2.1 Molecules to metabolism

2.1 Molecules to metabolism

Lesson one : Introduction to molecular biology



  • metabolism: the sum total of all reactions happening in cells, involving enzymes.
  • molecule: a particle made from more than one atom, covalently bonded together
  • anabolism: synthesis of complex molecules from simple molecules eg. joining together monomers to form macromolecules by condensation reactions.
  • condensation reaction: a reaction that removes water to form a bond
  • monomer: a small molecule, that can be joined together to form a macromolecule
  • catabolism: the breakdown of complex molecules into simpler molecules eg. hydrolysis of macromolecules into monomers.
  • hydrolysis: a reaction that adds water to break a bond
  • Organic molecule: based on carbon and found in cells, e.g.. lipid, carbohydrate, protein, nucleic acid

Activator: Can you think of any molecules in the movie ‘Superhealth’ me that were discussed by Morgan Spurlocks doctors? How do you think they might be classified, as lipids, carbohydrates, protein, or nucleic acids?

Biochemistry is based on the element carbon. Carbon is unique because an atom of carbon can form four covalent bonds with other atoms. This allows it to become an effective building block for macromolecules.

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Building and breaking down organic molecules (anabolic and catabolic reactions)

Anabolic reactions happen when we grow. Building proteins is an essential part of making you taller, building muscles, growing hair, etc. Effectively what happens when you build a protein is that monomers called amino acids are joined together to form a macromolecule called protein. This happens through a condensation reaction, where water is removed and a bond is formed in the place of where the OH and the H groups were that made water.

Catabolic reactions happen when we digest food. Breaking down molecules is also important in detoxification, and recycling. Effectively what happens when you break down macromolecules, is water is added to the molecule where the bond occurs, dividing the macromolecule into monomers. This kind of breakdown adding water, is hydrolysis.

It is worth adding that both anabolic and catabolic reactions rely on enzymes. For example the enzyme pepsin catalyses the digestion of proteins into amino acids.

Figure: A dipeptide being formed and broken down from two amino acids.

image credit bbc

image credit bbc


Task: Make a table of monomers and polymers for the following: Proteins, Starch, Glycogen, Cellulose. 

 Introduction to the main organic molecules:

Proteins – used for structural purposes. Also a wide variety of uses including enzymes, hormones, toxins

Carbohydrates – energy storage, and also structure in plants in the case of cellulose

Lipds – energy storage, insulation, protection

Nucleic acids – Short term energy storage (ATP), controlling the functions and characteristics of life i.e. DNA

 Lesson two: Drawing Organic Molecules:

objectives: Drawing molecular diagrams of glucose, ribose, a saturated fatty acid and a generalized amino acid.

Key skills:

  • Numbering carbohydrate rings. This is done by numbering the carbon after the oxygen as carbon 1, and then continuing in a clockwise direction
  • Showing the carbon backbone as lines. This is done by using a corner to represent a carbon atom. This avoids showing all of the atoms which are there, and is represents a conventional shortcut amongst biochemists.




Drawing Triglycerides

Structure of a Triglyceride: A complete triglyceride structure consists of three fatty acid chains, joined through a 3-carbon molecule called glycerol. Glycerol on its own, is a component of skin moisturisers, low-fat deserts, shampoo and the liquid in the new electronic cigarette.

A generalised triglyceride structure looks like this:


The difference between milk fat, and almond oil, is determined by the length and number of double bonds in the three fatty acid chains. The glycerol remains the same. A slightly more detailed look at the same molecule would be:

triglyceride detailed


This time you can see the actual atoms of carbon, hydrogen, and oxygen that make up this example of a triglyceride. You can see that the bonds between the molecule glycerol, and the three fatty acids are formed by the elimination of water. This is a common theme in organic chemistry.

Recognising organic molecules. You need to be able to recognise the following basic types of organic molecules:

  • Single and double sugars
  • Complex carbohydrates (like starch)
  • Amino acids
  • Triglycerides







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