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Full summary notes- A LEVEL- Unit 1 - Biological molecules
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- AQA
Full topic notes for Unit 1 Biological Molecules. Clear and carefully designed. Includes diagrams for understanding.
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M.REEVEYAQA Unit 1- Biological Molecules
Monomers → the smaller units from A condensation reaction joins two molecules together with
which larger molecules are made. E.g. the formation of a chemical bond and involves the elimination
monosaccharides, amino acids and of a molecule of water.
nucleotides.
A hydrolysis reaction breaks a chemical bond between two
Polymers → molecules made from a molecules and involves the use of a water molecule.
large number of monomers joined
together. E.g. proteins, polysaccharides condensation
and DNA.
hydrolysis
Monosaccharides (the monomers from
which larger carbohydrates are made).
-Glucose
-Fructose
-Galactose
Disaccharides (two monosaccharides
bonded together in a condensation
reaction with a glycosidic bond)
-Maltose = 2 glucose monosaccharides
-Lactose = 1x Glucose + 1x Galactose
-Sucrose= 1x Glucose + 1x Fructose
Polysaccharides- Formed by the condensation of many glucose units.
1. Starch (alpha glucose)
Starch stores energy in plants and is a mixture of two polysaccharides called amylose and amylopectin.
Insoluble so will not affect cell water potential
Compact so a lot of energy can be stored in a small space
Has many side branches which can be acted on by enzymes to release its energy.
2. Glycogen (alpha glucose)
Glycogen is the main energy storage molecule in animals
Branches = energy can be released quickly as enzymes can act simultaneously.
Coiled and compact- large energy stored
Insoluble- does not affect the water potential of cells.
3. Cellulose (beta glucose)
Cellulose gives rigidity to cell walls. Carbon 1 to 4 Glycosidic bond.
Straight, unbranched chain. H-bond cross links between parallel microfibrils.
, M.REEVEY
AQA Unit 1- Biological Molecules
Reducing sugars → sugars that can Test for Non-Reducing Sugars
donate an electron. All monosaccharides
and some disaccharides (maltose and 1. 2cm3 of liquid food sample is added to 2cm3 of Benedict's
lactose) are reducing sugars. Reagent. Water bath for 5 minutes to gently warm.
Non-reducing sugars → sugars that 2. If the colour does not change from blue to brick red then a
cannot donate electrons; therefore, they reducing sugar is not present.
cannot be oxidised (e.g. sucrose).
3. Another 2cm3 of the same food sample is then taken and
2cm3 of dilute HCl. Water bath for 5 minutes. The dilute HCl
will hydrolyse the disaccharides and polysaccharides into
their constituent monosaccharides.
Test for Reducing Sugars
4. After this some sodium hydrogen carbonate is added in
1. Add 2cm3 of food sample into a test order to neutralise the test tube as the Benedict's Reagent. pH
tube. paper is used to check that the solution is neutralised.
2. Add an equal volume of Benedict's 5. The solution can now be retested.
reagent.
6. Colour changes from the blue Benedict's Reagent to brick
3. Heat the mixture in a water bath (just red (orange-brown).
boiling) for five minutes.
4. If reducing sugar present the
Benedict's solution goes from blue → red Test for Starch
A chemical test for starch is iodine/potassium iodide.
If the solution turns blue/black in colour from orange-brown
then starch is present.
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