6.1.4 Coding VS Non-Coding DNA Flashcards
Coding DNA
DNA that is transcribed and translated to make a protein in gene expression. They are the templates for the formation of polypeptide chains.
It is also known as the exons of eukaryotic DNA.
A mutation to this section causes silent, missense or nonsense mutations.
Hox Genes
Coding DNA: Case Study
Found in animals, plants and fungi, and controls the development of most organ systems by specifying how structures develop in differing segments of the body.
Code for proteins that attach to molecular switches on DNA, turning other genes on and off. The DNA-binding piece of a Hox protein is called the homeodomain.
Even a single mutation to this gene can cause legs to grow in the place of an antennae in fruit flies.
Huntington’s Disease
Coding DNA: Case Study
The result of a mutation causing more than 40 short tandem repeats of the base sequence CAG that influences gene expression in the Huntington gene on chromosome 4.
Mutations in the germ-line cells that already have a high number of repeats are more likely to result in offspring with the disease.
Categorised as a progressive, inherited disease that breaks down basal ganglia nerve cells in the brain over time, resulting in cognitive and psychiatric disorder as well as loss of functional abilities.
Symptoms include:
- Cognitive disorder (e.g. amnesia, mental confusion etc.)
- Muscular disorder (e.g. involuntary movements, abnormality walking etc.)
- Behavioural disorder (e.g. compulsive behaviour, irritability etc.)
- Psychological disorder (e.g. delirium, hallucination etc.)
- Mood (e.g. anxiety, apathy etc.)
- Difficulty speaking, tremors, weight loss etc.
Non-Coding DNA
Introns have a range of functions, including regulating gene expression. Mutations to them can have no effect or prevent polypeptide synthesis as a mutation to a promoter sequence may prevent DNA polymerase from binding.
Less that 2% of human DNA in our genome actually codes for the production of a protein. The mutations studied usually only focus on those that affect the coding sections of our genome, but any mutations to ncDNA may still have an effect on the cell, the individual or future generations.
Role of Non-Coding DNA
- A significant, but unknown, amount of ncDNA produces other forms of RNA, such as t-RNA and mitochondrial-RNA. These are involved in gene repair, chromosomal structure and regulation.
- Up to 10% of ncDNA is believed to be “regulatory” genes, which activate and deactivate other genes on the body.
- Up to 50% of the genome is “repetitive” DNA sequences, including “telomeres” which occur at the ends of our chromosomes and may be linked to the process of aging. The effect of mutations in this area is currently unknown.
Operons
Non-coding DNA segments that may still control the action of regulatory proteins
