Understanding:
• Infections by a pathogen can be detected by the presence of its genetic material or by its antigens
Surface Markers
Pathogenic infections by microorganisms can be detected by the presence of specific markers on the cell’s surface
- These foreign markers which are capable of eliciting an immune response are called antigens
- The part of the antigen to which specific antibodies will bind is called an epitope (or antigenic determinant)
Specific infections can be identified by determining which antigens are present to form a complex with specific antibodies
- Infectious pathogens may possess multiple different antigens, with each antigen potentially possessing multiple epitopes
- The presence of particular antigens can be detected by undertaking an enzyme-linked immunosorbent assay (ELISA)
Surface Markers – Antigens versus Epitopes
Understanding:
• Predisposition to a genetic disease can be detected through the presence of markers
Genetic Markers
Certain genes may predispose individuals to particular disease conditions (e.g. BRCA genes predispose to breast cancer)
- Screening an individual’s genome for certain genetic sequences allows for the identification of disease predispositions
Genetic markers can be detected using gene probes – nucleotide sequences that are complexed to fluorescent labels
- The gene probe is complementary to specific target sequences and will hybridise and fluoresce if that sequence is present
- A large variety of genetic markers can be tested for using DNA microarrays (also commonly known as DNA chips / biochips)
In addition to testing for genetic diseases, gene probes can also be used to identify pathogenic genetic material
- Pathogens will have unique genetic sequences which, if detected by a gene probe, will indicate infection has occurred
- Pathogenic genetic material can be amplified and identified using modified PCR techniques
Genetic Markers – Gene Probes
Understanding:
• Metabolites that indicate disease can be detected in blood and urine
Metabolic Markers
A disease is an abnormal condition of the body that impairs normal functioning (i.e. deviation from homeostasis)
- Diseased cells will have an altered metabolism and may synthesise products that are not present in normal, healthy cells
- These metabolic products (metabolites) may be detected in blood or urine to enable identification of disease conditions
- Disease metabolites may be detected with monoclonal antibodies using an enzyme-linked immunosorbent assay (ELISA)
Metabolic Markers – Blood and Urine Samples
