Biological Molecules (OCR GCSE Combined Science A (Gateway))

Sugars in Complex Carbohydrates

• Carbohydrate molecules contain the elements carbon, hydrogen and oxygen

• In the human body, carbohydrates are broken down by enzymes in the mouth and small intestine

• Carbohydrates can be classed into different groups (monosaccharides, disaccharides and polysaccharides) depending on their complexity

  • Monosaccharides are simple sugars that consists of a single monomer unit e.g. glucose (C₆H₁₂O₆) or fructose

    • Glucose molecules contain lots of energy which can be released in respiration by breaking the bonds between the carbon atoms

  • A disaccharide is made when two monosaccharides join together

    • Maltose is formed from two glucose molecules

    • Sucrose is formed from one glucose and one fructose molecule

  • A polysaccharide is formed when lots of monomer units join together in long chains to form a polymer

    • Starch, glycogen or cellulose are all formed when lots of glucose molecules join together

    • Polysaccharides are insoluble and therefore useful as storage molecules

Glycogen, cellulose and starch are all made from glucose molecules

Amino Acids in Proteins

• Proteins are polymers formed from long chains of monomers called amino acids joined together

  • Amino acids contain carbon, nitrogen, hydrogen and oxygen atoms

• Just 20 different standard amino acids make up all the proteins found in the human body (although many more amino acids occur in nature)

• Amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins

  • Examples of proteins include enzymes, haemoglobin, ligaments and keratin

• In the human body, proteins that we ingest are broken down into the constituent amino acids

  • Enzymes in the stomach and small intestine break down the protein

  • These amino acids can then be used in the synthesis of new proteins

Amino acids join together to form proteins

Protein shape

• Different proteins have different amino acid sequences resulting in the peptide chain folding into different shapes

  • The function of a protein is determined by its shape

• Even a small difference in the amino acid sequence will result in a completely different protein being formed

• In this way, every protein has a unique 3-D shape that enables it to carry out its function

Fatty Acids & Glycerol in Lipids

• Lipids (fats and oils) are made up of triglycerides

• Their basic unit is one glycerol molecule chemically bonded to three fatty acid chains

• Lipids contain carbon, hydrogen and oxygen atoms

• Unlike carbohydrates and proteins, they don't form polymers (they don't form a long chain of repeating sub-units)

• Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature)

• In the human body lipids are broken down by enzymes called lipases in the small intestine

The structure of a triglyceride