1.7 Enzymes

Question 1

Enzyme definition

Answer 1

A biological catalyst, usually a protein, that speeds up a chemical reaction

Question 2

The enzyme lipase speeds up the _________ of the lipid triglycerides.

Answer 2

hydrolysis

Question 3

Sucrase speeds up the hydrolysis of
sucrose into _______ and ________.

Answer 3

glucose; fructose

Question 4

Another term that is used to describe an enzyme is _______.

Answer 4

catalyst

Question 5

Catalyst definition

Answer 5

A catalyst is a substance that speeds up a reaction without being consumed by the reaction.

Question 6

For a chemical reaction to move forward, it must overcome an ________ _______

Answer 6

energy barrier

Question 7

Enzymes bind a specific reactant called a _________; in doing so, they _____ the energy barrier so that the reaction proceeds at a ______ rate than it would without the enzymes

Answer 7

substrate; lower; faster

Question 8

Substrate definition

Answer 8

A substance that is recognized by and binds to an enzyme

Question 9

Each type of enzyme __________ the reaction of only one type of molecule or one
group of closely related molecules.

Answer 9

catalyzes

Question 10

Active site definition

Answer 10

A pocket or groove in an enzyme that binds its substrate

Question 11

The substrate interacts with only a very small _______ of the enzyme called the active site.

The active site is usually a pocket or groove that forms when the newly synthesized enzyme ____ into its correct 3D shape (________ structure).

Answer 11

region; folds; tertiary

Question 12

Induced-fit model definition

Answer 12

A model of enzyme activity that describes how an enzyme changes shape to better accommodate
a substrate

Question 13

What are the steps in the enzyme cycle?

Answer 13

1) An enzyme binds to one or more substrates,
forming an enzyme-substrate complex.

2) The enzyme then converts the substrate(s)
into one or more products.

3) Since enzymes remain unchanged after a
reaction, enzyme molecules can rapidly bind to
other substrate molecules, catalyzing the same
reaction repeatedly.

Question 14

The rate at which enzymes catalyze reactions varies depending on the ________ and ________ involved

Answer 14

enzyme; substrates

Question 15

Cofactor definition

Answer 15

A non-protein group that binds to an enzyme and is essential for catalytic activity

Question 16

Coenzyme definition

Answer 16

An organic molecule that acts as a cofactor of an enzyme

Question 17

True or false

Cofactor are often non-metals.

Answer 17

False

Cofactors are often METALS, such as iron, copper, zinc, and manganese.

Question 18

Many coenzymes ________ molecules from one enzyme to another.

Answer 18

shuttle

Question 19

Several control mechanisms modify enzyme activity and adjust _______ rates to meet a cell’s
requirements for chemical __________.

Answer 19

reaction; products

Question 20

The _____________ of both the enzyme and the substrate will influence the rate of a ________ reaction.

Answer 20

concentration; catalysis

Question 21

If there is excess substrate present, then the rate of reaction is _____________ to the enzyme concentration. This occurs because the amount
of enzyme _______ the rate of reaction.

Answer 21

proportional; limits

Question 22

If, however, the amount of enzyme is at a _______
intermediate concentration, then increasing the substrate concentration will increase the rate of reaction up to a point, called the _________ ______

Answer 22

constant; saturation level

Question 23

The rate of the reaction ________ as collisions become more _______.

Answer 23

increases; frequent

Question 24

However, as the enzyme molecules approach the _________ rate at which they combine with the substrate, increasing the substrate concentration has a _______ effect.

Eventually, the rate of reaction levels off. At this point, the enzyme molecules are ________ with substrate.

Answer 24

maximum; reduced; saturated

Question 25

Enzyme inhibitor definition

Answer 25

Enzyme inhibitors lower the rate at which an enzyme catalyzes a reaction.

Question 26

Inhibitor definition

Answer 26

Inhibitors are molecules that bind to an enzyme and decrease its activity.

