Unit 3 Questions Bio

The first enzyme in the pathway -The final product's structure is more unlike the substrate for the first enzyme in the pathway than any other, and thus the least likely to fit the active site of enzyme 1.

A final product of a four-step metabolic pathway serves as a noncompetitive inhibitor, binding to an enzyme in this pathway and temporarily turning off the pathway. Which enzyme is most likely to be targeted by the inhibitor?

Active site. -Enzymes can be activated when the substrate binds in the active site.

A substrate binds to an enzyme at a specific site, which is referred to as a(n) .

kinase, phosphatase -To remember the correct terms, think 'kinases are kind and giving,' and phosphatases take away phosphate groups.

An enzyme that adds a phosphate group is a _________ . An enzyme that removes a phosphate group is known as a __.

Sucrose is the substrate of sucrase -The substrate is at the beginning of the arrow, and the product at the tip of the arrow. Sucrose is a substrate for the enzyme sucrase. Sucrase catalyzes a reaction where it cleaves sucrose to glucose and fructose.

Below is a depiction of the enzyme cycle for sucrase. Which of the following is true?

Increased levels of molecule C will not result in increased levels of molecule D. Note that molecule C inhibits enzyme 3, as a result, decreases the levels of Molecule D. The correct answer is the option "Molecule C inhibits Enzyme 3". Molecule C, in this image inhibits enzyme 3, which would result in decreased levels of Molecule D. Thus, the production of Molecule C impedes the production of molecule D.

For the pathway below, which of the following statements is true?

The need for high temperatures is eliminated by lowering the activation energy needed for the reaction. -Enzymes reduce the amount of energy needed to start the reaction, or lower the amount of energy needed to climb the energy hill. Therefore, the enzyme actually eliminates the need for high temperatures by lowering the activation energy.

How do enzymes eliminate the need for high temperatures to complete a reaction?

The activation energy of enzyme-catalyzed reactions are lower than the uncatalyzed reaction -The activation energy is the amount of energy needed to get the reaction started and over the energy hill to form products. Enzymes reduce the amount of energy needed to start the reaction or lower the amount of energy needed to climb the energy hill.

How does the activation energy of enzyme-catalyzed reactions compare to those of corresponding uncatalyzed reactions?

First, the substrate and the enzyme come near to each other, and then the substrate can bind to the active site. The binding of the enzyme to the substrate makes the enzyme-substrate complex. After the substrate is changed to product, but before the product's release, the enzyme is still bound to the product, which is called the enzyme-product complex. Last, the enzyme releases the product from its active site.

Identify the components for each letter in the diagram provided below: A: enzyme-substrate complex; B: product; C: enzyme; D: enzyme-product complex; E: substrate

'Formation of the enzyme-product complex'. The induced fit refers to the conformational change that the enzyme undergoes when it binds to the substrate to form the enzyme-substrate complex. Therefore, the enzymatic cycle step that occurs after the induced fit is the formation of the enzyme-product complex.

In the enzyme cycle, which step immediately follows induced fit?

'Enzyme-Product Complex'. First, the substrate and the enzyme come near to each other, and then the substrate can bind to the active site. The binding of the enzyme to the substrate makes the enzyme-substrate complex. After the substrate is changed to product, but before the product's release, the enzyme is still bound to the product, which is called the enzyme-product complex. Last, the enzyme releases the product from its active site. The enzyme is now ready to accept a new substrate molecule and repeat the same steps.

In the figure provided, what component of the enzymatic cycle does the number 3 depict?

An enzyme slightly changes its shape to accommodate specific substrates. - It is actually the enzyme that undergoes a slight change in its conformation to accommodate a substrate. Also, the substrate has bonds broken and new bonds formed in the process of being converted into product. The substrate undergoes a much greater structural change than simply changing its conformation.

Induced fit describes which of the following?

'Active site, Competitive'. Since competitive inhibitors are able to bind the active site of the enzyme in place of the substrate, competitive inhibitors often have a similar structure to the substrate. The answer choice 'allosteric site, competitive', is incorrect because the allosteric site is usually bound by inhibitors that have a different shape than the substrate.

Inhibitors that have a similar structure to a substrate of an enzyme are most likely to bind to the enzyme's _____and be a _____ inhibitor.

