Enzymes

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1. Enzymes Overview

Here’s an experiment you should try at home.

Take any starchy food (a cracker, a piece of white bread, or a spoonful of mashed potatoes). Place it in your mouth and chew for a long time—an uncomfortably long time. Close your eyes, and focus on your taste buds. After a while, the starchy taste will be accompanied by the taste of sugar. Where did that sugar come from?

08_starch, amylase, maltoseStarch is a polymer of glucose. In your saliva, you have an enzyme called amylase. When you eat any food with starch, amylase breaks the starch into maltose, a disaccharide.

Enzymes are the substances that control the chemical reactions that occur in all living things – bacterial cells, daffodils, lizards, and, people. It’s hard to overstate their importance. Let’s see how they work.

2. Enzymes and Activation Energy

Enzymes are protein catalysts that speed up the chemical reactions in living things. Catalysts are substances that participate in a chemical reaction, without being changed or used up by the reaction. However much enzyme is present at the start of a reaction is how much there will be at the end.

Enzymes work by lowering the activation energy of a reaction. To understand this, think about a reactant (the chemical or chemicals that go into a chemical reaction) as a rock high on a hill (see “A” in the diagram below). Similarly, think of a product (the chemical or chemicals that come out of a chemical reaction) as that same rock, lower down on the same hill (as shown by letter “B”).

activation energy 1

The rock’s energy can only be released if you give the rock a push. That push is represented by “C.”

The push needed to start a reaction is activation energy. And one of the key roles of enzymes in any biological system is to lower the activation energy required to bring about the chemical reactions that sustain life.

Here’s how an enzyme would change the picture above.

activation energy 2(with enzyme)In this image, the rock still has the same amount of energy at the start (A) and at the end (B). The only thing that’s changed is the addition of the enzyme (attached to the rock up at “A”) Notice that the height of “D”, which represents the energy of the push you need to get the rock rolling down the hill, is now lower than the push that you needed before addition of the enzyme (“C” in the previous diagram). That’s what enzymes do: they lower activation energy.

That might not sound important, but it is. Think of how much heat is released when a car burns gasoline. That level of heat is typical of the activation energy required to make chemical reactions happen in non-living systems (like a car). In living organisms, the temperatures are always much lower. The only reason why they happen is because enzymes are moving those reactions along. Your body has thousands of enzymes, at work every second, controlling the reactions that keep you going.

To make sure you understand this, label the diagram below.

[qwiz style = “width: 640px; border: 3px solid black; “qrecord_id=”dank-enzyme_quiz1”]
[h] Enzymes and Activation energy

[i]

[q labels = “top”]

 

[l]activation energy with an enzyme

[fx] No. Please try again.

[f*] Good!

[l]activation energy without an enzyme

[fx] No. Please try again.

[f*] Excellent!

[l]overall energy released by the reaction

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]entire reaction with an enzyme

[fx] No. Please try again.

[f*] Good!

[l]entire reaction without an enzyme

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]product

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]reactant

[fx] No. Please try again.

[f*] Correct!

[x]

[restart]

[/qwiz]

3. Enzymes are highly specific

The thing that an enzyme acts upon is called a substrate. As a general rule, each enzyme interacts with only one substrate. For example, amylase, the enzyme discussed above, can break down the polysaccharide starch into the disaccharide maltose. Amylase won’t break down protein. It won’t break down fat. It won’t even break down other polysaccharides, such as cellulose (plant fiber).

enzymesSubstrateIn the image at left, you can see the interaction between an enzyme and its substrate. The enzyme (1) binds with the substrate (3) at a specific region of the enzyme called the active site (2). The fit between an enzyme’s active site and the enzyme’s substrate is as specific as the fit between a lock and a key. In the same way as a lock will respond to only one key, the enzyme can only act upon substrates that fit into its active site.

To visualize enzymes in action, let’s go back to the digestion of starch. Imagine that you’re eating a potato (which is mostly starch). As you chew on the potato, you expose the starch to saliva, which contains the enzyme amylase. If the amylase bumps into the starch in the right orientation, then the starch will bind with amylase, forming an enzyme substrate complex (shown above at 4). The enzyme will break to bonds holding the starch together, and release its product (shown at 5). Note that the enzyme (1) is unchanged, and ready to break down more substrate.

An extension of the lock and key idea is the notion of “induced fit.” When an enzyme binds with a substrate it actually changes its shape. You can see this illustrated below. Notice how the shape of the enzyme (represented in gray) slightly changes after it binds with its substrate.

