Biomedical Science I Exam II

Competitive inhibition occurs when a molecule similar to the substrate competes for the active site of the enzyme. To overcome competitive inhibition, excess substrate is added, which increases the chances of the substrate binding to the active site instead of the inhibitor. This increases the Km value, which represents the substrate concentration at which the reaction rate is half of the maximum velocity. Therefore, the given statement is false as excess substrate addition increases Km, rather than decreasing it.

In non-competitive inhibition, there is no change in Km, but there is a decrease in Vmax. This means that the affinity of the enzyme to the substrate remains the same, but the maximum rate of reaction is reduced.

The correct sequence of events for the Gs Signal Transduction Pathway is as follows: Ligand binds to the receptor, which activates the G-protein. The activated G-protein then stimulates Adenylyl Cyclase, leading to the production of cAMP. Finally, cAMP activates PKA. This sequence of events is the correct order in which the signaling molecules and enzymes are activated and interact with each other in the Gs Signal Transduction Pathway.

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A rapid acetylator is less likely to cause drug toxicity because this type of acetylator metabolizes drugs more quickly, leading to a faster elimination of the drug from the body. This reduces the chances of drug accumulation and toxicity.

In competitive inhibition, the inhibitor competes with the substrate for the active site, meaning that both the inhibitor and substrate cannot bind to the enzyme simultaneously. Irreversible inhibition involves covalent modifications, where the inhibitor forms a covalent bond with the enzyme, rendering it permanently inactive. Low Km indicates low substrate concentration required for the enzyme to reach half of its maximum velocity, indicating high affinity between the enzyme and substrate.

Erythromycin is known to inhibit the enzyme CYP3A4, which is responsible for metabolizing Diltiazem. As a result, the presence of erythromycin would lead to a decrease in the metabolism of Diltiazem. This means that less of the drug would be broken down and eliminated from the body, resulting in higher levels of Diltiazem in the bloodstream. To avoid potential side effects or toxicity from elevated levels of Diltiazem, the appropriate plan of action would be to reduce the dose of Diltiazem. This adjustment would help maintain therapeutic levels of the medication without risking adverse effects.

In a Gs transduction signaling pathway, the activation of the effector leads to the activation of cAMP. This is because the Gs protein acts as a molecular switch, activating adenylyl cyclase when it is bound to GTP. Adenylyl cyclase then catalyzes the conversion of ATP to cAMP. cAMP then acts as a second messenger, activating protein kinase A (PKA) which can phosphorylate and activate downstream target proteins such as CREB. Therefore, cAMP is a key mediator in transmitting signals from the Gs transduction pathway to activate various cellular processes.

1. As chemical reactions undergo, entropy (disorder) will increase: This statement is correct because as reactions occur, molecules become more disordered, leading to an increase in entropy.
2. Enzymes are specific catalysts that remain unchanged following a reaction: This statement is correct because enzymes are not consumed or altered during a reaction, allowing them to be reused.
3. Polymorphism among individuals can change the activity of enzymes which will affect the metabolism of the drug: This statement is correct because genetic variations can result in different enzyme forms or levels, leading to variations in drug metabolism.

Enzyme-linked receptor signaling involves the activation of receptor tyrosine kinases through dimerization, which allows the kinases to phosphorylate themselves (autophosphorylation). Ras is indeed a monomeric G protein that requires extrinsic enzymes (Guanine Nucleotide Exchange Factors) to activate it. Epidermal Growth Factor (EGF) binds to its receptor, leading to the activation of the MAPK signaling pathway. Lastly, most enzyme-linked receptors are indeed tyrosine kinase receptors, which phosphorylate tyrosine residues in their substrates.

