RNA and
Transcription
Getting the message out!
You already know that DNA
is the “boss” of the cell.
It directs all of the cell’s processes.
How can it do that when it’s
stuck inside the nucleus?
Answer: specialized messages!
1.The DNA sends its coded message from
inside the nucleus to the cytoplasm
through a process called transcription.
2. This message contains instructions for
making a specific protein through a
process called translation.
3. The protein puts the DNA’s instructions
into action, either inside or outside the cell!
How to get
the
message
out…
But who’s going to carry the
message from inside the
nucleus to the cytoplasm?
RNA: DNA’s overworked cousin
RNA is very similar in
structure to DNA.
The only differences are:
1. The sugar in RNA is
slightly different (ribose
instead of deoxyribose)
2. RNA has uracil (U)
instead of thymine (T)
3. RNA usually hangs out in
a single, unstable strand
These small changes in
structure make RNA
function very differently
from its DNA cousin.
RNA comes in three flavors
¾ Messenger RNA (mRNA): carries the
genetic message from DNA in the nucleus
to the cytoplasm
¾ Transfer RNA (tRNA): uses the RNA
message to construct proteins in the
cytoplasm
¾ Ribosomal RNA (rRNA): ribosomes are
made out of this kind of RNA. Proteins are
made inside of ribosomes.
mRNA
tRNA
A Ribosome
(rRNA)
Let’s take a closer look at how the
message gets from inside the
nucleus out to the cytosol…
We first must copy the coded message
from the DNA to an RNA molecule.
This process is called transcription.
Transcription has several steps:
1.
The strands of DNA are separated by the helicase
enzyme.
2. An enzyme called RNA polymerase starts adding
complementary RNA nucleotides to one of the
separated DNA strands. The nucleotides are joined
together by the ligase enzyme.
3. When RNA polymerase reaches a “stop sign” in the DNA
strand, it stops transcribing and releases the newly
formed RNA strand. The RNA leaves the nucleus for the
cytoplasm, where it can be used to make proteins.
4. The separated DNA strands come back together.
Check it out!
More pictures of transcription
Hey look, it’s more pictures of
transcription!
Now the mRNA can take the
genetic message out the cytosol,
where it can be used to make
proteins!
Stay tuned for the next installment
of this cellular saga to find out how
it happens …