Genes to Proteins

Genes to Proteins


Nearly every traits we possess from hair
and eye color, to height and shoe size is determined by our genes, genes are small
segments of DNA that code for proteins. Proteins perform many functions in our
body, some proteins serves as component of our cell membranes, other proteins make
up the structures our bodies like muscle skin, and fingernails, still more act as
enzymes catalyzing reactions of under body, when you break them down proteins
are made up of amino acids placed in a very specific order by cellular
organelles called ribosome, specific order of amino acids determines the
folding pattern of the protein and therefore the very specific function
that the protein will perform, our DNA is essentially a set of blueprints for
building the proteins that compose our body within the genetic code of the DNA are
the instructions for the correct amino acid sequences to build proper protein,
but how do our cells convert the messages stored in DNA to the proteins
our body needs, 2 problems stand in the way of accomplishing this
task, first the DNA is stored in the nucleus of the cell well the ribosomes responsibles for
building the proteins are found in the cytoplasm. How did the DNA instructions
get from the nucleus to the cytoplasm so the ribosomes can read the instructions
necessary to build the proteins? The second problem lies in the fact that
DNA speaks the language of nucleic acids while proteins speak the language of
amino acids, how can the language of DNA be converted to a language that
ribosomes can understand? the solution to both of these problems
lies in a single molecules ribonucleic acid or RNA. RNA is a nucleic acid just like
DNA but there are few key differences between these two molecules, first while
DNA’ has a double helix, RNA is only single-stranded so it forms a single
helix, secondly as the name suggests ribonucleic acid or RNA contains ribose
sugar in its structure well deoxyribonucleic acid or DNA contains deoxyribose sugar. The difference between these two sugars
is the presence of an extra oxygen on the ribose sugar. Another difference between DNA and RNA
lies in the nitrogenous bases they possess. DNA contains Adenine, Guanine
Cytosine and Thymine as you already know. RNA on the other hand contains a Adenine
Guanine, Cytosine and Uracil. Uracil is nitrogen bases that takes
the place of an Thymine in RNA. Uracil pairs with Ademine in RNA, just like Thymine does in DNA. Finally, one last difference is that RNA is much shorter than DNA.
well DNA contains thousands of genes RNA contains the information for only
one gene RNA is the special molecule able
to solve the problems associated with getting from gene to protein while DNA
is stuck inside the nucleus RNA is able to travel from the nucleus to the
cytoplasm to bring the genetic information to the ribosomes. RNA is also
bilingual speaking a language of DNA and of proteins. RNA is therefore able to
translate the DNA instructions into an amino acid sequence to build the
proteins of your body. There are three different types of RNA
that each play a role in the process of taking genes to proteins. messenger RNA or MRNA transfers RNA or TRNA and ribosomal RNA or RRNA.Llet’s take an
in-depth look at the process of protein synthesis and examine the role of each
type of RNA in order to make a protein the first thing
that must be done is to convert the genetic message in the DNA to a mobile
form that can move from the nucleus into the cytoplasm to find a ribosome this
process is called transcription. Transcription occurs inside the nucleus
and involves copying the information from a single gene on the DNA into a molecule
of messenger RNA or MRNA during transcription an enzyme called RNA
polymerase binds to a promoter site on the DNA the promoter site access the
start signal for transcription and marks the beginning of the gene of interest
once RNA polymerase binds to the promoter site the enzyme unwind the DNA
helix to expose the nucleotides of the gene. RNA polymerase then reads the DNA
strand and adds complementary nucleotides to build a molecule of
messenger RNA. RNA preliminaries moves down the DNA strand and the messenger
RNA grows behind the preliminaries the two DNA
strands close reforming the double helix once the
polymerase reaches a stop signal at the end of the gene the messenger RNA is
released and transcription is complete. Let’s take a closer look at the base
pairing that occurs as a string of messenger RNA formed. Remember that in RNA, Uracil pairs with Adenime instead of Thymine, looking at the
DNA strand the first base is cytosine represented by C, C pairs with G in RNA
just as it does in DNA, the next letter is A for Ademine, remember that in RNA Ademine does not pair with . Thymine. Uracil replaces Thymine in RNA.so in this case A will pair with U, just like in DNA G pairs with C, T will pair with aA again we have an A that would normally
paired with a T but in RNA there is no T so we use
Uracil U instead of Thymine, G pairs with C, G pairs with C just like in DNA.
