Course: SAT 170 Introductory Biotechnology

Unit 11 Learning Module

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- Unit 11
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Biotechnology in the Field of Medicine-Red Biotechnology

The field of medical biotechnology is rapidly growing in response to the discovery and perfection of techniques such as the polymerase chain reaction, tissue cultures, gene therapy, protein therapy, stem cell therapy, and genetically modified organisms (GMO’s) that we previously discussed. Medicine is moving in the direction of more personalized and preventative care through the employment of these methods. There are many facets to medical biotechnology that we will discuss in this unit including biodiagnostics, biopharmaceuticals, and tissue engineering.

Figure 1
Using biomarkers or gene variants for the detection of particular diseases both infectious and genetic, is an important aspect of the preventative and personalized medicine promised by modern medical biotechnology. Such applications of medical biotechnology are commonly referred to as biodiagnostics. Biodiagnostics allows for rapid and early detection of diseases which can provide more effective care and more robust treatment options.

The human genome project has provided valuable insight into the genes that are involved in a variety of human diseases including their chromosomal location as well as their sequences. By comparing the DNA of healthy and diseased individuals, gene variants that are associated with a particular disease become evident. One method that is used for the detection of disease is known as restriction fragment length polymorphism (RFLP) analysis. The basis for such an analysis comes from the fact that diseased genes will have slightly different sequences than normal genes. Such variations in the sequence can change the number and type of restriction sites that are present in a particular DNA sample (recall from unit 6 that a restriction site is a DNA sequence where a restriction enzyme will cut that DNA molecule). Thus, if two DNA samples are cut with the same restriction enzymes, the diseased DNA will be cut differently than the normal DNA. These differences can be examined using electrophoresis and blotting techniques (see unit 6 for a review of these techniques) which will show different banding patterns of the DNA samples.

Figure 1 - This diagram illustrates the different cuts that are made with restriction enzymes because of a variation in DNA sequences (shown here as polymorphism in restriction site) within a restriction site.

Figure 2 - This is an example of an electrophoresis gel that shows the different fragments that are made in different DNA samples because of the restriction fragment length polymorphisms (RFLPs).
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The major disadvantage of RFLP analysis is that it relies on the altered sequence being a part of a restriction site, which is a rare event. This problem is overcome using allele-specific oligonucleotide (ASO) analysis and the polymerase chain reaction (PCR). An allele specific oligonucleotide is a synthetic piece of DNA that can be used as a probe to bind to a piece of DNA. Because this binding is very specific, it can allow you to distinguish two DNA samples even if they only differ by a single nucleotide. Furthermore, it can be used as a diagnostic tool because presumably a disease gene will have a different sequence than a healthy gene and will, therefore, be detected by different ASO probes. PCR is among the most popular of diagnostic tools because of its sensitivity and specificity. Recall from unit 6, that PCR is used to amplify or copy segments of DNA using primers that can anneal to that target DNA. Thus, if a DNA sequence that is associated with a particular disease or infectious agent is known, it can be used to create primers specific to that sequence. If a sample collected from an individual contains that sequence of DNA or infectious agent, it will be detected in the PCR. The major advantage to using PCR for the detection of certain diseases is its sensitivity. Using other methods, such as the enzyme-linked immunosorbent assay (ELISA) can take months to detect the human immunodeficiency virus (HIV). Using PCR, it can be detected much earlier, thus allowing for earlier treatment. The same is true for tuberculosis which can lie dormant for periods of time and can be relatively slow progressing. With better detection comes better treatment of such diseases.

Both ASO analysis and PCR can be used to detect single nucleotide polymorphisms (SNPs).  A SNP is a single nucleotide change that varies from person to person. Although SNPs are not always associated with a particular disease they do occur regularly throughout the genome and provide the majority of the genetic variation between individuals. It is believed that SNPs represent variations in DNA sequences that may influence how we respond to stress and disease. Thus, SNPs can be used as a tool to predict an individual’s predisposition to diseases such as diabetes, cancer and heart disease. Many SNPs are clustered together on a chromosome in groups that are referred to as haplotypes. The Hap-Map project aims to identify the millions of different haplotypes associated with the human genome to improve our understanding of the role of SNPs in the development and progression of human disease. These SNPs are also detected using PCR.

Figure 3 - This is an example of a single nucleotide polymorphism (SNP). Notice how in DNA sample 1 the highlighted nucleotide pair is cytosine (C) and guanine (G), while in DNA sample 2 it is adenine (A) and thymine (T).

Prenatal testing is used for the detection of certain genetic diseases in utero. Two different techniques are often used for prenatal testing: amniocentesis and chorionic villus sampling. During these methods, fetal cells are collected and a karyotype of the DNA in those cells is created. Recall from unit 3 that a karyotype is a sort of chromosome map which provides information on the the shape, appearance and number of chromosomes in an individual’s cells. This information can provide valuable insight to the presence of certain genetic markers that are associated with particular diseases. Some diseases that are commonly tested for during the prenatal genetic testing include cystic fibrosis, Huntington’s disease, and sickle cell anemia.