Epidermal Growth Factor (EGF) acts as the first messenger in MAPK Signal Transduction, initiating the signaling cascade. Once the ligand (EGF) binds to the receptors, they dimerize, bringing them closer together. This dimerization enables the receptors to phosphorylate each other, leading to the activation of downstream signaling molecules. Ras, a heteromeric G protein, is activated by the binding of GTP. Once activated, Ras activates a kinase that phosphorylates MAPK, thereby transmitting the signal further downstream. The statement about Ras requiring extrinsic GTPase activity, involving Guanine Nucleotide Exchange Factors (GEF) and GTPase activating Proteins (GAP), is not mentioned in the given answer.

The statement is false because the secretion of oxytocin from the Posterior Pituitary Gland does not cause uterine contractions quickly. Instead, it is a slow process that occurs gradually over time. Additionally, the effects of oxytocin on uterine contractions are long-lasting, not short-lived.

An example of a ligand-gated channel is acetylcholine receptors found in neuromuscular junctions. This is correct because ligand-gated channels open or close in response to the binding of a specific molecule (ligand) such as acetylcholine.

For Mechanical-gated channels, distortion of the cell causes the channel to open. This is correct because mechanical-gated channels open or close in response to physical forces or mechanical distortion of the cell membrane.

The receptors of intracellular signaling can be located in the cytosol and nucleus of the cell. This means that they are present within the fluid portion of the cell (cytosol) as well as inside the nucleus, where the genetic material is housed. These receptors are responsible for receiving signals and transmitting them to the appropriate cellular machinery to initiate a response. The plasma membrane, endoplasmic reticulum, and mitochondria are not locations where intracellular signaling receptors are typically found.

SLCs are a group of proteins that are involved in the movement of solutes across cell membranes. They are responsible for solute influx, meaning they transport solutes into the cell. Unlike some other transport proteins, SLCs do not directly consume ATP in the movement of solute. Instead, they can use facilitated diffusion or secondary active transport, which do not require ATP. Additionally, some SLCs are found in tissues that participate in environmental exchange, allowing for the movement of solutes between the organism and its surroundings. GLUT1 is an example of an SLC protein that transports glucose out of the cell.

Kinases attach phosphate groups to molecules. This statement is correct because kinases are enzymes that catalyze the transfer of a phosphate group from ATP to a molecule, often a protein or a small molecule.

Hydrolases cleave water as part of a reaction. This statement is correct because hydrolases are enzymes that catalyze the cleavage of a molecule by adding water to it, resulting in the breaking of chemical bonds.

ATPases hydrolyze ADP --> ATP as part of a reaction. This statement is incorrect because ATPases are enzymes that hydrolyze ATP to ADP and inorganic phosphate (Pi) as part of a reaction.

Phosphatases remove phosphate groups off molecules. This statement is correct because phosphatases are enzymes that catalyze the removal of phosphate groups from molecules, often proteins or nucleotides.

Synthases form a large molecule from two small molecules. This statement is correct because synthases are enzymes that catalyze the synthesis of a larger molecule from two smaller molecules, often through the formation of a new bond.

CYP3A4 is an enzyme that is present in both the liver and small intestine, and it is responsible for metabolizing approximately 50% of drugs, as well as endogenous and exogenous compounds. Polymorphism of NAT-2 can lead to an increased risk of cancer.

A partial agonist competes with the agonist for the binding site. This means that when both the agonist and the partial agonist are present, they will both try to bind to the same receptor site, leading to a competition for binding.

Densensitization can occur via receptor sequesteration, down-regulation, and inactivation when a receptor is constantly exposed to ligands. This means that when a receptor is constantly exposed to ligands, it can become desensitized or less responsive. This can happen through various mechanisms such as sequestering the receptor away from the cell surface, reducing the number of receptors through down-regulation, or inactivating the receptor.

The Na+/K+ Pump is an antiport which pumps 3 Na+ in and 2 K+ out to restore membrane potential by primary active transport: This statement is incorrect. The Na+/K+ pump is an antiporter that pumps 3 Na+ out of the cell and 2 K+ into the cell, not the other way around.

SGLT2 transports glucose against its concentration gradient by coupling it to the movement of Na+ down its concentration gradient: This statement is correct. SGLT2 is a symporter that transports glucose into the cell against its concentration gradient by coupling it to the movement of Na+ down its concentration gradient.

