Download 5.4.3 Dopamine and DNA

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a) Discuss how the links between a range of human behaviours and the dopamine receptor DRD4
may contribute to the understanding of human behaviour
Dopamine Structure and Activity
Dopamine is a neurotransmitter found in the brain
It is a precursor molecule for the production of adrenaline and noradrenaline
Dopamine is involved with the control of voluntary movements
Parkinson’s disease is associated with very low levels of dopamine and patients find it difficult to
make these voluntary movements. This disease is treated by giving the dopamine precursor Ldopa
L-dopa treatment results in raised dopamine levels and increases the activity of the sympathetic
nervous system.
Raised dopamine levels have been linked to the development of schizophrenia and in
Parkinson’s sufferers, L-dopa treatment for Parkinson’s disease may cause behavioural changes
such as compulsive gambling
Dopamine increases general arousal and reduces inhibition
Like acetylcholine, dopamine is released from the presynaptic bulb and diffuses across the
synaptic cleft to bind to dopamine receptors on the postsynaptic membrane
So far, five different dopamine receptors have been discovered, referred to as DRD1 to DRD5.
Each receptor type is coded for by a separate gene
Dopamine can bind to each of these five receptor molecules but each receptor causes different
cellular effects, from controlling motivation and learning, to regulating the release of other
Some antipsychotic drugs, used to treat schizophrenia, bind to and block dopamine receptors,
without causing depolarisation of the post synaptic membrane and action potentials. They are
dopamine antagonists since they reduce the effect of dopamine
DRD4 Receptor Gene
There are many known allele variants of the DRD4 gene, as a consequence of mutations. The
variants differ in a specific sequence known as a variable number tandem repeat. Each variant
has a different number of repeats of a short section of nucleotides (the VNTR) in the DRD4 gene
A single individual human only has two alleles of the DRD4 gene since humans are diploid and
have pairs of homologous chromosomes. One allele was derived from each parent
If the gene has a different number of VNTR repeats, the primary structures of the protein receptor
will be different and this will change the receptors affinity for dopamine
Some of these variants are linked to some human behavioural conditions since the inheritance
of particular variants of the DRD4 gene affects the levels and action of dopamine in the brain
Hyperactivity, alcoholism, drug abuse and schizophrenia are disorders linked to different DRD4
gene variants. Some examples are on page 3
ADHD - Attention deficit hyperactivity disorder
Usually seen in children that act on impulse and cannot concentrate for any length of time
Ritalin is used to treat ADHD since it affects (reduces?) dopamine levels in the brain
A particular dopamine receptor variant of DRD4 is more common in individuals suffering from
Addictive and Risk Behaviours
Some DRD4 receptor gene variants are linked to addictive behaviours such as smoking and
Treatment of these addicts with a drug that blocks dopamine receptors reduces the addictive