Clare Kennedy: Genomics 101 - What is the difference between DNA and RNA?

In this explainer episode, we’ve asked Clare Kennedy, Clinical
Bioinformatician at Genomics England, to explain what the
difference is between DNA and RNA, in less than 10 minutes.


You can also find a series of short videos explaining some of the
common terms you might encounter about genomics on
our YouTube channel.


If you’ve got any questions, or have any other topics you’d like
us to explain, feel free to contact us
on info@genomicsengland.co.uk.


Want to find out more? Check out the blog 'Genomics 101: RNA vs
DNA, what's the difference?'


You can download the transcript or read it below.


Naimah: What is the difference between DNA and RNA? Today, I’m
joined by Clare Kennedy, who’s a Clinical Bioinformatician here
at Genomics England, who’s going to tell us more.


So first of all, Clare, what is DNA?


Clare: So, DNA stands for deoxyribonucleic acid, and although
this is quite a mouthful, DNA is essentially an instruction
manual for our body on how to function, and a copy of this manual
is stored within almost every cell of the body in a structure
called the nucleus. So, our DNA essentially comprises all of the
genetic information we inherit from our parents, and this
information is contained within two long strands of code, and we
inherit one strand of code from our mother and one from our
father, and both strands combine and they form a twisted ladder
like structure that we call the DNA double helix. So, each strand
is made up of small units called nucleotides, and these
nucleotides, they differ based on their chemical composition.
They can either contain a molecule of adenine, guanine, cytosine
or thiamine, and this is why we often see our DNA sequence
represented by the letters A, G, C or T. And in total, our entire
DNA sequence consists of three billion of these nucleotides.


So, as this DNA instruction manual is quite long, it needs to be
broken up into smaller sections that the body can read, and
that’s where genes come in. So, a gene is a segment of the DNA
and it contains a particular set of instructions, normally on how
to make a protein. So, proteins are essential for life and
they’re involved in almost every process within our body, and
that is why we have around 20,000 protein coding genes in our
DNA.


Naimah: So then can you tell me, what is RNA and how does this
differ from DNA?


Clare: So, like DNA, RNA, which stands for ribonucleic acid, is
an incredibly important molecule that encodes genetic
information, and it’s found in all cells of the body. So, RNA
consists of only a single strand of nucleotide units, and just
like DNA, RNA can be represented by four letters that reflect the
chemical composition of each nucleotide. These four letters do
differ slightly though, because RNA contains uracil instead of
thiamine, so you can distinguish a DNA sequence from an RNA
sequence by the presence of the letter U and the absence of the
letter T. So, while we think of the DNA as the instruction manual
for the body that contains all of our genetic code, RNA is the
reader of this instruction manual, and it helps the cell to carry
out these instructions, so the proteins can be made.


Naimah: So, can you tell me a bit more about this protein
production, and how are DNA and RNA involved?


Clare: So, protein production all starts in the nucleus with the
DNA. So, if we want to make protein, we must first read the
portion of the DNA or the gene that contains the instructions to
make this protein. So, because DNA is so long, it’s really
tightly packed into our nucleus, and the


region we’re interested in might not be accessible, so we first
need to open this region out. So, molecules and enzymes help us
open this region of the DNA, and once the gene is accessible,
they start to read it, and they start to transcribe the
instructions that are encoded within the gene into a type of RNA
called messenger RNA. So, as the name suggests, messenger RNA is
the communicator of the instructions contained within our DNA,
and this process is called transcription.


So, the messenger RNA then leaves the nucleus and enters the main
body of our cell, which is called the cytoplasm, and messenger
RNA is transported to the ribosome. Now, the ribosome is a piece
of machinery which will build the protein, and it’ll use the
instructions that are encoded by the messenger RNA. But we need
materials to build the protein, and that’s where a type of RNA
called transfer RNA comes in. So, transfer RNA is instructed to
hunt down the building blocks or the amino acids that we need to
build the protein, and it brings these back to the ribosome. And
then we have a third type of RNA that gets involved called
ribosomal RNA. So, ribosomal RNA helps the ribosome assemble
these amino acids into proteins in a process known as
translation.


So, it really is a group effort between the messenger RNA, the
transfer RNA and the ribosomal RNA. And once the protein has been
assembled, it might go through some more processing steps, and
it’s eventually exported by the cell to where it’s needed.


Naimah: Okay, so apart from their roles, are there other key
differences between DNA and RNA?


Clare: So, as we touched on earlier, the main difference between
DNA and RNA is in their structure. So, we have, DNA is in a
double stranded helical structure, whereas RNA is single
stranded. And because of DNA having this double standard helical
structure, it’s actually much more stable than RNA, which is more
susceptible to degradation by enzymes and other molecules. As DNA
contains our genetic code, it’s much longer than RNA, and you can
only find DNA in the nucleus of the cell as it’s much too large
to leave the nucleus, whereas you can see RNA in the nucleus and
in the cytoplasm. RNA and DNA also differ in the type of code or
the lettering they use, so they both use the A, G and C letters
in their code, while DNA’s is the T lettering and RNA’s is the U
lettering, and this is due to the differences in the chemical
compositions of the nucleotides that make up DNA and RNA.


And the nucleotides in DNA also contain different types of sugars
from the nucleotides used in RNAs. So, in DNAs, you would have a
deoxyribose sugar, whereas an RNA uses a ribose sugar. That’s
where we get the deoxyribonucleic acid and the ribonucleic acid.


Naimah: So Clare, we’ve talked about the difference between DNA
and RNA, but why are these important in clinical care?


Clare: So, we can use DNA and RNA to diagnose illness and to also
develop therapies against these illnesses.


Naimah: Can you give me some examples of where DNA and RNA are
used for diagnosing conditions?


Clare: Absolutely, so an excellent example is in the diagnosis of
cancer. So, the majority of cancers are caused by mistakes in the
genetic information encoded within our DNA, and result in the
production of malformed proteins. So, we can normally look at the
DNA and we can identify certain genetic mutations that cause the
cancer. So, examples are breast cancer, ovarian cancers, lung
cancers, essentially all types of cancers that you can think of
will have genetic mutations associated with them. But then there
are cases where no problem with the DNA can be identified, but
then when we look at the RNA, we do see a problem. So, a
particular example was recently shown in breast and ovarian
cancer, where a gene that encodes for a protein called BRCA1 was
not shown to have any genetic mutations, however when we looked
at the RNA produced from that gene, we could see there are
problems with that RNA and essentially identify a genetic cause
for that cancer.


Naimah: Could you also give me any examples of where RNA or DNA
are being used in therapies?


Clare: So, absolutely. So, most of us will have heard of RNA
vaccines in recent times, such as those that were generated
against COVID-19. And essentially how these vaccines work is they
deliver small messenger RNA from the virus into the body. The
body can then make a protein from this messenger RNA, and the
immune system recognises this as an invader and destroys it. So,
this low level of viral exposure essentially trains your immune
system to respond in the event of an infection, and really the
success of the MRNA vaccines against covid has really paved the
way for the use of MRNA vaccines against cancer. So, it’s
believed that we can stimulate an immune response that would
destroy a cancer cell using MRNA vaccines, and there are now some
studies that are looking at developing messenger RNA vaccines
against cervical cancer in particular.


So, DNA therapies can actually target genetic mutations and
correct them to prevent illness, and one such example is a gene
editing treatment that has been developed for the treatment of
blood disorders, such as sickle cell anaemia.


Naimah: That was Clare Kennedy explaining the difference between
DNA and RNA. If you’d like to hear more explainer episodes like
this, you can find them on our website at
www.genomicsengland.co.uk. Thank you for listening.