ENZYMES & DIGESTION

Noadswood Science, 2012

Enzymes & Digestion

To know how the enzymes in the digestive system aid digestion

Wednesday, April 19, 2023

Digestive System

Digestive System

Salivary gland

Mouth

Oesophagus (gullet or food

pipe)

Stomach

Rectum & anus

*Appendix

Small intestine

Large intestine

Mouth - putting food in your mouth is called feeding or ingestion. Teeth grind the food down, and saliva (produced from salivary glands) help make the food moist, easing swallowing (as well as the enzyme amylase which helps break down starch)

Oesophagus (gullet) - when you swallow, the trachea (windpipe) is shut off, and food passes down the oesophagus. Muscles in the wall above the food contract, making the piper narrower above the food, pushing it down (this is why you can eat, even when upside down)!Stomach - food is churned up with the strong acid (pH 1-2)

Digestive System

Salivary gland

Mouth

Oesophagus (gullet or food

pipe)

Stomach

Rectum & anus

*Appendix

Small intestine

Large intestine

Small intestine - small molecules are absorbed through the small intestine wall

Large intestine - food which we cannot digest (e.g. fibre) is passed into the large intestine, where water is removed. This forms a more solid material - faeces

Rectum & anus - faeces is stored in the rectum, eventually being pushed out of the anus - faeces is egested

*Appendix - in some animals, helps to break down cellulose, but no known use in humans

Enzymes

The enzymes involved in respiration, photosynthesis and protein synthesis work inside cells

Other enzymes are produced by specialised cells and released from them (the digestive enzymes are like this)

They pass out into the gut, where they catalyse the breakdown of food molecules

Enzymes

Enzymes are not living! They are special proteins which can break large molecules down.

There are specific enzymes, which break down specific nutrients: -

Amylase (carbohydrase) enzymes break down starch into simple sugars

Protease enzymes break down proteins into amino acids Lipase enzymes break down fats into fatty acids and glycerol

Anylase - starch to sugar Protease - protein to amino acids Lipase - fats to fatty acids & glycerol

Carbohydrates (amylase enzyme) Carbohydrates are digested in the mouth, stomach and small intestine Amylase is produced in the salivary glands, pancreas, and small

intestine

Chew a piece of bread for long enough, it will taste sweet (as the starch is broken down into simple sugars)

carbohydrates simple sugars

carbohydrates simple sugars

amylaseamylase

Proteins (protease enzyme)

Proteins are digested in the stomach and small intestine Protease is produced in the stomach (called pepsin),

pancreas and small intestine

Stomach acid is strong hydrochloric acid, helping digestion and killing harmful micro-organisms that may be in the food

protein amino acids

protein amino acids

proteaseprotease

Fats (lipase enzyme)

Fat is digested in the small intestine – bile (made in the liver) helps break fat into small droplets that are easier for the lipase enzymes to work on

Lipase is produced in the pancreas and small intestine

fat fatty acids + glycerol

fat fatty acids + glycerol

lipaselipase

Absoprtion

Digested food molecules are absorbed in the small intestine, passing through the wall of the small intestine into the bloodstream (where they are carried around the body to where they are needed)

Only small, soluble substances can pass across the wall of the small intestine

Large insoluble substances cannot pass through - this is why we need enzymes!

Digestion

The stomach produces hydrochloric acid, helping to begin digestion (and killing many harmful microorganisms that might have been swallowed along with the food)

The enzymes in the stomach work best in acidic conditions (low pH)

Digestion

After the stomach, food travels to the small intestine – the enzymes in the small intestine work best in alkaline conditions, but the food is acidic after being in the stomach

A substance called bile (produced in the stomach and stored in the gall bladder) neutralises the acid to provide the alkaline conditions needed in the small intestine (as well as breaking down fat)

Enzyme Locations

Summary of enzymes involved with digestion, what reaction they catalyse and where they are produced: -

Enzyme Reaction Catalysed Location Produced

Amylase Starch SugarsSalivary glands; pancreas;

small intestines

Protease Proteins Amino AcidsStomach; pancreas; small

intestines

LipaseLipids Fatty Acids +

GlycerolPancreas; small intestines

Summary

Amylase catalyses the breakdown of starch into sugars in the mouth and small intestine

Proteases catalyse the breakdown of proteins into amino acids in the stomach and small intestine

Lipases catalyse the breakdown of fats and oils into fatty acids and glycerol in the small intestine