MS II Practice Exam

Inosine monophosphate (IMP) plays a regulatory role by inhibiting PRPP glutamyl amidotransferase. PRPP glutamyl amidotransferase is an enzyme involved in the synthesis of purine nucleotides. By inhibiting this enzyme, IMP helps regulate the production of purine nucleotides, preventing their overproduction. This feedback mechanism ensures that purine nucleotide synthesis is balanced and controlled.

The femoral nerve is formed by the most superior (rostral) segments of the lumbar and lumbosacral plexus. This nerve originates from the ventral rami of the second, third, and fourth lumbar nerves. It provides motor innervation to the muscles of the anterior thigh and sensory innervation to the skin of the anterior and medial thigh, as well as the medial leg and foot. Therefore, the femoral nerve is the correct answer to the question.

The femoral nerve is correctly matched with the anterior thigh, patellar reflex, and leg extension. The femoral nerve innervates the muscles of the anterior thigh, including the quadriceps femoris muscle which is responsible for extending the leg. The patellar reflex is a reflex arc that involves the femoral nerve and causes contraction of the quadriceps muscle, leading to leg extension.

The small intestine has the fastest rate of protein turnover compared to the other tissues listed. This is because the small intestine is responsible for absorbing nutrients from food, and therefore requires a high turnover rate of proteins to efficiently carry out this function. The constant breakdown and synthesis of proteins in the small intestine allows for the rapid turnover needed to process and absorb nutrients effectively.

tendon sheath is dense IRREGULAR

Collagen fibers are not assembled in the rough endoplasmic reticulum, but rather in the extracellular space. The rough endoplasmic reticulum is where the synthesis of collagen occurs, but the assembly of collagen fibers happens outside of the cell.

Glutamine is not only found in tissue proteins, but it is also an important amino acid that plays various roles in the body. It is responsible for the transport of ammonia in a non-toxic form, which helps in detoxification. Furthermore, ATP is indeed required for the synthesis of glutamine from glutamate and ammonia. In the liver, glutamine is hydrolyzed to glutamate and ammonia, but it also serves other functions in different tissues. Therefore, the statement that the only fate of glutamine is hydrolysis to glutamate and ammonia is incorrect.

Glutamate dehydrogenase is responsible for brain metabolic deficits in hyperammonemia. In hyperammonemia, there is an excess of ammonia in the blood, leading to increased levels of glutamate in the brain. Glutamate dehydrogenase converts glutamate to alpha-ketoglutarate, which is an important step in the metabolism of glutamate. However, in hyperammonemia, the activity of glutamate dehydrogenase is impaired, leading to a buildup of glutamate and disruption of brain metabolism. This can result in neurological symptoms and deficits.

Tyrosine is synthesized from an essential amino acid called phenylalanine. Phenylalanine is converted into tyrosine through a process called hydroxylation. This conversion is catalyzed by the enzyme phenylalanine hydroxylase. Tyrosine is an important amino acid that plays a role in the production of neurotransmitters such as dopamine, norepinephrine, and epinephrine. It is also a precursor for the synthesis of important molecules such as thyroid hormones and melanin.

Tetrahydrofolate is important in reactions involving one carbon transfer groups. It serves as a cofactor in the transfer of one-carbon units in various biochemical reactions, including the synthesis of nucleotides, amino acids, and certain neurotransmitters. Tetrahydrofolate plays a crucial role in the metabolism of folate, which is essential for DNA synthesis and cell division. It acts as a carrier of one-carbon units, facilitating the transfer of methyl and formyl groups between different molecules. This makes tetrahydrofolate vital for various biological processes and makes it the correct answer in this case.

Post-capillary venules mediate plasma protein extravasation. These small blood vessels are located between capillaries and veins and play a crucial role in the movement of fluids and molecules between the bloodstream and surrounding tissues. Due to their unique structure and permeability, post-capillary venules allow for the leakage of plasma proteins, such as antibodies and clotting factors, into the surrounding tissues. This process is important for immune responses, inflammation, and wound healing. Arterioles, veins, capillary shunts, and the adventitial layer do not have the same capability to mediate plasma protein extravasation.

