70 Questions
What is the best-known example of a heme?
Iron porphyrin
What are the precursors of HEME biosynthesis?
Porphyrins
Where are heme proteins rapidly synthesized and degraded to keep up with losses?
Red blood cells
Which enzyme produces the secondary messenger cAMP?
Adenylyl Cyclase
What happens to cAMP in the cell?
It is broken down by Phosphodiesterase
Which type of receptor is coupled with a G protein?
GPCR (G Protein-Coupled Receptor)
What is the role of Phospholipase C in the second messenger system?
Produces IP3 plus DAG
In the cAMP pathway, what does Protein Kinase A do?
$PKA$ adds phosphates to specific proteins
6
All G proteins are active when bound to GTP and inactive when bound to GDP.
What happens when a G protein activates the enzyme in the second-messenger system?
The second-messenger molecules increase.
In the cAMP pathway, what is the significance of Phosphodiesterase?
It breaks down cAMP.
Where does heme biosynthesis occur?
Mitochondrion and cytosol
Which enzymes are sensitive to lead inhibition, leading to protoporphyrin and ALA accumulation in urine?
Ferrochelatase and ALA dehydratase
What is the result of deficiency in hydroxymethylbilane synthase?
Accumulation of porphobilinogen and δ-aminolaevulinic acid in the urine
Which type of porphyria is characterized by a deficiency in ferrochelatase?
Erythropoietic protoporphyria
Which enzyme deficiency leads to the accumulation of uroporphyrinogen I and coproporphyrinogen I in the urine?
Uroporphyrinogen III synthase
What is the composition of hemoglobin's heme?
Porphyrin ring and iron (Fe2+)
'Hemoglobin's quaternary structure changes from a taut (deoxy) to a relaxed (oxy) conformation when oxygen binds.' What factors shift the hemoglobin oxygen binding curve to the right?
Decreased pH, increased CO2, increased 2,3-BPG
Which hormone stimulates the synthesis and release of Cortisol?
Corticotropin Releasing Hormone (CRH)
Which hormone causes vasoconstriction, platelet aggregation, uterine contraction, and glucocorticoid release?
Angiotensin II
Which hormone is released by the adrenal medulla and stimulates a variety of tissue and organ responses including glycogenolysis, increases in heart rate, and relaxation of bronchial smooth muscle?
Epinephrine
Which hormone is secreted by the Parafollicular Cells of the thyroid and lowers blood calcium levels?
Calcitonin
Which hormone stimulates follicle maturation and ovulation in women, and testosterone synthesis and spermatogenesis in men?
Luteinizing Hormone (LH)
What is the main function of Gαi in hormonal signaling pathways?
Inhibits the production of cAMP from ATP
Which type of hormones bind to cell membrane receptors and activate intracellular kinases?
Lipophobic/hydrophilic hormones
What type of receptors are linked to a second-messenger-generating enzyme via membrane proteins called G proteins?
G protein–coupled receptors (GPCRs)
What is the role of G protein–coupled receptors (GPCRs) in cellular signaling?
Link receptors to a second-messenger-generating enzyme via membrane proteins called G proteins
Which type of hormone receptor binds to intracellular receptors and activates genes?
Lipophilic/hydrophobic hormones
Which hormone is responsible for promoting diuresis and sodium excretion?
Atrial Natriuretic Hormone (ANH)
Which type of hormones can bind to cell membrane or intracellular receptors?
All of the above
What is the primary cause of overproduction of uric acid?
Increased purine availability
Which hormone uses a cAMP-dependent pathway to function?
Anti-Diuretic Hormone (ADH)
What causes severe combined immunodeficiency (SCID) due to inhibited DNA synthesis and cell proliferation?
Adenosine deaminase (ADA) deficiency
What role does the endocrine system play in maintaining homeostasis?
Regulating blood glucose levels
What is the primary cause of gout?
Underexcretion of uric acid
What causes sickle cell trait?
Heterozygous form (one mutated gene)
What is the characteristic of β-thalassemia?
