7.1 DNA Structure & Replication

A DNA profile was created for two genes in three individuals (A, B, and C).

Which of the following statements, relating to the images provided, are correct?

The relationship between DNA fragment length and distance moved through the gel is linear.

Fragment length is determined by the number of VNTRs.

There is a percentage increase of 50 % between the distance moved by fragment Y and that moved by fragment X.

Which row correctly identifies the enzymes in a replication fork?

Which of the following statements about DNA sequencing are correct?

Fragments of different length can be separated using gel electrophoresis.

PCR requires the use of primers, deoxyribonucleotides, RNA polymerase, and labelled dideoxyribonucleotides.

The terminator nucleotide indicates the base present at each position in the sequence.

Dideoxynucleotides are incorporated at specific points in the DNA sequence.

Hershey and Chase carried out an experiment to determine whether the molecule of heredity was protein or DNA; their results after centrifugation are shown below.

Note the following:

• Extracellular material is found in the supernatant.
• The y-axis shows the percentage of each radioactive element present in the supernatant; the remainder of each element ends up in the pellet.

Which of the following can be concluded from the results shown?

When DNA polymerase adds a new nucleotide to a growing DNA strand, which part of the last nucleotide does it form a bond with?

Okazaki fragments are short sections of DNA formed during DNA replication.

 Which of the following statements correctly describes why they form?

What is the correct sequence of events during DNA replication?

1. DNA gyrase releases the strain within supercoiled areas of DNA.
2. Helicase unwinds the DNA double helix.
3. DNA Primase catalyses the synthesis of a short RNA primer.
4. DNA polymerase I replaces RNA primers with DNA.
5. DNA polymerase III adds nucleotides to the template strand.
       

   	first	→	→	→	last
   A	I	II	III	IV	V
   B	II	I	III	V	IV
   C	I	II	V	III	IV
   D	II	III	IV	V	I

The majority of the eukaryotic genome contains non-coding regions of DNA.

 Which of the following are functions of non-coding DNA?

The shaded boxes in the diagram below (left) indicate Variable Number Tandem Repeats (VNTR) from three different loci that were amplified (via PCR) from DNA found at a crime scene. The diagram on the right shows DNA profiles of fragments amplified from the VNTR regions of four suspects.  

Which of these suspects was most likely at the crime scene?

The dideoxy chain-termination method of DNA sequencing developed by Fredrick Sanger uses dideoxynucleotides. These modified nucleotides lack a 3’-hydroxyl group.

 Which of the following best describes the effect of lacking a 3’-hydroxyl group.

In the 1950s, Hershey and Chase demonstrated that DNA, not protein, is a factor of heredity responsible for carrying genetic information from one generation to another. They used viruses that were labelled with either radioactive sulphur (³⁵S) or radioactive phosphorus (³²P) to infect bacteria.

Which of these statements correctly describes the results of their experiment?

Rosalind Franklin’s X-ray diffraction investigations provided crucial evidence that DNA was a double helix - this was instrumental to Crick and Watson developing their model of the structure of DNA.

Which statements about the structure of DNA were not answered by Franklin’s work?  

Molecular visualisation software can be used to look at the three-dimensional structure of complex macromolecules such as the nucleosome.

 Which of the following statements about molecular visualisation software are correct?