Slide 1
This question
is asking you to orient yourself to the polarities of the two strands of the
DNA molecule. The easiest way to approach this problem is to look for
the DNA polymerase.
Slide 2
The DNA polymerase is always at the
3' end of the newly synthesized DNA. Each piece of nucleic acid has a 3'
and a 5' end - note that there are several molecules of DNA polymerase found
on this diagram so we can orient ourselves in several different places.
The opposite end of the strand is the 5' end and the 3'end of one strand
must align with the 5' end of another strand.
Slide 3
This question
requires you to use both the polarity rules and the base-pairing rules.
First, we have to align the 5' end of the given strand with the 3' end
of its complimentary strand. Then we need to use the base-pairing rules.
Slide
4
Using the polarity and base-pairing rules we see that A is the correct
answer. The 5' end of the given strand aligns with the 3' end of the A
strand. Then we see that A base pairs with T, C with G, A with T, and so
on.
Slide 5
This question is similar to the previous question but
now the possible answers are written 5' to 3'. Remember, DNA molecules
are 3-dimensional and can be oriented in any way. However, when they
physically connect to each other they need to be paired 5' to 3' and 3' to 5'.
So to answer this question you need to align the 5' end of the given strand with the 3' end of the complimentary strand.
Slide 6
The correct
answer to this question is B. When you align the 5' end of the given
strand with the 3'end of the answer - you can then use the base-pairing rules
to find the complimentary strand.
Please let me know if you have any questions about these practice problems.