Question 27

Competitive inhibition definition

Answer 27

A situation in which a competitor substance binds to a normal substrate binding site to block
enzyme activity

Question 28

Noncompetitive inhibition

Answer 28

A situation in which molecules bind to an enzyme
at a site that is not the active site, thus blocking enzyme activity

Question 29

Reversible inhibition

Answer 29

In reversible inhibition, the binding of the inhibitor to the enzyme is weak and readily reversible.

Enzyme activity returns to normal following the release of the inhibitor.

Question 30

Irreversible inhibition

Answer 30

In irreversible inhibition, some inhibitors
bind so strongly to the enzyme through the formation of covalent bonds that they completely disable the enzyme.

Question 31

Many irreversible inhibitors that act on critical enzymes are highly ______ to the cell.

Answer 31

toxic

Question 32

Allosteric site definition

Answer 32

A binding site on an enzyme that binds regulatory molecules.

Question 33

Allosteric regulation definition

Answer 33

The regulation of one site of a protein by binding to another site on the same protein. It may either inhibit or stimulate enzyme activity.

Question 34

Binding of an allosteric activator molecule ______ the enzyme in a shape that causes its active site to have a high ________ for its substrate.

In this state, the enzyme ____ its substrate.

Answer 34

stabilizes; affinity; binds

Question 35

Binding of an allosteric inhibitor stabilizes an _________ form of the enzyme.

The inhibitor molecule changes the ______ of the enzyme in such a way that the substrate is _________ from the active site.

Answer 35

inactive; shape; released

Question 36

Allosteric regulators are important molecules, functioning to control chemical _________ in a cell.

Answer 36

activity

Question 37

An allosteric inhibitor is a ________ of the biochemical pathway that it regulates.

Answer 37

product

Question 38

Feedback inhibition definition

Answer 38

The regulation of a pathway by one of the products of this pathway.

Question 39

Feedback inhibition prevents cellular resources from being _______ in the _________ of molecules at intermediate steps in the pathway.

Answer 39

wasted; synthesis

Question 40

Enzymes usually reach _________ activity within a narrow range of temperatures and pH values.

At levels outside this range, enzyme activity _____ off.

This usually produces a _______ curve when enzyme activity is plotted, with the peak where temperature and pH produce maximal activity.

Answer 40

maximal; drops; peaked

Question 41

As the pH either increases or decreases away from its optimal value, the rate of the catalyzed reaction __________

Answer 41

decreases

Question 42

The more the pH value deviates from the _________ value, the more _________ the effects on the structure and function of the active site of the enzyme become, until the rate of the reaction falls to _____.

Answer 42

optimal; extreme; zero

Question 43

Temperature has a general effect on all kinds of chemical reactions. As the temperature ____, the rate of a chemical reaction usually increases.

This effect reflects increases in the ______ motion of the molecules.

As the temperature rises, there are more frequent and stronger ________.

Answer 43

rises; kinetic; collisions

Question 44

Temperature has an effect on all proteins, including enzymes.

As the temperature rises, the kinetic motions of the amino acid chains of an enzyme _________.

At the same time, the strength and frequency of the ________ between the enzyme molecules and any surrounding molecules also ________.

Answer 44

increase; collisions; increases

Question 45

In the range of 0 to about 40°C, the reaction rate _______ for every 10°C _______ in temperature

Answer 45

doubles; increase

Question 46

Above 40°C, the increasing kinetic motion begins to unravel, or _______, an enzyme.

The hydrogen bonds and other forces that hold together the enzyme’s 3D structure ______.

As this happens, the enzyme loses its ability to __________.

Answer 46

denature; break; function

Question 47

The denaturation process reduces the rate of _________ in enzyme activity.

Answer 47

increase

Question 48

The rate of an enzyme-catalyzed reaction _____ at a temperature at which kinetic motion is the _________ but no significant _________ of the enzyme has occurred.

Answer 48

peaks; greatest; unfolding

Question 49

Explain how lactose intolerance relates to enzymes.

Answer 49

Lactose intolerance is the inability to properly break down lactose, the primary disaccharide in milk.

To absorb the lactose, the digestive cells need to secrete an enzyme called lactase.

Lactase catalyzes the efficient breakdown of lactose in the monosaccharides glucose and galactose.

