Exam 2 flashcards
What are common dietary sources of fructose?
Fruits, honey, sucrose (table sugar), corn syrup, and sorbitol.
What enzyme phosphorylates fructose in the liver?
Fructokinase.
Why does fructose metabolism bypass PFK-1, the key regulatory enzyme in glycolysis?
Fructose enters glycolysis downstream of PFK-1, making it a rapid energy source.
What is essential fructosuria?
A benign autosomal recessive disorder caused by fructokinase deficiency, leading to fructose excretion in urine.
Why does essential fructosuria not cause severe symptoms?
Fructose is not trapped inside cells and is excreted in the urine.
What is hereditary fructose intolerance (HFI)?
A severe autosomal recessive disorder caused by aldolase B deficiency, leading to fructose-1-phosphate accumulation.
What are the symptoms of HFI?
Hypoglycemia, vomiting, hepatomegaly, jaundice, and failure to thrive.
How does HFI lead to hypoglycemia?
Fructose-1-phosphate accumulation inhibits glycogenolysis and gluconeogenesis.
How is HFI managed?
Avoiding fructose, sucrose, and sorbitol in the diet.
What metabolic disturbances are seen in HFI?
Hypoglycemia, lactic acidosis, hypophosphatemia, hyperuricemia, hypermagnesemia, and hyperalaninemia.
What tissues primarily metabolize fructose?
The liver and kidneys.
What happens to fructose in the absence of aldolase B?
It accumulates as fructose-1-phosphate, causing toxicity.
How does fructose contribute to triglyceride synthesis?
It bypasses glycolytic regulation and is rapidly converted to acetyl-CoA.
Why does fructose metabolism increase uric acid levels?
ATP depletion leads to increased purine degradation and uric acid production.
Why does fructose metabolism favor fat storage?
Excess acetyl-CoA from fructose metabolism is used in lipogenesis.
What role does sorbitol play in fructose metabolism?
Sorbitol can be converted to fructose via sorbitol dehydrogenase.
Why do diabetics have complications related to sorbitol accumulation?
High glucose levels increase sorbitol production, leading to cataracts and neuropathy.
What is the rate-limiting step of fructose metabolism?
Aldolase B activity.
Why does fructose have a lower impact on insulin secretion than glucose?
It bypasses glucokinase, which regulates insulin secretion in the pancreas.
How does high fructose consumption contribute to metabolic syndrome?
Increased lipogenesis, insulin resistance, and hyperuricemia.
What enzyme converts galactose to galactose-1-phosphate?
Galactokinase.
What is classic galactosemia?
An autosomal recessive disorder caused by galactose-1-phosphate uridyltransferase deficiency.
What are symptoms of classic galactosemia?
Vomiting, jaundice, hepatomegaly, mental retardation, cataracts, and failure to thrive.
How does galactosemia cause cataracts?
Accumulation of galactitol in the lens.
How is galactosemia diagnosed?
By detecting elevated plasma galactose and urine-reducing substances.
What is the treatment for galactosemia?
A galactose-free diet.
Why are individuals with galactosemia prone to E. coli infections?
The immune system is compromised due to metabolic disturbances.
How does galactose metabolism affect bilirubin conjugation?
Galactose-1-phosphate accumulation inhibits UDP-glucuronate synthesis.
What enzyme deficiency causes mild galactosemia with only cataracts?
Galactokinase deficiency.
What tissues lack sorbitol dehydrogenase, leading to galactitol accumulation?
The lens, kidneys, and Schwann cells.
How does galactose affect glycogen synthesis in well-fed states?
It is converted to glucose-1-phosphate and stored as glycogen.
What happens when aldose reductase converts excess galactose?
It forms galactitol, causing osmotic damage.
Why does galactosemia cause hyperbilirubinemia?
Inhibited UDP-glucuronate synthesis prevents bilirubin conjugation.
How does hypoglycemia occur in galactosemia?
Inhibited gluconeogenesis due to accumulated galactose-1-phosphate.
What dietary changes prevent symptoms of galactosemia?
Avoiding dairy and other galactose-containing foods.
What enzyme deficiency causes the most severe form of galactosemia?
Galactose-1-phosphate uridyltransferase deficiency.
How does galactose metabolism support brain function?
UDP-galactose is used for glycoprotein and glycolipid synthesis.
Why does UDP-galactose deficiency impact connective tissues?
It is required for glycosaminoglycan synthesis.
What is the first step in galactose metabolism?
Phosphorylation by galactokinase.
Why do symptoms of galactosemia appear early in infancy?
Milk consumption introduces galactose immediately after birth.
How does alcohol metabolism contribute to hypoglycemia?
Alcohol increases NADH levels, inhibiting gluconeogenesis by favoring lactate and malate formation.
What enzyme metabolizes ethanol in the liver?
Alcohol dehydrogenase.
What is the toxic intermediate produced during alcohol metabolism?
Acetaldehyde.
What enzyme converts acetaldehyde to acetate?
Aldehyde dehydrogenase.
Why does alcohol metabolism lead to lactic acidosis?
