bio topic 1

• The pH affects enzymes, interfering with the bonds holding the enzyme together when it's too high or too low, changing the shape of the active site and denaturing the enzyme.
• All enzymes have a pH that they work best at, which is called the optimum.
• The optimum pH is different for different enzymes, depending on where they work.
• For many enzymes, the optimum pH is neutral pH 7, but not always.
• Pepsin is an enzyme used to break down proteins in the stomach, it works best at pH 2, making it well-suited to the acidic conditions in the stomach.
• Amylase catalyses the breakdown of starch to maltose.
• Starch can be detected using iodine solution, which changes from brown-orange to blue-black if starch is present.
• The effect of pH on amylase activity can be investigated by putting a drop of iodine solution into every well of a spotting tile, heating a beaker of water to the optimum temperature of the amylase being used, and timing how long it takes for the amylase to break down all of the starch.
• The experiment can be repeated with butter solutions of different pH values to see how pH affects the time taken for the starch to be broken down.
• Variables that need controlling in the experiment include the concentration and volume of the amylase and starch solutions and the temperature of the reaction mixture.
• Enzymes need the right conditions, such as the right temperature, for them to work best, these are called optimum conditions.
• The optimum temperature for an enzyme is the temperature at which it is most active.
• Enzymes in the human body normally work best at around 37 °c.
• Substrate concentration also affects the rate of reaction, with a higher substrate concentration leading to a faster reaction.
• This is because it's more likely that the enzyme will meet up and react with a substrate molecule.
• After a certain point, adding more substrate makes no difference as all the active sites are full.
• Carbohydrates, proteins and lipids are big molecules, which are essential for life.
• Organisms need to be able to break down these molecules into their smaller components, so they can be used for growth and other life processes.
• These breakdown reactions are catalysed by enzymes.
• Many of the molecules in the food we eat are too big to pass through the walls of our digestive system, so digestive enzymes break them down into smaller, soluble molecules.
• These can pass easily through the walls of the digestive system, allowing them to be absorbed into the bloodstream.
• They can then be used by cells to be used by the body.
• Plants store energy in the form of starch, a carbohydrate.
• When plants need energy, enzymes break down the starch into smaller molecules (sugars).
• These can then be respired to transfer energy to be used by the cells.
• The emulsion test for lipids involves grinding a solid food sample, transferring some of the food into a test tube, adding 2 cm of ethanol, shaking the test tube well for about a minute, pouring the solution into a test tube containing 2 cm of distilled water, and observing for the presence of lipids as a milky emulsion.
• The buret test for proteins involves transferring 2 cm of a food sample to a test tube, adding 2 cm of potassium hydroxide solution to make the solution alkaline, adding a few drops of copper(I) sultate solution, and observing the colour change from blue to pink or purple.
• The iodine test for starch involves adding a few drops of iodine solution to a food sample and observing the colour change from brown to blue-black.
• Calorimetry experiments involve burning a small amount of dry food to measure the amount of energy it contains, which is released as heat and is known as neot.
• Reducing sugar changes colour from brown to yellow or brick-red as the concentration increases.
• Different types of enzymes catalyse the breakdown of carbohydrates, proteins and lipids.
• Carbohydrases convert carbohydrates into simple sugars.
• Amylase is an example of a carbohydrase that breaks down starch and maltose.
• Proteases catalyse the conversion of proteins into amino acids.
• Lipases catalyse the conversion of lipids into glycerol and fatty acids.
• Organisms also need to be able to synthesise carbohydrates, proteins and lipids from their smaller components.
• Enzymes are used to catalyse the reactions involved in synthesising carbohydrates, proteins and lipids.
• Carbohydrates can be synthesised by joining together simple sugars.
• Glycogen synthase is an enzyme that joins together lots of chains of glucose molecules to make glycogen, a molecule used to store energy in animals.
• Proteins are made by joining amino acids together.