06_induced fit

Induced fit, from wikipedia

 

Keep in mind that while all of my examples above show enzymes breaking things apart, enzymes are also used to build the molecules that your body is made of.

[qwiz style = “width: 640px; border: 3px solid black; “qrecord_id=”dank-enzyme-quiz2”]
[h] Enzymes and substrates: interactive diagrams

[q labels = “top”]

 

[l]active site

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]enzyme

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]enzyme-substrate complex

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]product

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]substrate

[fx] No. Please try again.

[f*] Excellent!

[q labels = “top”]

 

[l]product

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]substrate

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]enzyme-substrate complex

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]enzyme

[fx] No. Please try again.

[f*] Excellent!

[l]active site

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]active site modified by induced fit

[fx] No. Please try again.

[f*] Good!

[l]enzyme still bound to product

[fx] No, that’s not correct. Please try again.

[f*] Good!

[x]

[restart]

[/qwiz]

4. Enzymes and their environment

Most enzymes have specific environmental conditions in which they work best. Working best means catalyzing more reactions in a given time. The best conditions are called “optimal.”

09_Denatured-enzyme

denaturation, from http://sciencelearn.org.nz/

The reason why this is so is that enzymes only work if they fit with their substrate: their shape, especially, at the active site, is all-important. Because enzymes are proteins, their shape is based on many interactions between the amino acids that make up the enzyme. If you change an enzyme’s environment, you’ll change its shape, which will decrease or block its ability to interact with its substrate. This process of changing an enzyme’s shape in a way that reduces its activity is called denaturation. And an enzyme that has lost its activity in this way is said to be denatured.

enzymesPh

Enzymes and pH

Here’s graph that shows how changing pH (how acidic or basic a solution is) can change enzyme activity and cause denaturation. Here’s how to understand the graph.

The Y axis in this graph is level of enzyme activity. The higher on the Y axis, the more the enzyme is interacting with its substrate and changing it into product. Notice that the highest level is at number 2 (which represents some number on the pH scale). In other words, whatever pH is below number 2 is the pH optimum (the best pH for this enzyme).

If you lower the pH below the optimum (making the solution more acidic), the enzyme’s activity falls. At number 1, the activity is very low, because the solution is too acidic. That acidity has denatured the enzyme. Similarly, if you increase the pH above the optimum, the activity level also falls. That’s what is happening at number 3.

enzymesTemperatureEnzymes are also affected by temperature. The impact of temperature usually fits the graph shown at left. In very cold temperatures, enzymes won’t catalyze much. That’s because cold means that the molecules aren’t moving. There’s very little chance that the enzyme will bump into its substrate and be able to catalyze its reaction. This low level of activity due to cold is shown at number 1.

As temperatures increase, molecules start to move faster. Collisions between enzyme and substrate increase in frequency. The rising line between 1 and 2 represents this increase in activity.

At number 2, the enzyme is operating at its optimal rate, converting as much substrate as it can into product. However, if the temperature rises too much, the enzyme gets denatured by the heat (much like cooking meat changes its character, too much heat cooks the enzyme). At that point, the enzyme can’t bind with its substrate, and its activity falls to zero.

Denaturation of enzymes is closely related to the body’s need for homeostasis (your body’s need to maintain consistent internal conditions). Your kidneys, for example, are constantly adjusting the pH of your blood. Your skin and circulatory system work to keep your temperature constant. It’s all to keep your enzymes operating at an optimal level.

5. Enzymes Flashcards

The flashcards that follow will help you to master the following key terms related to enzymes. To see a definition, just hover your cursor over any of the terms.

  1. Catalyst
  2. Enzyme
  3. Chemical Reaction
  4. Activation energy
  5. Reactant
  6. Product
  7. Substrate
  8. Active Site
  9. Enzyme-Substrate Complex
  10. Lock and Key Model
  11. Induced Fit Model
  12. Optimum
  13. Denature

[qdeck style=”width: 528px; border: 2px solid black; ” qrecord_id=”dank-enzyme-deck1″]

[h] Flashcards: Enzymes

[i] If you haven’t used a set of flashcards on sciencemusicvideos before, here’s what you need to know.

  • Click ‘Check Answer’ to see the answer to each card.
  • If you know it, click ‘Got it.”
  • If you don’t know it as well as you’d like, click ‘Need more practice,’ and that card will go to the bottom of the deck so you can practice it again.
  • ‘Shuffle’ lets you shuffle the deck.

[!]Card 1++++++++++++++++++[/!]

[q]A process in which substances interact in a way that changes ionic or covalent bonds is called a _________ __________ [textentry]

[a]A process in which substances interact in a way that changes ionic or covalent bonds is called a chemical reaction.