The most important reason that the epithelium must be restored promptly following injury is to protect the wound from infection. The intact epithelium acts as a physical barrier that prevents the entry of pathogens into the body. When the epithelium is damaged, it exposes the underlying tissues to potential infection. Therefore, prompt restoration of the epithelium is crucial to minimize the risk of infection and promote proper wound healing.

Nitric oxide is known to have various physiological functions. One of its functions is neurotransmission, which means it acts as a signaling molecule in the nervous system. It helps in the communication between nerve cells. Another function is vasodilation, which refers to the widening of blood vessels, allowing for increased blood flow. Nitric oxide helps in relaxing the smooth muscles of blood vessels, leading to vasodilation. Therefore, the correct answer is neurotransmission and vasodilation.

Cross-linking by lysyl oxidase occurs outside fibroblasts. Lysyl oxidase is an extracellular enzyme that catalyzes the formation of cross-links between collagen molecules, which contributes to the stability and strength of collagen fibers. Fibroblasts are responsible for synthesizing collagen, but the cross-linking process occurs outside of these cells in the extracellular matrix. This is an important step in collagen maturation and the formation of a functional collagen network in tissues.

PRPP Glutamyl amidotransferase is the correct answer because it catalyzes the committed step in de novo purine synthesis. This enzyme is responsible for transferring an amide group from glutamine to PRPP (phosphoribosyl pyrophosphate), forming 5-phosphoribosylamine, which is a key intermediate in the synthesis of purine nucleotides. The other enzymes listed are also involved in purine synthesis but do not catalyze the committed step.

During the conversion of PRPP (Phosphoribosyl pyrophosphate) to IMP (Inosine monophosphate), a total of 4 ATPs (Adenosine triphosphates) are consumed. This conversion involves multiple enzymatic steps, each requiring the hydrolysis of one ATP molecule. Therefore, the correct answer is 4.

During the synthesis of AMP (adenosine monophosphate), fumarate is produced as an additional biochemically relevant molecule. Fumarate is an intermediate in the citric acid cycle, also known as the Krebs cycle, which is a series of chemical reactions that occur in the mitochondria to generate energy. Fumarate is converted to malate, which then enters the next step of the cycle. Therefore, fumarate is an important molecule in cellular metabolism and energy production.

In Lesch-Nyhan patients, uric acid levels increase due to several factors. Firstly, PRPP (phosphoribosyl pyrophosphate) activates PRPP amidotransferase, an enzyme involved in the synthesis of purine bases. This activation leads to an increased production of purine bases, which are then converted into uric acid. Secondly, the patients have a deficiency in salvaging purine bases, resulting in an accumulation of these bases and their subsequent conversion to uric acid. Lastly, the increased concentration of PRPP in Lesch-Nyhan patients further enhances the production of uric acid. Therefore, all of the above factors contribute to the elevated uric acid levels in Lesch-Nyhan patients.

PRPP phosphoribosyl transferase is not involved in the salvage and conversion pathway of thymine to dTTP. The salvage and conversion pathway is a process by which thymine, a nucleotide base, is recycled and converted into dTTP, a building block for DNA synthesis. Nucleoside phosphorylase is responsible for breaking down thymine into its nucleoside form. Thymidine kinase then phosphorylates the nucleoside to form thymidine monophosphate (TMP), which is further converted to dTMP by thymidylate kinase. Therefore, PRPP phosphoribosyl transferase is not part of this pathway.

Allopurinol is a medication commonly used to treat gout by inhibiting the enzyme xanthine oxidase, which is responsible for the production of uric acid. By reducing uric acid levels, allopurinol helps prevent gout attacks. Lower levels of PRPP glutamyl amidotransferase activity would be expected in gout patients after treatment with allopurinol because allopurinol decreases the production of uric acid, which is synthesized from PRPP (phosphoribosyl pyrophosphate). Therefore, when uric acid production is reduced, the activity of PRPP glutamyl amidotransferase, which is involved in the synthesis of uric acid, would also be expected to decrease.