Decreased synthesis of β globin chains
What is the consequence of sickled RBCs getting trapped in small capillaries?
Hemolytic anemia
What is the result of HGPRT deficiency?
$\text{Lesch-Nyhan Syndrome}$
What causes posthepatic jaundice?
Bile duct obstruction or gallstones
What is the consequence of hyperbilirubinemia?
Skin and eye yellowing due to deposition of bilirubin in the blood
What are the precipitating factors for sickle cell disease?
Low oxygen levels, high pCO2, low pH, and high HbS concentration
What happens in homozygous form of sickle cell anemia?
Results in sickle cell anemia
What is the imbalance in thalassemia?
Imbalance in the synthesis of one of the two globin chains leading to anemia
How is bilirubin excreted from the body?
Conjugated in the liver and excreted in bile
Which water-soluble vitamin is involved in reactions of energy production as a coenzyme for pyruvate dehydrogenase and for a TCA cycle enzyme?
Thiamine (B1)
Which fat-soluble vitamin is associated with the normal lipid absorption mechanisms, including emulsification by bile, normal mucosal cells, and transport in chylomicrons?
Vitamin K
Which water-soluble vitamin is required by enzymes involved in amino acid metabolism, such as transaminases?
Pyridoxine (Vitamin B6)
Which fat-soluble vitamin is stored in the body in the liver and adipose tissue?
Vitamin D
Which water-soluble vitamin is a constituent of the coenzymes FAD and FMN, functioning as electron carriers for oxidoreductases?
Riboflavin (B2)
Which fat-soluble vitamin functions as a hormone and is associated with lipids of the diet?
Vitamin A
Which water-soluble vitamin is a constituent of the coenzymes NAD+ and NADP+, functioning as electron carriers for oxidoreductases?
Niacin (Nicotinic Acid) (B3)
Which fat-soluble vitamin functions as an antioxidant and requires normal lipid absorption mechanisms for absorption?
Vitamin E
Which deficiency results in a disease marked by dermatitis, dementia, and diarrhea?
Niacin
What is the characteristic symptom of Vitamin A deficiency?
Night blindness
Which condition is linked to Vitamin C deficiency?
Scurvy
What does severe thiamine deficiency result in?
Eye muscle weakness, poor muscular coordination, and memory loss
What is the main consequence of Vitamin B12 deficiency?
Megaloblastic anemia and neurological damage
What does excess upper body fat indicate?
A higher risk of metabolic diseases
What is the normal range for Body Mass Index (BMI)?
18.5-25 kg/m2
What is the characteristic symptom of Vitamin K deficiency?
Bleeding disorders like hemorrhagic disease of the newborn
What are the consequences of folate deficiency?
Impaired DNA synthesis and cell division leading to megaloblastic anemia and neural tube defects
Which vitamin is a coenzyme in the hydroxylation of proline and lysine residues in collagen production?
Vitamin C
Which vitamin is required for the post-translational modification of coagulation factors II, VII, IX, and X?
Vitamin K
Which vitamin functions as an antioxidant in the blood and in membranes, protecting membrane phospholipids from attack by reactive oxygen species?
Vitamin E
Which vitamin is involved in the conversion of homocysteine to methionine?
Vitamin B12
What is the active form of Vitamin D responsible for enhancing the absorption of calcium and phosphorus from the small intestines?
1,25-dihydroxycholecalciferol (calcitriol)
What is a consequence of Vitamin C deficiency?
All of the above
Which vitamin is required for nucleotide synthesis and synthesis of methionine from homocysteine?
Vitamin B9 (Folic Acid)
In what form are animal sources absorbed and incorporated into chylomicrons?
