DNA was originally thought of as a protein. In the 1950s, Alfred Hershey and Martha Chase showed that DNA is a factor of heredity responsible for carrying genetic information from one generation to another.
The sequence of DNA can be determined by a machine and technique developed by Frederick Sanger, called the dideoxyribonucleotide chain termination method.
Describe how nucleotides containing dideoxyribonucleic acid stop DNA replication.
Results from a paternity test using gel electrophoresis are shown in the image below. DNA was isolated from a mother, her child and two potential fathers. Primers designed to amplify different satellite DNA regions were used and amplified alleles are shown in the results below.
Use the gel electrophoresis DNA profiles in the image above to determine which male is the child's father.
The DNA fragments separated in the gel electrophoresis in part (c) vary in size from 100 bp (base pairs) up to 5 000 bp. DNA fragments of known size were used to create the plot shown in the graph below.
Use the line of best fit on the graph to determine the base pair length for DNA fragments that travelled 5 cm on the gel electrophoresis plate. Give answers to the nearest whole number.
Today, visualisation software can be utilised to analyse DNA in very high detail. The association between protein and DNA within the nucleosome can be seen.
Describe what may be visualised when analysing a nucleosome.
Many visualisation techniques have been used to understand and study the structure of DNA. Watson and Crick used visualisation techniques, such as Franklin’s X-ray diffraction, to build a physical model of DNA. Their models were also influenced by the findings of other researchers, such as Erwin Chargaff.
Describe how the research findings of Franklin and Chargaff facilitated Watson and Crick to determine the structure of DNA.
