DNA Review Questions
1. What components make up a typical nucleotide?
Phosphate group, 5 carbon sugar, nitrogenous base
2. What are Chargaff’s rules? How did they help in determining the structure of DNA?
That in any sample of DNA, the concentration of A = concentration of T and C = G. This
helped Watson and Crick confirm their idea that A would bind (via hydrogen bonds) to T
and C would bind to G  base pairing rule.
3. What makes RNA different from DNA?
RNA is typically single stranded, whereas DNA is double. RNA has ribose sugar and
uracil whereas DNA has deoxyribose and thymine.
4. Outline the experiments performed by Griffith. What conclusion did Oswald draw
from his results?
Griffith mixed heat treated (killed) pneumonia-causing bacteria with harmless bacteria.
As a result, the harmless bacteria “transformed” into the disease version. Oswald
isolated individual compounds such as DNA, proteins, etc. Only DNA worked, so he
concluded DNA caused the change.
5. Why were two types of radioisotopes used in the Hershey-Chase experiment?
Phosphorus was chosen because it is found in DNA, not proteins. Sulfur was chosen
because it is found in protein, not DNA.
6. What did the x-ray crystallography work from Franklin tell Watson and Crick about
the shape of DNA?
It was a double helix with a consistent 2 nm width.
7. What is the basic structural difference between a purine and a pyrimidine? Why don’t
they pair up with each other?
Purines are two-ringed structures and pyrimidines are single-ringed. If they paired up, it
would either make the DNA too narrow (two pyrimidines) or too wide (two purines).
8. Compare and contrast the processes of DNA replication and transcription.
Replication copies DNA in S phase using helicase to unwind the DNA and DNA
polymerase to add free nucleotides of DNA to the growing strand. Transcription uses
RNA polymerase to both unwind the DNA and add free nucleotides of RNA that are
complementary to one strand.
9. What must happen to a strand of mRNA before it can leave the nucleus?
It must be spliced (introns cut out, exons glued together) and capped (modified guanine
added to 5’ end, poly A tail to the 3’ end)
10. Describe how codons and anticodons are used in translation. What is a triplet?
Codons are the three nucleotides of mRNA being read whereas anticodons are part of
tRNA that are the complement to the codons. This ensures that the proper amino acid
is brought in during translation.
11. How does translation begin and end?
Begins with a start codon (AUG) and ends with a stop codon (UAG, UGA, UAA).
12. How is tRNA used in protein synthesis?
tRNA has the complementary anticodon and carries the amino acid into the ribosome.
13. Do all point mutations result in a change in protein structure? Explain.
No, some mutations can take place in a non-coding region of DNA (outside a gene), or
on an intron. They could also change a codon that still codes for the same amino acid.
These are all silent mutations.
14. What is meant by a frameshift?
mRNA is read in triplet – three nucleotides at a time. This is known as the reading
frame. When a nucleotide is deleted or added, then the reading frame will change –
frameshift.
15. Outline the four types of chromosome mutations.
Deletion – piece of a chromosome DNA lost during crossing over.
Duplication – piece of DNA kept so there is two pieces after crossing over.
Inversion – piece of DNA is reinserted upside-down during crossing over.
Translocation – non homologous chromosomes exchange info during crossing over.
16. What do the bands on a gel represent?
Various lengths of DNA.
17. Why do certain strands of DNA move farther than others in a gel? Why do they
move at all?
They move because DNA has a negative charge and is attracted to the positive end of
the gel. Smaller strands can move faster through the porous gel than larger ones
can.
18. Outline how you could extract DNA from a sample of animal tissue.
Use detergent to remove both membranes, salt to neutralize DNA, protease (such as
pepsin) to break down proteins, cold alcohol to precipitate DNA.
19. How do restriction enzymes work?
They find a specific sequence of DNA and cut unevenly to produce single-stranded
ends of DNA called “sticky ends”.
20.What is a dideoxy nucleotide?
A synthetic nucleotide that has florescent markers and is lacking an oxygen on the 3’
carbon.
21. How are the various lengths of DNA created when sequencing a strand of DNA?
Whenever taq polymerase takes in a ddNTP (dideoxynucleotide), the replication
process must stop, and start over again with a new strand.
22. What role does temperature play in PCR?
It separates the two strands of DNA, taking the place of helicase. It makes it so hot, the
genes unzip…lol, roflcopters, etc, etc.
23. What is recombinant DNA?
DNA that contains a segment from another organism.
24. When inserting a gene into a cloning vector, why do we have to use the same
restriction enzyme on both the gene and the cloning vector?
So the sticky ends are the same and the two pieces can splice.
25. Outline how you could clone a cat from a sample of its tissue.
Starve a cell in G0 to make it totipotent. Take out the nucleus and insert it into an egg
that already had its nucleus removed. Insert into the womb of a surrogate and
BHAM! Clone!
26. Why is it clones will not live as long a lifespan as the organism they were cloned
from?
Their DNA has already undergone the loss of telomers that the nuclear donor had
experienced.
27. What is RFLP? How does it work?
Restriction fragment length polymorphism – DNA profiling. The number and location of
restriction cut sites varies from person to person, so a gel would show bands that
are in different locations.
28. When sequencing the human genome, geneticists employed the shotgun
sequencing method. What is this?
When you cut a large genome into smaller, more manageable pieces and have
separate labs sequence each piece.