BIOCHEM Flashcards
What are some causes of cobalamin deficiency?
Cobalamin deficiency may occur with:
- Malabsorption (e.g. Diphyllobothrium latum, sprue, enteritis)
- Absence of intrinsic factor (e.g. pernicious anemia or gastric bypass surgery)
- Absence of terminal ileum (due to Crohn disease or resection)
- Vegan diet
What two conditions can lead to vitamin E deficiency and what are the signs?
Vitamin E deficiency is rare and primarily occurs in:
- children with cystic fibrosis (due to fat malabsorption secondary to decreased bile salts and pancreatic insufficiency)
- abetalipoproteinemia (fat malabsorption)
Signs are hemolytic anemia, peripheral neuropathy, posterior column degeneration, retinal degeneration, and myopathy. Vitamin E deficiency signs can mimic those of vitamin B12 deficiency, but vitamin E deficiency is without increased methylmalonic acid levels or megaloblastic anemia.
What protein is insulin first synthesized as and where does this occur?
Insulin is first synthesized as preproinsulin in the rough endoplasmic reticulum
What is the second reaction of basic alcohol metabolism? Where does it take place?
Acetaldehyde enters the mitochondria and is oxidized by acetaldehyde dehydrogenase (ALDH) to form acetate and NADH.
What are the main functions of Vitamin A?
Vitamin A: functions as a component of visual pigments and in cell differentiation
Thiamine deficiency results in which 2 syndromes?
A vitamin B1 (thiamine) derivative, thiamine pyrophosphate (TPP), is an important coenzyme for several reactions. some of which can be remembered with the mnemonic, ATP:
α-ketoglutarate dehydrogenase
Transketolase
Pyruvate dehydrogenase
Vitamin B1 is also a cofactor for branched-chain ketoacid dehydrogenase.
Vitamin B1 (thiamine) most often plays a role in decarboxylation of α-keto acids.
In the United States, thiamine deficiency is most common in alcoholics (due to poor nutrition and that excess alcohol limits the body’s ability to absorb and store thiamine.)
Thiamine deficiency may lead to beriberi (“Ber1Ber1”) and Wernicke-Korsakoff syndrome.
Beriberi has a dry (muscle wasting and neuropathy) and wet (dilated cardiomyopathy) component.
Wernicke-Korsakoff syndrome is composed of Wernicke’s encephalopathy (triad of confusion, ophthalmoplegia, and ataxia) and Korsakoff’s psychosis (memory loss, confabulation and personality change).
In what cells is glucagon predominantly synthesized?
Glucagon is cleaved from a larger peptide chain inpancreatic α-cells of the islets of Langerhans.
Excess intake of what vitamin can decrease the efficacy of L-DOPA therapy in Parkinson’s disease?
A core treatment in Parkinson’s disease is L-DOPA therapy. Supplemental vitamin B6 can convert L-DOPA to dopamine peripherally (as opposed to in the CNS), rendering treatment less efficacious.
Why do alcoholics develop hypoglycemia?
Pyruvate and oxaloacetate depletion leads to inhibition of gluconeogenesis and stimulation of fatty acid synthesis, which results in fasting hypoglycemia.
What are the signs of pyridoxine deficiency?
Pyridoxine deficiency causes:
- Neurological pathology: Peripheral neuropathy and convulsions (due to defective neurotransmitter synthesis).
- Anemia: Sideroblastic anemias due to defective heme synthesis.
What is the function of folate?
Folate is converted to tetrahydrafolate (THF), which is a carbon carrier critical for synthesis of nitrogenous bases (particularly thymine, adenine, and guanine) in nucleic acids, especially in states of rapid cell division (pregnancy, erythropoiesis).
What are three pathologies of vitamin D deficiency?
Vitamin D deficiency causes:
- Rickets in children (imperfect calcification, softening, and distortion of the bones classically resulting in bowed legs)
- Osteomalacia in adults (soft bones and bone pain).
- Hypocalcemic tetany (decreased extracellular calcium levels cause increased excitability of voltage gated sodium channels, leading to increased muscle contractions)
What are the key signs of acute vitamin A toxicity?
