Coding and non-coding DNA
Definition
Non-coding DNA
DNA that does not code for a protein, some of which switches genes on or off.
- Coding DNA is DNA that is used to make a protein.
- Non-coding DNA is DNA that does not code for a protein.
- Some non-coding DNA sits near genes and helps to control them.
- So a stretch of non-coding DNA can still be important, even though it is not made into a protein.
Note
Non-coding does not mean useless: much of it has a controlling job.
Example
A region of non-coding DNA in front of a gene can act like a switch that turns the gene on or off.
How non-coding variants affect genes
Definition
Gene expression
The process of using a gene to make its protein, which can be switched on or off.
- Gene expression means whether a gene is used and how much protein is made from it.
- Some non-coding DNA controls the expression of nearby genes.
- A variant in this non-coding DNA can turn a gene on or off, or change how much protein is made.
- This can change the phenotype, the organism's features.
- It does this without changing the amino acid sequence of the protein itself.
Common Mistake
Do not assume the phenotype only changes when a protein changes: altering how much protein is made can change it too.
Key Idea
Non-coding variants change the phenotype by changing gene expression, not by changing the protein's own sequence.
Self review
- What is the difference between coding and non-coding DNA?
- What is meant by gene expression?
- How can a variant in non-coding DNA affect the phenotype?
- Does a non-coding variant change the protein's amino acid sequence?
