JK - 2010
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Introduction
So learning about this stuff is kinda hard…
Yes! Learning about RNA, RNA transcription, and protein synthesis can
be very difficult! That’s because they are long, complicated and sometimes
boring processes to learn. But don’t worry; you’ve come to the right place!
RNA, RNA Transcription & Protein Synthesis for Dummies is an attempt to
simplify these processes so even a dummy can understand them.
Chapter 1
Where does RNA start?
To explain what RNA is you first have to understand DNA. You are made
up of DNA which stands for deoxyribonucleic acid and contains the
instructions to make cells. These instructions are stored in the nucleus of the
cell and are like the blueprints that make up you! DNA is constructed of
nucleotide pairings of cytosine to guanine, adenine to thymine and vice versa.
These nucleotide pairs match up like puzzle pieces fitting pyrimidines into
purines and creating a hydrogen bond between them. Your genetic
information is coded into the sequence of these bases, these sequences are
called genes.
Purine
Pyrimidine
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The nucleotides pairings are attached to a 5 carbon sugar, called
deoxyribose, which is then connected to a phosphate molecule which
connects to the phosphate molecules above and below it to create the
backbone of the structure. This makes a ladder formation which is then
twisted into a double helix.
Double Helix
Structure
That’s great, but I still don’t know about RNA!
Chapter 2
RNA transcription
Now we can get to RNA! RNA is formed by a process known as
transcription, where the RNA is transcribed, or copied from an existing strand
of DNA. Transcription takes place in the nucleus and starts with a strand of
DNA having its hydrogen bonds split by an enzyme. This does not harm the
enzyme and it can go on to find other strands of DNA to split even after it has
split one. With the hydrogen bonds broken, the DNA unwinds its double
helix and the nucleotide bases (Guanine, Cytosine, Adenine, and Thymine)
are all exposed. Messenger RNA or mRNA then comes into the nucleus and
searches for a specific chromosome in the DNA that contains a gene with
enough DNA to be copied. The Nucleotides of mRNA match up to the
exposed bases and use one side of it as a template. Like DNA only certain
bases can match up, Cytosine pairs with Guanine and Guanine with Cytosine,
but here’s the curve ball, when Thymine is on the DNA side it pairs with the
mRNA nucleotide Adenine, but when Adenine is on the DNA side, it pair a
nucleotide called Uracil which is not found in DNA. (See Fig. 1.1.)
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Fig. 1.1
Guanine
Messenger RNA
A strand
of RNA
Cytosin
e
Adenine
Thymine
Uracil
Enzyme splitting
the hydrogen
bonds
Hydrogen Bonds
A split strand of DNA
When the mRNA is completed it detaches from the DNA strand it used as a
template, the DNA is undamaged and can go back together as it was. The
completed strand of RNA (fig 1.2) then goes off to find a ribosome so protein
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synthesis can take place.
Fig 1.2
Guanine
Uracil
Cytosine
Adenine
5 Carbon Pentose
Sugar (Ribose)
A
completed
strand of
RNA found
in the
nucleus of
a cell
Phosphate Molecules
Remember! Adenine matches to Uracil in RNA
m but Thymine still matches to Adenine from DNA!
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Chapter 3
So what’s RNA have to do with protein synthesis?
After RNA transcription is complete is goes off in search of a ribosome.
Once it finds a ribosome it attaches itself to it and waits for a transfer RNA or
tRNA that matches its start codon to find it.
Codon: A distinctive set of 3 nucleotides in mRNA. The codons in tRNA are
called anti-codons. Codons match up to anti-codons.
Start Codon: A specific codon of AUG that cues the start of a strand of RNA.
Stop Codon: A specific codon that cues the end of a strand of RNA.
Once the start codon in the mRNA finds a matching anti-codon
from a tRNA the process of protein synthesis can start and a second tRNA that
also has matching codons attaches itself beside the first strand of tRNA, then a
third strand attaches, then a fourth and so on. Each tRNA attaches to an amino
acid in the cytoplasm which it then brings to the ribosome with it. So when the
tRNA anti-codons are matching with the mRNA codons the specific amino
acids carried by the tRNA line up beside each other as well.
A set of three codons makes an amino acid. Certain combinations make up
certain amino acids. These amino acids are needed to make protein. Certain
amino acids have certain properties, tryptophan for example, (UAU or UAC) is the
amino acid found in foods like turkey that make you sleepy.
A chart of
codons
that form
amino
acids.
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The enzymes in the ribosome then cause peptide bonds to form between
the amino acids through dehydration synthesis. After the amino acids are
joined the tRNA can leave and head back to the cytoplasm to find another
amino acid.
When two amino acids are bonded together it creates a peptide bond.
A chain of three or more amino acids becomes a polypeptide. There are
many different combinations of polypeptides. Any of these four factors can
be changed to make it a unique polypeptide.




Shape
Sequence
Amount
Kind of amino acid
The polypeptide chain grows until it reaches an end codon in the mRNA
which is the signal for the chain to release from the mRNA. End Codons
are one of the three sets of UAG, UAA and UGA.
Along the lengths of these polypeptides there are sulphur molecules
located in key points. This creates a unique shape that with the sulphur
creates a protein.
These proteins can become structural proteins and make up protoplasms
like micro-tubules in cells or protein plugs in cell membranes or they may
be destined to become an enzyme. This is done by associating with the
appropriate vitamine. Or the protein may become a hormone. In any case
the protein will, in some way, control some aspect of your being.
(referenced from bio duotang, page 11)
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Congratulations! You now learned everything you need to know about
RNA, RNA transcription, and Protein synthesis for Bio 30, even if you
knew nothing about it before!
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