Acute vitamin A toxicity causes:
- Nausea
- Vomiting
- Visual disturbances
- Vertigo
What vitamin deficiency may be seen in carcinoid syndrome?
Carcinoid syndrome is a complication of carcinoid tumors (most commonly of the small bowel) in which serotonin is systemically elaborated in great excess. Tryptophan is compensatorily shunted to make serotonin, decreasing conversion to niacin. Therefore,niacin deficiency is a potential complication of carcinoid syndrome.
In what general class of hormones is glucagon?
Glucagon is a 29 amino-acid peptide hormone.
Which B vitamin generally plays a role in the decarboxylation of α-keto acids?
Vitamin B1 (thiamine) most often plays a role in decarboxylation of α-keto acids.
A vitamin B1 (thiamine) derivative, thiamine pyrophosphate (TPP), is an important coenzyme for several reactions. some of which can be remembered with the mnemonic, ATP:
- α-ketoglutarate dehydrogenase
- Transketolase
- Pyruvate dehydrogenase
Vitamin B1 is also a cofactor for branched-chain ketoacid dehydrogenase.
Vitamin B1 (thiamine) most often plays a role in decarboxylation of α-keto acids.
What is the pathophysiology of the edema seen in kwashiorkor?
Decreased protein consumption leads to decreased protein production. Because of the decreased protein production the capillary oncotic pressure decreases and this leads to tissue edema in kwashiorkor. The following mnemonic might be useful: You need water to wash → kwashiorkor has excess water (edema).
What two important pathways are activated by IRS-1?
- Insulin exerts its effect by binding to the extracellular domain of an intrinsic tyrosine kinase receptor.
- The activated intracellular domain of the tyrosine kinase receptor phosphorylates the insulin receptor substrate-1 (IRS-1) protein.
- IRS-1 plays a key role in insulin signal transduction by activating the Phosphoinositide-3 kinase (PI-3 kinase) pathway and the MAPK pathway.
PI-3 Kinase Pathway
- The PI-3 kinase pathway is responsible for the fusion of vesicles containing the GLUT4 transporter into the membrane of myocytes and adipocytes.
- Thus, the PI-3 pathway leads to increased glucose uptake by myocytes and adipocytes. Additionally, PI-3K is involved in upregulation of glycolysis, as well as glycogen and lipid synthesis.
MAPK Pathway
- The MAPK pathway regulates the expression of genes that increase cell growth and DNA synthesis.
Finally, the insulin signal is terminated when the insulin-receptor complex is endocytosed and degraded.
What is the toxic byproduct of ethylene glycol metabolism? What specific organ damage may be seen in toxicity?
Ethylene glycol is metabolized to oxalic acid (via alcohol dehydrogenase and several subsequent reactions).
Oxalic acid combines with metal ions to deposit crystals in kidney tubules, leading to metabolic acidosis and acute renal failure.
Why are infants are given a vitamin K injection at birth to prevent hemorrhagic disease of the newborn?
Since vitamin K is synthesized by intestinal flora and neonatal intestines are not yet colonized by bacteria, infants are given a vitamin K injection at birth to prevent hemorrhagic disease of the newborn.
What is the primary stimulus for insulin release?
Increased glucose concentration inside β-cells is the primary stimulus for insulin release.
Name a vitamin that, when taken in excess, can synergistically act with warfarin.
Excess (taking megadoses of vitamin E): decreased synthesis of vitamin K-dependent coagulation factors in the liver, thereby working synergistically with warfarin.
What is lacking in the diet of a child with marasmus? Contrast this with the malnutrition that results in kwashiorkor.
In contrast to kwashiorkor, which is caused by insufficient protein intake despite adequate calories,marasmus (from Greek meaning “dying away” or “withering”) results from inadequate protein and overall calories.
How is breastfeeding implicated in the onset of kwashiorkor in some parts of the world?
In some areas, kwashiorkor presents between ages 1-3 when a child that received enough protein while breastfeeding is displaced by a new child.