genetics and epigenetics
What are proteins?
● Large, complex molecules that plays a critical role in the body
● Your body makes new ones as needed, must replenish old and degraded ones.
● Are built from a simple set of supplies
● Chains of amino acids, over 20 to choose from, and specific combinations changes the function and structure of the protein
Types of proteins:
● Structural: help to hold cells and tissue together eg. Collagen
● Enzymes: catalyze chemical reactions and aid in metabolism eg. Monoamine oxidase
● Cell signaling: peptide neurotransmitters, receptors for hormones, neurotransmitters, and cytokines
DNA:
● DNA is recipe that tells your cells how to build proteins, which amino acids to use, and which order to put them in
● Encodes info needed to synthesis proteins
● Long chain/sequence of nucleotides
● DNA can be copied, allows for cell division and reproduction
● Genes are segments of DNA that code for particular proteins
● DNA molecule partially unravels, exposing the structural gene that is to be transcribed
● A strand of messenger RNA is transcribed from one of the exposed DNA strands and carries the genetic code from the nucleus into the cytoplasm of the cell
The role of DNA
● 4 nucleotide bases that can make up DNA
○ Adenine
○ Thymine
○ Guanine
○ Cytosine
● Adenine and thymine bind
● Guanine and cytosine bind
Genetic code
● DNA is sequenced, the end product is simply a string of letters, with each letter representing one of the four nucleotides
● Proteins have 20 amino acids, but DNA has 4 nucleotide bases to encode that info
● Gene are organized in codons, each is 3 nucleotides long, and "codes" for a specific amino acid
○ Eg. AAG codes for the amino acid lysine, and GAC for aspartic acid
○ 43 possible codons (total of 64), a lot of them are redundant
mRNA
● Carries protein info from DNA in a cell’s nucleus to the cell's cytoplasm
● Process of transcription is the first step in gene expression, during transcription a gene is copied into a strand of messenger RNA
● The sequence of each mRNA strand matches the DNA sequence of that gene
○ The sole exception to this is that in RNA, thymine is replaced by uracil. Since it’s a 1:1 swap, the meaning of the sequence is not affected.
● The second step of gene expression is when mRNA strands are translated into proteins by ribosomes
Optogenetics
● Transgenic technique that combines genetics and light to control targeted cells in living tissue
○ Based on the discovery that light can activate proteins
● Protein can occur naturally or can be inserted into cells
● Fiber-optic light delivered to selective brain regions such that all neurons exposed to the light respond immediately
Genetic (mendelian) inheritance
● Traits Come from Genes: Traits like eye color or hair type are controlled by genes. You inherit one copy of each gene from your mom and one from your dad.
● Dominant and Recessive Genes: Some genes are "dominant" and show up if you inherit just one copy
(like brown eyes), while others are "recessive" and need two copies to show up (like blue eyes).
● Genes are Passed Down Randomly: The way genes are
passed from parents to children is random, which is why siblings can look similar but still be different.
Epigenetics
● how your behaviors and environment can cause changes that affect the way your genes work
● Genetic mutations alter meaning
● Epigenetics changes alter activity
● Epigenetic changes are often caused by physical changes in the structure of chromatin
○ DNA wrapped around clusters of proteins: histones
■ Further bundled chromosomes
○ Combination of protein and DNA in chromosomes: chromatin
■ Helps regulate behaviour of genes; keeps them in inactive state
■ If gene is needed, section of DNA unfurls, making gene accessible
● Fraga and colleagues
○ Twins have nearly identical patterns of gene expression early in life, but remarkably different by age 50
Histone acetylation
● epigenetic mark that relaxes/loosens the chromatin and increases gene transcription
Histone methylation
● epigenetic mark that tightens/condenses the chromatin and decreases gene transcription
The role of the environment
● Can influence gene activity by regulating the behaviour of epigenetic writers and erasers
○ Addition/removal of acetyl and methyl groups can help the brain respond and adapt to environment
Different levels of maternal care
High licking/grooming
Offspring less anxious, produce less stress hormone, females becoming high lick/grooming mothers
Low licking/grooming
More DNA methylation in a gene encoding the glucocorticoid receptor(mediates stress response)
Less of receptor is made in the hippocampus
Means less able to turn off stress response = more anxious
Effects of maternal behaviour mediated through epigenetic mechanisms