[!]Card 2++++++++++++++++++[/!]

[q]In a chemical reaction, the substances that participate in the reaction are called [textentry]

[a]In a chemical reaction, the substances that participate in the reaction are called reactants.

[!]Card 3++++++++++++++++++[/!]

[q]In a chemical reaction, the substances that result from the reaction are called [textentry]

[a]In a chemical reaction, the substances that result from the reaction are called products.

[!]Card 4++++++++++++++++++[/!]

[q]A substance that speeds up the rate of a chemical reaction is a(n)[textentry]

[a]A substance that speeds up the rate of a chemical reaction is a catalyst.

[!]Card 5++++++++++++++++++[/!]

[q]The protein catalysts that speed up chemical reactions in cells are called [textentry]

[a]The protein catalysts that speed up chemical reactions in cells are called enzymes.

[!] CARD 6+++++++++++++++++++++++++++++++++[/!]

[q]The energy required to get a chemical reaction started is known as __________ energy.
[textentry]
[a]The energy required to get a chemical reaction started is known as activation energy.

[!] CARD 7+++++++++++++++++++++++++++++++++[/!]

[q]The substance an enzyme acts upon is called the [textentry]
[a]The substance an enzyme acts upon is called the substrate

[!] CARD 8+++++++++++++++++++++++++++++++++[/!]

[q]The specific area on an enzyme where it binds with its substrate is called its _______ _______ [textentry]
[a]The specific area on an enzyme where it binds with its substrate is called its active site

[!] CARD 9+++++++++++++++++++++++++++++++++[/!]

[q]At the moment when an enzyme binds with its substrate at the active site, it forms an ___________-_____________ __________. [textentry]
[a]At the moment when an enzyme binds with its substrate at the active site, it forms an enzyme-substrate complex.

[!] CARD 10+++++++++++++++++++++++++++++++++[/!]

[q]The idea that a substrate usually has only one enzyme that it can interact with is captured in the __________ ____ ____________ model  [textentry]
[a]The idea that a substrate usually has only one enzyme that it can interact is captured in the lock and key model

[!] CARD 11+++++++++++++++++++++++++++++++++[/!]

[q]The idea that in an enzyme-substrate complex, an enzyme will bend in a way that stresses the bonds of the substrate is called the _________-_________ model of enzyme action.  [textentry]
[a]The idea that in an enzyme-substrate complex, an enzyme will bend in a way that stresses the bonds of the substrate is called the induced-fit model of enzyme action.

[!] CARD 12+++++++++++++++++++++++++++++++++[/!]

[q]Every enzyme has a pH or temperature ___________ at which it functions best. [textentry]
[a]Every enzyme has a pH or temperature optimum at which it functions best.

[!] CARD 13+++++++++++++++++++++++++++++++++[/!]

[q]When heat, pH changes, or other factors in an enzyme’s environment cause it to change shape, the enzyme loses its ability to function. At that point, the enzyme is said to be [textentry]
[a]When heat, pH changes, or other factors in an enzyme’s environment cause it to change shape, the enzyme loses its ability to function. At that point, the enzyme is said to be denatured.

[x]

If you want more practice, please press the restart button below. Otherwise, follow the links below.
[restart]
[/qdeck]

6. An enzymes quiz

[qwiz style = “width: 640px; border: 3px solid black; ” qrecord_id=”dank-test1″]
[h] Quiz: Enzymes
[i] Here’s how the quiz works:

  • Each question is multiple choice, but the entire quiz is like a series of flashcards.
  • If you get the question right, it comes off the deck.
  • If you get the question wrong, it goes to the bottom of the deck, so you can try it again.

[!] Question 1++++++++++++++[/!]

[q] A substance produced by an organism that acts as a catalyst to bring about a specific biochemical reaction is a

[c] biocatalyst

[c] promoter

[c] chemoenhancer

[c*] enzyme

[f] No. The term that’s correct practically means ‘life catalyst,’ but there’s a better term on this list. Try something that rhymes with ‘time.’

[f] No. “Promoters” sounds logical, but it’s not the best term. Try something that rhymes with ‘time.’

[f] No. The term that you’re looking for is indeed something that enhances the rate of chemical reactions, so you made a logical choice. Try something that rhymes with ‘time.’

[f] Excellent. The catalysts used by every organism to bring about the chemical reactions needed to sustain life are enzymes.

[!] Question 1a++++++++++++++[/!]

[q] Use the choices below to label the enzyme, the substrate, and the enzyme-substrate complex.

