Enzymes

Question 1

Describe enzymes as catalysts

Answer 1

increase the reaction rate by decreasing the energy barrier

does not effect delta G or Keq

Question 2

Characteristics of enzymes that differ from other proteins

Answer 2

• higher reaction rate
• Milder reaction conditions (standard atm pressure, neutral pH, temps less than 100 C)
• High reaction specificity
• Can be regulated (inhibitors, etc)

Question 3

measurement of enzyme activity

Answer 3

measured in units:

amount of substrate converetd to product in a given amount of time (1 umol/min)

Question 4

Specific activity

Answer 4

number of units per mg protein

Question 5

optimum pH of human enzymes

Answer 5

37 C

Question 6

Discuss pH optimum of enzymes

Answer 6

• optimum pH dependent on where the enzyme is located
• pepsin in stomach ~ pH 2
• Trypsin in intestine ~ pH 8

Question 7

Oxidoreductase

Answer 7

transfer protons (H) and electrons to go from C-C to C+C

catalyze oxidation-reduction reactions

Question 8

Examples of oxidoreductase enzymes

Answer 8

Deydrogenase, Oxidase, reductase, peroxidase, catalase, oxygenase, hydrolases

Question 9

Transferase

Answer 9

Transfer C-, N-, P- containing groups (glcosyl, methyl, phosphoryl)

usually transfer to a cofactor

Question 10

Examples of transferases

Answer 10

kinase, phosphomutase, transaldolase, transketolase

Question 11

Hydrolase

Answer 11

• cleaves bonds by adding water

- cleavage of C-C, C-O, C-N and other bonds

Question 12

Examples of hydrolases

Answer 12

esterases, glycosidases, peptidases, phosphatases

Question 13

Lyases

Answer 13

cleaves C-C, C-S, C-O, and C-N

results in a C=C (double bond)

Question 14

Examples of Lyases

Answer 14

Decarboxylases, aldolases, hydratases, dehydratases, synthases

Question 15

Isomerases

Answer 15

Catalyze geometric rearrangement

** rearrange but dont change the molecular weight

Question 16

Examples of Isomerases

Answer 16

Racemases, epimerases, isomerases, mutases

Question 17

Ligases

Answer 17

• adding two substrates together
• Form bonds between C, O, S, N
• coupled with hydrolysis of ATP (ATP –> ADP)

Question 18

Active site

Answer 18

area on the enzyme where catalysis occurs

Question 19

Catalysis by proximity

Answer 19

bring enzymes and substrate together so there is a higher chance of them meeting and interacting

Question 20

Acid Base Catalysis

Answer 20

Ionizable functional groups of amino acyl side chains move or accept protons by acting as acids/bases

Question 21

Catalysis by strain

Answer 21

enzymes that break bonds (hydrolase, lyases) may bind in such as way that they create strain to break the bond

“bend and snap!”

Question 22

Covalent Catalysis

Answer 22

covalent bond established between enzyme and substrate to make enzyme substrate complex

ESC then becomes the product for the rest of the reaction

Question 23

Prosthetic Group

Answer 23

Binds to enzyme
Tightly bound
Covalent
Most commonly metal ions (Co, Cu, Mg, Mn, Zn)

Question 24

Metaloenzymes

Answer 24

enzymes with a metal containing prosthetic group

Question 25

Cofactors

Answer 25

Binds to enzyme or substrate Inorganic substances required for enzyme activity Ex: Mg 2+ is required for enzymes that involve ATP

Question 26

Coenzymes

Answer 26

loosely bound shuttles groups within the reaction Ex: Coenzyme A transferes acyl group Folates transfer Carbon group

Question 27

Isoenzymes

Answer 27

physically distinct enzymes which catalyze the same reaction kinetic differences (Km, pH, temp)

Question 28

Kcat

Answer 28

how fast enzyme releases product/ unit of time highter Kcat = better

Question 29

Km

Answer 29

binding affinity Km= 1/2 Vmax lower Km = better

Question 30

Catalytic efficienct

Answer 30

Kcat/Km

Question 31

Michaelis menton [S] >> Km

Answer 31

V= vmax zero order reaction

Question 32

Michaelis menton [S] << Km

Answer 32

first order reaction

Question 33

Lineweaver burke intercepts and slope

Answer 33

y-intercept = 1/vmx x-intercept = -1/Km Slope = Km/Vmax

Question 34

Competitive Inhibitor

Answer 34

structurally similar to substrate (competes) Binds only to free enzyme Increase Km Vmax stays the same overcome by addition of [S]

Question 35

Noncompetitive Inhibitor

Answer 35

Bind to E or to ES DOES NOT BIND ACTIVE SITE --> doesnt compete with S for binding Decreases Vmax increasing [S] does NOT overcome inhibition

Question 36

Uncompetitive Inhibitor

Answer 36

Binds only to ES Changes both Km and Vmax (slope stays the same) As [S] increases so does the inhibition because it uses ES

Question 37

Enzyme coopertivity

Answer 37

binding of one substrate causes the binding of subsequent molecules

Question 38

Allosteric Enzyme

Answer 38

has more than one substrate binding site | usually more than one subunit

Question 39

Hill coefficient

Answer 39

measure of the degree of coopertivity larger = greater coopertivity n=1 no coopertivity and the equation is michaelis menton

Question 40

Conformational changes in allosteric enzymes

Answer 40

low [S] the enzyme is tensed | high [S] the enzyme is relaxed

Question 41

Homotrophic regulation

Answer 41

binding of S increases the activity of other catalytic sites almost always positive (activator)

Question 42

Heterotrophic regulation

Answer 42

regulatory molecule distinct from the substrate