Digestion in the Mouth
In the mouth food is chewed into smaller pieces. The teeth are used for biting and crushing the food, while the lips and cheeks prevent the food from falling out.
Pieces of food are mixed with saliva that contains the enzyme (amylase) that breaks down starch into glucose. The food is then swallowed.
Digestion in the stomach
The stomach muscles churn the food and mix it with the digestive juice produced by glands lining the stomach. The digestive juices break down proteins. A meal consisting of porridge will stay for less than an hour but a mixed meal containing protein and fat may be in the stomach for up to two hours.
Enzymes are proteins that are chemicals that dissolve food. They help up the rate of which can be digested. Salivary glands and the pancreas produce and pour their through tubes into the digestive canal.
Without enzymes food will take forever to digest, but with them it only takes a few hours. Enzymes have definite shape and are not used up in the reaction. One enzyme can be used many times over. Enzymes can either join or break up two molecules.
A reaction where enzymes join molecules together is known as an anabolic reaction.
Examples of anabolic reactions:
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Hundreds of glucose units are joined to form a long molecule of , which is then added to the .
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Proteins made up of hundreds of amino acids are added to make up a
A reaction where enzymes break molecules up is known as a catabolic reaction. Different enzymes act on different types of food groups and are therefore very specific. The names of enzymes usually end in -ase and are often named according to the substance on which they act.
The students concluded that the mixture has starch in it because the white paste turned blue black when iodine was added. However when the washing was added the colour changed again. This meant that the washing liquid obviously had enzymes in it to break down the starch.
The experiment concluded that an enzyme in the saliva broke down the starch found in banana.
Earlier it was said that are proteins. When we fry an egg the clear runny egg white changes to a white when it is heated up. Once this happens it can never be changed back to a runny . We say it has become denatured because it has changed its shape.
Enzymes are very sensitive to pH and and in extreme cases they become denatured. This means that by changing shape they cannot function properly.
Temperature affects enzymes
As the temperature rises the enzyme works much quicker, but if it gets too hot, above 45ºC the enzymes will denature.
Cold temperatures cause enzymes to become inactive.
pH affects enzymes
Enzymes are affected by changes in and alkaline conditions. Some enzymes like to work in an acid condition while others in an alkaline condition. Stomach enzymes work best in an acid condition; this is provided by the hydrochloric acid found there.
What does pH mean?
A solution can either be acid or alkaline. Lemon juice and hydrochloric acid found in the stomach are both examples of an acid. Soap is an example of an . The pH ranges from 0 to 14. Anything below 7 is an acid and above 7 is an alkaline or basic. Pure water is neither acidic nor basic and has a pH of 7 so it is said to be neutral. Human blood has a pH of about 7.4.
Most enzymes work best at a certain level of acidity or alkalinity.
Glucose, fats and amino acids are carried in the blood to where they are needed.
Carbohydrates - glucose
Glucose is used in cellular to provide energy. Energy is used for many activities. When there is more than the body needs it will store it as fat.
Fats - fatty acids and glycerol
Fats are used to make cell membranes, other structures and for energy. Any extra gets stored as fat.
Proteins - Amino acids
Amino acids are used to make new during , and replacing old cells. Amino acids cannot be stored as fat so they are sent to the liver where they are broken down. Part of it is sent to the kidneys to be added to the urine while the remaining part is used for energy.
