13 terms in 3.8
Alteration of the sequence of bases in DNA can alter the structure of proteins
A gene mutation is a change to the base sequence of a DNA molecule. Several types exist, and they most often arise when DNA copies itself before cell division.
The control of gene expression
Alteration of the sequence of bases in DNA can alter the structure of proteins
Gene mutations can happen by chance at any time. Certain environmental factors, called mutagenic agents, make mutations happen more often.
The control of gene expression
Alteration of the sequence of bases in DNA can alter the structure of proteins
A mutation changes the base sequence of a gene. Because bases code for amino acids, a changed sequence can produce a different chain of amino acids — a different polypeptide.
The control of gene expression
Alteration of the sequence of bases in DNA can alter the structure of proteins
Each amino acid in a protein is coded for by a three-base sequence called a codon (or triplet). A substitution mutation swaps one base for another, producing a new codon. The genetic code is described as degenerate, meaning most amino acids are coded for by more than one codon. Because of this redundancy, a substitution that changes the third base of a codon very often still codes for the same ami
The control of gene expression
Alteration of the sequence of bases in DNA can alter the structure of proteins
Adding or deleting a base shifts every codon after that point. This scrambles the amino acid sequence from that position onwards.
The control of gene expression
Alteration of the sequence of bases in DNA can alter the structure of proteins
A gene mutation is a change to the sequence of bases in DNA, and these changes can arise spontaneously during DNA replication or be triggered by mutagenic agents — environmental factors such as UV radiation or certain chemicals that increase the rate at which mutations occur. Because the base sequence of a gene codes for the order of amino acids in a protein, some mutations alter the resulting polypeptide's structure and potentially its function. However, the impact of a mutation depends on its type: a substitution (one base swapped for another) may have no effect due to the degenerate genetic code, whereas an insertion or deletion can cause a frame shift that disrupts every codon downstream, with far-reaching consequences for the protein produced.
The control of gene expression
Gene expression is controlled by a number of features
Not every gene in a cell is active at the same time — which genes are switched on or off is tightly controlled, and mutations (spontaneous, heritable changes to DNA base sequences) can disrupt this control in ways that range from harmless to life-threatening. Much of the genome consists of non-coding DNA — sequences that do not code for proteins but play a crucial role in regulating when and how much a gene is expressed. Understanding these control mechanisms explains how genetically identical cells can become specialised, and why some mutations cause disease while others have no effect at all.
The control of gene expression
Gene technologies allow the study and alteration of gene function
Modern gene technologies give scientists the tools to read, manipulate, and alter the genetic information inside cells — opening up both medical and agricultural applications that were impossible just decades ago. Techniques such as automated sequencing (using machines to rapidly decode the order of bases in DNA) and genome projects have revealed how genes are organised and regulated across entire organisms. Understanding these technologies matters because they allow scientists to investigate what individual genes actually do, correct faults caused by mutations (changes to the base sequence of DNA), and deliberately engineer new traits — building directly on the gene expression principles covered in earlier subtopics.
The control of gene expression
Using genome projects
Scientists have used large-scale projects to read the complete DNA sequence of many organisms. These projects include the Human Genome Project, which finished mapping all human DNA in 2003.
The control of gene expression
Using genome projects
Sequencing the complete DNA of a simple organism reveals every protein it can make. Scientists can use this protein list to find antigens — molecules that trigger an immune response — and design vaccines against them.
The control of gene expression
Using genome projects
In complex organisms like humans, knowing the full DNA sequence does not tell you all the proteins the organism makes. Non-coding DNA and genes that control other genes make the relationship far more complicated.
The control of gene expression
Using genome projects
Scientists keep improving the technology used to read DNA sequences. Modern sequencing machines now do this work automatically, making the process much faster and cheaper than before.
The control of gene expression
Using genome projects
Large-scale genome sequencing projects have read the complete DNA instructions of many organisms, including humans, using increasingly automated technology. In simpler organisms, knowing the genome makes it possible to predict the proteome — the full set of proteins an organism can produce — which opens up practical applications such as identifying antigens (molecules that trigger an immune response) for vaccine development. In more complex organisms like humans, this translation from genome to proteome is far less straightforward, because much of the DNA does not code for proteins and some genes act as regulators that control whether other genes are switched on or off.
The control of gene expression