Higher Human Biology The role of enzymes

Learning Intentions By the end of this lesson we will be able to: 1. State what enzymes are. 2. Describe the properties of enzymes. 3. Explain how enzymes perform their function 4. Explain how enzymes function is related to their structure. 5. State how enzymes are affected by pH 6. Compare and contrast the effect of pH and temperature on enzymes.

Introduction to Enzymes Chemical reactions all occur at different rates. Some are very quickly and some are extremely slow. =

Introduction to Enzymes We can speed up some chemical reactions by: ◦ Increasing the temperature of reactants ◦ Increasing the concentration of reactants ◦ Decreasing the particle size of reactants ◦ Adding a catalyst Since it is not always appropriate to increase the temperature of a living organism, biological catalysts called ENZYMES are used to increase the rate of reactions.

Catalysts A catalyst is a substance which can speed up a reaction without being used up or chemically changed. ◦ When a catalyst is present, the reaction requires less energy to start it; lower activation energy. ◦ When a catalyst is present the reaction is faster.

Enzymes Enzymes are Biological Catalysts, made of protein. An enzyme will speed up a reaction but will remain unchanged by it. This means it is reusable.

Energy input needed to break chemical bonds and start a chemical reaction (activation energy) is reduced when an enzyme is used Activation Energy Biochemical reactions may involve joining molecules together or splitting complex molecules – in each case energy is needed to break chemical bonds and start the reaction. This is called the activation energy. When the bonds break they become unstable and are now in the transition state - the reaction can start.

Enzyme anatomy An enzyme is usually represented by a simple diagram. Enzyme Substrate Active site

Enzyme anatomy An enzyme will interact with its specific substrate at the active site. Enzyme Substrate

Enzyme anatomy When the enzyme and the substrate bond at the active site this forms the enzyme-substrate complex. Enzyme – Substrate complex The enzyme will now work its magic on the substrate!

After the enzyme has acted on the substrate it will release the product. Enzyme Enzyme anatomy Product

Enzyme activity stages Separate enzyme and substrate 1.2. Enzyme – Substrate complex 3. Enzyme and product

Lock and key theory Enzymes are substrate specific. The active site is a specific shape. This means they only act on a single substrate.

Breakdown of Hydrogen Peroxide Hydrogen peroxide (H 2 O 2 ) is a harmful by-product of reactions inside cells. H 2 O 2 can be broken down into water H 2 O and oxygen O 2. Hydrogen peroxideWater + Oxygen ( H 2 O 2 ) (H 2 O) (O 2 )

Catalase Catalase is an enzyme which catalyses the following reaction. Hydrogen peroxideWater + Oxygen ( H 2 O 2 ) (H 2 O) (O 2 ) =

Investigation Aim: The aim of this experiment is to investigate how temperature affects the activity of the enzyme catalase. 20ml H 2 O drops of detergent (5 test tubes)

Investigation Each test tube will be incubated for 5 minutes at a different temperature. 10 ◦ 20 ◦ 30 ◦ 40 ◦ 50 ◦ Water bath

Investigation A 1g piece of liver will be added to each test tube after 5 minutes incubation and left for a further10 minutes. Water bath Liver sample

Temperature v Enzyme Activity Temperature ( o C) Increasing rate of Reaction Optimum temperature Increasing enzyme activity Enzyme being denatured

Lock & Key Theory - Specificty Enzyme H 2 O 2 (Substrate) Active site Oxygen and Water (Products)

Lock and key Enzyme H 2 O 2 ( Substrate ) Active site Shape altered.

Induced Fit The shape of an active site is specific to the shape of a substrate However, the active site is flexible. The shape of the active site can change slightly when it comes into contact with a substrate molecule so that the active site fits it better.

When there are two or more reactants, the shape of the active site determines the orientation of the reactants (how they line up) This ensures that they are held together in such a way that the reaction between them can take place. Substrate Affinity

Product Affinity The active site holds the two reactants closely together in an induced fit. Once the reaction has taken place the, products have a low affinity for the active site and are released.

Temperature and Enzymes Enzymes are affected by a change in temperature. If the temperature is particularly low, the enzyme activity will be very slow. As the temperature increases the enzyme activity increases, but only up to a certain point.

Temperature and Enzymes The temperature at which the enzyme works at its quickest is called the Optimum temperature. Most human enzymes have an optimum temperature around 37 o C Once the temperature is too high the enzyme (being a protein) is damaged and we say it has been denatured. Enzyme Denatured Enzyme

Enzyme Actions Enzymes can catalyse 2 different types of reaction… Degradation: the chemical breakdown of a substance from a complex molecule to a simple one as illustrated by amylase and catalase. Synthesis: the building of a complex molecule from simpler molecules.

