Chp. 19 Enzymes

Question 1

What are the six categories of enzymes based on the reactions they catalyze?

Answer 1

• Oxidoreductase
• Transferase
• Hydrolase
• Lyase
• Isomerase
• Ligase

These categories help in the classification of enzymes according to their specific functions.

Question 2

What type of reactions do oxidoreductases catalyze?

Answer 2

Redox reactions

Includes reductases and oxidases.

Question 3

What is the function of transferases?

Answer 3

Transfer a group from one molecule to another

Examples include transaminases, transmethylases, and kinases.

Question 4

What do hydrolases do?

Answer 4

Cleavage of bonds by adding water

Examples include phosphatases, peptidases, lipases, and glycosidases.

Question 5

What is the role of lyases?

Answer 5

Catalyze removal of groups to form double bonds or the reverse

Examples include decarboxylases and synthases.

Question 6

What is the function of isomerases?

Answer 6

Catalyze intramolecular rearrangements

Examples include epimerases and mutases.

Question 7

What do ligases catalyze?

Answer 7

Formation or breaking of C-C, C-S, C-O, or C-N bonds

Ligases are essential for joining two larger molecules.

Question 8

What is the common suffix for enzyme names?

Answer 8

-ase

This suffix is typically used for enzymes, reflecting their function.

Question 9

How does an enzyme affect the activation energy of a reaction?

Answer 9

It lowers the activation energy

This results in a faster reaction rate.

Question 10

What are the two stages of enzyme-catalyzed reactions?

Answer 10

• Formation of enzyme-substrate complex
• Slow conversion of substrate into product

The rate is limited by enzyme availability.

Question 11

What is the active site of an enzyme?

Answer 11

The part of the enzyme that combines with the substrate

Active sites have specific shapes complementary to their substrates.

Question 12

What does the lock-and-key model of enzyme action suggest?

Answer 12

The enzyme and substrate fit exactly

This model does not account for conformational changes in proteins.

Question 13

Describe the induced fit model of enzyme action.

Answer 13

The enzyme active site is a flexible pocket that changes to accommodate the substrate

This model explains enzyme specificity more accurately.

Question 14

What is enzyme specificity?

Answer 14

The ability of an enzyme to bind only one or a very few substrates

Urease is an example of an enzyme with high specificity.

Question 15

What are the four classes of enzyme specificity?

Answer 15

• Absolute
• Group
• Linkage
• Stereochemical

Each class describes how specific an enzyme is to its substrates.

Question 16

What is a cofactor in enzyme activity?

Answer 16

A nonprotein prosthetic group required for enzyme function

bound to the enzyme for it to maintain the correct configuration of the active site (slide 27)

Includes organometallic compounds, metal ions, and organic compounds.

Question 17

What is a coenzyme?

Answer 17

An organic molecule bound to an enzyme by weak interactions/hydrogen bonds

Coenzymes often carry electrons or small groups.

Question 18

What effect does pH have on enzyme activity?

Answer 18

Extreme pH changes can denature the enzyme

low=acidic, high=basic

Each enzyme has a pH optimum for maximal function.

Question 19

What is feedback inhibition?

Answer 19

A product of a reaction inhibits an earlier enzyme in the pathway

This is a common regulatory mechanism in metabolic pathways.

Question 20

What are zymogens?

Answer 20

Inactive forms of enzymes that are activated when needed

Example: Pepsinogen is activated to pepsin in the stomach.

Question 21

What distinguishes irreversible inhibitors from reversible inhibitors?

Answer 21

Irreversible inhibitors: bind tightly to enzymes, preventing E-S complex formation
Reversible Inhibitors: often structurally resemble the substrate and bind at the normal active site

(higher concentration wins)

Reversible inhibitors often resemble the substrate and compete for the active site.

Question 22

What is the optimum temperature for enzyme function in humans?

Answer 22

37°C

This temperature is typically close to the physiological temperature of the human body.

Question 23

What are irreversible inhibitors?

Answer 23

Substances that permanently inhibit enzyme activity, including:
* Arsenic
* Snake venom
* Nerve gas

Irreversible inhibitors bind to enzymes in a way that permanently disables their function.

Question 24

What are reversible, competitive inhibitors also called?

Answer 24

Structural analogs

These inhibitors resemble the structure and charge distribution of natural substances for enzymes.

Question 25

How do reversible, competitive inhibitors affect enzyme activity?

Answer 25

They occupy the enzyme active site, preventing the substrate from binding and inhibiting reaction. ## Footnote This competition for the active site means that the degree of inhibition depends on the concentrations of both the enzyme and the inhibitor.

Question 26

What is competitive inhibition?

Answer 26

The inhibitor and the substrate compete for binding to the active site ## Footnote The outcome of this competition affects the rate of enzyme activity.

Question 27

What do proteolytic enzymes do?

Answer 27

They cleave the peptide bond in proteins ## Footnote This action breaks the peptide bonds that maintain the primary protein structure.

Question 28

What determines the specificity of proteolytic enzymes?