Retinol and retinyl esters
Study Notes
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Sickle cell anemia is an autosomal recessive disease, caused by mutations in the beta-globin gene producing sickle hemoglobin (HbS)
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Homozygous form (both mutated genes) results in sickle cell anemia, while heterozygous form (one mutated gene) is sickle cell trait
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Sickle cell disease affects approximately 10% of African Americans
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Hemolytic anemia and recurrent pain result from sickled RBCs getting trapped in small capillaries
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Precipitating factors include low oxygen levels, high pCO2, low pH, and high HbS concentration
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Thalassemia is an imbalance in the synthesis of one of the two globin chains, leading to anemia
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β-thalassemia is characterized by decreased synthesis of β globin chains, and homozygous form is known as Cooley's anemia
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Hemoglobin turnover and heme degradation lead to the production of bilirubin
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Bilirubin is conjugated in the liver and excreted in bile, giving stool its brown color
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Hyperbilirubinemia can result from massive hemolysis, damage to liver cells, or inefficiency in conjugation activity
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Jaundice is a manifestation of skin and eye yellowing due to deposition of bilirubin in the blood
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Prehepatic jaundice can be caused by hemolysis, autoimmune diseases, or abnormal hemoglobin
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Intrahepatic jaundice can be caused by infection, drugs, or neonatal conditions
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Posthepatic jaundice can be caused by bile duct obstruction or gallstones
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Nucleotide synthesis occurs through a series of reactions involving amino acids, phosphoribosylpyrophosphate (PRPP), tetrahydrofolate (FH4), and purine and pyrimidine nucleotides.
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HGPRT deficiency, which affects the purine salvage pathway, can lead to Lesch-Nyhan Syndrome, characterized by neurologic abnormalities and self-mutilation.
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Gout is a condition characterized by hyperuricemia, recurrent attacks of joint inflammation, and uric acid crystal deposition in cartilage, joints, and kidneys.
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Gout can be genetic or secondary to other diseases.
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Underexcretion of uric acid is the primary cause of gout.
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Thiamine deficiency: severe deficiency leads to beriberi, a disease with neurological disorders, cardiovascular issues, and muscle weakness
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Inhibition of glutamate production and GABA in the TCA cycle due to thiamine deficiency
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Severe thiamine deficiency results in Wernicke-Korsakoff syndrome, characterized by eye muscle weakness, poor muscular coordination, and memory loss, commonly seen in chronic alcoholism
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Niacin deficiency results in pellagra, a disease marked by dermatitis, dementia, and diarrhea (the three Ds)
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Niacin deficiency also linked to an unbalanced amino acid ratio with insufficient tryptophan
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Folate deficiency impairs DNA synthesis and cell division, leading to megaloblastic anemia and neural tube defects
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Vitamin B12 deficiency, or pernicious anemia, is caused by an autoimmune destruction of stomach cells responsible for producing intrinsic factor, leading to symptoms including megaloblastic anemia and neurological damage
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Vitamin C deficiency results in a variety of health issues, most notably scurvy, characterized by weakness, anemia, and joint pain
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Vitamin A deficiency results in night blindness and a decreased ability to regenerate rhodopsin, leading to potentially permanent blindness
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Vitamin K deficiency is linked to bleeding disorders, such as hemorrhagic disease of the newborn and is often treated with vitamin K antagonists like warfarin
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Excess calories, obesity, and a genetic component contribute to the development of type II diabetes
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Hepatic insulin resistance and pancreatic dysfunction are caused by fatty liver and a fatty pancreas
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Metabolic syndrome is characterized by a cluster of conditions including insulin resistance, hypertension, and abnormal blood lipid levels.
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Body Mass Index (BMI) is a measure of body weight relative to height, with a normal range being 18.5-25 kg/m2
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The distribution of body fat, specifically excess visceral and abdominal subcutaneous fat, is associated with increased health risks in obesity.
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Excess upper body fat is linked to a higher risk of metabolic diseases and is often used as a clinical marker.
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A waist-to-hip ratio greater than 0.8 for women and greater than 1.0 for men indicates an increased health risk associated with obesity.
Test your knowledge on nucleotide synthesis, metabolism, and related pathways. Explore the causes of overproduction of uric acid and the role of enzymes like adenosine deaminase.
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