Living Cells Enzymes Mr G Davidson

Introduction to Enzymes Chemical reactions all occur at different rates. Some are very quick and some are extremely slow. Saturday, December 08, 2018 Mr G Davidson

Introduction to Enzymes We can speed up some chemical reactions by: Increasing the temperature 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. Saturday, December 08, 2018 Mr G Davidson

Catalysts A catalyst is a substance which can speed up a reaction without itself being altered in the reaction. When a catalyst is present, the reaction requires less energy to start it; activation energy . When a catalyst is present the reaction is quicker. A catalyst remains unchanged in the reaction and can be re-used. Saturday, December 08, 2018 Mr G Davidson

Breakdown of Hydrogen Peroxide Hydrogen peroxide (H2O2) is a harmful by-product of reactions inside cells. H2O2 can be broken down into water H2O and oxygen O2. Hydrogen peroxide Water + Oxygen (H2O2) (H2O) (O2) Saturday, December 08, 2018 Mr G Davidson

Breakdown of Hydrogen Peroxide Hydrogen peroxide can be broken down to water and oxygen by increasing the temperature. If it is placed in water baths of increasing temperatures, the number of bubbles of oxygen released increases with temperature. Saturday, December 08, 2018 Mr G Davidson

Biological Catalysts Enzymes are biological catalysts. Catalase is an enzyme, made by living cells, which can break down hydrogen peroxide. If we add a piece of living tissue to hydrogen peroxide, we can see bubbles of oxygen being released. The more bubbles released, the more catalase there is in the tissue. Saturday, December 08, 2018 Mr G Davidson

Specificity Catalase can only speed up the breakdown of hydrogen peroxide, not any other reaction. It is said to be specific. Each enzyme catalyses only one reaction. The substance the enzyme catalyses is called the substrate. Saturday, December 08, 2018 Mr G Davidson

Specificity All enzymes are made of protein. Enzymes have an area on their surface which is a specific shape, and it is here that the substrate attaches. This area is called the active site. Saturday, December 08, 2018 Mr G Davidson

Specificity The enzyme’s shape and the substrate’s shape are said to be complimentary. The substrate locks onto the enzyme at the active site and the reaction occurs. This is called the Lock and Key Theory. Saturday, December 08, 2018 Mr G Davidson

Specificity The reaction produces the products. Some enzymes are responsible for breaking down large substrates into smaller products, while others are responsible for the building up of large products from smaller substrates. Saturday, December 08, 2018 Mr G Davidson

Lock & Key Theory Substrate Active site Enzyme Product Product Saturday, December 08, 2018 Mr G Davidson

Starch & Amylase Starch is a carbohydrate. It contains energy and is found in many foods. Starch molecules are very large and cannot pass through cell membranes. Therefore, they need to be broken down to smaller molecules. Saturday, December 08, 2018 Mr G Davidson

Starch & Amylase This is done by an enzyme called AMYLASE. Amylase is found in our saliva. The starch is broken down to molecules of a sugar called maltose. AMYLASE STARCH MALTOSE (Enzyme) (Substrate) (Product) Saturday, December 08, 2018 Mr G Davidson

Starch & Amylase Starch molecule Maltose molecules Saturday, December 08, 2018 Mr G Davidson

Controls When we carry out any experiment, it is important to have a control. The control allows us to make a valid comparison. e.g. if we are testing the action of amylase by putting it in starch solution, a control would be to have another tube and put water in the starch solution. This way we know it is the amylase that is responsible for the changes that occur. Saturday, December 08, 2018 Mr G Davidson

Synthesis Reactions So far, we have looked at enzymes which break down molecules, e.g. amylase breaks down starch. How is the starch built up in the first place? Plants make glucose using sunlight. This glucose is converted to glucose-1-phosphate. Saturday, December 08, 2018 Mr G Davidson

Synthesis Reactions An enzyme called PHOSPHORYLASE is used to join glucose-1-phosphate molecules together to make starch. This is called a synthesis reaction. PHOSPHORYLASE GLUCOSE-1-PHOSPHATE STARCH (Enzyme) (Substrate) (Product) Saturday, December 08, 2018 Mr G Davidson

Synthesis Reactions There are many other synthesis enzymes which allow organisms to build up structural molecules as well as storage molecules, e.g. The liver converts excess glucose to glycogen for storage. Skin cells convert amino acids into collagen which allows the skin to be flexible but tough. Saturday, December 08, 2018 Mr G Davidson

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. Saturday, December 08, 2018 Mr G Davidson

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 37oC Once the temperature is too high the enzyme (being a protein) is damaged and we say it has been denatured. Saturday, December 08, 2018 Mr G Davidson

Temperature v Enzyme Activity Temperature (oC) 10 20 30 40 50 Increasing rate of Reaction Optimum temperature Increasing enzyme activity Enzyme being denatured Saturday, December 08, 2018 Mr G Davidson

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. Saturday, December 08, 2018 Mr G Davidson

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. Saturday, December 08, 2018 Mr G Davidson

Effect of pH on Enzymes Enzyme Activity (%) pH 20 40 60 80 100 1 2 3 4 5 6 7 8 9 10 11 12 pH Enzyme Activity (%) Pepsin Catalase Lipase Saturday, December 08, 2018 Mr G Davidson