Answer 28

A hydrophobic pocket ## Footnote This pocket is formed by a cluster of hydrophobic amino acids in the 3-D structure of the protein.

Question 29

What is the cleavage specificity of chymotrypsin?

Answer 29

Chymotrypsin cleaves at the carboxylic end of M=met, W=trp, F=tyr, Y=phe ## Footnote Chymotrypsin is a type of proteolytic enzyme with specific targets.

Question 30

What are pancreatic serine proteases?

Answer 30

A category of enzymes that hydrolyze peptide bonds and evolved divergently from a common ancestor ## Footnote They share similar primary and tertiary structures but have different specificities.

Question 31

What is the cleavage specificity of trypsin?

Answer 31

Trypsin cleaves on the carbonyl side of basic amino acids K=lys, R=arg ## Footnote This specificity is crucial for its function in protein digestion.

Question 32

What is the cleavage specificity of elastase?

Answer 32

Elastase cleaves on the carbonyl side of G=Gly and A=Ala ## Footnote Its specificity allows it to act on small, flexible amino acids.

Question 33

What are some diagnostic uses of enzymes in medicine for acute myocardial infarction?

Answer 33

Biomarker levels altered include: * Creatine kinase - MB * Myoglobin * Troponin I ## Footnote These biomarkers help in diagnosing heart attacks.

Question 34

What enzymes are used in the diagnosis of pancreatitis?

Answer 34

Amylase and Lipase ## Footnote Elevated levels of these enzymes indicate pancreatic inflammation.

Question 35

What is an analytical reagent in the context of enzyme use in medicine?

Answer 35

An enzyme used to measure another substance = urea being converted to NH3 via urease ## Footnote This process is essential for measuring blood urea nitrogen (BUN).

Question 36

Enzyme Specificity Classes: Absolute

Answer 36

enzyme reacts with only one substrate ## Footnote This therapy helps manage a genetic disorder affecting lipid metabolism.

Question 37

Enzyme Specificity Classes: Group

Answer 37

enzyme catalyzes reaction involving any molecules with the same functional group

Question 38

Enzyme Specificity Classes: Linkage

Answer 38

enzyme catalyzes the formation or break up of only certain category or type of bond

Question 39

Enzyme Specificity Classes: Stereochemical

Answer 39

Enzyme recognizes only one of the two enantiomers

Question 40

Transition State

Answer 40

Features both a substrate and product & falls apart to yield product - dissociates from the enzyme When the substrate interacts with the enzyme, its shape changes which is less energetically stable. (high energy = low stability)

Question 41

First Possible Transition State

Answer 41

enzyme might put "stress" on a bond facilitating bond breakage (slide 22) substrate + product = fall apart to yield product

Question 42

Second Possible Transition State Change

Answer 42

the enzyme brings two reactants close to one another and in proper orientation (slide 23) -Removes possibility of side reactions -Allows correct orientation=Correct Reaction

Question 43

Third Possible Transition State Change

Answer 43

the enzyme might modify the pH of the microenvironment, donating or accepting a H+

Question 44

How does an enzyme possibly decrease the activation energy of the reaction?

Answer 44

Binding Energy

Question 45

Apoenzyme

Answer 45

Polypeptide portion of enzyme: No enzyme-substrate complex=no reaction (slide 27)

Question 46

Holoenzyme

Answer 46

Active Enzyme

Question 47

Methods Used to Regulate Enzyme Activity

Answer 47

1. Produce the enzyme only when substrate is present 2. Allosteric Enzymes 3. Feedback Inhibition 4. Zymogens 5. Protein Modification

Question 48

Methods Used to Regulate Enzyme Activity: Allosteric Enzymes

Answer 48

effector molecules change the activity of an enzyme by binding at a second site

Question 49

4 General Stages in an Enzyme Catalyzed Reaction

Answer 49

1. Enzyme + Substrate Binding 2. Transition State 3. Catalyzes 4. Product Release

Question 50

Allosteric Enzymes -Positive Allosteric vs. Negative Allosteric

Answer 50

positive: effector binding converts the active site to an active configuration=higher activity of enzyme negative: effector binding converts the active site to an inactive configuration=lower activity of enzyme

Question 51

Methods Used to Regulate Enzyme Activity: Feedback Inhibition

Answer 51

Allosteric enzymes are the basis for feedback inhibition: product later in a series of enzyme-catalyzes reactions inhibits earlier allosteric enzymes in the series

Question 52

Methods Used to Regulate Enzyme Activity: Zymogens and Proenzymes

Answer 52

enzyme made in an inactive form (zymogens), converted to an active form - by hydrolysis of the enzyme (proteolysis), when needed at the active site in the cell = when needed the inactive form is removed

Question 53

Why is it important for cells to regulate the levels of enzyme activity?

Answer 53

To Maintain Cellular Homeostasis

Question 54

Methods Used to Regulate Enzyme Activity: Protein Modification

Answer 54

a chemical group is covalently after to or removed from the protein ex. addition or removal of a phosphate group

Question 55

Proteolytic Enzyme Specificities

Answer 55

*Chymotrypsin *Trypsin *Elastase