Using Bioinformatics: Genetic Research
©Northwest Association for Biomedical Research—Updated October 2012
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8. Show Slide #2 and remind students that double-stranded DNA is
complementary and anti-parallel. The strand of DNA that encodes a gene
is often called the coding strand or the sense strand. By complementary
we mean that when there is an adenine (A) on one strand, there is always
a thymine (T) on the other stand, and when there is a guanine (G) on one
strand, there is always a cytosine (C) on the other strand. By anti-parallel
we mean that the two strands are in opposite orientations. The 5’ portion
(where the DNA strand “begins”) of the top DNA strand is on the opposite
“side” from the 3’ portion of the bottom strand. By convention, DNA
sequences are written from left to right in a 5’ to 3’ direction. When both
strands of a sequence are shown, the top strand is typically shown in a 5’ to
3’ direction, with the bottom strand in the opposite orientation.
9. Ask students to predict what the complementary DNA sequence (3’ to 5’) will
be for the DNA strand shown on Slide #2, writing down their predictions on
a piece of paper. Give students 2-3 minutes to think through and write down
their predictions before continuing.
10. Show Slide #3 and have students compare their predictions to the answer
on the slide. We often refer to the protein coding strand as the sense strand
and the non-coding strand as the anti-sense strand, but by just looking
at the DNA sequence, you are unlikely to know which is which. The non-
coding strand is also called the template strand, as this is the DNA strand
that is used as a template to make the messenger RNA (mRNA).
Bioinformatics & Proteins: Slide #2
LESSON 4
Anti-parallel: DNA strands are “anti-
parallel” to one another, meaning they
are parallel (or side-by-side) but run in
opposite directions, with the beginning
(or 5’ region) of one DNA strand found
at the same location as the end (or 3’
region) of the opposite DNA strand.
Gene: The unit of heredity. A segment of
DNA that codes for a specific protein.
Coding strand: Of the two DNA
strands, the coding strand is the
strand that has the same sense as the
messenger RNA. We can use the DNA
sequence from the coding strand to
predict a protein sequence by looking at
the genetic code. This strand is the same
sequence as the mRNA. Also called the
sense strand.Only one strand is used
for one gene, but different strands can
encode different genes.
Sense strand: This strand is the same
sequence as the mRNA. Also called the
coding strand.
5’ and 3’: The 5’ region is the beginning
of the DNA or RNA strand, while the
3’ region is the end of the DNA or RNA
strand. Scientists often say that DNA is
“read 5’ to 3’” which means that the
sequence is read or examined from the
beginning (5’) to the end (3’), left to
right. Genes are also transcribed and
translated in a 5’ to 3’ direction.
Complementary: Complementary
bases are two bases that are able to pair
with each other and create a base pair.
In DNA, adenine (A) and thymine (T)
are complementary, and the A on one
DNA strand interacts with the T on the
opposite (or complementary) DNA strand
to form a bond to complete double
stranded DNA. Similarly, guanine (G) and
cytosine (C) are complementary because
they always interact with one another.
This complementary interaction happens
between each base on the DNA strands.