[l]enzyme

[fx] No, that’s not correct.  Please try again.

[f*] Correct!

[l]enzyme-substrate complex

[fx] No, that’s not correct.  Please try again.

[f*] Correct!

[l]product

[fx] No.  Please try again.

[f*] Great!

[l]substrate

[!] Question 2++++++++++++++[/!]

[fx] No, that’s not correct.  Please try again.

[f*] Good!

[q] Biochemically, enzymes are almost always

[c] carbohydrates

[c] lipids

[c*] proteins

[f] That’s not correct. Think of the macromolecule with the most complex shape and structure, and you’ll have the answer.

[f] No. Lipids are used for energy storage, insulation, and waterproofing, but they don’t act as enzymes.  Think of the macromolecule with the most complex shape and structure, and you’ll have the answer.

[f] Exactly. Almost all enzymes are proteins.

[!] Question 3++++++++++++++[/!]

[q] The thing an enzyme acts upon is called a (n)

[c] product

[c] target

[c] reactant

[c*] substrate

[f] No. An enzyme catalyzes a reaction, and a product is what results.

[f] No. While ‘target’ is a logical choice, there’s a special word for the substance  that an enzyme acts upon.

[f] No. That’s a very logical and general choice, but there’s a more specific answer.

[f] Exactly. Enzymes act upon substrates.

[!] Question 4++++++++++++++[/!]

[q] From the choices below, choose the best match: Enzymes fit with their substrates as a _______________ fits with a __________________.

[c] as a wheel fits with a road.

[c] as a harmony fits with a song.

[c] as a flower fits with a bouquet.

[c] as dog fits with a cat.

[c*] as lock fits with key

[f] No. Many different kinds of wheels fit with many different kinds of roads. The key ideas here are specificity and complementary shape.

[f] No. Many kinds of harmonies can work with any one particular song (based on the artist’s preference). The key ideas here are specificity and complementary shape.

[f] No. Many different types of flowers can work in a bouquet (based on the florist’s preference). The key ideas here are specificity and complementary shape.

[f] No! Dogs don’t fit with cats (at least, not usually). The key ideas here are specificity and complementary shape.

[f] Right. In the same way as only one specially cut key fits into a lock, there is usually a one to one relationship between enzyme and substrate, and that relationship is based on complementary shape.

[!] Question 5++++++++++++++[/!]

[q] The ‘lock and key’ model of enzyme action has more recently been supplemented by the notion that an enzyme will actually change its shape to closely bind with and modify its substrate. This model of enzyme action is called

[c] modified binding

[c] substrate approximation

[c] adaptive conformation

[c*] induced fit

[c] enzymatic adaptation

[f] No. Your choice is a sensible description, but that’s not the name of this model of enzyme-substrate interaction. The correct name of the model has to do with an improved fit coming about between enzyme and substrate. Think about that (which, by the way, includes a huge hint) the next time you see this question.

[f] No. Your choice is a sensible description, but that’s not the name of this model of enzyme-substrate interaction. The correct name of the model has to do with an improved fit coming about between enzyme and substrate. Think about that (which, by the way, includes a huge hint) the next time you see this question.

[f] No. Your choice is a sensible description, but that’s not the name of this model of enzyme-substrate interaction. The correct name of the model has to do with an improved fit coming about between enzyme and substrate. Think about that (which, by the way, includes a huge hint) the next time you see this question.

[f] Exactly. The idea here is that the binding of enzyme and substrate induces (causes) a modification in the shape of the enzyme’s active site, which improves its binding with the substrate and assists in in converting the substrate into the product.

[f] No. Your choice is a sensible description, but that’s not the name of this model of enzyme-substrate interaction. The correct name of the model has to do with an improved fit coming about between enzyme and substrate. Think about that (which, by the way, includes a huge hint) the next time you see this question.

[!] Question 6++++++++++++++[/!]

[q] An enzyme binds its substrate at its

[c] reaction site

[c] binding site

[c*] active site

[f] No. ‘Reaction site’ is a logical choice, but not the one that’s used. Because an enzyme is a three dimensional object, only a small part of its surface is going to actively touch the substrate and interact with it in a way that catalyzes the reaction. See if you can find the huge hint in the previous sentence, and use it to answer this correctly next time.

[f] No. The enzyme will bind with the substrate, but there’s a specific word for this binding area. Because an enzyme is a three dimensional object, only a small part of its surface is going to actively touch the substrate and interact with it in a way that catalyzes the reaction. See if you can find the huge hint in the previous sentence, and use it to answer this correctly next time.