Once the messenger RNA has been created during transcription it
must move from the nucleus into the cytoplasm to find a ribosome, remember
that ribosomes are tiny cellular organelles responsible for manufacturing
proteins, ribosomes are made up of ribosomal RNA or rRNA for short and protein, there are thousands of ribosomes found in the cytoplasm of every cell their job
is to read the messenger RNA and help translate the genetic message into a
protein, the process of making a protein from messenger RNA is called translation.
Translation occurs in the cytoplasm where a ribosome binds to the messenger
RNA. The ribosome reads the messenger RNA, three nucleotides at a time. A set of
three nucleotide bases on a strand of messenger RNA is known as a codon. Each codon translates into one amino
acid in the protein. A codon is like one word in the language of nucleic acids, while an amino acid is like one word in the language of proteins, this process is
called translation because we are literally translating one language into
another, just like English can be translated into Spanish and vice versa. The language of nucleic acids, like RNA can be
translated into the language of proteins. The key to translating one language to
the other lies in the universal genetic code. This chart summarizes the universal
genetic code, it may look complex but once you know how to read it the chart becomes a simple and useful
tool. In the center of the chart are the names of the amino acids coded for by
each codon, in this case the names are abbreviated. The three bases of the
codons are found on the margins of the chart. The name of the correct amino acid
is found with the three letters of the codon intersect on the chart. The first
base in a codon is found along the left side of this chart. The second base is at
the top of the chart. The third base in the codon is found along the right side
of the chart. Let’s do some examples, here is a strand
of RNA with the bases separated into codons. Given the first codon AUG, we use
the chart to find which amino acid would be coded for in the amino acid sequence. The
first base is A, so it would be found somewhere in this row on the chart. The
second letter is U, so it would be found somewhere in this column. This row and this column intercept in this square, so the correct amino acid is found
somewhere in this square. The last base in the codon G, narrows it down for us,
the correct amino acid for this codon is Methionine. This is the start codon and
will initiate most proteins. Let’s try another one, the second codon in this messenger RNA is ACG. The first letter is A, so the correct amino acid will be found
somewhere in this row. The second letter is C, so it’ll be found somewhere in this
column. We can see that this row and this column intercept in this box here. You
can see that there’s only one amino acid in this box so really the third letter,
which is G, doesn’t really matter because regardless of the third letter the
correct amino acid will be Threonine, abbreviated as Thr. The third codon is
GAG. The first letter G, second letter A the correct amino acid is somewhere in this
box. We decide between those two amino acids, by looking at the final letter G
so we know that the correct amino acid is Glutamine, Glu. let’s skip to the last
codon, codon 7 to finish up our examples here. Codon seven reads UAG. Fiirst
letter is U in this row, second letter is A in this column, the third letter is G.
This gives us a stop codon which would signal the end of the gene and the end
of translation. At this point the newly-formed polypeptide would be
released. The universal genetic code can also be represented in a circular table
that looks like this, again it may look complex, but it’s actually quite simple
once you know how to use it. The first base is in the center of the circle. The second base is in the next circle, and the third base is in the outermost circle. Let’s do some examples, codon 4 reads CUU. The first base C lets us know the correct amino acids is found in this
squadron of the chart. The second letter U narrows it down to this. You can see
the third letter doesn’t really matter here, regardless of whether is a U C A or G
the correct amino acid will be Leucine. Here’s another example, codon 6
AGC. The first base A let us know that the correct amino
acids found in this squadron of the circle chart. The second base G narrows it
down, the third-base C lets us know that the correct amino acid is Sirine.
