Tutor profile: Jasmine T.
How can I make my writing more memorable?
They key to this question is two-fold. The first suggestion I always make is to always include more specifics than explanations or elaborations. Make your writing colorful. Add in an analogy or tell a story that the reader can visualize. The reason this is so impactful is because writing is not inherently emotional, images are. Writing is not inherently meaningful, narratives are. The second suggestion I make is to make your writing come full circle. If you have a compelling hook in the beginning or a meaningful thread throughout your piece, come back to that hook or thread in the very last sentence. If it was central to the piece as a whole, your readers will remember it, and that satisfying ending will undoubtedly stick with them.
I can't keep track of competitive, noncompetitive, and uncompetitive inhibition. What's the difference??
1. COMPETITIVE INHIBITION: This occurs when an inhibitor steals the substrate's binding site in the enzyme, thereby blocking the substrate from binding. What happens to Vmax? Nothing, because as long as significantly more substrate is added, the substrate can outcompete the inhibitor and minimize its effects on the rate of the reaction. As long as there are functional enzymes that have the potential to bind substrate, the Vmax doesn't change. What happens to Km? It increases, because it now takes a higher concentration of substrate to reach Vmax (due to the fact that inhibitor is blocking some substrate binding sites), so logically it would also take a higher concentration of substrate to reach 1/2 Vmax. This makes sense because Km is an inverse measure of binding affinity, which in this case is decreasing due to the inhibitor blocking the binding of substrate to enzyme. 2. NONCOMPETITIVE INHIBITION: This occurs when an inhibitor binds not at the substrate binding site but at another site entirely (known as an allosteric site), changing the shape of the enzyme and thereby inactivating the enzyme altogether, WHETHER OR NOT the enzyme is already bound to a substrate. What happens to Vmax? It decreases, because as enzymes are getting inactivated by inhibitor, this is equivalent to reducing the concentration of enzyme, which would reduce the speed at which substrate can be turned over into product. What happens to Km? Nothing, because the new Vmax is being driven by functional enzymes only, which require the same substrate concentration to reach 1/2 Vmax as before any inhibitor was added. This also makes sense because noncompetitive inhibition would not have any effect on the binding affinity of the substrate to the enzyme. 3. UNCOMPETITIVE INHIBITION: This occurs when an inhibitor binds to an allosteric site of an enzyme (like noncompetitive inhibition) but ONLY WHEN the enzyme is already bound to a substrate. This essentially causes the enzyme to hold on to the substrate and prevent the release of a product. What happens to Vmax? It decreases, because if enzymes are unable to release their substrate, they're useless, thereby reducing the concentration of functional enzyme and decreasing the rate of the reaction. What happens to Km? It decreases, because as the enzyme-substrate complex is now stabilized, this means the enzymes seems to have a higher affinity for the substrate.
What is a "membrane potential" really, and what creates this membrane potential in a cell?
You may remember from your physics classes that a voltage is the electric potential difference between two points. In other words, it is the difference in electric potential energy between two points, independent from charge. This difference in potential is what drives current! We can apply the same concept to membrane potentials. A membrane potential is just the difference in potential energy (aka voltage) between the interior and exterior of a cell, which has the capacity to move charges (ions) around. You may also remember that voltage is created by a separation of charges. In the context of a cell, how is this accomplished? Put simply, it's created by the distribution of anions and cations on either side of the cell membrane. Whether one side of the membrane is positive or negative depends on the relative concentrations of ions on either side. So for example, let's take the resting membrane potential of a neuron, which sits at about -70mV (this negative value indicates a "negative" INTRACELLULAR environment relative to a more "positive" extracellular environment). The interior of a neuron has relatively LOW concentrations of POSITIVELY charged sodium ions (Na+) and calcium ions (Ca2+) and relatively HIGH concentrations of NEGATIVELY charged proteins compared to the extracellular environment, which contributes to that relatively negative resting membrane potential. While the neuron also has higher concentrations of positively charged potassium ions and lower concentrations of negatively charged chloride ions, these contribute to the overall membrane potential less than the other ions.
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