Metabolism X Flashcards
What reaction is catalyzed by Homocysteine methyltransferase and what cofactor is required?
Homocysteine –> methionine (requires B12) (p.109)
How is homocysteine converted to cysteine?
Homocysteine is converted to cystathionine via cystathionine syntase. Serine and B6 are required for this reaction. Cystathionine is then converted to cysteine (p.109)
Describe the pathology associated with cystinuria?
A hereditary defect of renal tubular amino acid transporter for cysteine, ornithine, lysine, and arginine in the PCT of the kidneys (p.109)
What are the symptoms of cystinuria?
Excess cysteine in the urine which may cause precipitation of hexagonal crystals and renal staghorn caliculi (p.109)
How is cystinuria inherited?
Autosomal recessive condition. It is relatively common (1:7000) (p.109)
How is cystinuria treated?
Good hydration and urinary alkalization (p.109)
Describe the pathology associated with maple syrup urine disease?
Blocked degradation of branched amino acids (Ile, Leu, Val) due to decreased a-ketoacid dehydrogenase (B1) causing increased a-ketoacids in the blood (especially Leucine) (p.109)
What are the symptoms of maple syrup urine disease?
Severe CNS defects, mental retardation, death. Urine smells like maple syrup (p.109)
How is maple syrup urine disease inherited?
Autosomal recessive (p.109)
What is Hartnup disease?
A disorder characterized by defective neutral amino acid transporters on renal and intestinal epithelial cells (p.109)
What is the clinical manifestation of Hartnup disease?
Tryptophan excretion in urine and decreased tryptophan absorption in the gut. It leads to pellagra (p.109)
How is Hartnup disease inherited?
Autosomal recessive (p.109)
What condition can Hartnup disease lead to?
Pellagra (p.109)
How is glycogenolysis coordinated with muscle activity?
Calcium/ Calmodulin in muscle activates phosphorylase kinase so that glyconeolysis is coordinated with muscle activity (p.110)
How do glucagon (from the liver) and epinephrine (from the liver and muscle) regulate glycogenolysis?
By activating a cascade which increases cAMP, acting on protein kinase A which induces glycogenolysis (p.110)
How does insulin affect glycogenolysis?
It inactivates glycogen phosphorylase and glycogen phosphorylase kinase via protein phosphatase which decreases glycogenolysis (p.110)
How do glycogen branches differ from glycogen linkages?
Glycogen branches have a(1,6) bonds; linkages have 1(1,4 bonds) (p.110)
How does skeletal muscle utilize glycogen?
Glycogen undergoes glycogenolysis to become glucose-1-phosphate. Glucose-1-phosphate becomes glucose-6-phosphate which is rapidly metabolized during exercise (p.110)
How do hepatocytes utilize glycogen?
Glycogen is stored and undergoes glycogenolysis to maintain blood sugar at appropriate levels (p.110)
Outline the process of glycogen synthesis.
Glucose-6-phosphate Glucose-1-phosphate. Glucose-1-phosphate –> UDP glucose via UDP glucose pyrophosphorylase. UDP glucose –> storage form of glycogen via glycogen synthase. Storage form attains branches and linkages via branching enzyme, glycogen phosphorylase, and debranching enzyme (p.110)
How many glycogen storage diseases are there and what conditions are characteristic of all glycogen storage diseases?
12 types, all which result in abnormal glycogen metabolism and an accumulation of glycogen within cells (p.111)
Describe the findings associated with Von Gierke’s disease (type I).
Glycogen storage disease; severe fasting hypoglycemia, increased glycogen in the liver, increased blood lactate, hepatomeagly (p.111)
Describe the findings associated with Pompe’s disease (type II).
Glycogen storage disease; Cardiomeagly and systemic findings (heart, liver, muscle) leading to early death (p.111)
Describe the findings associated with Cori’s disease (type III)
Glycogen storage disease that is a milder form of von Gierke’s disease with normal blood lactate levels. Gluconeogenesis is intact (p.111)
Describe the findings associated with McArdle’s disease (type V).
Glycogen storage disease; increased glycogen in muscle that can not be broken down which leads to painful cramps and myoglobinuria with strenuous exercise (p.111)
What enzyme is deficient in von Gierke’s disease?
Glucose-6-phosphatase (p.111)