[f] Terrific. The enzyme binds with its substrate at its active site.

[!] Question 7++++++++++++++[/!]

[q] The relationship in shape between enzyme and substrate is best described as

[c*] complementary

[c] contrasting

[c] a mirror image

[c] harmonious

[f] Exactly. The shape of an enzyme fits with the shape of a substrate in a complementary way, like two pieces of a puzzle.

[f] No. Try to find a word that conveys the idea that enzymes fit with their substrates like pieces of a puzzle fit together.

[f] No. The shape of an enzyme and a substrate fit together, but they’re not mirror images. See if you can find a word that conveys this ‘fitting together.’

[f] No, but that’s an interesting choice. Sounds that fit together are harmonious. But there’s a choice that better conveys the matching fit between enzyme and substrate.

[!] Question 8++++++++++++++[/!]

[q] If you added 4 milligrams of an enzyme to a reaction, and were able to recover all of the available enzyme at the reaction’s end, how much enzyme should you be able to recover?

[c*] 4 miligrams

[c] 2 milligrams

[c] 8 milligrams

[c] 0 milligrams

[f] That’s right. Enzymes are catalysts that are not consumed in the reactions they participate in. Therefore, you should be able to recover at the end all of the enzyme that you had at the start.

[f] No. Enzymes are catalysts that are not consumed in the reactions they participate in. Therefore, you should be able to recover at the end all of the enzyme that you had at the start.

[f] No. Enzymes are catalysts that are not consumed in the reactions they participate in. Therefore, you should be able to recover at the end all of the enzyme that you had at the start.

[f] No. Enzymes are catalysts that are not consumed in the reactions they participate in. Therefore, you should be able to recover at the end all of the enzyme that you had at the start.

[!] Question 9++++++++++++++[/!]

[q] In the diagram below that shows the progress of two chemical reactions, which number shows the pathway of the reaction when it’s catalyzed by an enzyme?

[c] 1

[c*] 2

[c] 3

[c] 4

[f] No. Number 1 shows the progress of a non-enzyme catalyzed reaction. You can tell because the activation energy required to get the reaction going (shown at 4) is much higher than the activation energy required with an enzyme (shown at 3). Keep that in mind when you see this question again.

[f] Excellent! Number 2 shows the progress of an enzyme catalyzed reaction. You can tell because the activation energy required to get the reaction going (shown at 3) is much lower than the activation energy would be without an enzyme (shown at 4). Lowering activation energy is exactly what enzymes do.

[f] No, but you’re on the right track. Number 3 is showing the reduced amount of energy required to start a reaction (activation energy) when an enzyme is present (compare 3 to 4). Keep that in mind when you see this question again.

[f] No. Number 4 shows the activation energy required when an enzyme isn’t catalyzing a reaction. The main effect of an enzyme is to lower activation energy (compare number 4 to number 3). Keep that in mind when you see this question again.

[!] Question 10++++++++++++++[/!]

[q] In the diagram below that shows the progress of two chemical reactions, which number shows the activation energy of the enzyme catalyzed reaction.

[c] 1

[c] 2

[c*] 3

[c] 4

[f] No. Number 1 shows the progress of a non-enzyme catalyzed reaction. You can tell because the activation energy required to get the reaction going (shown at 4) is so high. Now, knowing what number 4 is, see if you can figure out the answer to this question when you see it again.

[f] No. Number 2 shows the progress of an enzyme catalyzed reaction. You can tell because the activation energy required to get the reaction going is much lower than the activation energy would be without an enzyme (shown at 4). With that hint, see if you can get this question right when you see it again.

[f] Fantastic. Number 3 is showing the reduced amount of energy required to start a reaction (activation energy) when an enzyme is present (compare 3 to 4).

[f] No. Number 4 shows the activation energy required when an enzyme isn’t catalyzing a reaction. The main effect of an enzyme is to lower activation energy. Keep that in mind when you see this question again, and you should be able to figure it out.

[!] Question 11++++++++++++++[/!]

[q] In the graph below, which line would represent the reaction catalyzed by an enzyme?

[c*] 1

[c] 2

[f] Exactly! Enzymes speed up reaction rates. That’s why the slope of line one is steeper: more product is being converted to substrate over time.

[f] No. The key idea of this graph is that enzymes make reactions go faster. Line number one has a less steep slope than line number 2, indicating that the rate of product creation is lower. Keep that in mind when you see this question again.

[!] Question 12++++++++++++++[/!]