Decrease in temperature. -An enzyme will have the highest activity when it is under optimal conditions. In this case, the fever of 99.8 is above the optimal temperature, so lowering the temperature will increase activity.

Lipase is an enzyme with an optimum temperature of 98.6°F and an optimum pH of 7.0 in the duodenum in the human body. If a person is experiencing a fever of 99.8°F, what will increase the activity of the lipase enzyme?

'Feedback'. The keywords here are that glutathione accumulates and binds to an enzyme in the pathway to prevent synthesis. Feedback inhibition occurs when a product of a pathway turns into an inhibitor of an enzyme earlier in the pathway.

Low levels of glutathione are associated with certain types of ovarian and breast cancers. In the synthesis of glutathione, glutathione accumulates in the cell, binding to an enzyme in the pathway and temporarily preventing the synthesis of glutathione. Which type of inhibition is described by this scenario?

Increasing the amount of glycine in the diet -One way to increase glutathione levels is to increase the activity of glutathione synthetase. Glutathione synthetase activity can be increased by increasing the amount of substrate, or glycine available.

Low levels of glutathione are associated with neurological, immunological, and cardiovascular impairments. Two enzymatic reactions are involved in the synthesis of glutathione. In the second enzymatic reaction, glutathione synthetase converts glycine to glutathione. What would potentially decrease risks associated with low levels of glutathione?

'Feedback'. Feedback inhibition, a kind of reversible non-competitive inhibition, regulates the rate of many metabolic pathways. When the end product of a pathway is needed by the cell and consumed by cellular reactions, the pathway remains active. When the end product is no longer needed by the cell, the end product ceases to be consumed and begins to accumulate. Upon accumulation of the end product, it binds to the first enzyme in the pathway and initiates the inhibition of the pathway. The inhibition of the first enzyme in the pathway decreases the activity of each subsequent pathway intermediate. When the product concentration falls, there would no longer be inhibition of the first enzyme in the pathway and the pathway could resume its production of the end product again. While feedback inhibition often targets the first step in a biochemical pathway, this type of inhibition can occur for any step in the pathway. The end product will target the most important step in a biochemical pathway. The answer choice 'allosteric' is incorrect because allosteric is not a type of inhibition. Inhibition involving an inhibitor that binds to an allosteric site is called non-competitive inhibition.

One way a cell can avoid overproduction of a molecule is by using a particular type of inhibition in which this same molecule acts as an inhibitor for an enzyme in its production pathway. This type of regulation is known as __________ inhibition.

Significantly decrease -A drop in pH from 6.8 to 4.0 is a significant change in pH. Recall that the hydrogen bonds and ionic bonds that hold protein structures together can be broken by changes in pH. The disruption in protein structure due to this pH change will also significantly decrease amylase activity.

Salivary amylase, an enzyme responsible for partial digestion of carbohydrates, has optimum activity at a pH value of 6.8. What is the impact on the activity if the pH is decreased to 4.0?

True -If less energy is needed to get the reaction over the energy hill, it goes faster. Enzymes help bring all of the items needed for a reaction together in the best way, so less energy is needed for the reaction to get started. This lowers the activation energy for the reaction and speeds up the reaction so that it can go much faster than if the enzyme were not present.

Select True or False: the lower the activation energy for a reaction, the faster the reaction rate.

Enzyme-Substrate Complex -Recent studies on enzymes have shown that while the substrate and active site are somewhat complementary prior to substrate binding, many enzymes will adjust their active site conformation slightly when the substrate binds, and the Enzyme-Substrate complex is formed, to improve the fit. This is known as induced fit. Think about giving a friend a hug. Your arms are wide open as they come towards you, but only when they are next to you do you close your arms around them. Thus, their proximity causes an induced fit with your arms that is a better fit to their body shape than the initial posture of having your arms wide open. Just as you require recognition of your friend prior to embracing them, an enzyme will have some indication from the shape and properties of the molecule, whether it is the correct substrate or not. When the molecule is recognized as the substrate, the enzyme will adjust to form itself around the substrate more tightly to facilitate the reaction it catalyzes.

The concept of the induced fit applies to which part of the enzymatic cycle?

Specificity -Enzymes have a high degree of specificity. They will bind to one specific class of molecules and usually catalyze only one type of reaction.

