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  • Writer's picturekenneth tang

Quick overview for O-level Biology (Biological molecules)

Here are some essential points for the topic of Biological molecules:

  1. Water is essential for all organisms such as plants & animals. Thus we need to know some of its uses. Examples include usage for thermoregulation & the transport of substances

  2. Carbohydrates

  • An organic molecule made up of carbon, hydrogen & oxygen

  • Generic formula: C(n)H(2n)O(n)

  • An individual carb molecule contains 4kcals of energy

  • 3 types: Monosaccharides, Disaccharides & polysaccharides (What are some examples?)

  • The uses of carbohydrates are usually as a source of energy or structural support (what are some examples?)

  • Condensation reaction of monosaccharides to form di/polysaccharides

  • Hydrolysis reaction to derive monosaccharides from di/polysaccharides

  • Food tests: Benedict's test/ Iodine test to identify the presence of reducing sugar or starch

3.1 Proteins

  • An organic molecule made up of carbon, hydrogen, oxygen, NITROGEN & sometimes sulfur

  • The smallest unit is known as an amino acid

  • An amino acid provides 4kcal of energy

  • Amino acid general structure: Amino grp, Carboxyl grp, Variable R grp & Hydrogen

  • Amino acids are linked together by peptide bonds (condensation reaction)

  • A chain of amino acids is known as a polypeptide

  • Multiple/single polypeptides fold into proteins

  • Proteins are used to form tissue in organisms & enzymes

  • Food tests: Biuret's test to identify the presence of protein

3.2 Enzymes

  • Act as catalysts that speed up biological reactions (lower activation energy) & are not modified in the process & can be reused

  • Enzymes are substrate specific due to the specific shape of their active site

  • Lock & key hypothesis: Key is the substrate while lock is the enzyme. The substrate must fit in the active site of the enzyme for the reaction to occur

  • Steps of catalysis: Substrate enters enzyme active site, enzyme-substrate complex formation (catalysis), the release of products from enzyme

  • Factors that affect enzyme-catalyzed reactions: Temperature & pH

  • Denaturation: Destruction of the active site in the enzyme rendering it permanently useless & unable to carry out further reactions

4. Fats

  • An organic molecule made up of carbon, hydrogen & oxygen

  • Composed of 1 glycerol molecule to 3 fatty acid molecules

  • Hydrolysis of it requires 3 H20

  • Each fat molecule provides 9kcal of energy

  • Uses: Production of hormones, storage of energy, insulation, etc

  • Food tests: Ethanol emulsion test to detect the presence of fats

Overall, it is important to have a strong understanding of the biological roles & chemistry behind the 3 main biomolecules to excel in O level Biology.

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