PSYC39H3 Lecture 4: LEC 04
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LEC 04: Origins of Criminal Behavior: Biological Factors
Basic biological concepts: DNA & Protein Synthesis: 1
- Basic dogma: DNA RNA Protein
- DNA is a lengthy sequence nucleotides whose order provides the ‘genetic code’ of all living
- An amino acid is a chemical that has a carboxyl group (COOH) at one end, an amine group (NH2)
group in the middle and different radical groups at the other end
- Proteins are the ‘end product’ of genes and consist of long chains (>100) amino acids
Basic Biological Concepts: DNA & Protein Synthesis: 2
- Functionally, there are two types of protein:
o Structural Proteins
o Enzymes (“Functional Proteins”) that speed up chemical reactions
- Synaptic Receptors that activate neurons in response to neuro-transmitters are proteins
- The simplest way of conceptualizing learning at the molecular level is that with environmental
exposure, more receptor molecules are manufactured.
- This increases that likelihood the particular pathway within the network will be preferentially
Basic Biological Concepts: DNA & Protein Synthesis: 3
- The greater the density of receptor molecules, the greater the likelihood that a particular
pathway will be activated, and activated more quickly.
- The increased speed of the learned pathway increases the likelihood that this particular
information will arrive at a “decision-node” before other, potentially contrary information.
- This affects the decision-making will strongly bias which information from our total store will be
- Eventually, there are so many receptors in the preferred pathway that the behaviour become
virtually or actually automatic…such as reading.
- Additionally, genes can exist in different variations called alleles. Some alleles producing
receptor proteins that are less effective as receptor proteins, also affecting the efficiency of
neurotransmission and learning.
Basic Biological Concepts: DNA & Protein Synthesis: 4
- These ideas led Behavioural Geneticists to imagine that “Genes are Destiny” since genes
determine the amino acid sequences (structure) of all proteins, including those that synthesize
neurotransmitter and receptor protein molecules.
Basic Biological Concepts: DNA & Protein Synthesis: 5
- Two problems with the “Genes are Destiny” dogma:
- Multiple Genes
o Most behaviours and behavioural disorders are controlled by many different transmitter
systems, receptors and receptor subtypes, and consequently many different genes.
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o Consequently, many genes are involved rendering prediction of behavioural outcomes
by genes alone difficult if not impossible.
- Epigenetics – the changes in phenotype and gene expression without changing the DNA
o In the context of epigenetics, DNA methylation refers to the covalent attachment of a
methyl group to the C5 position of cytosine residues
o Genes are held inhibited unless they are uninhibited by the epigenetic mechanisms
Epigenetic de-methylation mechanism
Epigenetic modulation effects
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