Packing ratio is determined by dividing the length of DNA packed into a structure by the length of the structure.
Chromosome 11 consists of about 1.35 x 108 base pairs and the distance between adjacent base pairs is 3.4 nm. The chromosome is about 5 µm in length during metaphase.
Calculate the packing ratio of chromosome 11. Show your working.
A group of scientists studied the replication of DNA in Escherichia coli bacteria.
During their investigation, radioactive nucleotides were added to DNA that was actively replicating in a short pulse of about 5 seconds. This allowed the radioactive nucleotides to be incorporated into the new DNA strands.
This was followed by a "chase" period, during which an abundance of unlabelled nucleotides was added to the DNA for different amounts of time, between 7 and 120 seconds. After the isolation and centrifugation of the DNA molecules, the results were obtained.
The graph below shows the results of their investigation.
Contrast the results obtained at a "chase" period of 7 seconds with those obtained at 120 seconds.
A mutation of the HTT gene may increase the risk of a person developing Huntington disease later in their lives. Blood samples from four different individuals were taken and the base sequences of a part of their HTT gene were sequenced using the chain termination method. These were compared to the normal base sequence of the HTT gene by reading from the smallest to the largest fragments.
The results from the gel electrophoresis are shown in the diagram below.