The prevalent cause of gout is under-excretion of uric acid. Gout is a form of arthritis that occurs when there is a buildup of uric acid in the body, leading to the formation of urate crystals in the joints. Under-excretion of uric acid occurs when the kidneys are not able to effectively remove enough uric acid from the body. This can be due to various factors such as kidney disease, certain medications, or lifestyle factors. Over-production of uric acid and genetic defects in nucleotide metabolism can also contribute to gout, but under-excretion is the most common cause. Treatment with chemotherapeutic agents is not a prevalent cause of gout.

The definitive diagnosis for gout is the presence of uric acid crystals at the site of inflammation. Gout is a type of arthritis that occurs when there is a buildup of uric acid in the body, leading to the formation of sharp, needle-like crystals in the joints. These crystals cause inflammation and severe pain, commonly affecting the big toe. The presence of uric acid crystals can be confirmed by examining fluid aspirated from the affected joint under a microscope. Hyperuricemia, which is an elevated level of uric acid in the blood, is a risk factor for developing gout but is not sufficient for a definitive diagnosis. Bone deformities may occur in chronic gout but are not specific to the diagnosis.

Patients lacking or deficient in Vitamin B12 would be expected to accumulate 5-methyl tetrahydrofolate. This is because Vitamin B12 is necessary for the conversion of 5-methyl tetrahydrofolate to tetrahydrofolate, which is a coenzyme involved in the synthesis of DNA, RNA, and certain amino acids. Without sufficient Vitamin B12, this conversion cannot occur, leading to the accumulation of 5-methyl tetrahydrofolate.

5, 10 methylene-THF is used to transfer a one carbon group to dUMP and results in the formation of dihydrofolate and thymidylate. This is because 5, 10 methylene-THF is a key intermediate in the synthesis of thymidylate, which is necessary for DNA synthesis. The transfer of a one carbon group from 5, 10 methylene-THF to dUMP leads to the formation of thymidylate and dihydrofolate. Thymidylate is then used in DNA synthesis, while dihydrofolate can be converted back to tetrahydrofolate for further use in one carbon transfer reactions.

The obturator nerve does not contain sensory fibers distal to the patella. The femoral nerve, sciatic nerve, deep peroneal nerve, and tibial nerve all contain sensory fibers that extend beyond the patella. The obturator nerve primarily innervates the muscles of the medial thigh and does not provide sensory innervation to the lower leg or foot.

Collagen IV is not a major tissue type of connective tissue because it is a specific type of collagen protein found in the basement membrane, which is a specialized form of extracellular matrix. Connective tissue is composed of cells and extracellular matrix, and the major tissue types include fibroblasts, mast cells, macrophages, and lymphocytes. Collagen IV, although an important component of connective tissue, is not considered a major tissue type itself.

Epithelia are a type of tissue that line the surfaces of organs and body cavities. The basal layer of epithelium adheres to the basement membrane, which is a thin layer of connective tissue that provides support and anchorage for the epithelial cells. This adherence helps to maintain the integrity and stability of the epithelial tissue.

Macrophages are immune cells that play a crucial role in the immune response. They are known for their ability to phagocytose (engulf and destroy) pathogens and cellular debris. Macrophages are also involved in antigen presentation, where they present antigens to activate other immune cells. Additionally, macrophages secrete cytokines, which are signaling molecules that help regulate the immune response. However, macrophages do not synthesize type I collagen, which is primarily produced by fibroblasts and osteoblasts. Therefore, type I collagen synthesis is not a function attributable to macrophages.

Type IV collagen is found within basement membranes but not connective tissues. Basement membranes are thin, sheet-like structures that provide support and anchor cells in various tissues. Type IV collagen forms a network within the basement membrane, providing structural integrity and stability. In contrast, connective tissues contain Type I collagen, which is a fibrillar collagen and forms the main structural component of tendons, ligaments, and skin. Type III collagen is also found in connective tissues, specifically in the extracellular matrix. Fibril associated collagens, such as Type IX collagen, are associated with fibrillar collagens and contribute to the organization and stability of connective tissues.

