I'm often asked questions about viruses, DNA, RNA, genes and health.
I’m happy to address this by starting with a quick review of what DNA is and
its relationship to RNA and protein... quick basic Molecular Biology!
It's good for everyone to understand a little about how their body and life works. ☺
People usually understand it right away when I use my food / restaurant analogy.
In the nucleus of each of your cells is your set of 46 chromosomes
(2 of each, one from your mom and one from your dad for each of the 23).
(Dogs have 39 different chromosomes… one of many reasons they are better
than people ☺ )
Anyway, each chromosome is a long chain of DNA.
DNA is a long chain with a sugar-phosphate backbone.
The sugar is not glucose, it is deoxy-ribose, a very chemically stable sugar.
Attached to each of the sugars in the chain is 1 of 4 possible chemicals called nucleotides.
Based on the first letters of their chemical names, we call the 4 nucleotides A, T, C and G.
Think of the chromosomes as the volumes in a 23-volume encyclopedia of cooking.
Chromosome # 1 has all of the recipes that start with an A, volume #2 has
all of the “B” recipes, etc. until we get to #23 that has the X, Y, and Z recipes.
(Pretty cool how I managed to get last one to be the X and Y chromosome, which how the numbering really works in humans :P ).
Instead of English, the recipes are written in a code where each letter
is encoded using 3 adjoining nucleotides. For example, “G-A-C” equals the letter D.
By the way... each part of the chromosome representing a recipe is called a gene
Just to recap, your DNA is the master set of all recipes that
you’ll need for any kind of restaurant. It is valuable and you
want it to last, so it’s printed on acid-free paper to last a
lifetime (stable DNA). The DNA contains information on how to
make foods… it is the information and not the food. And the
different restaurants are all of the types of cells in your body.
A skin cell makes lots of a protein called keratin
(so its kitchen will need that recipe) but a red blood cell
doesn’t serve keratin, it serves mostly a protein called hemoglobin
(so its kitchen doesn’t need the recipe for keratin but it
does need the the one for hemoglobin, etc.)
If you were the boss of a new Chinese restaurant,
you'd need all of the recipes for Chinese dishes (the skin cell),
but not the ones for Italian dishes (the red blood cell).
So, you go through each volume of the encyclopedia, and
whenever you find a Chinese recipe, you xerox it on to
some cheaper recyclable paper. The less stable paper is RNA.
It has a Ribose backbone instead of Deoxyribose, and it
degrades in much less than a lifetime. If it’s for a daily
special, it might only last a matter of hours!
To recap, the subset of recipes needed for a particular cell
type are copied (transcribed
) from the DNA into RNA (an enzyme
made of protein called RNA polymerase does that job). The RNA
uses more or less the same code as DNA, except it uses “U”s
in place of “T”s used in the DNA code. But the RNA is still
information… not food.
This Transcription process takes place in the main office (the nucleus).
Then you hand the xeroxed Chinese recipes for tonight’s menu out of the
office and into the kitchen. The “kitchen” is called ribosomes.
They read the recipes and Translate
them into the various products (keratin, etc.)
needed in the Chinese restaurant (skin cell). They do this by reading
the recipe, 3 letters at a time, and translating that “codon” into one
of the amino-acids (the building blocks of protein).
By the way, for anyone interested to see the actual genetic code of how the DNA nucleotide sequence translates
into a protein's amino-acid sequence, click the link below.
Did you ever notice how some Chinese restaurants make a certain
dish differently than you're used to? Usually it’s a little “off”… but
once in a while it’s the best ever. How does this happen???? Mutations!
Mutations are when a mistake happens while reading the code
(which could be because the code got damaged, or just a copying error).
There are two places where the code can be mutated.
The first place is in the production of new sets of encyclopedia
(this is when a cell divides and needs to replicate all of its
chromosomes so that each daughter cell gets a full set).
These mutations happen, but quite rarely, because there is
even a proof-reading mechanism built in. When there is a mutation like this,
the recipe is permanently corrupted and the kitchen will make it wrong
every time… and if that restaurant starts a chain, all of
the franchises will make it that new way, too.
The second place that a mutation can occur is at the point
of xeroxing the recipes. There could be speck of dirt on the copy
machine and it could turn a G into a C on the copy! This happens
at a higher probability because the xeroxing process happens fast
and sloppy. In that case the kitchen will make the dish wrong for
a while, until they get a new copy without the mistake in it.
Once in a great while, changing or deleting or adding an ingredient
makes the recipe better instead of worse. If the new version appeals
to the majority of customers, eventually the mutant will be selected
for and displace the original recipe!
Now you understand the basic flow of genetic information!