Option C : Human Biochemistry

The aim of this option is to give students an understanding of the chemistry of important molecules found in the human body and the need for a balanced and healthy diet. Although the role these molecules play in the body should be appreciated, the emphasis is placed on their chemistry, and students who have not followed a course in biology will not be at a disadvantage. Students will not be required to memorise complex structures but will be expected to recognize functional groups and types of bonding within molecules. Structures of some important biological molecules are given in the data booklet.

C.1 Diet (2h)

C.1.1     Describe what the human body requires for a healthy diet.
                    Students should recognise the importance of a balanced diet, including minimum requirements and the need for
                    essential minerals.

C.1.2 Calculate the calorific value of a food from enthalpy of combustion data.

C.1.3     Discuss the benefits and concerns of using genetically modified (GM) foods.
                    Crops and animals can be modified to provide more food, be more resistant to disease and be more tolerant to
                    heavy metals. Concerns include the release of genetically modified organisms into the environment where they
                    could spread and compete with the naturally occurring varieties.

C.2 Proteins (3h)

C.2.1     State the basic structure of 2-amino acids.
                    There are approximately 20 common 2-amino acids (a -amino acids) found in organism. 2 amino acids have the
                    following formula.

                                                                                H
                                                                                 |
                                                                    H₂H ---C---COOH
                                                                                 |
                                                                                 R

C.2.2 Describe the condensation reaction of amino acids to form polypeptides.

C.2.3     Explain how proteins can be analysed by chromatography and electrophoresis.
                    To use either of these techniques the peptide bonds in the proteins must first by hydrolysed to release individual
                    amino acids. Include the use of R_f values in paper chromatography. Give isoelectric points, students should be
                    able to determine a suitable pH to achieve good separation in electrophoresis.

C.2.4 Describe and explain the primary, secondary, tertiary and quaternary structure of proteins.

C.2.5 List the major functions of proteins in the body.
These are structure, biological catalysts (enzymes) and energy sources.

C.3 Carbohydrates (2.5h)

C.3.1      Describe the structural features of monosaccharides.
                    Monsaccharides contain a carbonyl group (C=O) and at least two -OH groups, and have the empirical formula
                    CH₂O.

C.3.2 Describe the straight-chain formula of glucose and the structural difference between a -glucose and b -glucose.

C.3.3 Describe the condensation of monosaccharides to form disaccharides and polysaccharides.

Limit examples to :

disaccharides - lactose and sucrose

                   polysaccharides - starch
C.3.4     List the major functions of polysaccharides in the body.
                    These are energy sources, energy reserves (eg. glycogen) and precursors for other biologically important
                    molecules.

C.4 Fats (2.5h)

C.4.1 Describe the composition of fats and oils.

C.4.2 Describe the difference in structure between saturated and unsaturated fats, and explain the difference in their melting
points.

C.4.3 Calculate the number of C=C double bonds in an unsaturated fat using addition reactions.
The number of C=C bonds can be determined from the number of moles of I₂ which add to one mole of fat.

C.4.4 Describe the hydrolysis of fats to form soaps and the action of soaps.

C.4.5 List the major functions of fats in the body.
These are energy sources, insulation and cell membranes.

C.5 Vitamins (2.5 H)

C.5.1 Define the term vitamin.

C.5.2 Deduce whether a vitamin is water or fat soluble from its structure.

C.5.3 Describe the structures and major functions of retinol (vitamin A), calciferol (vitamin D) and ascorbic acid (vitamin
C).

Vitamin A - required for the production of rhodopsin (light-sensitive material in the rods of the retina).

Deficiency can cause night blindness and xerophthalmia.

Vitamin D - required for the uptake of calcium from food. Deficiency can cause weak bones (rickets).

Vitamin C - essential in the production of collagen : the protein of connective tissue. Deficiency can cause

scrobutus (scurvy).

C.5.4 Describe the effects of food processing on the vitamin content of food.
Most vitamins are unstable at higher temperatures so will be affected by prolonged cooking.

C.6 Hormones (2.5h)

C.6.1     Outline the production and roles of hormones in the body.
                        Hormones are chemical messengers produced in glands controlled by the pituitary gland, which in turn is
                        controlled by the hypothalamus. Limit examples of production and roles to adrenalin, thyroxine, insulin and sex
                        hormones.

C.6.2 Compare the structures of cholesterol and the sex hormones.
Stress the common steroid backbone but the difference in functional groups (see the data booklet).

C.6.3 Describe the mode of action of oral contraceptives.

C.6.4 Outline the use and abuse of steroids.

C.7 Enzymes (3h)

C.7.1 Outline the basic characteristics of enzymes.
Include :

enzymes are proteins

activity depends on tertiary and quaternary structure

the specificity of enzyme action.

C.7.2 Determine V_max and the value of the Michaelis constant (K_m) by graphical means.

C.7.3 Describe the significance of V_max and K_n.

C.7.4 Describe the concept of the active site in enzyme structure.

C.7.5 Explain competitive inhibition and non-competitive inhibition.

C.7.6 State and explain the effects of heavy metal ions, extremes of temperature and pH changes on enzyme activity.

C.7.7     Describe the uses of enzymes in biotechnology.
                    Possible examples include proteases in biological detergents, glucose isomerase converting glucose to fructose
                    and streptokinase in breaking down blood clots.

C.8 Nucleic Acids (2h)

C.8.1     Describe the structure of nucleotides and their condensation polymers (nucleic acids).
                    A nucleotide contains a phosphate group, a pentose sugar group and an organic base. Students should be able to
                    recognise, but need not recall, the structures of the five nucleotide bases : adenine, cytosine, guanine, thymine and
                    uracil.

C.8.2 Describe the double helical structure of DNA.
Students should be able to describe the hydrogen bonding between specific pairs of nucleotide bases.

C.8.3 Outline the role of DNA as the repository of genetic information, including the triplet code.

C.8.4 Describe the principles and uses of DNA profiling.
Include forensic uses and paternity cases.

C.9 Metal Ions in Biological Systems (2h)

C.9.1 Explain that different metal ions fulfill different roles in the body due to their different chemical properties.
Emphasise differences in charge density, redox properties and complex ion formation.

C.9.2 Describe the importance of the difference in Na⁺ and K⁺ concentrations across the cell membrane.
Explain active transport using the Na⁺/K⁺ pump as an example.

C.9.3 Outline the importance of copper ions in electron transport and iron ions in oxygen carriers.
Use cytochromes and haemoglobin as examples.

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