Examples Amalase catalyses a degredation reaction breaking down starch to amalase. Phosphorylase catalyses a synthesis reaction building starch from Glucose-1-Phosphate. GLUCOSE-1-PHOSPHATESTARCH PHOSPHORYLASE (Product)(Substrate) (Enzyme) STARCHMALTOSE AMYLASE (Product)(Substrate) (Enzyme)

Effect of pH on Enzymes pH is a measure of how acid or alkali something is. The pH scale goes from 1 to 14, with 1 being very acidic, 14 being very alkaline and 7 being neutral. The shape of an enzyme can be affected by changes in pH and this will affect how well the enzymes work.

Effect of pH on Enzymes Like temperature, enzymes have an optimum pH, i.e. a pH when they are most efficient. The optimum pH varies from enzyme to enzyme. Our digestive system has a range of pH’s as the food passes through it, and this creates ideal conditions for specific enzymes.

Effect of pH on Enzymes pH Enzyme Activity (%) Pepsin Catalase Lipase

Higher Human Biology Enzyme and substrate concentration

Success criteria By the end of this lesson we will be able to: 1. State how enzyme concentration affects activity. 2. State how substrate concentration affects activity. 3. Predict the results of a given experimental situation involving different enzyme and substrate concentrations. 4. Design a valid experiment to investigate the effects of substrate and enzyme concentration of any given enzyme.

Enzyme concentration Enzymes = workers More workers = more work

Enzyme concentration As the concentration of enzyme is increase, the rate of reaction will also increase. Excess substrate Limited concentration of substrate available

Enzyme concentration Enzyme activity is related to active site availability. Enzyme moleculesSubstrate molecules Vs.

Enzyme concentration Enzyme activity is related to active sit availability. Enzyme moleculesSubstrate molecules Vs.

Enzyme concentration Enzyme activity is related to active sit availability. Enzyme moleculesSubstrate molecules Vs.

Substrate concentration When substrate concentration is increased, the rate of reaction also increases up to the point of active site saturation (available enzymes working at full capacity).

Substrate concentration Enzyme activity is related to active sit availability. Enzyme moleculesSubstrate molecules Vs.

Substrate concentration Enzyme activity is related to active sit availability. Enzyme moleculesSubstrate molecules Vs.

Substrate concentration Enzyme activity is related to active sit availability. Enzyme moleculesSubstrate molecules Vs.

Substrate concentration Enzyme activity is related to active sit availability. Enzyme moleculesSubstrate molecules Vs.

Enzyme inhibitors The villains of the enzyme world.

Inhibitors An inhibitor is a substance which slows down the rate of an enzyme controlled reaction. An inhibitor may even be able to halt an enzyme controlled reaction.

Enzyme inhibitors There are 2 categories of enzyme inhibitors. Competitive inhibitors Non competitive inhibitors

Enzyme inhibitors video

Competitive inhibitors A competitive inhibitor is a substance which is chemically similar to a substrate. Enzyme Substrate Inhibitor

Competitive inhibitors A competitive inhibitor will bind to the active site, physically blocking it. Enzyme – Inhibitor complex Substrate Active site blocked

Non Competitive inhibitors A non competitive inhibitor is a substance which attaches itself to the enzyme and changes its shape. Enzyme Substrat e Inhibitor This means the substrate cannot bind to the enzyme at the active site. The lock no longer fits the key.

Competitive vs. Non competitive Competitive and Non competitive inhibitors have slightly different effects. Enzyme molecules Substrate and Competitive inhibitor molecules Vs.

Competitive vs. Non competitive Competitive and Non competitive inhibitors have slightly different effects. Enzyme molecules Substrate and Competitive inhibitor molecules Vs.

Competitive vs. Non competitive Competitive and Non competitive inhibitors have slightly different effects. Enzyme molecules Substrate and Competitive inhibitor molecules Vs.

Competitive vs. Non competitive Competitive and Non competitive inhibitors have slightly different effects. Enzyme molecules and non competitive inhibitors Substrate and Competitive inhibitor molecules Vs.

Competitive inhibitors No inhibitor Competitive inhibitor present Increasing substrate concentration Increasing reaction rate A competitive inhibitor will slow down the rate of the reaction but with increased substrate concentration, the effect becomes weaker.

Non Competitive inhibitors No inhibitor Non Competitive inhibitor present Increasing substrate concentration Increasing reaction rate A non competitive inhibitor will slow down the rate of the and prevent the reaction from reaching the full potential reaction rate. Increasing the substrate concentration has no effect on the rate of reaction passed the inhibited maximum.

Competitive Inhibitors Competitive inhibition is when molecules of inhibitor compete for the active site with the substrate. The inhibitor’s molecular structure is similar to the substrate. A competitive inhibitor will block the active site. If concentration of inhibitor is low reaction rate will remain high. However, the more molecules of the inhibitor there are the greater the decrease in reaction rate. The degree of inhibition is affected by concentration of inhibitor and substrate

Non-Competitive Inhibitors Non-competitive inhibitors don’t combine with the active site. Instead the inhibitor attaches to another part of the enzyme. This alters the active site indirectly, which means the substrate is unable to combine with the enzyme. The degree of inhibition depends on the inhibitor concentration only.