Enzymes - AP Biology

DNA helicase is an enzyme that is able to slip between the two strands of DNA and disrupt the hydrogen bonds that keep the DNA in the double helix structure. This disruption opens up the DNA helix, and exposes sections of DNA that can then be transcribed or replicated. As helicase moves down the double helix, the DNA reforms into a double helix since the enzyme is no longer blocking the hydrogen bonds.

These are all definitive traits of an enzyme. Enzymes are proteins which are extremely helpful in speeding up certain reactions without being depleted by the reactions themselves (as such, they are catalysts for these reactions). Enzymes reduce the amount of energy needed for a reaction to occur, generally because they facilitate reactions by recognizing reactants and bringing them into contact with each other. This occurs when the reactants bind to certain parts of the enzyme (active sites), which causes the enzyme to change shape and bring the reactants into contact with each other (and then the reactants can bind to form the product).

Peptidyl transferase is the enzyme that works in conjunction with tRNA molecules to extend a growing polypeptide chain at the ribosome during translation. Ligase is not used at all in translation, nor is topoisomerase or ATP synthase. tRNA synthetase is used to bind the correct amino acids to corresponding tRNA molecules, but it is not used to extend the polypeptide at the ribosome.

While all the answer choices are important in DNA replication, only DNA Polymerase I performs this particular function. Ligase helps bind the newly replaced DNA nucleotides to the rest of the DNA strand. DNA polymerase III is the main synthesizing enzyme of DNA replication, and creates the majority of the DNA strand. DNA polymerase II is less well known than I and III, but it is believed to perform as a repair enzyme which removes incorrectly paired segments of DNA (which can then be filled back in by DNA polymerase I).

Enzymes have an "optimal temperature," or best temperature that they work at. If that temperature is below or above its optimal temperature, the enzyme will decrease in activity; if the temperature change is great enough, the enzyme could even denature (no longer work).

An enzymes function is to speed up chemical reactions by lowering the activation energy. If our bodies did not have enzymes, the reactions would take place, but too slowly for our cells to adequately function.

The questions is asking how enzymes affect reactions. The function of an enzyme is to speed up chemical reactions, which will increase the overall rate of the reaction, thus "increasing the rate of the reaction" is the correct answer.

The function of an enzyme is to speed up chemical reactions. They do this by lowering the activation energy, which is the minimum energy that must be available for a chemical reaction to occur. If the energy required is lowered, the reaction can go faster. Thus the correct answer is an enzyme changes "the activation energy of the reaction."

A reactant is a substance that undergoes change during a reaction. During an enzyme reaction specifically, the reactant is called the substrate, as a substrate is the substance in which an enzyme acts on and changes.

Both pH and temperature can affect how productive an enzyme is. If an enzyme is functioning in an environment that is not at its optimal pH or optimal temperature, the enzyme's activity will decrease.

Denature means to destroy the properties of a protein or other biological macromolecule. If an enzyme (which is a protein) stops working, it has denatured.

The correct answer is "allosteric site." A molecule that binds to an enzyme's allosteric site induces a conformational change in the enzyme, decreasing or increasing the affinity of the enzyme’s binding sites to the substrate. The binding site binds and orients the substrate. The catalytic site lowers the activation energy of the reaction. The binding site and the catalytic site together make up the active site. Cofactors are parts of certain enzymes and are required for those enzymes to function.

Statement I is false because increasing the substrate concentration will only help overcome competitive inhibition. Noncompetitive inhibition can only be overcome if the inhibitor is removed from the enzyme.

Statement II is also false because competitive inhibitors do not change the active site. They bind to the active site and prevent substrates from binding. Noncompetitive inhibitors bind elsewhere on the enzyme and alter the shape of the active site, thereby preventing substrate binding.

Statement III is true because noncompetitive inhibition does not affect the enzyme affinity for substrates. The enzyme still has the same affinity, but the substrates can’t bind because of the altered active site.

Competitive inhibition occurs when an substrate or inhibitor compete with the normal substrate for binding the active sight of an enzyme. The proper functioning of the enzyme depends on the concentration ratio of inhibitor to enzyme or substrate to enzyme. The competitive inhibition of the enzyme in this case by the antibiotic has potentially bactericidal or bacteriostatic effect on the bacteria until that antibiotic concentration decreases. Negative feedback involves the product of a set of metabolic reactions inhibiting the formation of a precursor of that metabolic pathway, thereby decreasing its own production.

Negative feedback interrupts a metabolic pathways by producing a substrate that inhibits enzymes in the beginning steps of the metabolic cycle. If a chemical is "mimicking" substrate C or causing Substrate C to be produced before other steps in a cycle, the enzyme is inhibited by the excess of substrate C thus the pathway can not continue. Most such molecules are proteins that interact with enzymes.

A substrate that acts as a "positive motivator" of, or to enhance a metabolic pathway, is also known as a positive feedback regulator or a substance that has a positive feedback mechanism.

Noncompetitive inhibition is a type of enzymatic alteration that results in changes to enzymatic function without alterations to the active site. If the active site was to be blocked, this compound would function via competitive inhibition. The other terms do not describe any type of enzymatic inhibition process in the human body. Be able to distinguish the difference between competitive and noncompetitive inhibition.

The lock and key model states that the active site of an enzyme precisely fits a specific substrate. The induced fit model states that the active site of an enzyme will undergo a conformational change when binding a substrate, to improve the fit. The induced fit model accounts for the broad specificity of enzymes as the active site is not rigid, but can undergo a conformational change to better fit the substrate binding.

The lock and key model states that the active site of an enzyme precisely fits a specific substrate. The induced fit model states that the active site of an enzyme will undergo a conformational change when binding a substrate, to improve the fit.