransferase. Galactitol accumulates in lens of eye. Other toxic substances accumulate as well Sx: Failure to thrive, jaundice, hepatomegaly, infantile cataracts, intellectual disability. E.coli sepsis in neonates Tx: exclude galactose and lactose
40
What is Sorbitol?
Glucose trapped in its alcohol component (via aldose reductase) Some tissues then convert sorbitol to fructose using sorbitol dehydrogenase. Without this enzyme, sorbitol can accumulate, causing osmotic damage (cataracts, retinopathy, peripheral neuropathy seen with chronic hyperglycemia in diabetes)
41
Lactase deficiency
Insufficient lactase enzyme, leading to dietary lactose in tolerance. Lactase function on the brush border Biopsy normal. Stool demonstrates low pH and breath shows high hydrogen content
42
What are the essential amino acids?
Glucogenic: Methionine, Valine, Histidine Glucogenic/ketogenic: Isoleucine, Phenylalanine, Threonine, Tryptophan Ketogenic: Leucine, Lysine
43
What are the Acidic amino acids?
Aspartic acid | Glutamic acid
44
What are the Basic amino acids?
Histidine Arginine Lysine
45
Hyperammonemia
Aquired (liver disease) Hereditary (urea cycle enzyme deficiencies) Results in excess NH4+, which depletes alpha-ketoglutarate, leading to inhibition of TCA
46
Treatment of Hyperammonemia
Limit protein diet Lactulose to acidify GI tract to trap NH4+ Rifaximin to lower colonic ammoniagenic bacteria Benzoate or phenylbutyrate to bind amino acid and lead to excretion
47
N-aceylglutamate synthase deficiency
Leads to hyperammonemia Required cofactor to carbomoyl phosphate synthase I Presents in neonates as poorly regulated respiration and body temp, poor feeding, developmental delay, intellectual disability
48
Ornithine transcarbamylase deficiency
Most common urea cycle disorder X-linked recessive Interferes with the body's ability to eliminate ammonia Excess carbomoyl phosphate is converted to orotic acid Findings: Increase in orotic acid in blood and urine, Decrease in BUN, Symptoms of hyperammonemia. NO megaloblastic anemia (vs orotic aciduria)
49
Phenylketonuria
Due to low phenylalanine hydroxylase or low tetrahydrobiopterin cofactor. Tyrosine becomes essential Itellectual disability, growth retardation, seizures, fair skin, eczema, musty body odor Tx: Low phenylalanine and high tyrosine diet
50
Maple syrup urine disease
Autosomal recessive Blocked degradation of branched amino acids (isoleucine, leucine, valine) due to low alpha-ketoacid dehydrogenase (B1) Causes increased alpha-ketoacids in blood Causes severe CNS defects, intellectual disability, death Tx: restrict isoleucine, leucine and valine in diet. Increase thiamin supplimentation
51
Alkaptonuria (ochronosis)
Congenital deficiency of homogentisate oxidase in the degradative pathway of tyrosine to fumarate Homogentisic acid accumulates in tissue Dark connective tissue, brown sclera, urine turns black when prolonged exposure to air
52
Homocystinuria
Many types, all autosomal recessive All forms result in excess homocysteine Increased homocysteine in urine, intellectual disability, osteoporosis, marfanoid habitus, kyphosis, lens subluxation, thrombosis (major cause of death!!), atherosclerosis Tx: Supplement with PYRIDOXINE (vit B6). Also restrict methionine *Look at pathway*
53
Cystinuria
Autosomal recessive. Common Hereditary defect in renal and intestinal amino acid transporter that prevents reabsorption of Cysteine, Ornithine, Lysine and Arginine (COLA) Excess cystine can lead to stones Tx by alkalizing the urine
54
What are the four types of Glycogen storage diseases you need to know?
