Brown's GCSE/IGCSE/O level KS4 science-CHEMISTRY Revision Notes
Oil, useful products, environmental problems, introduction to
13. Amino acids, proteins, enzymes & chromatography
What is an amino acid? What are
proteins? What do proteins do? How are proteins formed from amino acids? How can
we use chromatography to investigate protein structure? A spot of protein
cooking chemistry! What happens when meat or eggs are cooked?
Index of KS4 Science GCSE/IGCSE
Chemistry Oil & Organic Chemistry Pages: 1.
Fossil Fuels : 2. Fractional distillation of crude oil & uses of fractions : 3.
ALKANES - saturated hydrocarbons and combustion : 4.
Pollution, carbon monoxide, nitrogen oxides, what
makes a good fuel?, climate change-global warming :
5. Alkenes - unsaturated hydrocarbons :
6. Cracking - a problem of supply and demand, other products :
7. Polymers, plastics, uses and problems :
8. Introduction to Organic Chemistry - Why so many series of
organic compounds? : 9. Alcohols - Ethanol
- properties, reactions, biofuels :
10. Carboxylic acids and esters : 11. Condensation polymers, Nylon & Terylene,
comparing thermoplastics, fibres and thermosets
12. Natural Molecules - carbohydrates - sugars
- starch : 13. Amino acids, proteins,
enzymes & chromatography : 14. Oils, fats,
margarine and soaps :
15. Vitamins, drugs-analgesic medicines & food
additives and aspects of cooking chemistry! : 16. Ozone, CFC's and free
radicals : 17. Extra notes, ideas and links on
Global Warming and Climate Change : Multiple Choice and Gap-Fill Quizzes:
m/c QUIZ on Oil Products (GCSE/IGCSE easier-foundation-level)
m/c QUIZ on Oil Products (GCSE/IGCSE harder-higher-level) :
IGCSE/GCSE m/c QUIZ on other Aspects of Organic Chemistry
3 Easy linked GCSE/IGCSE Oil Products word-fill worksheets
13. Naturally Occurring Molecules from plants
13a. Proteins and Amino Acidsand
- Amino acids
are carboxylic acids
(like ethanoic acid) but one of the hydrogen atoms of the 2nd carbon atom is substituted with an
amino group (a nitrogen + two hydrogens gives -NH2). Another
hydrogen on the same 2nd carbon can be substituted with other groups of
atoms (R) to give a variety of amino acids.
The simplest is aminoethanoic acid or 'Glycine'
another amino acid called 2-aminopropanoic acid or 'Alanine'
- All amino acids have the general structure H2N-CH(R)-COOH
(see diagram by 5b heading).
can vary, think of it as the 'Rest of the
- R = H for Glycine, R = CH3 for
- Amino acids can polymerise together, by condensation
polymerisation, forming proteins or polypeptides.
- The peptide linkage is formed by
elimination of water between two amino acids.
+ HNH-CH(R)-COOH ==> H2N-CH(R)-CO-HN-CH(R)-COOH
+ H2O etc. so ...
- n H2N-CH(R)-COOH ==>
-NH-CO-CH(R)-NH-CO-CH(R)-NH-CO-CH(R)-NH-CO-CH(R)- etc. n units long
- So proteins are
condensation polymers of amino acids.
- Proteins have the same
(amide) linkages as nylon but with different units.
- Proteins are an important component of
tissue structure and enzymes (powerful biological chemical catalysts) are
also protein molecules.
Proteins tend to adopt a particular three dimensional shape (3D) which aids
When proteins are heated with aqueous
hydrochloric acid or sodium hydroxide solution they are hydrolysed to amino acids.
(deoxyribonucleic acid) are the molecules that carry the genetic code or
molecular 'blueprint' for all forms of life. For example it encodes through
its base components the exact sequence of amino acids needed to synthesise a
A spot of cooking
Food is cooked for
The high cooking
temperature kills harmful microbes-bacteria, as long as cooked for the
required time at a high enough temperature.