Trypsin is the most important peptidase in protein digestion because it is responsible for the hydrolysis of peptide bonds in proteins. It is produced in the pancreas and released into the small intestine, where it acts on proteins to break them down into smaller peptides. Trypsin is able to cleave peptide bonds specifically at the carboxyl side of the basic amino acids, such as lysine and arginine, which makes it a crucial enzyme in protein digestion.

Facilitated Amino Acid Transporters are responsible for moving amino acids to the portal system. The other options mentioned, such as γ-glutamyltranspeptidase, Na+-dependent amino acid transporters, and Na+,K+-pump, do not specifically function in transporting amino acids to the portal system. Therefore, the correct answer is Facilitated Amino Acid Transporters.

Carboxypeptidase is not an endopeptidase because it cleaves peptide bonds at the C-terminus of a polypeptide chain, while endopeptidases cleave peptide bonds within the chain. Chymotrypsin, trypsin, and pepsin are all endopeptidases as they cleave peptide bonds within the polypeptide chain.

C is also technically right.

Hydroxyproline plays the most critical role in the stability of the collagen triple helix. Hydroxyproline is a modified form of proline that is essential for the proper folding and stability of collagen. The hydroxylation of proline to hydroxyproline allows for the formation of hydrogen bonds within the collagen molecule, which contributes to the stability and strength of the triple helix structure. Without hydroxyproline, collagen would not be able to maintain its structural integrity, leading to decreased stability and potential structural abnormalities.

Urea is quantitatively the most important nitrogen-containing compound in urine because it is the primary waste product of protein metabolism in humans. It is produced in the liver through the breakdown of amino acids and is then excreted by the kidneys. Urea helps to remove excess nitrogen from the body, which is essential for maintaining nitrogen balance. Other nitrogen-containing compounds, such as ammonia and creatinine, are also present in urine but in smaller quantities compared to urea. Therefore, urea is considered the most important nitrogen-containing compound in urine.

Mutation in the arginase enzyme of the urea cycle causes arginemia. Arginase is responsible for the final step in the urea cycle, converting arginine into urea and ornithine. When there is a mutation in the arginase gene, the enzyme is not produced or is produced in a non-functional form, leading to a buildup of arginine in the blood and a deficiency of urea production. This can result in symptoms such as intellectual disability, developmental delay, and liver problems.

The glucose-alanine cycle is a major route for ammonia detoxification in the skeletal muscle. This cycle involves the conversion of pyruvate into alanine, which can then be transported to the liver. In the liver, alanine is converted back into pyruvate, releasing ammonia in the process. The liver can then convert the ammonia into urea for excretion. Therefore, the skeletal muscle plays a crucial role in removing ammonia from the body through the glucose-alanine cycle.

The correct answer is NH4+ + CO2 + 2 ATP --> carbomoyl phosphate. This reaction is the rate-limiting step in the urea cycle because it requires the input of energy in the form of ATP and the conversion of ammonia (NH4+) and carbon dioxide (CO2) into carbomoyl phosphate. This step is catalyzed by the enzyme carbomoyl phosphate synthetase I, which is regulated by the concentration of N-acetylglutamate. The other reactions listed in the options are important steps in the urea cycle, but they are not the rate-limiting step.

Leucine and lysine are considered exclusively ketogenic amino acids because they can only be converted into ketone bodies and cannot be used for glucose synthesis. This means that they are primarily metabolized to produce energy through ketogenesis rather than being used for other metabolic processes such as protein synthesis or glucose production.

Maple syrup urine disease is a genetic disorder that affects the metabolism of branched chain amino acids (BCAAs) - leucine, isoleucine, and valine. In this condition, the body is unable to break down these amino acids properly, leading to a buildup of toxic byproducts. This results in a sweet-smelling urine, similar to the smell of maple syrup. Defective metabolism of tryptophan, tyrosine, aromatic amino acids, or phenylalanine is not associated with maple syrup urine disease.

