Enzymes and the Digestive System, unit 1.2

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Major parts of the digestive system:

  • Salivary glands- pass enzymes by the salivary duct into the mouth, enzymes contain amylase to break down starch into maltose
  • Oesophagus- carries food from the mouth to the stomach, is made of a thick muscular wall
  • Stomach- muscular sac with an inner layer that stores enzymes. Stores and digests foods, protease is produced from glands within the wall. Contains strong HCl to kill microorganisms. Glands in stomach wall produce mucus that prevents stomach being digested by its own enzymes
  • Pancreas- large gland below the stomach that secretes pancreatic juice into the small intestine, which contains protease, lipase and amylase
  • Small intestine- long muscular tube, adapted for absorption by villi, which have their own microvilli and good blood supply, for increased surface area and diffusion. Glands in intestine walls produce more enzymes for digestion
  • Large intestine- absorbs water, so food within intestine becomes drier and forms faeces
  • Rectum- faeces are stored here before egestion via the anus

Physical breakdown: Food is cut into smaller pieces by the teeth, so that the surface area for digestion is increased, then it is churned up by the stomach muscles.

Chemical breakdown: Enzymes break down large, insoluble molecules into smaller units, by hydrolysis, which is the splitting of molecules by adding water to the chemical bonds that hold them together. Enzymes are otherwise known as hydrolases. Usually one enzyme splits a chain into sections which are then hydrolysed by another enzyme to give smaller molecules.

Carbohydrase/ Amylase breaks down carbohydrates, ultimately to monosaccharides.

Lipase breaks down lipids (fats and oils) to glycerol and fatty acids.

Protease breaks down proteins, ultimately to amino acids.

Once these smaller molecules have been absorbed and carried to their destination in the body, they are often rebuilt up again to large molecules, which is called assimilation.

Monomers are the individual units that make up longer chains, which are called polymers. Biological molecules like carbohydrates and proteins are polymers. Most are made up of just C, H, O and N.

In carbohydrates, a single monomer is a basic sugar known as a monosaccharide. Two monosaccharides are combined to form a disaccharide. Monosaccharides are sweet-tasting and soluble, and have the general formula (CH2O)n, where n is any number from 3-7.

The best known monosaccharide is glucose. It is a hexose (6-carbon) sugar with the formula C6 H12 O6.

All monosaccharides and some disaccharides (eg maltose) are reducing sugars, meaning that they can donate electrons to another chemical.
The test for reducing sugars involves reducing Benedict's reagent. 2cm3 of Benedict's reagent is added to the same amount of the food sample in a test tube, and heated gently in a boiling water bath for 5 minutes. If the solution is blue to start off with, a low concentration of sugar will give a yellow colour, ranging to red for high.

Certain combinations of monosaccharies form certain disaccharides:

  • Glucose


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