Passage
Beta-thalassemia is a blood disorder caused by reduced production of the β-globin subunit of hemoglobin. The erythrocytes in patients with beta-thalassemia are abnormally small, lack sufficient functional hemoglobin, and are decreased in number. These individuals require lifelong blood transfusions to correct their erythrocyte shortage. Each unit of blood transfused contains many milligrams of iron and, consequently, blood iron levels increase due to repeated transfusions. The excess iron is then continuously deposited in the organs, leading to organ damage.Transferrin (Tf) is a protein that binds free iron in the blood and plays a key role in erythropoiesis, which requires uptake of iron from the blood in a process facilitated by Tf and its cell surface receptor (TfR). Iron-bound Tf, known as holotransferrin (holoTf), binds TfR to form a complex that is brought into the developing erythrocyte in an endosome. Acidification of the endosome triggers a conformational change in holoTf, which allows the release of free iron into the cell and the recycling of the remaining complex components to the cell surface. Non-iron-bound Tf is referred to as apotransferrin (apoTf), and due to its iron-binding capability, researchers believe that apoTf injections may help prevent deposition of excess iron in the organs of patients with beta-thalassemia.To investigate the effect of apoTf administration in a mouse model of beta-thalassemia, mice homozygous for an inactivating deletion in the murine β-globin gene (Hbb th−3 /Hbb th−3 ) were given blood transfusions followed by apoTf injection. Measurements of non-transferrin-bound iron in the blood (NTBI), plasma holoTf, and urinary holoTf were taken immediately and at 15 days post-injection. Results revealed that NTBI decreased over the tested period. Experimenters hypothesized that apoTf mediated certain regulatory changes that reduced NTBI in Hbb th−3 /Hbb th−3 mice by increasing urinary holoTf excretion.
-Transferrin circulating in the blood consists of 679 amino acids, but it is composed of 698 amino acids when it is post-translationally extracted from liver cells, the primary site of transferrin synthesis. Given this information, researchers would most likely be able to extract and isolate the shorter transferrin peptide from:

Question

Passage
Beta-thalassemia is a blood disorder caused by reduced production of the β-globin subunit of hemoglobin.  The erythrocytes in patients with beta-thalassemia are abnormally small, lack sufficient functional hemoglobin, and are decreased in number.  These individuals require lifelong blood transfusions to correct their erythrocyte shortage.  Each unit of blood transfused contains many milligrams of iron and, consequently, blood iron levels increase due to repeated transfusions.  The excess iron is then continuously deposited in the organs, leading to organ damage.Transferrin (Tf) is a protein that binds free iron in the blood and plays a key role in erythropoiesis, which requires uptake of iron from the blood in a process facilitated by Tf and its cell surface receptor (TfR).  Iron-bound Tf, known as holotransferrin (holoTf), binds TfR to form a complex that is brought into the developing erythrocyte in an endosome.  Acidification of the endosome triggers a conformational change in holoTf, which allows the release of free iron into the cell and the recycling of the remaining complex components to the cell surface.  Non-iron-bound Tf is referred to as apotransferrin (apoTf), and due to its iron-binding capability, researchers believe that apoTf injections may help prevent deposition of excess iron in the organs of patients with beta-thalassemia.To investigate the effect of apoTf administration in a mouse model of beta-thalassemia, mice homozygous for an inactivating deletion in the murine β-globin gene (Hbb th−3 /Hbb th−3 ) were given blood transfusions followed by apoTf injection.  Measurements of non-transferrin-bound iron in the blood (NTBI), plasma holoTf, and urinary holoTf were taken immediately and at 15 days post-injection.  Results revealed that NTBI decreased over the tested period.  Experimenters hypothesized that apoTf mediated certain regulatory changes that reduced NTBI in Hbb th−3 /Hbb th−3 mice by increasing urinary holoTf excretion.
-Transferrin circulating in the blood consists of 679 amino acids, but it is composed of 698 amino acids when it is post-translationally extracted from liver cells, the primary site of transferrin synthesis.  Given this information, researchers would most likely be able to extract and isolate the shorter transferrin peptide from:

Quizplus · Accepted Answer

11ecba2d_0ff9_3f0b_a3bf_f9b4890dbfb1_MD0008_00 Blood is the only fluid connective tissue in the body and is composed of living blood cells and nonliving plasma. The cellular components of blood originate from the bone marrow: Erythrocytes play a role in oxygen transport, leukocytes contribute to immune defense, and platelets are crucial in blood clotting. Plasma is the liquid portion of blood and is ~90% water, with the remaining 10% composed of other substances (eg, proteins, respiratory gases). Per the question, transferrin isolated from liver cells has 698 amino acids; however, circulating transferrin has 679 amino acids. It is likely that the 19 missing amino acids make up a signal sequence, a short amino acid sequence present at the N-terminus of immature proteins. The signal sequence directs proteins to the rough endoplasmic reticulum for entry into the secretory pathway before being cleaved from the polypeptide. In this case, transferrin is trafficked through the entire pathway for secretion into extracellular space. Once secreted from liver cells, the shortened transferrin enters circulation and is incorporated into the plasma. (Choice A) Based on the passage, transferrin binds free iron in blood, not lymph. Hydrostatic pressure (the force exerted by blood against vessel walls) forces some liquid and smaller molecules to leak out of the capillaries. This liquid, at this point known as interstitial fluid, is present in the space between the blood vessels and surrounding cells. The interstitial fluid is then collected by the lymphatic vessels. The fluid, now called lymph, is filtered through lymph nodes (pockets on the lymphatic vessels containing white blood cells) and returned to the circulatory system. (Choice C) Transferrin functions to shuttle free iron from blood plasma into developing erythrocytes. Although lingering transferrin may be present in mature erythrocytes, it is not present in all blood cells (ie, leukocytes). (Choice D) DNA replication and RNA transcription occur in the nucleus. Translation occurs in the cytoplasm. Therefore, the transferrin peptide could be isolated from the cytoplasm but not the nucleus of a liver cell. Educational objective: Plasma is the liquid portion of blood, and is made up of water, electrolytes, gases, hormones, nutrients, metabolic waste, and proteins. Although derived from blood, lymph is not a component of blood.

Passage Beta-Thalassemia Is a Blood Disorder Caused by Reduced Production of of the β-Globin