[q] In the diagram below, the enzyme-substrate complex is represented by

[c] 1

[c] 2

[c] 3

[c*] 4

[c] 5

[f] No. Number 1 represents the enzyme. See if you can find a part of the diagram that shows the enzyme and the substrate coming together to form an enzyme-substrate complex.

[f] No. Number 2 represents the active site, which is where the enzyme will bind with its substrate. See if you can find a part of the diagram that shows the enzyme and the substrate coming together to form an enzyme-substrate complex.

[f] No. Number 3 represents the substrate. See if you can find a part of the diagram that shows the enzyme and the substrate coming together to form an enzyme-substrate complex.

[f] Fantastic! Number 4 represents the enzyme-substrate complex.

[f] No. Number 5 represents the products of the reaction. See if you can find a part of the diagram that shows the enzyme and the substrate coming together to form an enzyme-substrate complex.

[!] Question 13++++++++++++++[/!]

[q] In the diagram below, the active site is represented by

[c] 1

[c*] 2

[c] 3

[c] 4

[c] 5

[f] No. Number 1 represents the entire enzyme. See if you can find a part of the diagram that shows where the enzyme will bind with the substrate.

[f] Awesome! Number 2 represents the active site, which is where the enzyme will bind with its substrate.

[f] No. Number 3 represents the substrate. See if you can find a part of the diagram that shows where the enzyme will bind with the substrate.

[f] No. Number 4 represents the enzyme-substrate complex. See if you can find a part of the diagram that shows where the enzyme will bind with the substrate.

[f] No. Number 5 represents the products of the reaction. See if you can find a part of the diagram that shows where the enzyme will bind with its substrate.

[!] Question 14++++++++++++++[/!]

[q] In the diagram below, the enzyme is represented by

[c*] 1

[c] 2

[c] 3

[c] 4

[c] 5

[f] Yes! Number 1 represents the entire enzyme.

[f] No. Number 2 represents the active site, which is where the enzyme will bind with its substrate. See if you can find the number which represents the entire enzyme.

[f] No. Number 3 represents the substrate, which is about to bind with the enzyme. See if you can find the number which represents the enzyme.

[f] No. Number 4 represents the enzyme-substrate complex, which includes both enzyme and substrate, at a moment when the two are temporarily bonded together as the enzyme catalyzes its reaction. See if you can find the number which represents just the enzyme.

[f] No. Number 5 represents the products of the reaction. The products, you can see, were formerly the substrate, which is shown in the same color. See if you can identify the enzyme, which is the thing that changed the substrate into the products.

[!] Question 15++++++++++++++[/!]

[q] In the diagram below, the product of the reaction is represented by

[c] 1

[c] 2

[c] 3

[c] 4

[c*] 5

[f] No. Number 1 represents the  enzyme. See if you can identify the product that the enzyme creates after interacting with the substrate, which is shown at number 3.

[f] No. Number 2 represents the active site, which is where the enzyme will bind with its substrate. See if you can identify the product that the enzyme creates after interacting with the substrate, which is shown at number 3.

[f] No. Number 3 represents the substrate, which is about to bind with the enzyme. See if you can identify the product of the reaction, which is shown in the same color as the substrate, and which appears at the end of the reaction.

[f] No. Number 4 represents the enzyme-substrate complex, which includes both enzyme and substrate. This complex forms as the two are temporarily bonded together as the enzyme catalyzes the reaction. See if you can identify the product of the reaction, which is shown in the same color as the substrate, and which appears at the end of the reaction.

[f] Excellent.  Number 5 represents the products of the reaction. The products, you can see, were formerly the substrate, which is shown in the same color.

[!] Question 16++++++++++++++[/!]

[q] In the diagram below, the substrate of the reaction is represented by

[c] 1

[c] 2

[c*] 3

[c] 4

[c] 5

[f] No. Number 1 represents the  enzyme. See if you can identify the substrate, which is what the enzyme interacts with.

[f] No. Number 2 represents the active site, which is where the enzyme will bind with its substrate. See if you can identify the substrate, which is what the enzyme interacts with.

[f] Excellent. Number 3 represents the substrate, which is about to bind with the enzyme.

[f] No. Number 4 represents the enzyme-substrate complex, which includes both enzyme and substrate. See if you can identify just the substrate, which is what the enzyme interacts with.

[f] No.  Number 5 represents the products of the reaction. The products, you can see, were formerly the substrate, which is shown in the same color.  See if you can identify just the substrate, which is what the enzyme interacts with.

[!] Question 17++++++++++++++[/!]

[q] What’s the name for the process where environmental changes (in temperature or pH, for example) cause an enzyme’s shape to change, destroying its function?