People with lactose intolerance do not produce enough lactase, and therefore lactose is not digested or absorbed properly.

The lactose is then consumed by bacteria living in the gut.

Question 50

Effects of enzymes on animal feed

Answer 50

degradation of the components of feed to improve nutrient digestion and uses of the feed

Question 51

Effects of enzymes on brewing

Answer 51

faster maturation of beer; removal of carbohydrates in light beer

Question 52

Effects of enzymes on dairy

Answer 52

cheese making; removal or conversion of lactose in milk

Question 53

Effects of enzymes on detergent

Answer 53

breakdown of starch and fatty acid stains as an active biological component of powder and liquid detergents; colour brightening and softening

Question 54

Effects of enzymes on starch

Answer 54

production of glucose, dextrose, fructose

Question 55

Effects of enzymes on wine and juice

Answer 55

degradation of the protein pectin for clarification and increase in juice yield

Question 56

What is a substrate? What is an active site? How are they related?

Answer 56

A substrate is a substance that is recognized and binds to an enzyme.

An active site is the location on an enzyme where a substrate binds and is the location of the enzymatic reaction.

Question 57

Why is an enzyme considered a biological catalyst?

Answer 57

Enzymes are considered biological catalysts because they can be used repeatedly and are not wasted after they catalyze a reaction.

Question 58

Describe the induced-fit hypothesis of an enzyme-substrate interaction.

Answer 58

In the induced-fit hypothesis, the conformation of the enzyme changes slightly to allow for a more precise binding of the substrate.

Question 59

What is the functional role of a coenzyme or a cofactor in an enzyme-induced reaction? Give an example of an enzyme that requires a cofactor or a coenzyme.

Answer 59

Coenzymes and cofactors are required for an enzyme to properly catalyze a reaction.

Pyruvate dehydrogenase requires the cofactor magnesium.

Question 60

How does the rate of a reaction change as a result of each of the following factors?
(a) enzyme concentration

Answer 60

As the concentration of enzyme increases, so does the rate of the reaction.

Question 61

How does the rate of a reaction change as a result of each of the following factors?
(b) substrate concentration

Answer 61

The rate of a reaction will increase with increasing substrate concentration until the enzyme reaches its saturation level.

At this point there is no change in the rate of the reaction.

Question 62

How does the rate of a reaction change as a result of each of the following factors?
(c) temperature

Answer 62

Temperature above the optimal point will slowly cause decrease of enzymatic activity and ultimately stop it at the point of denaturation; lower temperature will decrease the activity due to a decrease of available energy.

Question 63

How does the rate of a reaction change as a result of each of the following factors?
(d) pH

Answer 63

Significant deviation from the optimal pH will cause enzyme denaturation.

Question 64

Describe noncompetitive enzyme inhibition. Provide an example to support your answer.

Answer 64

A noncompetitive inhibitor binds to the enzyme at a site other than the active site.

It changes the conformation of the enzyme so that it no longer binds its normal substrate.

Alanine non-competitively inhibits pyruvate kinase forming a feedback loop preventing more alanine production.

Question 65

Describe the different effects of an activator and an inhibitor on an allosterically regulated enzyme.

Answer 65

The activator binds in such a way that it stabilizes the active conformation of the enzyme, and it is then able to better bind the substrate.

An inhibitor stabilizes the inactive conformation of the enzyme, so it cannot bind to its normal substrate.

Question 66

Describe how feedback inhibition reduces the waste of cellular resources.

Answer 66

The products of a reaction pathway inhibit the production of more products.

Therefore, if there is too much product in the cell, the pathway is inhibited, and the resources needed for the intermediate steps in the pathway are not wasted.

Question 67

Why is it important for the human body to maintain a proper temperature and a proper pH at all times?

Answer 67

Maintenance of proper temperature and pH is important in providing optimal conditions for the body’s enzymes to perform their activity.

Question 68

You are making a gelatin dessert, but the directions tell you not to use fresh pineapple because the gelatin will not solidify. Gelatin is a structural protein made from collagen. Pineapple contains an enzyme, bromelain, which is a protease.

