Download Biochemical Pathways - NCEA Level 2 Biology

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
Gene 1
Gene 2
Expression
of gene 1
produces
enzyme 1
Enzyme 1
A
Gene 3
Expression
of gene 2
produces
enzyme 2
Enzyme 2
B
Expression
of gene 3
produces
enzyme 3
Enzyme 3
C
D
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.

Phenylalanine
Minor Metabolic Products
E1
E3
Tyrosine
Melanin
E2
Homogentisic acid
E4
Further metabolic Products
E = enzyme