The enzyme glucokinase only binds its substrate glucose and converts glucose into the product glucose-6-phosphate. Which property of enzymes is described by this scenario?

The molecule represented as "circle" is a substrate for the enzyme X. The correct answer is the option "star." The molecule represented as "star" is the last product of the pathway. Typically, the last product of the pathway when inhibits the enzymes of the earlier steps such as Enzyme X or Y, in this case, is known as feedback inhibition.

Using the hypothetical pathway, which downstream product could inhibit Enzyme X due to feedback inhibition?

Triangle. The molecule represented as the "triangle" is the substrate of the enzyme Y. The levels of the substrate increase when an enzyme stops functioning, whereas the levels of the product decrease. In this case, when the enzyme Y stops functioning, the levels of the molecule represented as a "triangle" increase (accumulate), whereas the levels of the molecule represented as the "heart" decrease.

Using the hypothetical pathway, which molecule would accumulate if Enzyme Y stopped working?

Star. The levels of the substrate increase when an enzyme stops functioning, whereas the levels of the product decrease. In this case, when the enzyme Z stops functioning, the levels of the molecule represented as a "heart" increase (accumulate), whereas the levels of the molecule represented as the "star" decrease.

Using the hypothetical pathway, which molecule would decrease if Enzyme Z stopped working?

'Competitive inhibitors bind reversibly to the active site and do not change the enzyme tertiary structure; non-competitive inhibitors bind reversibly or irreversibly to the allosteric site and change the enzyme tertiary structure.' Competitive inhibitors bind reversibly and non-competitive inhibitor can also bind reversibly. A competitive inhibitor is usually a molecule similar in structure to a substrate that can bind to an enzyme's active site even though the molecule is unable to react. This non-substrate molecule competes with the substrate for the active site. Enzymes can also be inhibited by substances called non-competitive inhibitors. Some non-competitive inhibitors attach to the enzyme at an allosteric site, which is a site other than the active site. Competitive inhibitors bind to the active site so that the substrate cannot, thereby inhibiting the reaction. The presence of the non-competitive inhibitor changes the shape of the enzyme enough to interfere with binding of the normal substrate. Some non-competitive inhibitors are used in the regulation of metabolic pathways, but others are poisons. Non-competitive inhibitors distort the tertiary protein structure and alter the shape of the active site. Any enzyme molecule thus affected can no longer bind its substrate, so the enzyme cannot catalyze a reaction. Although some non-competitive inhibitors bind reversibly, others bind irreversibly and permanently inactivate the enzyme molecules, thereby greatly decreasing the reaction rate. In non-competitive inhibition, increasing the substrate concentration does not increase the reaction rate as it does in the presence of a competitive inhibitor.

What are differences between competitive and non-competitive inhibitors?

The enzyme is used again. The enzyme will bind to a substrate. -After the process of changing the substrate into product is complete, the product is released from the active site of the enzyme and the enzyme is again available to bind to a new substrate molecule. The entire process of conversion of substrate to product that is facilitated by the enzyme can then be repeated.

What happens to the enzyme at the end of the cycle?

'Non-competitive.' Non-competitive inhibitors attach to the enzyme at an allosteric site, which is a site other than the active site. The presence of the non-competitive inhibitor changes the shape of the enzyme enough to interfere with binding of the normal substrate. Such inhibitors distort the tertiary protein structure and alter the shape of the active site so the enzyme can no longer bind its substrate, so the enzyme cannot catalyze a reaction. Although some non-competitive inhibitors bind reversibly, others bind irreversibly and permanently inactivate the enzyme molecules, thereby greatly decreasing the reaction rate. In non-competitive inhibition, increasing the substrate concentration does not increase the reaction rate as it does in the presence of a competitive inhibitor. The answer choice 'competitive', is incorrect because competitive inhibition involves the binding of an inhibitor to the active site and the diagram shows the inhibitor binding the enzyme at the allosteric site.

What type of inhibition is shown in the image provided below?

