IB Chemistry HL Option B Biochemistry B.9 Biological pigments

IB Chemistry HL Option B Biochemistry B.9 Biological pigments

• Biological pigments are coloured compounds produced by metabolism.
• The colour of pigments is due to highly conjugated systems with delocalized electrons, which have intense absorption bands in the visible region.
• Porphyrin compounds, such as hemoglobin, myoglobin, chlorophyll and many cytochromes are chelates of metals with large nitrogen-containing macrocyclic ligands.
• Hemoglobin and myoglobin contain heme groups with the porphyrin group bound to an iron(II) ion.
• Cytochromes contain heme groups in which the iron ion interconverts between iron(II) and iron(III) during redox reactions.
• Anthocyanins are aromatic, water-soluble pigments widely distributed in plants. Their specific colour depends on metal ions and pH.
• Carotenoids are lipid-soluble pigments, and are involved in harvesting light in photosynthesis. They are susceptible to oxidation, catalysed by light.
• Explanation of the sigmoidal shape of hemoglobin’s oxygen dissociation curve in terms of the cooperative binding of hemoglobin to oxygen.
• Discussion of the factors that influence oxygen saturation of hemoglobin, including temperature, pH and carbon dioxide.
• Description of the greater affinity of oxygen for foetal hemoglobin.
• Explanation of the action of carbon monoxide as a competitive inhibitor of oxygen binding.
• Outline of the factors that affect the stabilities of anthocyanins, carotenoids and chlorophyll in relation to their structures.
• Explanation of the ability of anthocyanins to act as indicators based on their sensitivity to pH.
• Description of the function of photosynthetic pigments in trapping light energy during photosynthesis.
• Investigation of pigments through paper and thin layer chromatography.
(The structures of chlorophyll, heme B and specific examples of anthocyanins and carotenoids are given in the data booklet in section 35; details of other pigment names and structures are not required. Explanation of cooperative binding in hemoglobin should be limited to conformational changes occurring in one polypeptide when it becomes oxygenated. Knowledge of specific colour changes with changing conditions is not required.)

[emma]

Thank you so much. I had to go through option b by myself… But your videos helped me go through this without getting overwhelmed :>