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Chapter 1 - Biological Molecules 
 
Carbohydrates 
Long-chain carbohydrates (​polysaccharides​) are made up from many smaller, repeating 
units (​monosaccharides​)
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​Glucose​ is an 
example of a monosaccharide and has ​two different isomers (​ alpha and beta)
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● Add 2cm3 of the food sample to a test tube
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● Add an equal volume of Benedict’s reagent
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● A positive result forms a yellow/orange/brick-red solution
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● Complete the Benedict’s test and obtain a negative result
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● Boil the sample
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Polymers of Glucose 
 
Polysaccharide  Structure/Function 

Where is it found? 

Starch 

Made from ​alpha​ glucose
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is storage of energy
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It is ​large​ so 
that it cannot diffuse out of cells
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Glycogen 

Made from ​alpha​ glucose
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Made of 
amylose​ and a
​ mylopectin​
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Amylopectin is ​highly​ ​branched 
and ​short-chained​ for rapid hydrolysis 
and ​quick​ r​ elease​ ​of​ e
​ nergy​
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It has ​straight​,  Found in the ​cell​ ​walls​ of 
unbranched​ chains that allow hydrogen  plant​ cells
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An individual hydrogen 
bond is weak, but together they form a 
strong​ u
​ nit​ and add strength to the cell 
wall to allow it to w
​ ithstand the 
pressures of osmosis
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Specifically found in the 
liver​ and m
​ uscle​ c
​ ells​ of 
humans
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The main groups of lipids are ​triglycerides a
​ nd ​phospholipids
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● Insulation - ​Fats are slow conductors of heat, so can retain heat within the body
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● Protection - ​Fat is stored around vital organs for protection, such as the kidneys
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Between 
each fatty acid chain and the glycerol, there is an ​ester​ ​bond​ formed via a condensation 
reaction
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They also ​release water when oxidised​, making them good sources of water for 
organisms
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These molecules have h
​ ydrophilic heads ​and h
​ ydrophobic tails​
...
This helps to form a hydrophobic barrier between the 
inside and outside of cells as cell surface membranes contain a ​phospholipid bilayer​
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Test for lipids: 
● Add 5cm3 of ethanol to the sample per 2cm3 of the sample
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● Then, add 5cm3 of distilled water and shake gently
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Light passing through the emulsion ​refracts​ as it passes from oil droplets to water 
droplets, making it appear cloudy
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They form 
peptide​ bonds between monomers
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Primary Structure - S
​ equence of amino acids
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Tertiary Structure - T
​ he final 3D structure of a protein
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Quaternary Structure - ​Large proteins that form complex molecules containing a 
number of individual polypeptide chains
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Test for Proteins: 
● Place the solution is a clean, dry test tube
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● If protein is present, the solution will turn purple
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Enzymes 
An enzyme is a ​biological catalyst t​ hat speeds up the rate of a biological reaction by 
lowering the activation energy​ of a reaction by ​providing an alternate route ​for the 
reaction to occur
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Factors affecting enzyme activity: 
 
Factor 

Description 

Temperature 

A temperature too high denatures 
the active site of the enzyme and 
changes the tertiary structure so 
that no E-S complexes can be 
formed
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This 
denatures the enzyme so that no 
E-S complexes can be formed
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Substrate 
concentration 

As substrate concentration 
increases, the rate of reaction 
increases until all the substrates 
are saturated
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This does not change the shape of the active site
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Non-competitive inhibitors - B
​ ind to the ​allosteric site​ of an enzyme
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No active 
site-substrate complexes can be formed as the enzyme is ​denatured

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