Introduction to Biochemistry

Learning Outcomes The diverse functions of biological molecules depend on their structures and shapes. Metabolic reactions take place in highly controlled aqueous environments. Reactions of breakdown are called catabolism and reactions of synthesis are called anabolism. Biopolymers form by condensation reactions and are broken down by hydrolysis reactions. Photosynthesis is the synthesis of energy-rich molecules from carbon dioxide and water using light energy. Respiration is a complex set of metabolic processes providing energy for cells. Explanation of the difference between condensation and hydrolysis reactions. The use of summary equations of photosynthesis and respiration to explain the potential balancing of oxygen and carbon dioxide in the atmosphere. (Intermediates of aerobic respiration and photosynthesis are not required.)

The diverse functions of biological molecules depend on their structures and shapes

The diverse functions of biological molecules depend on their structures and shapes

Metabolic reactions take place in highly controlled aqueous environments Metabolism is the set of life-sustaining chemical transformations within the cells of organisms. The three main purposes of metabolism are the conversion of food/fuel to energy to run cellular processes, the conversion of food/fuel to building blocks for proteins, lipids, nucleic acids, and some carbohydrates, and the elimination of nitrogenous wastes.

Metabolic reactions take place in highly controlled aqueous environments Nearly all biological molecules assume their shapes and therefore function depending on the physical and chemical properties of the water surrounding them Reactants and products of metabolic reactions, nutrients as well as water products, depend on water for transport within and between cells. THe reactivity of many functional groups on biological molecules depends on the concentration of H and OH surrounding them

Reactions of breakdown are called catabolism and reactions of synthesis are called anabolism.

Classification of biomolecules Anabolic - complex molecules from smaller inorganic or organic substances Catabolic - complex molecules broken to smaller fragments

Metabolic pathways Most anabolic processes are condensation reactions. Condensation reaction monomers require 2 function groups and the release of a small molecule (H2O, HCl, NH3 etc). Most catabolic processes are hydrolysis reactions.

The most important of these catabolic/anabolic pairings are respiration and photosynthesis.

Aerobic vs anerobic 120J (lactic acid) 2900J

Summary questions 1. (a) Photosynthesis describes the process used by plants to synthesise energy- rich molecules such as carbohydrates from carbon dioxide and water using visible light. (i) State the summary equation for the formation of a carbohydrate with the formula C6H12O6 from carbon dioxide and water. (ii) Determine the change in the oxidation number of carbon during photosynthesis. (iii) Outline the role of chlorophyll in photosynthesis b) The summary equation for respiration is the reverse of photosynthesis. (i) State the primary function of respiration in animals. (ii) Explain how photosynthesis and respiration help to maintain the balance between oxygen and carbon dioxide in the atmosphere.

Answers 1. (a) (i) 6CO2(g) + 6H2O(l) → C6H12O6(aq) + 6O2(g) (ii) From (+IV) in carbon dioxide to (0) in glucose. (iii) The role of chlorophyll is to absorb light energy and transfer it to plants by storing the energy in the bonds of the organic products of photosynthesis. (b) (i) The primary function of respiration is to transfer energy to cells in animals. (ii) The two processes exist in equilibrium as the carbon dioxide absorbed from the atmosphere during photosynthesis is released back into the atmosphere during respiration, similarly the oxygen released into the atmosphere during photosynthesis is removed from the atmosphere during respiration

Questions 2. Biopolymers are formed by condensation reactions. (a) Explain why at least two different organic products can be formed when two 2-amino acids condense together and give one example of two different 2-amino acids that can condense together to form more than two different organic products.. (b) Use Section 33 of the IB databooklet to identify the three different 2-amino acids that have condensed together to form part of the polymer depicted below: (c) Use the cyclic forms of α-glucose and fructose given in Section 34 of the IB data booklet to write the equation for the formation of sucrose. 3. Explain the difference between condensation and hydrolysis reactions in terms of anabolism and catabolism.

Answers

Questions In the human body, a series of metabolic reactions can lead to the following summary equation: CH3C(O)COOH + CH3CH(OH)CH3 CH3CH(OH)COOH + CH3C(O)CH3 2-oxopropanoic acid + propan-2-ol 2-hydroxypropanoic acid + propanone Which of two reactants, 2-oxopropanoic acid or propan-2-ol, is oxidised and which one is reduced? Deduce the redox half-equations for both processes using protons or water where necessary

Answers Propan-2-ol has two more hydrogens than propanone so it must be being oxidized Therefore the 2-oxopropanoic acid must be being reduced. We can see that this is the case because it gains two hydrogen atoms CH3CH(OH)CH3 —> CH3C(O)CH3 + 2H+ + 2e- CH3CH(OH)CH3 + 2H+ + 2e- —> CH3CH(OH)COOH

Questions The human brain receives almost all of its energy from glucose, which is completely oxidised to carbon dioxide and water in aerobic respiration. Determine the mass of carbon dioxide produced in the brain per day if its daily consumption of glucose is 140g

Answers Mr glucose = 180.16g Moles glucose consumed = 140/180.16 = 0.777 moles So 6 (from mole ratio). x0.777 = 4.66 moles carbon dioxide