It may improves the
It may improve the
flavour and taste (but remember some foods might taste better raw e.g.
It makes it easier
for the body to digest the food.
Most of meat from
animals consists of protein together with smaller amounts of water and fat.
Eggs and fish are also good sources of protein.
have a definite shape (diagram 1. above).
During the cooking of
meat irreversible chemical changes take place.
The complex and
specific structure of protein molecules is partly broken down in the
The high cooking
temperature promotes particular chemical reactions to happen.
The structure changes
and some of the chemical bonds are broken and new molecules can be formed
that have a different taste-flavour and texture giving the food its own
characteristic 'cooked' character.
The breaking down of
protein complex protein molecules is called denaturing.
A similar process
happens in the cooking of carbohydrate foods like potatoes which are broken
down into far more readily digestible molecules.
Chromatography - a method of analysis
means breaking down a
molecule with water to form two or more products.
When proteins are heated with aqueous acid
they are hydrolysed to amino acids.
Acid hydrolysis of complex
carbohydrates (e.g.. starch) gives simple sugars.
Paper or Thin layer chromatography is used to separate
coloured compounds (illustrated above).
1 to 5 represent five pure compounds, 6 is a
mixture. Red, brown and blue make up the mixture because its spots
horizontally line up with the three known colours.
The substances (solutes)
to be analysed must dissolve in the solvent, which is called the
mobile phase because it moves. The solvent may be water or an organic
liquid like an alcohol (e.g. ethanol) or a hydrocarbon, so-called
The paper or thin layer of
material on which the separation takes place is called the stationary or
immobile phase because it doesn't move.
The distance a substance
moves, compared to the distance the solvent front moves (top of grey area on
diagram 2) is called the reference or Rf value and has a
value of 0.0 (not moved - no good), to 1.0 (too soluble - no good either), but
Rf ratio values between 0.1 and 0.9 can be useful for analysis and
distance moved by dissolved substance (solute) / distance moved by solvent
However, amino acids and sugars are colourless,
but can still be separated in this way, so read on!
Thin layer or paper chromatography
can still used
to separate and identify the products of hydrolysis of
carbohydrates and proteins because you make them coloured by using another
The hydrolysis can be done by boiling the
carbohydrate or protein with hydrochloric acid.
The hydrolysed mixture is then 'spotted'
onto the pencil base line of the chromatography paper.
Known sugars or amino acids are also
spotted onto the base line too.
The prepared paper is then placed
vertically in a suitable solvent, which rises up the paper.
Since the products are colourless, the
dried chromatogram is treated with another chemical to produce a
You can then tell which amino acids made
up the protein or the sugars from which the carbohydrate was formed.
The number of different spots tells
you how many different amino acids or sugars made up the natural
Spots which horizontally match the
standard known molecule spots confirm identity.
gives one spot
because only glucose is formed on hydrolysis.
thin layer/paper chromatography.
Note that if organic
compounds are gases or volatile (easily vapourised) liquids, they can be
gas-liquid chromatography (in section 6. of the GCSE Extra
Industrial Chemistry page).
Multiple Choice Quizzes and Worksheets
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on other aspects of Organic Chemistry
3 linked easy Oil Products gap-fill quiz worksheets
ALSO gap-fill ('word-fill') exercises
originally written for ...
... AQA GCSE Science
Useful products from
crude oil AND
... OCR 21st C GCSE Science
Worksheet gap-fill C1.1c Air
pollutants etc ...
... Edexcel 360 GCSE Science
Crude Oil and its Fractional distillation
... each set are interlinked,
so clicking on one of the above leads to a sequence of several quizzes
Level Organic Chemistry revision notes
Revise KS4 Science GCSE/IGCSE/O level
Chemistry Revision-Information Study Notes for revising for AQA GCSE Science, Edexcel
GCSE Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science WJEC/CBAC
GCSE science-chemistry CCEA/CEA GCSE science-chemistry
(and courses equal to US grades 8, 9, 10)
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