Pyridoxal phosphate is an important cofactor in reactions of transamination. Transamination is a process where an amino group is transferred from an amino acid to a keto acid, forming a new amino acid and a new keto acid. Pyridoxal phosphate, the active form of vitamin B6, serves as a coenzyme in this reaction by acting as a carrier for the amino group. It forms a Schiff base with the amino acid, allowing the transfer of the amino group to the keto acid. Therefore, pyridoxal phosphate is essential for the proper functioning of transamination reactions.

After a meal, glucose serves as the preferential energy substrate in most tissues, including the brain, skeletal muscle, kidney, and blood immune cells. However, the gut does not rely heavily on glucose as an energy source. Instead, the gut primarily utilizes other substrates such as fatty acids and amino acids for energy metabolism. This is because the gut is responsible for absorbing nutrients from the food, rather than utilizing them for energy production.

The kidney is responsible for maintaining the body's acid-base balance, which includes regulating pH levels. Glutamine, an amino acid, plays a crucial role in this process. It acts as a buffer, helping to maintain the pH of bodily fluids within a normal range. Therefore, the kidney is the tissue where glutamine is used for pH regulation.

In sepsis, blood immune cells, such as white blood cells, play a crucial role in fighting off infections. Glutamine is used as a preferential substrate for energy production and nucleotide synthesis in these cells. Glutamine provides the necessary fuel for the immune cells to carry out their functions effectively during sepsis. The brain, skeletal muscle, gut, and kidney may also use glutamine for energy production, but in the context of sepsis, blood immune cells have a higher demand for glutamine due to their increased metabolic activity.

During fasting, the body's primary source of energy is glucose. However, after a certain period of fasting, glucose levels start to decrease, and the body needs to find alternative sources of energy. In this case, branched chain amino acids (BCAAs) serve as a major source of energy substrates. Skeletal muscle is the tissue where BCAAs are broken down and used as an energy source during fasting. This is because skeletal muscle is the largest reservoir of amino acids in the body and can readily release BCAAs for energy production.

Paracrine signaling is a form of cell communication where a signaling molecule is released by a cell and acts on neighboring cells. In this case, the growth-promoting factor produced by fibroblasts that regulates epidermal cells fits the definition of paracrine signaling. The fibroblasts release the growth factor, which then acts on nearby epidermal cells to regulate their growth. This is a localized form of signaling that does not involve long-distance transmission of the signal. The other options do not fit the criteria for paracrine signaling as they either involve different types of signaling or do not involve neighboring cells.

Norepinephrine and dopamine are both stress hormones. Norepinephrine is released in response to stress and is involved in the "fight or flight" response. It increases heart rate, blood pressure, and blood sugar levels. Dopamine is also involved in the stress response and plays a role in motivation, reward, and movement. Both norepinephrine and dopamine help the body cope with stress and prepare for action.

Hyaline cartilage is the precursor to developed bone tissue. During bone development, hyaline cartilage serves as a template for bone formation. It provides a scaffold for bone cells to deposit new bone tissue. As the bone grows, the hyaline cartilage is gradually replaced by bone cells, resulting in the formation of mature bone tissue. The other options, fibrous cartilage, elastic cartilage, articular cartilage, and SOX9, are not directly involved in the precursor process of bone tissue development.

A mutation in the gene that encodes the protein Sox9 can cause various abnormalities in skeletal development, such as angulation of long bones, decrease in the number of ribs, craniofacial abnormalities, and abnormalities in the vertebral column. However, missing limb(s) is not typically associated with a mutation in the Sox9 gene.

Osteoclasts are not involved in modulation. Osteoclasts are responsible for bone resorption, breaking down bone tissue. Modulation refers to the process of adjusting or regulating something. Osteocytes, osteoblasts, and progenitor cells are all involved in the modulation of bone tissue through various functions such as maintaining bone density, bone formation, and differentiation into bone cells. However, osteoclasts have a different role in bone remodeling, as they break down and remove old or damaged bone tissue.