Regardless of which chart you use this genetic code is called universal, because
it is the same for all organisms. Whether you are a bacterium, a pineapple plant, a
fish or human each codon codes for the same specific amino acid. For example, the
codon UUG codes for the amino acid Leucine no matter what your species
is. The universal genetic code represents strong evidence supporting the theory of
evolution and the idea that all life shares one common. That common evolutionary ancestor must have had this genetic code and passed it on to all its
descendants the numerous spieces we see alive today. Yet another player in the
process of translation is transfer RNA or TRNA for short. Transfer RNA are
single strands of RNA folded up into a compact shape, at one specific amino acids are attached to the tRNA. The tRNA brings the proper amino acids to the
ribosome to be linked together in a chain called a polypeptide. A polypeptide
is a long string of amino acids that will eventually fold to become
a protein. In order to put the amino acids in the correct order the tRNA has
what is called an anticodon, a series of three basis that is complementary to the codon on the messenger RNA. The anticodon on the transfer RNA fits into the codon
on the messenger RNA like a puzzle piece. Ensuring that the anticodon and the
codon pair up correctly, is how the proper sequence of amino acid is created. Let’s see an example of how codon and anticodon fit together to
ensure that the correct amino acid is added. Let’s say that your first codon on the
messenger RNA is AUG, a transfer RNA molecule with the anticodon UAC would
fit perfectly and carry with it the amino acid Methionine. If the next codon was GAG, a transfer RNA with the anticodon CUC would match and bring the amino acid
Glutamic acid. The Methionine and Glutamic acid would then bind together
using a peptide bond becoming the first link in the polypeptide chain. Transfer
RNA would continue bringing amino acids to the growing polypeptide chain, each
amino acid would bond to the previous one using a peptide bond. Once the
ribosome reaches a stop codon the polypeptide is complete. It detaches from the RNA ribosome complex and becomes
folded into a specific shape that will determine its function as a protein. The proteins produced by transcription
and translation give us the traits we possess from pigments that give us hair
and eye color to enzymes that can determine dietary restrictions. In order
to be expressed these traits coded in DNA must be transcribed to messenger RNA and then translated to proteins. Now that you have an overview of the process
involved in taking genes to proteins let’s review and add just a bit more
information. We start with a strand of DNA in the nucleus, RNA polymerase binds
to the promoter site on the DNA and begins transcription. A strand of messenger RNA is produced that is complementary to the nucleotide bases on the DNA. Messenger RNA leaves the
nucleus bringing with it the genetic message from the DNA. Once in the
cytoplasm, the messenger RNA binds to a ribosome complex made up of two
subunits; one large subunit and one small subunit. A transfer RNA carrying Methionine docks to the start
codon of the messenger RNA. The tRNA is docking at the peptidyl or proteins site
on the large ribosomal subunit this site is called the P site for short. The anticodon of the tRNA is
complementary to the code of the mRNA to ensure that the proper amino acid has
arrived. Next to the P site is the accepting or A site on the ribosome. The
next transfer RNA will dock here to bring a second amino acid to the chain.
Once the two transfer RNAs are in place, a peptide bond forms between the amino acids and a new link in the polypeptide chain is created. The
ribosome then moves down to read the next codon the mRNA, this pushes the
first transfer RNA from the P site to the exit or E site and it is
released. The second transfer RNA has moved to the P site leaving the A site
available to accept the next transfer RNA. The tRNA with the appropriate
anticodon will dock to the codon in the A site, bringing with it the correct
amino acid for the chain. A peptide bond forms between the
adjacent amino acids and the ribosome again moves down to be the next codon. The
tRNA in the E site is released and a new transfer RNA moves into the A site. The
peptide bonds continued forming between adjacent amino acids as the polypeptide
chain grows. The ribosome continues moving down the messenger RNA strand
until a stop codon is reached. At that point the ribosomal subunits fall apart
and the protein has released. Another, ribosome can find the start codon on the
messenger RNA and begin making another protein from the same strand of
messenger RNA. In fact many ribosomes can bind and translate proteins from the
same messenger RNA strand all at once. By doing this your body can produce many
copies of the same protein at a rapid pace generally the processes of
transcription and translation occur without error. Occasionally however, a mistake is made this is called a mutation we will
discuss mutation in the next lesson.