Molecules to metabolism 2.1

The structure of living organisms can be partly explained by the molecules which they are made from. Live is based on carbon because the way in which carbon atoms form covalent bonds is central to the structure of the molecules which make up the bodies of all animals, plants and bacteria.

Key words

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Revision summary list for 2.1 Molecules to metabolism

Carbon based compounds

  • Molecular biology is explaining biological processes in terms of the chemicals involved.
  • The is a diversity of Carbon based compounds in living things because carbon atoms can form four covalent bonds.
    e.g. carbohydrates, lipids, proteins & nucleic acids.
  • All the enzyme-catalysed reactions in a cell make up its metabolism. There are two types:
    • Anabolism: forming macromolecules from monomers by condensation.
    • Catabolism: breaking complex macromolecules into simpler molecules by hydrolysis.
  • Some biological compounds can be synthesized ouside of living things: e.g. urea.

Drawing molecules

  • Draw diagrams of:
    • αD-glucose & βD-glucose,
    • D-ribose,
    • a fatty acid
    • an amino acid with generalised R-group.
  • Identification of biochemicals from diagrams to include:
    • monosaccharides
    • disaccharides,
    • lipids (triglycerides, phospholipids and steroids)
    • amino acids
    • polypeptides and peptide bonds.
  • Knowledge of the Benedicts reagent test for reducing sugars and iodine to test for starch.

Revision mind map

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Review questions

This is a self marking quiz containing questions covering the topic outlined above.
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Which of the following processes could be described as catabolism?

Anabolism is building up of large complex molecules from smaller simple units (Hint to remember: anacondas are long snakes).

Catabolism is the breakdown of large complex molecules into smaller ones.

What is the biological term which describes all the enzyme catalysed reactions which take place in the cell?

All the enzyme catalysed reactions are described as the cell's metabolism.
These reactions are classified as anabolic or catabolic depending on whether they make bigger molecules from small ones, or vice versa.

Which of the following molecules contains only carbon, hydrogen and oxygen atoms?

Carbohydrates, lipids and phospholipids do not contain nitrogen.
Amino acids and DNA contain nitrogen.


What did the theory of vitalism propose about organic molecules?

The formation of urea, known since 1773 experiments where the synthesis of an organic compound from two inorganic molecules was achieved for the first time weakened significantly the vitalistic hypothesis.

This hypothesis proposed that could not be synthesised from inorganic components.


Which of the following correctly identifies the monomers which make a polysaccharide molecule.

Polyaccharides are composed of a chain of simple sugar molecules, like glucose.


Which one of the molecule diagrams below correctly represents an amino acid molecule?

Note: in amino acids there is always an NH2 and a COOH and one R group


What type of molecule is shown by the model below?

Fatty acids have a long chain of carbon atoms surrounded by hydrogen and a carboxyl "COOH" group at the end.
This is a steroid molecule, testosterone.

As a lipid it has mostly carbon and hydrogen, and just two oxygen molecules.


To test for starch which of the following points best describes the procedure?

Benedict's reagent is used to test for reducing sugars.
Iodine is used to test for Starch - and turns blue / black


The image below shows the results of a chemical test for a biological molecule.

What is the test and which molecule does this positive result show the presence of?

Benedict's reagent turns from a blue colour to an orange / red colour in the presence of a reducing sugar.

What does the R-group on a diagram of an amino acid represent?

There are about 20 different amino acids found in living organisms and each has a different molecular structure in the R-group.

This can be a simple -H atom, in alanine, or a more complicated strcture.

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Revision fun activity

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