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DNA - Replication, Transcription, and Translation
Transcript of DNA - Replication, Transcription, and Translation
It's the molecule responsible for the development of all living organisms.
DNA is the reason why a seedling can grow into a tree...
...and why a human can have blue eyes.
Transcription, Translation, and Replication
by: Monika Balce
Honours Bio 12
WHAT is DNA?
In order to do all of this properly though, DNA goes through three processes...
DNA contains the code for making lots and lots of different proteins. RNA contains the information to make just one single polypeptide chain (AMINO ACID CHAIN), or just one protein!
Background RNA Info
DNA has two strands
RNA has only one.
And to create each of these proteins for the body,
types of RNA also exist
Ribosomal (as in ribosome) RNA
-> amino acids are used in every cell of your body to build the proteins you need to
Basically, they are the chemical building blocks.
-> ribosomes are the
in a cell.
messenger RNA and
Ribosomes are made of
parts or subunits:
The large and small subunit
these ribosomes are "translators" -> they
Think of ribosomes as translators who make an English speaker understand Chinese!
part of organism survival, and DNA must
of itself for cells to divide.
Replication happens in
RECAP 3 ->
is the cell cycle phase in which
the cell spends most of its time preparing for cell division.
DNA is a double strand, so an enzyme called
the double strand into
two single strands
*It's a helix breaker.
How does it unzip it? By
(hydrogen bonds) between the
bases A, C, G and T.
This way, the bonding locations for
NEW complementary bases
can be exposed. Now the two single strands are ready to become two new
Another enzyme called
makes sure that an exposed Adenine from the
is paired with a
(A & T)
, an exposed Guanine from the original strand is paired with a
, and so on.
New DNA nucleotides
(which include the
new complementary bases
) move into the nucleus.
show the new bases.
taking a more advanced look, DNA is
because each original strand contains
(which is why
one strand, from bottom to top, is 5' - 3'.
The other strand, from top to bottom, is 3' - 5'.
We read it as 5 prime to 3 prime.
Top of the strand is 3'. 3' is the location of the
first phosphate group
Bottom of the strand is 5'. 5' is the location of the
first deoxyribose sugar
RECAP 4 ->
DNA nucleotides are made up of:
(A, G, C, T)
*In RNA, the sugar is ribose.
breaks the helix open
- Bottom to top is 5' - 3'
or sugar to phosphate ->.
- Top to bottom is 3'- 5' or phosphate to sugar ->).
And because DNA is
5' - 3' strand
will always have nucleotides
(the opposite of its 3' is
new strand with added nucleotides
this new strand is being built in a
continuous straight line
5' to 3' direction
. We call it the
The opposite strand, the
3' - 5' strand
, is called the
be added to its
end because it would mean the DNA is being built in
- 5' direction
(we don't read books from right to left)
. Remember that...
Again, this shows how DNA is
5' - 3' DIRECTION.
Top of the strand is 3'.
Bottom of the strand is 5'.
3 prime to 5 prime
always BUILT or READ
5'- 3' DIRECTION
(like we read books from left to right)
This process continues along the DNA strands and forms
Each DNA molecule will have
one original strand
one new strand
1 "parent" strand
1 "daughter" strand
Transcription lets the instructions of DNA be used. During transcription, the gene is rewritten into
mRNA holds the
the cell needs to make a
specific type of protein
Think of mRNA as a
of DNA that can leave the cell's nucleus.
Transcription's happening while you read this very sentence. In fact, your body's cells are carrying out transcription as each
a billion mRNA = a billion proteins being produced
section of DNA
that codes for a certain protein.
First, the gene is also unzipped and split apart - like in
- by the enzyme
(sibling of DNA polymerase but for RNA):
Again, basically DNA is
in order to make
RECAP 5 ->
RNA is a
pairs with Adenine
(A + U)
instead of Thymine
(A + T)
. Thymine exists only in DNA.
And in this case, RNA is called
RNA because it
information from DNA to the
Remember that the
are the sites of
(a protein-making factory)
After RNA polymerase unzips the gene DNA strand,
T A C
(a sequence of nucleotides/bases, or
marks the start of transcription along this strand.
Then RNA nucleotides float in and bond to their corresponding bases on the gene DNA strand. A joins with U
(*RNA = URACIL replaces THYMINE)
and G joins with C.
**This special parent-daughter feature earns DNA the title
A functional single strand
A U G
This mRNA strand can now leave the nucleus and head over to the ribosomes.
It's time to create a protein:
it's very important to understand the nature of mRNA's chemical message.
There are only
bases/nucleotides in RNA:
A, U, G, C
To make a protein, around
20 different amino acids
are needed. If there was
per amino acid, it obviously wouldn't work.
If there were
per amino acid, there would be combinations
than 20, which still isn't enough!
So, the nucleotides/bases work in
A U G
), resulting in 64 combinations :)
Where DNA contains a protein synthesis code,
version of it is a
Translation occurs in
Once the mRNA arrives at a ribosome,
- which is the
RNA component of the ribosome
and essential for protein synthesis -
the strand into the correct position on the ribosome.
of the ribosome holds the mRNA strand. The
of the ribosome will hold the
The first codon of mRNA is
A U G
. This codes for the amino acid
. Methionine is
the first amino acid in any protein.
This is why
A U G
Therefore, the mRNA strand's start codon is marked.
The ribosome is ready to translate the mRNA into a protein!
comes in during the second step of translation ->
This process ensures that the amino acids are put into the
sequence for building the protein.
[hence the name] a
specific amino acid
to the ribosome.
They have relevant features that are
to protein formation:
each has a
for the amino acid
each has an
on the other end.
each is the
exact same length
-> allows the ribosome to hold it in a position where
can form between the amino acids.
An anticodon is also a
or has three bases that are
to the mRNA bases
U A C
pairs with mRNA's
A U G
Think of tRNA as cars that stop for gas. mRNA is the gas station. The 'gas' the tRNA gets forms fuel, which is
the amino acid chain.
The exposed codons of the mRNA are aligned with its
proper complementary tRNA anticodons
in the ribosome.
While this happens, its
is also aligned at the
of the tRNA.
Or, you can say each tRNA carries a
corresponding amino acid.
tRNA C U A
codes for the amino acid
of these amino acids lets
link them together.
This sequential alignment starts as
(the FIRST amino acid in ANY PROTEIN) bonds to the
amino acid after it.
is made between them.
*Remember: 2 amino acids are joined by a dipeptide (ONE peptide bond), 3 amino acids are joined by a tripeptide (TWO peptide bonds), etc.
A U G
C A G
---- so on
amino acid chain
grows and grows as amino acids are added.
And the tRNA that is freed of its amino acid goes back to the cell cytoplasm to take
tRNA is reusable and recyclable
; the process continues.
amino acid chain
Termination is self-explanatory. Translation of an mRNA strand can't go on forever. So translation keeps on running until a
The tRNA whose bases are complementary to an mRNA's
(there are 3 terminator codons out of 64)
U A A
U G A
U A G
does NOT carry an amino acid.
Thus, the sequence ends.
These three steps (
) are what allows
DNA (the instruction book)
to make the amino acids bond together through
RNA (the construction worker)
. In turn they form an
amino acid chain
that creates part of a
for the body. *
*Remember that proteins are made up of numerous amino acids
, be it a protein for hair or a protein for the brain.
DNA is the
foundation of life
. Without DNA, life wouldn't exist at all.