Non-competitive -Enzymes can be inhibited by substances called non-competitive inhibitors. Some non-competitive inhibitors attach to the enzyme at an allosteric site, which is a site other than the active site. The presence of the non-competitive inhibitor changes the shape of the enzyme enough to interfere with binding of the normal substrate. Some non-competitive inhibitors are used in the regulation of metabolic pathways, but others are poisons. Such inhibitors distort the tertiary protein structure and alter the shape of the active site. Any enzyme molecule thus affected can no longer bind its substrate, so the enzyme cannot catalyze a reaction. Although some non-competitive inhibitors bind reversibly, others bind irreversibly and permanently inactivate the enzyme molecules, thereby greatly decreasing the reaction rate. In non-competitive inhibition, increasing the substrate concentration does not increase the reaction rate as it does in the presence of a competitive inhibitor.

When an inhibitor binds reversibly to a site of the enzyme that is not the active site, what type of inhibition results?

Phosphatase

Which class of enzymes impacts protein function by temporarily removing a phosphate?

'Tertiary.' Although the primary structure of the enzyme (the amino acids connected through peptide bonds) is clearly important for establishing the particular sequence of amino acids and the identities of the amino acids in the sequence, the tertiary structure of the enzyme is the level that places the right amino acids into the right locations in 3D space so that the enzyme can act like a baseball glove and wrap itself around the correct substrate. A baseball glove is designed to catch baseballs, not other types of balls, so it is specific for baseballs. In this way, the enzyme is designed to catch one type of substrate, based on the locations of the R groups of the amino acids in 3D space (tertiary structure), when it wraps up just the right way around the substrate in the active site.

Which level of protein structure provides enzymes with their substrate specificity?

'Turn the enzyme "on" or "off". The amino acid sequence, or protein primary structure, is built from the 20 naturally-occurring amino acids. These structures do not have phosphate groups as part of their structure. Therefore, phosphorylation/dephosphorylation of a protein does not change the protein's primary structure. It is still made of the same amino acids in the same sequence. Phosphate groups are added/removed by phosphorylation/dephosphorylation. Adding or removing a phosphate group is like 'flipping a switch' on the enzyme's activity. It is a way of modulating, or regulating, enzyme activity.

Which of the following are possible effect(s) that phosphorylation/dephosphorylation can have on the activity of an enzyme?

They can bind multiple substrates. Enzymes are called catalysts, which means they help speed up a reaction, and they are not used up by the reaction. They have the right amino acids in the right places to help change the substrate into product, and they still have these amino acids when the reaction is over. All of these factors assist the enzyme in lowering the activation energy, which means that less energy is required to start the reaction (or get it over the energy hill) than when the enzyme is not present. Therefore, when the enzyme lowers the activation energy this results in a faster reaction.

Which of the following characteristic of an enzyme is responsible for speeding up the reaction?

Heat can disrupt hydrophobic interactions at the center of the protein. pH can disrupt ionic interactions, and hydrogen bonds. Reducing agents can break disulfide bonds.

Which of the following factors can affect the protein folding and activity of an enzyme?

'In the presence of an enzyme- dotted line.' The path with the bold line represents the one with the higher amount of energy needed to get the reaction started and over the energy hill to form products, or a higher activation energy. For the path represented by the dotted line, the reactants need less energy to climb the hill, or a lower activation energy, to get the reaction over the hill to form products.

Which one of the following paths requires less activation energy to convert the reactants into the products? The options include the path indicated by a bold line, and the path indicated by a dotted line.

'Enzymes are reusable'. In the final step of the enzymatic cycle, the product is released and the enzyme is able to bind to a new substrate and begin the cycle again. The enzyme-substrate and enzyme-product complex demonstrate the specificity of the enzyme to bind one specific substrate and catalyze one specific reaction.

Which property of enzymes is illustrated in the final step of the enzymatic cycle?

Competitive -Competitive inhibitors compete with the substrate to bind to the active site of the enzyme.

Which type of inhibition occurs when a particular drug binds to the active site of an enzyme?

Competitive inhibitor -A competitive inhibitor is usually a molecule similar in structure to a substrate that can bind to an enzyme's active site even though the molecule is unable to react. This non-substrate molecule competes with the substrate for the active site. When the inhibitor binds to an active site, it prevents the substrate from binding and thereby inhibits the reaction.

You are in charge of designing a drug that inhibits the activity of a specific enzyme. An important criteria for the drug selection is to ensure that the drug directly competes with the original substrate by binding to the active site of the enzyme. Which of the following kind of inhibitor would be an ideal choice?