Enzymes and the digestive system - chapter 2

Noted for the whole of AQA biology chapter 2

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Unit 2 - Enzymes and the digestive
Enzymes and digestion - 2.1
The human digestive system is made up of a long muscular tube and it associated
glands. These glands secret enzymes in order to break down large molecules into
smaller ones, this allow them to absorbed.
The digestive system provides an interface with the environment because food
substances enter the body through it.
Major parts of the digestive system
The oesophagus - Carries food from the mouth to the stomach. Adapted for
transport rather than digestion. Made from a thick muscular wall.
The stomach - It is a muscular sac with an inner layer that produces enzymes. Stores
and digests food, especially proteins. It has glands, which produce enzymes in order
to digest proteins. Other glands in the stomach produce mucus, the mucus prevents
the stomach being digested by its own enzymes.
The small intestine - Long muscular tube. Produces enzymes in its wall for the
further digestion of food. The inner walls are folded in villi, in order to give the small
intestine a large surface area. The surface area is then increased further as on the villi
there are microvilli on the epithelial cells of each villus. This adapts the small intestine
for its purpose of absorbing the products of digestion into the bloodstream.

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The large intestine - Absorbs water, most of which has come from the secretion in
the digestive glands. The food in the large intestine therefore becomes drier and
thicker in consistency in order to form faeces.
The rectum - The final section of the intestines. The faeces are stored here, before
being removed by anus in the process of egestion.
The salivary glands - Situated near the mouth, they pass their secretions via a duct
into the mouth.…read more

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Carbohydrates - monosaccharides - 2.2
Some carbohydrate molecules are large whilst others are small.
Carbon atoms readily form bonds with other carbon atoms; this allows a sequence of
carbon atoms of various lengths to build up, which form a backbone along which
other atoms can attach to.
Carbon containing molecules are referred to as organic as life on earth is based upon
the versatile carbon atom.
The making of large molecules
Carbohydrates are made up of a chain of individual molecules.…read more

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Carbohydrates - disaccharides and polysaccharides - 2.3
Glucose + Glucose = Maltose
Glucose + Fructose = Sucrose
Glucose + Galactose = Lactose
When monosaccharides join a molecule of water is lost, therefore the reaction is
called a condensation reaction. The bond that is formed is called a glycosidic
When water is added to a disaccharide it breaks the glycosidic bond releasing the
monosaccharides. This is called hydrolysis.…read more

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Add another 2cm3 of the food sample to 2cm3 of dilute hydrochloric acid in a
test tube and place the test tube in gently boiling water bath for 5 minutes.
The dilute hydrochloric acids will hydrolyse any disaccharide present and break
it into its monosaccharides.
5. Slowly add hydrocarbonate solution to the test tube in order to neutralise
the hydrochloric acid.
6. Repeat steps 2 and 3 with the newly formed monosaccharides, in order to
see if a non-reducing sugar was present.…read more

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Saliva contains salivary amylase. This begins to hydrolyse any starch
in the food into maltose. It also contains mineral salts in order to
maintain a neutral pH. This is the optimal pH for amylase to work in.
4. Once the food is swallowed it enters the stomach with has acidic
conditions. The acid denatures the amylase and prevents the
further hydrolysis of starch.
5. The food is passed into the small intestine where it mixes with
pancreatic juice secreted from the pancreas.
6.…read more

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They have to be fed special non-milk food rich in calcium and
vitamin D
Proteins - 2.5
Proteins are large molecules.
Each organism has numerous proteins that differ from species to species.
The shape of one type of protein differs from all over proteins.
Proteins are the most important molecules to life.
Enzymes are a group of proteins essential for life, and are made from
proteins; there is a huge variety in their functions as there are many
enzymes.…read more

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Protein structure cont.…read more

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Enzymes are biological catalysts. They alter the rate of reactions without
going under permanent changes themselves. They do not make reactions
happen but speed them up.
Enzymes and lowering activation energy
For some reactions to take place naturally a number of conditions must be
1. There must be sufficient energy to alter the arrangement of their
2. The energy of the products must be less than that of the
3.…read more

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For an enzyme to work it must come into physical contact with its substrate
and have an active site that fits the substrate.
Measuring enzyme-catalysed reactions
The two most frequently measured events are:
1. The formation of the products of the reactants
2.…read more


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