All are autosomal recessive. All result in abnormal glycogen metabolism and an accumulation of glycogen within cells Type I: Von Gierke Type II: Pompe Type III: Cori Type V: McArdle
55
Von Gierke disease: | Findings, deficient enzyme
Deficient in Glucose-6-phosphate Severe fasting hyperglycemia, Increase glycogen in liver, Increase blood lactate, Increase triglycerides, Increase uric acid, hepatomegaly Tx: Frequent oral glucose/cornstarch, avoid fructose and galactose
56
Pompe disease: | Findings, deficient enzyme
Deficient in Lysosomal alpha-1,4-glucosidase (Acid alpha-glucosidase) Cardiomegaly, hypertrophic cardiomyopathy, exercise intolerance and systemic findings leading to early death "Pompe trashes the Pumps" (hearth, liver, muscle)
57
Cori disease: | Findings, deficient enzyme
Deficient in Debranching enzyme Milder form of Von Gierke (type 1) with normal blood lactate levels Gluconeogenesis is intact
58
McArdle disease: | Findings, deficient enzyme
Deficient of Skeletal muscle glycogen phophorylase Increase glycogen in muscle, but muslce cannot break it down Painful muscle cramps, red urine with strenuous exercise, arrhythmia from electrolyte abnormalities
59
Fabry disease: Findings and inheritance
XR Findings: Peripheral neuropathy of hands/feet. Angiokeratomas, Cardiovascular/Renal disease
60
Fabry disease: Deficient enzyme and Accumulated substrate
Deficiency: Alpha-galactosidase A Accumulation: Ceramide trihexoside
61
Gaucher Disease: Findings and inheritance
AR; Most common Findings: Hepatosplenomegaly, pancytopenia, osteroporosis, aseptic necrosis of femur, bone crisis, Gaucher cells (macrophages with "crumpled tissue" look) Tx: Recombinant glucocerebrosidase
62
Gaucher Disease: Deficient enzyme and Accumulated substrate
Deficiency: Glucocerebroside (beta-glucosidase) Accumulation: Glucocerebroside
63
Niemann-Pick Disease: Findings and inheritance
AR Findings: Progressive neurodegeneration, hepatosplenomegaly, foam cells, "cherry-red" spot on macula
64
Neimann-Pick Disease: Deficient enzyme and Accumulated substrate
Deficiency: Sphingomyelinase Accumulation: Sphingomyelin
65
Tay-Sachs Disease: Findings and inheritance
AR Findings: Progressive neurodegeneration, developmental delay, "cherry red" spot on macula, lysosomes with onion skin, NO hepatosplenomegaly
66
Tay-Sachs Disease: Deficient enzyme and Accumulated substrate
Deficiency: Hexosaminidase A Accumulation: GM2 ganglioside
67
Krabbe Disease: Findings and inheritance
AR Findings: Peripheral neuropathy, developmental delay, optic atrophy, globoid cells
68
Krabbe Disease: Deficient enzyme and Accumulated substrate
Deficiency: GalactocerebrosidASE Accumulation: GalactocerebroSIDE
69
Metachromatic Leukodystrophy: Findings and inheritance
AR Findings: Central and peripheral demyelination with ataxia, dementia
70
Metachromatic Leukodystrophy: Deficient enzyme and Accumulated substrate
Deficiency: Arylsulfatase A Accumulation: Cerebroside sulfate
71
Hurler Syndrome: Findings and inheritance
AR Findings: Developmental delay, gargoylism, airway obstruction, CORNEAL CLOUDING, hepatosplenomegaly
72
Hurler Syndrome: Deficient enzyme and Accumulated substrate
Deficiency: alpha-L-iduronidase Accumulation: Heparane sulfate, Dermatan sulfate
73
Hunter Syndrome: Findings and inheritance
XR Findings: Mild Hurler + aggressive behavior. NO corneal clouding
74
Hunter Syndrome: Deficient enzyme and Accumulated substrate
Deficiency: Iduronate sulfatase Accumulation: Heparan sulfate, dermatan sulfate
75
Medium-chain acyl-CoA dehydrogenase deficiency
AR disorder of fatty acid oxidation Decreased ability to break down fatty acids into acetyl-CoA. Accumulation of 8-to-10 carbon fatty acyl carnitines in the blood and HYPOglycemia. May present in infancy or early childhood with vomiting, lethargy, seizures, coma, and liver dysfunction Minor illness can lead to sudden death. Avoid fasting!
