Show what you know in a creative manner. 1, 27 – What are enzymes? Why are they important? 2, 29, 30 – Explain Figure 8.13 in the handout. Define all the terms associated with the diagram. 4, 5, 28 – Explain Figure 8.14 in the handout and describe how enzymes affect the curve. 6, 7, 8, 25, 26 – Describe the terms in boldface, explain why enzymes are substrate-specific, and describe the difference between the lock-and-key and induced-fit models. 9, 10, 23, 24 – Describe how enzymes catalyse reactions in their active sites. 11, 12, 21, 22 – Describe the effects of temperature and pH on enzyme activity. 13, 20 – Differentiate between cofactors and coenzymes. 14, 15, 19 – Differentiate between competitive inhibitors and noncompetitive inhibitors. 16, 17 - Describe allosteric regulation and the concept of cooperativity in haemoglobin. 3, 18 –Describe how allosteric regulation plays a role in feedback inhibition.

1, 27 What are enzymes? Why are they important?

Enzymes

Enzymes are biological catalysts Change the rates of a reaction (x 106-1012) without being consumed Lower energy barriers  initial energy investment or activation energy(EA) Cells can carry out necessary metabolic reactions even at moderate temperatures Progress of the reaction Products Course of reaction without enzyme Reactants with enzyme EA EA with is lower ∆G is unaffected by enzyme Free energy

2, 29, 30 – Explain Figure 8. 13 in the handout 2, 29, 30 – Explain Figure 8.13 in the handout. Define all the terms associated with the diagram. 4, 5, 28 – Explain Figure 8.14 in the handout and describe how enzymes affect the curve.

6, 7, 8, 25, 26 – Describe the terms in boldface, explain why enzymes are substrate-specific, and describe the difference between the lock-and-key and induced-fit models.

Enzymes are substrate specific H2O H HO OH O CH2OH Sucrase Sucrose Glucose Fructose C12H22O11 C6H12O6 + Substrate Active site Enzyme Tertiary/Quaternary structure accounts for specificity Active site – pocket or groove on surface of protein Substrates have to be compatible with the active site  lock and key model Substrates can cause the enzyme’s shape to change slightly to enhance activity “induced fit” Can act on 1000 substrate molecules per second Enzyme-substrate complex

9, 10, 23, 24 – Describe how enzymes catalyse reactions in their active sites.

The catalytic cycle of an enzyme Substrates Products Enzyme Enzyme-substrate complex 1 Substrates enter active site; enzyme changes shape so its active site embraces the substrates (induced fit). 2 Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. 3 Active site (and R groups of its amino acids) can lower EA and speed up a reaction by • acting as a template for substrate orientation, • stressing the substrates and stabilizing the transition state, • providing a favorable microenvironment, • participating directly in the catalytic reaction. 4 Substrates are Converted into Products. 5 Products are Released. 6 Active site Is available for two new substrate Molecules.

11, 12, 21, 22 – Describe the effects of temperature and pH on enzyme activity.

Enzyme action is affected by conditions within the cell temperature pH concentration of substrate and product

Factors affecting enzyme action Temperature increase in effective collisions optimum temperature – most rapid enzyme action rapid fall – enzymes denatured above a given threshold temperature

Factors affecting enzyme action 2. pH narrow range activity falls of rapidly on both sides of optimum structure is affected by degrees of acidity and alkanity

Factors affecting enzyme action 3. Substrate concentration [S] E + S  ES  E + P below saturation point –  [S]   E that can bind to S point of saturation onwards -  [S]  no further increase in reaction rate

Factors affecting enzyme action 4. Enzyme concentration [E] If excess substrate is available, rate  [E] [P]  [E], c.p.

11, 12, 21, 22 – Describe the effects of temperature and pH on enzyme activity. 13, 20 – Differentiate between cofactors and coenzymes

Enzyme action is affected by conditions within the cell presence of cofactors/coenzymes presence of enzyme inhibitors competitive inhibitors noncompetitive inhibitors

14, 15, 19 – Differentiate between competitive inhibitors and noncompetitive inhibitors.

Enzyme inhibitors (c) Noncompetitive inhibition (b) Competitive inhibition A competitive inhibitor mimics the substrate, competing for the active site. Competitive inhibitor A substrate can bind normally to the active site of an enzyme. Substrate Active site Enzyme (a) Normal binding A noncompetitive inhibitor binds to the enzyme away from the active site, altering the conformation of the enzyme so that its active site no longer functions. Noncompetitive inhibitor (c) Noncompetitive inhibition

16, 17 - Describe allosteric regulation and the concept of cooperativity in haemoglobin.

Metabolic control depends on allosteric regulation Regulatory molecules activate/inhibit enzyme shape and function by binding to allosteric sites Protein action at active site is affected by binding at a different site

3, 18 – Describe how allosteric regulation plays a role in feedback inhibition.

Feedback inhibition Metabolic pathways make use of more than one enzyme End product is an allosteric inhibitor that switches off enzyme action e.g. synthesis of isoleucine from threonine