High NADH levels favor conversion of pyruvate to lactate.
How does alcohol inhibit fatty acid oxidation?
High NADH levels delay oxidation and promote triglyceride accumulation in the liver.
What condition results from excessive triglyceride storage in the liver?
Alcoholic steatosis (fatty liver).
How does alcohol-induced hypoglycemia affect fasting individuals?
Inhibits gluconeogenesis, leading to dangerous blood sugar drops.
Why is NAD+ depletion a major issue in alcohol metabolism?
NAD+ is needed for glycolysis, fatty acid oxidation, and the TCA cycle.
How does alcohol consumption affect glycogen stores?
Depletes glycogen stores, increasing hypoglycemia risk.
What metabolic shift occurs in chronic alcoholics?
Increased reliance on ketone bodies due to impaired glucose metabolism.
What is the primary reason alcohol can worsen diabetic ketoacidosis (DKA)?
Increased NADH shifts metabolism toward ketogenesis.
How does alcohol contribute to gout?
Increased NADH levels promote uric acid formation.
What vitamin deficiency is common in chronic alcoholism?
Thiamine (Vitamin B1) deficiency.
Why does alcohol delay the metabolism of lactate?
NAD+ is required to convert lactate back to pyruvate.
How does alcohol affect the electron transport chain (ETC)?
Excess NADH inhibits the TCA cycle and reduces ATP production.
What is Wernicke-Korsakoff syndrome?
A neurological disorder due to thiamine deficiency, common in alcoholics.
Why does alcohol consumption cause mitochondrial dysfunction?
High NADH disrupts oxidative phosphorylation.
How does binge drinking increase hypoglycemia risk in diabetics?
Alcohol metabolism inhibits gluconeogenesis and depletes glycogen.
How does acetaldehyde contribute to alcohol toxicity?
It forms adducts with proteins, leading to liver damage.
What is the primary function of the electron transport chain (ETC)?
To generate ATP through oxidative phosphorylation.
Where is the ETC located?
In the inner mitochondrial membrane.
What is the final electron acceptor in the ETC?
Oxygen (O₂).
What happens to oxygen at the end of the ETC?
It combines with electrons and protons to form water.
What complex in the ETC is NOT a proton pump?
Complex II (Succinate dehydrogenase).
How does NADH contribute to the ETC?
It donates electrons to Complex I.
What is the role of FADH₂ in the ETC?
It donates electrons to Complex II.
What molecule shuttles electrons between Complex I/II and Complex III?
Ubiquinone (CoQ).
What molecule transfers electrons from Complex III to Complex IV?
Cytochrome c.
What enzyme synthesizes ATP using the proton gradient?
ATP synthase (Complex V).
How does proton movement drive ATP synthesis?
Protons flow back into the matrix through ATP synthase.
What is the role of the proton gradient in oxidative phosphorylation?
It stores energy used to drive ATP production.
What happens when ETC complexes are inhibited?
ATP production decreases, leading to cell death.
What toxin inhibits Complex IV?
Cyanide.
What toxin inhibits Complex I?
Rotenone.
What is the effect of an uncoupling agent like thermogenin?
It dissipates the proton gradient, generating heat instead of ATP.
How does the malate-aspartate shuttle function?
It transfers electrons from cytosolic NADH into the mitochondria.
What disease is linked to ETC dysfunction?
Leigh syndrome.
What happens when mitochondria are damaged?
ATP production decreases, leading to energy deficits.
How is ATP transported out of the mitochondria?
Via the ATP/ADP translocase.
What enzyme breaks down triglycerides in adipose tissue?
Hormone-sensitive lipase.
What molecule transports free fatty acids in the blood?
Albumin.
Where does beta-oxidation occur?
In the mitochondria.
What is the primary product of beta-oxidation?
Acetyl-CoA.
How are long-chain fatty acids transported into mitochondria?
Via the carnitine shuttle.
What enzyme activates fatty acids for beta-oxidation?
Acyl-CoA synthetase.
What deficiency impairs fatty acid transport into mitochondria?
Carnitine deficiency.
What are ketone bodies?
Acetoacetate, β-hydroxybutyrate, and acetone.
When are ketone bodies produced?
During fasting or low-carbohydrate diets.
What organ cannot use ketone bodies for energy?
The liver.
What is the rate-limiting enzyme in ketogenesis?
HMG-CoA synthase.
How does insulin affect fat metabolism?
It inhibits lipolysis and promotes fat storage.
What hormone stimulates lipolysis?
Glucagon.
How does beta-oxidation provide energy?
By generating NADH and FADH₂ for the ETC.
What is the fate of odd-chain fatty acids?
They produce propionyl-CoA, which enters the TCA cycle.
What is the function of lipoprotein lipase?
It breaks down triglycerides in lipoproteins for tissue uptake.
What is the main storage form of lipids in the body?
Triglycerides.
What are the major sources of dietary fat?
Triglycerides, phospholipids, and cholesterol.
What is the role of bile salts in fat digestion?
They emulsify fats to aid in digestion.
What is the primary energy source during prolonged fasting?
Fatty acids and ketone bodies.