76
Pyruvate dehydroginase deficiency
Congenital or aquired Alcoholics b/c low B1 Sx: Neuro defects, lactic acidosis, Increase in serum alanine in infancy (if pyruvate cannot be converted to acetyl CoA, then it will go the lactic acid cycle Tx: Diet high in leucine and lysine (these can bypass the pyruvate dehydrogenase)
77
Lead poisoning: Affected enzyme and accumulated substrate
Affected: Ferrochelatase and ALA dehydratase (blood) Accumulated: Protoporphyrin, ∂-ALA
78
Acute Intermittent Porphyria: Affected enzyme and accumulated substrate
Affected: Porphobilinogen deaminase Accumulated: Porphobilinogen, ∂-ALA, Coporphobilinogen (urine) Treat with glucose and heme, which inhibit ALA synthase
79
Symptoms of Acute Intermittent Porphyria (5P's)
``` Painful abdomen Port-wine-colored urine Polyneuropathy Psychological disturbances Precipitated by drugs (cytochrome P450 inducers), alcohol, starvation ```
80
Porphyria Cutanea Tarda: Affected enzyme and accumulated substate
Affected: Uroporphyrinogen decarboxylase Accumulated: Uroporphyrin (tea-colored urine)
81
Sumptoms of Porphyria Cutanea Tarda
Blistering cutaneous photosensitivity. Most common porphyria
82
Branched-chain alpha-ketoacid dehydrogenase, Pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase all require 5 cofactors. What are they?
``` Thiamine pyrophosphate Lipoate Coenzyme A FAD NAD ``` (Tender Loving Care For Nancy)
83
Signaling pathway of insulin
Tyrosine kinase signaling Increase the synthesis of glycogen, proteins, fatty acids, and nucleic acids Stimulation promotes glycogen synthesis by activating protein phosphatase, an enzyme that dephosphorylates (activates) glycogen synthase
84
What process is responsible for the vast majority of renal acid excretion in chronic acidotic states?
Acidosis stimulates renal ammoniagenesis, a process by which renal tubular epithelial cells metabolize glutamine to glutamate, generating ammonium that is excreted in the urine and bicarbonate that is absorbed in the blood
85
Primary carnitine deficiency; symptoms
Muscle weakness Cardiomyopathy Hypoketotic hypoglycemia Elevated muscle triglycerides Deficiency impairs fatty acid transport from the cytoplasm into the mitochondria, preventing B-oxidation of fatty acids into acetyl CoA. This leads to cardiac and skeletal myocyte injury (lack of ATP from citric acid cycle) and impaired ketone body production by the liver during fasting periods
86
Primary carnitine deficiency; MOA
x
87
Wet Beriberi
CARDIAC INVOLVEMENT Symmetrical peripheral neuropathy of the distal extremities, with resulting sensory and motor impairments
88
Dry Beriberi
Symmetrical peripheral neuropathy of the distal extremities, with resulting sensory and motor impairment NO cardiac involvement
89
Use of glycerol in gluconeogenesis
Glycerol produced by the degradation of triglycerides in adipose tissue can be used by glycerol kinase in the liver and kidney to synthesize glucose during gluconeogenesis
90
What do fibrates inhibit? What consequence can this have?
Fibrates inhibit cholesterol 7alpha-hydroxylase 7alpha-hydroxylase catalyzes the rate-limited step in the synthesis of bile acids. Reduced bile acid results in decreased cholesterol solubility in bile and favors the formation of cholesterol gallstones
91
Metabolism of 1g of protein produces how many calories?
4 calories
92
Metabolism of 1g of Carbs produces how many calories?
4 calories
93
Metabolism of 1 gram of fat produces how many calories?
9 calories
94
Familial chylomicronemia (type I)
Defect in Lipoprotein lipase and ApoC-2 Elevated Chylomicrons Can cause ACUTE PANCREATITIS, Lipemia retinalis, and eruptive xanthomas
95
Familial hypercholesterolemia (Type IIA)
Defect in LDL receptor and ApoB-100 Elevated LDL Can cause PREMATURE ATHEROSCLEROSIS, tendon xanthomas and Xanthelasmas
96
Familial dysbetalipoproteinemia (Type III)
Defect in ApoE Elevated Chylomicron and VLDL remnants Can casue PREMATURE ATHEROSCLEROSIS, Tuboeruptive and palmar xanthomas
97
Familial hypertriglyceridemia (Type IV)
Defect is polygenic Elevated VLDLs Associated with coronary disease, pancreatitis and diabetes
98
Orotic Aciduria
AR Disorder of de novo pyrimidine synthesis. Defect in uridine 5'-monophosphate (UMP) synthase. Presents in children. Physical and mental retardation, MEGALOBLASTIC ANEMIA, and large amounts of urinary orotic acid Tx: Uridine supplementation (uridine is converted to UMP via nucleotide kinases)
99
Myoglobin. Yeah, what is it exactly?
Well, its a monomeric protein. Its the primary oxygen-storing protein in skeletal and cardiac muscle tissue Only found in bloodstream after muscle injury Since its only a single heme group, it doesn't have heme-heme interactions, making the oxygen-dissociation curve hyperbolic (mega-left-shift)

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