[c] decatalyzation

[c] deformation

[c*] denaturation

[c] deenzymification.

[f] No. You probably recognized ‘catalyst’ in this choice, but that is not the answer. Next time you see this question, think of the fact that environmental factors have changed the nature of the enzyme. One word in the previous sentence essentially tells you the answer.

[f] No. The environmental changes have, indeed, deformed the enzyme, but there’s a better and more widely used term. Next time you see this question, think of the fact that environmental factors have changed the nature of the enzyme. One word in the previous sentence essentially tells you the answer.

[f] Exactly. Changing an enzyme’s shape destroys its ability to catalyze a reaction. This change is called denaturation. The verb is ‘to denature.’

[f] No. You probably recognized ‘enzyme’ in this choice, but this is not the correct term (not is it a real word). Next time you see this question, think of the fact that environmental factors have changed the nature of the enzyme. One word in the previous sentence essentially tells you the answer.

[!] Question 18++++++++++++++[/!]

[q] Enzymes have a pH optimum: a pH at which they’ll have maximum activity. In the diagram below, the optimum is shown at

[c] 1

[c*] 2

[c] 3

[f] No. The optimum is where the enzyme’s activity will be the highest. Enzyme activity is shown on the Y axis, with higher meaning more activity. Next time you see this question, look for the high point on the graph.

[f] Nice job!. Number 2 represents enzyme’s pH optimum, the pH where the enzyme’s activity will be at its highest rate.

[f] No. The optimum is where the enzyme’s activity will be the highest. Enzyme activity is shown on the Y axis, with higher meaning more activity. Next time you see this question, look for the high point on the graph.

[!] Question 19++++++++++++++[/!]

[q] Enzymes have a pH optimum: a pH at which they’ll have maximum activity. In the diagram below, which number shows where the enzyme has lost its activity because of conditions that are too acidic?

[c*] 1

[c] 2

[c] 3

[f] Exactly. In the pH scale, lower means more acidic. At point 1, activity is low (shown on the Y axis) and the pH is below the optimum pH, which means more acidic (far to the left on the X axis).

[f] No. Number 2 represents enzyme’s pH optimum, the pH where the enzyme’s activity will be at its highest rate.  Next time, look for an number that shows lower activity (lower on the Y axis), and lower pH (to the left on the X axis).

[f] No. At number 3 the activity is low (as shown by the position on the Y axis), but the position on the X axis indicates a higher pH, which would mean more basic. Next time, choose a more acidic point on the graph (but with the same level of activity).

[!] Question 20++++++++++++++[/!]

[q] In the diagram below, which number shows the optimum temperature for this enzyme?

[c] 1

[c*] 2

[c] 3

[f] Enzyme activity is shown on the Y axis. At point number 1, enzyme activity is very low. At the optimum temperature, activity would be highest.

[f] Excellent: the optimum temperature is the one where activity would be the highest on the Y axis, as shown at point 2.

[f] Enzyme activity is shown on the Y axis. At point number 3, enzyme activity is very low. At the optimum temperature, activity would be highest.

[!] Question 21++++++++++++++[/!]

[q] In the diagram below, which number shows point where denaturation has caused enzyme activity to fall.

[c] 1

[c] 2

[c*] 3

[f] No. Enzyme activity is shown on the Y axis. At point number 1, enzyme activity is very low. But this is probably because the temperature is low, which means that there’s very little kinetic energy in the system. With so little energy, the reaction is proceeding slowly, even with an enzyme present. Denaturation usually comes about by excessive temperature. Think of that the next time you see this question.

[f] No. Enzyme activity is shown on the Y axis. At point number 2, activity is very high, which means that the enzyme is probably in good shape (not denatured).  Denaturation usually comes about by excessive temperature. Think of that next time you see this question.

[f] Excellent. At point 3, temperature is high (as shown on the X axis), and activity is low (as shown on the Y axis). Excessive heat can cause enzymes to denature, destroying their activity.

[!] Question 22++++++++++++++[/!]

[q] Which of the following environmental changes would be LEAST LIKELY to cause enzymes to denature.

[c*] too much substrate.

[c] too much heat

[c] too much salt.

[c] a pH way above the optimum.

[f] That’s right. If there’s too much substrate, the enzyme will go ahead and start converting the substrate into product. It’s changes in conditions like the pH, temperatures, and/or ionic concentration (too many charged particles) that cause enzymes to denature. The reason why is that enzymes are proteins, and proteins have a 3-D shape that’s determined forces like hydrogen bonds and ionic bonds which can easily be disrupted by chemical or physical changes in the enzyme’s environment.