ABC transporters utilize primary active transport to transport solutes into cells: This statement is incorrect. ABC transporters utilize primary active transport to transport solutes out of cells, not into cells.

SLCO1B1 transports solutes via a uniporter by facilitated diffusion: This statement is correct. SLCO1B1 is a uniporter that transports solutes into the cell by facilitated diffusion.

The Na+-Amino Acid transporter utilizes a symporter: This statement is correct. The Na+-Amino Acid transporter is a symporter that transports amino acids into the cell by coupling their movement to the movement of Na+ into the cell.

A mutation in SLCO1B1 reduces the metabolism of cholesterol lowering drugs, leading to decreased efficacy and increased levels in the blood. This can potentially lead to muscle disease. In a resting cell, there is a higher concentration of Na+ outside the cell and a higher concentration of K+ inside the cell. Facilitated diffusion is a passive process that does not require energy and moves molecules down their concentration gradient.

Enzymes function optimally within a specific range of temperature and pH. Any deviation from this range can denature the enzyme and affect its functional ability. CYP450 enzymes are primarily found in the liver and are responsible for catalyzing oxidative reactions during phase I of biotransformation. Vmax, or maximum velocity, is the rate at which the enzyme is saturated with substrate. It is dependent on the rate at which the product dissociates from the enzyme.

The activation of PKA leads to the amplification of cAMP because PKA phosphorylates and activates adenylyl cyclase, which in turn catalyzes the conversion of ATP to cAMP, leading to an increase in cAMP levels. Requires the alpha-subunit to activate Adenylyl Cyclase because the alpha-subunit of the G-protein directly interacts with and activates adenylyl cyclase. Can lead to the phosphorylation of CREB because cAMP activates PKA, which then phosphorylates CREB, leading to its activation.

SGLT2 transporters require the input of energy eventually because they actively transport glucose and sodium against their concentration gradients. They use the energy from the sodium ion gradient created by Na+/K+ ATPase to drive the transport. SGLT2 is a symporter that transports both glucose and sodium together, meaning they are co-transported across the cell membrane. These transporters are located in the convoluted proximal tubule of the kidneys, where they reabsorb glucose and sodium from the filtrate back into the bloodstream. Inhibition of SGLT2 would lead to excess blood glucose because it prevents the reabsorption of glucose, causing it to be excreted in the urine. However, inhibition of SGLT2 is not used as a treatment for Type I Diabetes Mellitus.

ABC transporters are a family of proteins that possess a Beta-sheet domain which binds ATP. They are involved in the efflux of substrates, such as hydrophilic drugs, and can transport solutes from kidney cells into the blood. Additionally, a mutation resulting in a gain of function of P-gp, which is a type of ABC transporter, can lead to reduced drug levels in tissue. These statements accurately describe the characteristics and functions of ABC transporters.

Cholera toxin causes rapid production of Gs signaling which leads to diarrhea and dehydration. Phosphodiesterases (PDEs) regulate signaling by converting cAMP into 5'-AMP, the inactive form. PKA is activated when 4 cAMP molecules bind to its regulatory subunit.

The presence of negatively-charged amino acids on the entrance of the pore restricts the entrance of anions but not cations. Na+ can enter the pore but can't move through the selectivity filter due to the presence of carbonyl oxygens in the selectivity filter which can't fully bind to. The dehydration of K+ ions allows for entry into the selectivity filter. The inner and outer helices provide stabilization to the channel by interacting with lipids in the membrane.

Aquaporins are protein channels that facilitate the transport of water molecules across cell membranes. They do not allow the passage of ions due to their narrow pore size, which hydrated ions are too large to fit into. Molecules, including water, pass through aquaporin channels by moving down their concentration gradient. This means that they move from an area of higher concentration to an area of lower concentration. Therefore, the correct statements are that ions are unable to pass through aquaporins due to a narrow pore, and molecules pass through the channels by moving down their concentration gradient.