Download Metabolic pathways File

Metabolic pathways
The metabolic pathways chart
All known reactions in living cells have been drawn on a single diagram. Each reaction is linked to the other
reactions it interacts with; the whole is known as the ‘metabolic pathways chart’. The chart is somewhat
mind-boggling the first time you see it, and you do not need to know the detail. But with careful study it
begins to make sense.
Q1 What is meant by:
a
metabolism
b
metabolic pathways?
The chart used today is built on many years’ work. The current chart, at the time of writing, is the 22nd
edition published in 2003. The chart is largely the work of one man, Donald Nicholson.
Born in 1916, Donald Nicholson graduated in chemistry in 1936. In 1946, after working for a large
pharmaceutical firm, he moved to Leeds Medical School where he taught the metabolic reactions of bacteria.
In the 1950s about 20 different pathways were known, and Dr Nicholson realised that it is only when the
pathways are put together that they really make sense.
Dr Nicholson drew the first chart by hand in 1955. It was rather like putting the pieces of a jigsaw together.
The first printed copies of his metabolic pathways chart appeared in 1961, and were enthusiastically
received. Since then millions of copies of the chart have been printed, and the charts are now freely available
on the Internet for anyone to download.
At the age of 80, Dr Nicholson bought a computer and created the first page-size ‘Minimaps’ of individual
pathways. They show where in the cell the metabolic processes in the pathway occur. They are a popular
format as they are A4 size.
In 2009 Dr Nicholson was working on ‘Animaps’, animated maps showing what happens to molecules when
they enter the active sites of enzymes, and how bonds break and are formed.
Go to the home page of the International Union of Biochemistry & Molecular Biology (IUBMB) Nicholson
website. Click on the ‘Metabolic Pathways Chart’ in the right-hand menu and then click to download. This
may take a few moments, but when it downloads you will have the full and latest metabolic pathways chart
on your screen. If the text is too small to read, make sure the setting in the top tool bar is on at least 125%.
The overall chart will be so large that you will need to move it around the screen to see the whole of it.
Q2 Different groups of molecules on the metabolic pathways chart are shown in different colours. What
colour are the saccharides, including the hexoses and pentoses? You will find them in the top left corner
of the chart. Hint: increasing the viewing size to about 600% makes it easier to see the text colour.
Q3 State the colour given to amino acids by finding ornithine and glycine. They are in the bottom right-hand
corner of the chart.
Q4 Find glucose in the horizontal centre, not far from the top of the chart. Follow the reactions down to
pyruvate, then round the Krebs cycle, shown in black on a yellow background. Follow the H + from the
Krebs cycle along the carriers of the electron transport chain, down to the bottom of the chart where it
becomes H atoms. Notice where they combine with oxygen to form water (droplets are shown). Also
notice the output of ATP. What colour is ATP given in?
Q5 Reduce the size of your view of the metabolic pathways chart to about 50%. Locate glucose again (you
should just about be able to see it). Notice how the three main stages of respiration form the backbone
of all the reactions taking place inside a cell. Suggest why this might be so.
Q6 The oxygen that combines with hydrogen to form water sits at the end of a long arrow on the chart.
Follow this back and:
a
name the molecule which the oxygen has been produced from
b
name the overall process in which the oxygen is produced.