Enzymes and Digestion

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  • Created on: 25-01-15 20:00
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Enzymes and digestion
Carbohydrates
All monosaccharides and some disaccharides (e.g. maltose) are reducing sugars. A reducing sugar
is a sugar that can donate electrons to another chemical, in this case, Benedicts reagent. We can
therefore use Benedicts to test for a reducing sugar.
The sugar solution is added to an equal volume of Benedicts reagent and the two are heated in a
water bath.
The results of the Benedicts test vary according to the concentration of reducing sugar present,
demonstrating its semi-quantitative nature as the differences in colour can be used to estimate
the approximate amount of reducing sugar in the sample.
When monosaccharides join to form a glycosidic bond, a molecule of water is released, and so it is
called a condensation reaction. When water is added to the disaccharide under suitable
conditions, it breaks the glycosidic bond in a hydrolysis reaction.
To test for non-reducing sugars we must first hydrolyse the molecule to break it down into its
monosaccharide components To do this, first test with Benedicts to determine whether it is a
non-reducing sugar, if the solution remains blue (negative result) then add dilute hydrochloric acid
to the solution and heat in a water bath for approximately 5 minutes. Slowly add some sodium
hydrogencarbonate to the test tube to neutralise the solution and check the pH. Re-test the
solution with Benedicts in a water bath and if a non-reducing sugar was present, a positive result
will now be given.
Polysaccharides are long chains of monosaccharide molecules. They are large and insoluble,
making them suitable for storage. Starch is a polysaccharide found in many parts of plants, formed
by the linking of glucose molecules. Starch is easily detected by its ability to change
yellow/orange potassium iodide solution to a blue/black colour.

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Proteins
Amino acids are the basic monomer units which combine to make a polymer called a polypeptide.
Every amino acid has a central carbon atom to which four different chemical groups are attached:
Amino group (-NH2)
Carboxyl group (-COOH) ­ an acidic group hence amino acid
Hydrogen atom (-H)
R group ­ varies for each amino acid
The peptide bond is formed by a condensation reaction and split by hydrolysis.…read more

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The secondary structures can be twisted even further to give the complex, often unique structure
of each protein. This struture is maintained by a number of different bonds, including:
Disulfide bonds which are strong and not easily broken.
Ionic bonds which are formed between carboxyl and amino acid groups. They are weaker
than disulfide bonds and easily broken by changed in pH.
Hydrogen bonds which are numerous but weak and easily broken.…read more

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Enzymes
Enzymes are globular proteins that act as catalysts, they lower the activation energy, allowing
reactions to take place at lower temperatures than normal.
Only a small region of the large enzyme moleule is functional. This is known as the active site,
which forms a small, hollow depression within the much larger enzyme molecule. The molecule on
which the enzyme acts is called the substrate, which is of a complementary shape to the active
site and so they can bind and for the enzyme-substrate complex.…read more

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This is called enzyme denaturation and it is a permanent
change.
Effect of pH
Each enzyme has an optimum pH and in a similar way to a rise in temperature, a change in pH
reduces the effectiveness of an enzyme and may eventually cause it to stop working altogether, it
becomes denatured.…read more

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