Lecture 10: Enzymes I

Question 1

Why are enzymes preferred over inorganic catalysts in biological systems?

Answer 1

1. Greater specificity 2. Milder conditions (T, pH) 3. Higher rates 4. Regulated

Question 2

What type of reaction is catalyzed by Oxidoreductase?

Answer 2

Transfer of electrons (hydride ions or H-atoms)

Question 3

What type of reaction is catalyzed by Transferases?

Answer 3

Group transfer reactions

Hint: Molecule to Molecule TRANSFER

Question 4

What type of reaction is catalyzed by Hydrolases?

Answer 4

Hydrolysis reactions (transfer of function groups to water)

Question 5

What type of reaction is catalyzed by Lysases?

Answer 5

Cleavage of C–C, C–O, C–N, or other bonds by elimination; leaving double bonds or rings, or addition of groups to double bonds

Question 6

What type of reaction is catalyzed by Isomerases?

Answer 6

Transfer of groups within a molecule to yield and ISOMER

Question 7

What type of reaction is catalyzed by Ligases?

Answer 7

Formation of C–C, C–S, C–O, and C–N bonds by condensation reactions coupled to cleavage of ATP or similar cofactor

LIGASE = Oppositie’ish of LYASE; see ATP, loss of H2O, think LIGASE

Question 8

What are the three types of non-protein components of enzymes?

Answer 8

Prosthetic Groups, Cofactors, Coenzymes

Question 9

How are prosthetic groups incorporated into proteins?

Answer 9

Tightly by covalent or noncovalent forces

Question 10

How are cofactors bound to protein structure?

Answer 10

Bound in a transient, dissociable manner–either to enzyme or substrate

Question 11

How are Coenzymes used in enzymatic reactions?

Answer 11

Group transfer agents, transports substrates from one point within the cell to another

Question 12

Metal Ions often serve as what enzyme addition?

Answer 12

Cofactor

Question 13

The prosthetic group Thiamin pyrophosphate (TPP) has the dietary precursor ________, transfers a ______ group, and its defiency is related to ________.

Answer 13

Thiamin (B₁)

Aldehyde Transfer

Beriberi

Question 14

The prosthetic group α-Lipoic Acid (lipoamide) has the dietary precursor ________, transfers a ______ group, and its defiency is related to ________.

Answer 14

Not a vitamin

Acyl Group Transfer

None

Question 15

The prosthetic group Coenzyme A (CoA) has the dietary precursor ________, transfers a ______ group, and its defiency is related to ________.

Answer 15

Pantothenic Acid (B5)

Acyl Group Transfer

Rarely Observed

Question 16

The prosthetic group Nicotinamide Adenine Dinucleotide (NAD⁺) has the dietary precursor ________, transfers a ______ group, and its defiency is related to ________.

Answer 16

Niacin (B₃)

Redox Reactions (transfer of hydride ion)

Pellagra

– Eating a lot of unproccessed corn, gains

Question 17

The prosthetic group Flavin Adenine Dinucleotide (FAD) has the dietary precursor ________, transfers a ______ group, and its defiency is related to ________.

Answer 17

Riboflavin (B₂)

Redox reactions (transfer of electrons)

Cheilosis (swelling, cracked lips)

Question 18

What is the following structure?

What does it play a role in?

Answer 18

Thiamine Pyrophosphate (TPP)

Pyruvate Dehydrogenase (PDH)

• TPP is bound to Pyruvate Dehydrogenase (E1)

Question 19

What is the following structure?

What does it play a role in?

Answer 19

Lipoic Acid

Covalently linked to Dihydrolipoyl tranacetylase (E2) of PDH

Question 20

What is the following structure?

What does it play a role in?

Answer 20

CoEnzyme A (CoA)

Substrate for Dihydrolipoyl Transacetylase (E2) of PDH

Question 21

FAD and FAMN carry how many electrons?

Answer 21

2

Question 22

What is the following structure?

What does it play a role in?

Answer 22

FAD and FMN complex

Universal Electron Carrier ( 2x e^- )

Question 23

What is the following structure?

What does it play a role in?

Answer 23

FADH₂

Fully reduced form of FAD and FMN complex (universal electron carriers)

Question 24

What is the following structure?

What does it play a role in?

Answer 24

FADH⁺

Semi-reduced form of FAD and FMN complex (universal electron carrier, 2x e^-

Question 25

What is the following structure? What form is it in?

What does it play a role in?

What vitamin does in contain?

What is the orange shaded group?

Answer 25

NAD+ (Oxidized)

Universal electron carrier in redox reactions

B₃

Adenine

Question 26

What is the following structure? What form is it in?

What does it play a role in?

What vitamin does it contain?

Answer 26

NADH (reduced)

Involved in redox reactions, carrying electrons in reactions

Niacin (B₃)

Question 27

What Amino Acid is Niacin derived from?

What can a deficiency in this result in?

Why would one also see neurological symptoms?

Answer 27

Trp

Pellagra

Serotonin (neurotransmitter) is also derived from Trp

Question 28

What is the following structure?

What does it play a role in?

What would a deficiency in this molecule possibly result in?

What is commonly supplemented to prevent this?

Answer 28

Tetrahydrofolate

Carrier of one C-group in amino acid and nucelic acid synthesis

Deficiency can result in low birth weight and/or spina bifida

Folic Acid

Question 29

The following image is an example of what enzyme-substrate interaction?

Answer 29

Induced fit

• Conformational change

Question 30

What are the four presented methods of enzyme catalysis? Briefly describe each.

Answer 30

1. Proximity - concentration and orientation are altered in the active site to enhance reaction rate
2. A/B Catalysis - Ionizable R-groups of AA and prosthetic groups contribule to catalysis by acting as A/B’s; Hint: Look for R-groups: tyrosine, cysteine, arginine, lysine, histidine, aspartic acid and glutamic acid (https://www.youtube.com/watch?v=eE4WgONS6-k)
3. Strain - Enzymes bind in an unfavorable conformation to weaken bond for cleavage
4. Covalent - Formation of covalent bond to create more reactive enzyme; ex. Group Transfer Reactions (Transferase, Isomerase)