(a) What effect does a protease have on a protein like collagen?

Answer 68

A protease is an enzyme that begins protein catabolism by breaking the peptide bonds that link the amino acids in the polypeptide chain.

This disrupts the gelatin and stops it from setting.

Question 69

Humans produce enzymes in the mouth, stomach, and small intestine that aid in the process of digestion. As we age, we tend to produce less of these enzymes. What effect could this have on digestion and nutrition?

Answer 69

As we age, it becomes harder to utilize the nutrients in our food due to loss of function of digestive enzymes.

This can lead to malnutrition and/or digestive problems

Question 70

Digestion cannot take place unless water is present. Explain this statement.

Answer 70

Carbohydrates and proteins are broken down by hydrolysis into smaller subunits by the addition of water molecules.

Without water, hydrolysis cannot happen, therefore, digestion cannot take place.

Question 71

What are enzymes?

Answer 71

-a biological catalyst

Speeds up chemical reactions

Helps to break down/build molecules

REUSABLE

Have very specific shapes and only react with specific substances

Question 72

substrate

Answer 72

the substance that reacts with
an enzyme

Question 73

true or false:

substrates and enzymes bond together

Answer 73

true

Question 74

active site

Answer 74

a pocket/groove in an enzyme that
binds to the substrate

Question 75

induced fit hypothesis

Answer 75

describes how enzymes
change shape to better attach to a substrate

Question 76

Enzyme-Substrate Complex

Answer 76

term used to describe
enzymes bonded to substrate(s)

Question 77

cofactor and examples

Answer 77

non-protein
group that binds to
enzymes and helps them
function

Often metals such as
copper, iron, zinc etc.

Question 78

coenzyme

Answer 78

Coenzyme – an organic
molecule that acts as a
cofactor of an enzyme

may be derived from
vitamins

Question 79

how does concentration affect enzyme activity?

Answer 79

the concentration of both enzyme and substrate will influence the rate of reaction

Rate of reaction is proportional to enzyme concentration (enzymes limit reaction speed)

Question 80

enzyme inhibitors

Answer 80

Lower enzyme reaction rate

Bind to enzymes to inhibit activity

Question 81

competitive inhibitor

Answer 81

binds to active site to prevent
substrate from binding

Question 82

Non-competitive Inhibitor

Answer 82

binds to enzyme and changes the
shape, indirectly prevents substrate from binding

Question 83

irreversible inhibitors

Answer 83

often highly toxic to cells as they
prevent enzymes from functioning

(Ex. Cyanide binds to
cytochrome oxidase and interferes with cellular respiration)

Question 84

allosteric regulation

Answer 84

regulation of enzyme function using other molecules that bind to the enzyme

Question 85

allosteric site

Answer 85

a binding site on an enzyme where allosteric molecules attach

Question 86

allosteric inhibition

Answer 86

stabilizes enzyme into an inactive form

Question 87

allosteric activation

Answer 87

stabilizes enzyme into an active form

Question 88

what is feedback inhibition and how does it affect enzyme activity?

Answer 88

the regulation of a pathway by one of the products of the pathway

-essentially once enough product is produced then the pathway shuts down until more product is needed

Question 89

process of feedback inhibition

Answer 89

A series of different enzymes
break down a large molecule
into several smaller molecules

The small molecules (the
finished product) can bind to
the first enzyme and inhibit it

The pathway shuts down until
the smaller molecules become
scarce; then the enzymes
become reactivated

Question 90

Temperature and pH can both affect _____________

Enzymes will often only ________ optimally within a specific range of temperatures and pH levels

Answer 90

enzyme activity; function

Question 91

how is treating lactose intolerance an application of enzymes?

Answer 91

taking lactase pills to help break down lactose in dairy products

Question 92

how is making cheese an application of enzymes?

Answer 92

enzymes used to solidify milk into cheese

Question 93

how is breaking down starch an application of enzymes?

Answer 93

enzymes used to break down plant starches into sugars

Question 94

how is stain removal an application of enzymes?

Answer 94

used to break apart certain types of staining molecules without heating (cold water detergents)