[f] No. Heat is a major factor behind enzyme denaturation. The reason why is that enzymes are proteins, and proteins have a 3-D shape that’s determined, in part, by weak forces like hydrogen bonds which can easily be disrupted. Too much heat can change an enzyme’s shape, denaturing it. Next time, choose another answer.

[f] No. Enzymes are proteins, and proteins have a 3-D shape that’s determined by interacting forces between the amino acids that make up the protein. One of those interactions is ionic attraction. Add too much salt to an enzymes’s environment, and the ions in the salt will disrupt the ionic bonds that help determine the enzyme’s shape. In the case of an enzyme, changed shape leads to denaturation. Next time, choose another answer.

[f] No. Enzymes are proteins, and proteins have a 3-D shape that’s determined by interacting forces between the amino acids that make up the protein. Those forces include hydrogen bonds and ionic attraction. Changes in pH can disrupt the interactions between the amino acids, changing the enzyme’s shape, and thereby altering its function. In the case of an enzyme, changed shape leads to denaturation. Next time, choose another answer.

[!] Question 23++++++++++++++[/!]

[q] Beano is a commercial enzyme product that claims to reduce flatulence (farting) by providing enzymes that break down certain carbohydrates that people sometimes have difficulty digesting. The product information tells you not to cook Beano with your food, but to ingest the enzyme tablets just before eating. Why can’t you cook Beano with your food?

[c] The enzymes in Beano, mixed with your food, would break all of the food down, leaving you with a soggy mush.

[c] The enzymes in Beano taste horrible, and would ruin any dish that you cooked.

[c] Beano needs an acidic environment, and needs to get down to your stomach before the food gets there.

[c*]  Beano contains enzymes. Like most enzymes, it will be denatured by high temperatures. Therefore cooking would ruin Beano’s activity.

[f] No. The problem relates to the effect that heat has on enzymes. If you cooked Beano with your food, you’d be exposing it to fairly extreme temperatures. Keep that in mind the next time you see this question.

[f] No. without being too personal, I’ve tried Beano myself. It has a slightly salty taste, a bit powdery, but nothing that would ruin a dish. The problem relates to the effect that heat has on enzymes. Keep that in mind the next time you see this question.

[f] No, but that’s reasonable guess, and you were probably thinking of the fact that the fluid in the stomach is highly acidic. But most digestion (and gas production) actually happens in the intestines, which is slightly basic in terms of pH. The key to this question has to do with cooking Beano. Heat has a problematic effect upon enzymes. Keep that in mind the next time you see this question.

[f] That’s exactly right. If you cooked Beano, you’d denature its enzymes, making it ineffective at helping you break down the carbohydrates that cause gas.

[!] Question 25++++++++++++++[/!]

[q] Which of the following diseases is NOT caused by an inherited enzyme deficiency (the body’s inability to produce an enzyme)?

[c] Tay-sachs disease

[c] Gaucher’s disease

[c] Phenylketonuria (PKU disease)

[c] Galactosemia

[c*] Sickle cell Anemia

[f] No. Tay-Sachs is an inherited disorder involving the body’s inability to produce an enzyme called Hexosaminidase A. Without this enzyme, a fatty substance builds up in the brain, causing a variety of neurological symptoms, and, eventually, death. Next time, choose a different condition.

[f] No.Gaucher’s disease is caused by the body’s inability to produce an enzyme called glucocerebrosidase. Without this enzyme, a fatty acid accumulates in white blood cells, causing damage to the spleen and liver, and other organs as well.  Some forms of this disease can be treated by enzyme replacement therapy. Next time, choose a different condition.

[f] No. PKU disease is caused by the body’s inability to produce an enzyme that breaks down the amino acid phenylalanine, which consequently can accumulate to toxic levels. The disease can be treated through a diet that removes the enzymes’s substrate–phenylalanine. Next time, choose a different condition.

[f] No. Galactosemia is caused by the body’s inability to produce the enzyme that breaks down galactose, a monosaccharide that results from digestion of milk. According to the Genetics Home Reference, ‘If infants with classic galactosemia are not treated promptly with a low-galactose diet, life-threatening complications appear within a few days after birth. Affected infants typically develop feeding difficulties, a lack of energy (lethargy), a failure to gain weight and grow as expected (failure to thrive), yellowing of the skin and whites of the eyes (jaundice), liver damage, and bleeding.’ Next time, Next time, choose a different condition.

[f] Correct. Sickle cell anemia is an inherited disease caused by a mutation in the gene for hemoglobin. While hemoglobin is a protein, it is not an enzyme.

[x]

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