Enzymes Department of Biochemistry Foundation Module – Phase: 1

Energy from breaking bonds in this molecule is used to form ATP   Energy from breaking bonds in this molecule is used to form ATP Energy ATP ADP + Pi ATP Energy

Energy The energy in ATP can be used to form bonds in other molecules. ATP ADP + Pi Energy

An anabolic reaction A catabolic reaction   Energy ATP ADP + Pi Energy

Substrates (Reactants) Anabolic Reactions Products Energy Supplied Anabolic reactions consume energy. Energy Released Substrates (Reactants)

Catabolic Reactions Substrate (Reactant) Energy Supplied Catabolic reactions release energy. Energy Released When bonds are broken, energy is released.

Activation Energy Activation Energy Energy Supplied In either kind of reaction, additional energy must be supplied to start the reaction. This energy is called activation energy. Energy Released

Enzymes Lower Activation Energy Enzymes lower the amount of activation energy needed for a reaction. Enzymes Lower Activation Energy Activation energy without enzyme Energy Supplied Activation energy with enzyme Energy Released

Essential of Enzyme Kinetics Steady State Theory E E E + + P S S In steady state, the production and consumption of the transition state proceed at the same rate. So the concentration of transition state keeps a constant.

Relationship between Enzyme Substrate product

Introducing the intermediate

Effect of Temperature on Enzyme Activity 30   40   50 

Effect of Temperature on Enzyme Activity 30   40   50 Increasing the temperature causes more collisions between substrate and enzyme molecules. The rate of reaction therefore increases as the temperature increases. Arrhenius Effect

  Enzymes denature when the temperature gets too high. The rate of reaction decreases as the enzyme becomes non functional 30   40   50

Effect of pH on Enzyme Activity Each enzyme has its own optimum pH Pepsin          Trypsin Rate of Reaction  1   2  3  4  5  6  7   8   9 pH

S + E ↓ P Product Substrate (mole) Increase Substrate Concentration 1 1 2 3 4 5 6 7 8 S + E ↓ P 80 60 40 20 Product (in a fixed period of time) 0 2 4 6 8 Substrate (mole)

Constant ES Concentration at Steady State P Concentration ES E Reaction Time

Enzyme Kinetics When y = 1/2 Vmax , x ([S]) → Km Vmax 1 vo vo 1/2 1/S - 1 Km 1 Vmax 1/S Km S Double reciprocal "Lineweaver Burk plot" Direct plot

Enzyme Kinetics V˳ =Vmax Km=[S] Km Vmax Direct plot 2 Non-competitive Double reciprocal Inhibition Maximum velocity Affinity with substrate

Km: Affinity with Substrate Vmax If vo = 2 When using different substrate Km = [S] Vmax S2 S1 S3 Km  1/ affinity 1/2 S1 S2 S3 Km1 Km2 Km3 Affinity changes

Enzyme Inhibition (Mechanism) Competitive Non-competitive Substrate E Cartoon Guide Compete for active site Inhibitor Different site E + S → ES → E + P + I ↓ EI E + S → ES → E + P + + I I ↓ ↓ IE + S →IES ← ← Equation  ↑ ↑ ↑ [I] binds to free [E] only, and competes with [S]; increasing [S] overcomes Inhibition by [I]. [I] binds to free [E] or [ES] complex; Increasing [S] can not overcome [I] inhibition. Description

Questions

Q:1 What is shown here? Label A, B and C

1 Q:2 Identify 1 - 5 2 3 5 4

Q:3 A similar-shaped molecule is competing with the substrate for active sites. What is this inhibition?

Feedback Inhibition A B C D X X X Q:4 Fill in the blanks C and D will ……….. because B is needed to produce C and C is needed to produce D. The amount of B in the cell will …………… if enzyme 1 is inhibited. A B C D X X X enzyme 1 enzyme 2 enzyme 3 Enzyme 1 is structured in a way that causes it to interact with D. When the amount of D ………….., enzyme 1 stops functioning. Feedback Inhibition

B C A D Q:5 Label A, B, C & D

Q:6 Identify the two Mechanisms of enzyme actions ? ?

Q:7 Which point shows the saturating velocity? B C Km s

Q:8 a.What is the role of Co2+

Q:8 b. Identify A, B and C B A C

Q:9 What is the feature of Oxygen that is seen here

A Q:10 Fill in the blanks ‘A’ shows, the rate of reaction against ………………. or ……………. and 'B' may be the rate of reaction against ………. or ………. B

Q:11  Identify the types of inhibitions

A:1  ATP 3 phosphate groups Base (adenine) A Sugar (ribose)

4 Substrate-Enzyme Complex 5 Products   1 Substrate 2 Active site 3 Enzyme 4 Substrate-Enzyme Complex 5 Products

A:3 Competitive Inhibition

Feedback Inhibition A:4 A B C D X X X C and D will decrease because B is needed to produce C and C is needed to produce D. The amount of B in the cell will decrease if enzyme 1 is inhibited. A B C D X X X enzyme 1 enzyme 2 enzyme 3 Enzyme 1 is structured in a way that causes it to interact with D. When the amount of D increases, the enzyme stops functioning.

A:5  

A:6

A:7 Saturating velocity = Vmax Km s

A:8 a. Co2+ acts as a co-factor

A:8 b.

A:9 Cooperativity

A A:10 ‘A’ shows, rate of reaction against temperature, and B may be rate of reaction against substrate concentration (enzyme concentration is limiting)Or enzyme concentration (substrate concentration is limiting) B

A:11