Ib Biochem Optional Unit

1. What is nutrition? What are nutrients? List the six groups nutrients are generally divided into.

Nutrition is the study of food and its use by the human body. Nutrients are food components (carbohydrates, fats, proteins, vitamins, minerals, and water) which provide growth energy and replacement.

2. Describe the requirements of the human body for a healthy diet.

A healthy diet provides the right amount of nutrients, ie not in defiency or in excess. The bulk of the RDA is carbohydrates (50%) for energy, 30% comes from fat, and the rest from proteins. Proteins are mostly responsible for giving the body the required amino acids to form new proteins. Out of the 20 amino acids, 10 cannot be synthesized by the body and must be ingested. 50 grams of complete proteins, foods that contains all amino acids, from red meant, fish, egg is sufficient for a daily requirement of protein. Vitamins are required in a small amount to regulate enzyme changes. The human body is 70% water and which dissolves the chemicals in our system (transporting wastes and nutrients). Minerals are required in small amounts for bone and teeth formation, red blood cells and other functions.

3. What is calorific value? Explain how the calorific value of a food is related to its enthalpy of combustion.

Calorifc value is the amount of energy stored in food, a raise temperature at 1g of H2O by 1п‚oC is needed to consume one calorie.

4. State the basic structure of 2-amino acids.

5. What are optical isomers? Why does the basic structure of 2-amino acids give rise to optical isomers?

Optical isomerisms are compounds that are mirror images of each other. If Rп‚â„-H, the 2-carbon atom is asymmetrical, allowing optical isomerism to occur.

6. Under what conditions are amino acids neutral? acidic? basic?

Amino acids are neutral when in neutral solutions. In acidic solutions, amino acids acts like a base accepting H+ ions, while in basic solutions, amino acids acts like acids donating H+ ions.

7. Discuss the physical properties of amino acids.

Amino acids are colourless crystalline solids with high melting points, generally soluble in water but insoluble in organic solvents.

8. What is a peptide chain and how is it formed?

A peptide chain is an amide made by the joining of amino acids by peptide bond. They are formed by condensation reactions that produces a water molecule.

9. Discuss the technique of paper chromatography. Your answer should explain the following terms: (a) stationary phase, (b) adsorption, (c) Rf value.

Chromatography is suitable for the identification of components in a very small sample of hydrophilic substances such as amino acids. The water in the paper fibres acts as the stationary phase as the solvent flows by capillary action up the paper in ascending chromatography. One solvent, usually water, is adsorbed on the cellulose in the paper; adsorption is the concentration of one substance at the surface of another. The other solvent, such as a mixture of 1-butanol and ethanoic acid (usually called diluting agent), travels up the paper. Each amino acid has a particular solubility in the diluting and stationary solvent. Amino acids with higher solubility in diluting solvent will travel higher up in ascending chromatography. Rf values (ratio of fronts) of the sample is compared to pure amino acids under the same conditions. (Rf = compound / solvent)

10. Discuss the technique of electrophoresis. Your answer should explain the following; (a) isoelectric point, (b) solubility of an amino acid at its isolelectric point, (c) solubility of amino acid at pH values higher and lower than the isolectric point.

How a protein behaves in the presence of an electric field depends on the relative numbers of these charged groups which is affected by the acidity or basicity of the solution. The isoelectric point, pI, of a protein is the pH at which the positive and negative charges are exactly balanced, the protein molecule has no net charge and it shows no net migration in an electric field at that pH. This is also the case with individual amino acids. The solubility of an amino acid is found to be a minimum at its isoelectric point, since molecules of the amino acid have a net charge of zero, they can join together and precipitate. At a lower pH, the basic group(s) attract H+ to form +NH3, i.e., a positive charge. At a higher pH, the acidic R group on the amino acid donates its H+ to produce COO-, i.e., a negative charge. Thus, the solubility of an amino acid increases at pH values higher or lower than its isolelectric point.

11. Explain how proteins can be analyzed by chromatography and electrophoresis.

In chromatography, the result of pure amino acids developed at the same time under the same conditions of solvent and temperature can be compared. The Rf values are different, so by comparing the Rf values amino acids in a mixture to be identified. If several components of the mixture have similar Rf values in the same solvent it is possible to use two dimensional chromatography to improve separation. The sample spot is placed in the corner of a piece of paper, chromatography is developed once with one solvent, then after the paper is dry, it is turned at a right angle and then developed by another solvent to achieve more separation.

Electrophoresis separates the amino acids by using the pH values. When the isoelectric point of an amino acid is the same as the pH of the buffer, the amino acid will have no net charge and not move. But when the isoelectric point is lower than the pH, it will have a negative charge and move towards the positive pole. The reverse is true for isolectric points that are higher than the pH (moves towards the negative pole). The greater the difference between pH and pI, the faster the migration.

12. Describe and explain the primary, secondary, tertiary, and quaternary structure of proteins.

The primary structure is the sequence of amino acids. The order is determined