Enzymes in digestion

how enzymes are used in digestion and waht breaks down carbohydrates, proteins and fats (lipids). For the edexcel GCSE science course (B2)

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Enzymes in Digestion
When you eat food it is mostly made up of large insoluble molecules that your body cannot absorb
straight into the blood stream so they need to be broken down or digested into smaller, soluble
molecules that can be absorbed into cells.
Digestive enzymes (unlike normal enzymes) work outside the cells of the body and are produced by
specialised cells found in glands (like the salivary glands and the pancreas) and in the lining of your
gut. They get mixed up with the food in the gut and break them down.
The gut does 3 main things to aid digestion...
1) Helps break up food into smaller pieces with a large surface area for enzymes to work on.
2) Mixes food with digestive juices so enzymes come into contact with as much food as possible
3) Moves food from 1 area to the next
Digesting carbohydrates
Enzymes that break carbs down are called carbohydrases. Starch is the most common carb an is
broken down into sugars like glucose. The reaction is catalysed by amylase. It is produced in the
salivary glands (meaning digesting starts in your mouth) but is also found in the pancreas and small
intestine. No digestion takes place in the pancreas as all the enzymes made there go to the small
intestine, where most the start is digested.

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Digesting proteins
Proteins are found in fish, meat and cheese and are broken down into amino acids. It is catalysed by
protease enzymes. They are produced from the stomach, pancreas and small intestine. The
breakdown takes place in the stomach and small intestine.
Digesting fats
Lipids (aka fats and oils) are broken down into fatty acids and glycerol. The breakdown takes place
in the small intestine. It is catalysed by lipase enzymes which are made in the pancreas and small
intestine.…read more

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Once food is broken down into soluble molecules they leave the small intestine and pass into the
blood supply to be carried to cells.
Using the digested food
Glucose is used by the cells in respiration.
Fatty acids and glycerol may be used as a source of energy to build cell membranes, make
hormones and as fat stores.
The amino acids build the proteins your cells need. This protein synthesis takes place on the
ribosomes.…read more


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