How they are affected by mutations. Biochemical Pathways How they are affected by mutations.

Biochemical Pathways All biochemical pathways are catalysed by enzymes. The coding for these enzymes is controlled by a gene. If an organism has a faulty gene, it may not be able to make the enzyme.

Biochemical Pathways This means that the biochemical pathway would stop at that point and there would be an accumulation of the chemical prior to the faulty enzyme.

A Biochemical Pathway A B C D Gene 1 Gene 2 Gene 3 Enzyme 1 Enzyme 2 Expression of gene 1 produces enzyme 1 Expression of gene 2 produces enzyme 2 Expression of gene 3 produces enzyme 3

Diseases of Inborn Errors of Metabolism

Phenylketonuria - PKU This is a serious disease, which if left untreated, can result in severe mental retardation. It results from a defect in the enzyme E1 that converts phenylalanine to tyrosine. This results in an accumulation of phenylalanine and other minor metabolic products in the body.

Phenylketonuria - PKU People with this disease are lightly pigmented, although there is usually enough tyrosine in their diets to allow them to make melanin. All babies in NZ are tested for PKU at birth, and if it is present the children are put on a strict diet which can prevent the effects.

Phenylketonuria - PKU This diet greatly reduces the amount of phenylalanine accumulated. Phenylalanine is one of the essential amino acids, which is not made by the body, so it can be controlled by diet. A small amount of phenylalanine has to be given to maintain normal growth.

Albinism The most common type of Albinism is due to lack of the enzyme E3 that makes melanin from tyrosine. Because Albino people cannot make melanin, they have white hair and pink eyes, and their eyes and skin are very sensitive to sunlight. Albinism is widespread in the animal kingdom. (rats, rabbits, snakes, birds)

In Humans

In Other Animals

Alkaptonuria This is due to lack of enzyme E4 that processes homogentisic acid. Its absence means that homogentisic acid accumulates in the tissues. People with this condition appear normal as children, but are detected when their nappies start turning black

Alkaptonuria As they grow, they develop a blue-black discolouration of the ears, whites of the eyes, tips of the nose, and other areas where cartilage is just under the skin. Their urine turns black after exposure to sunlight for several hours. They often have severe arthritis, caused by accumulation of the metabolite in the cartilage of the joints.

E1 E3 E2 E4 E = enzyme Phenylalanine Tyrosine Melanin Homogentisic acid Further metabolic Products Minor Metabolic Products Melanin E1 E2 E4 E3 E = enzyme