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DNA - Replication, Transcription, and Translation

What are DNA's 3 major processes? How important is DNA? What's 5 prime and 3 prime? What's DNA/RNA polymerase?! Here the three processes of DNA are explained in as much a concise, easily understood way as possible; answers are given.
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Mon b

on 27 May 2014

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Transcript of DNA - Replication, Transcription, and Translation

DNA is the most important molecule that exists in this world.


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?
Deoxyribonucleic acid.
In order to do all of this properly though, DNA goes through three processes...
Replication
Transcription
Translation
...to make
RNA
.
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
(double helix).

RNA has only one.
And to create each of these proteins for the body,
3
types of RNA also exist
.
Messenger RNA

(mRNA)
Transfer RNA

(tRNA)
Ribosomal (as in ribosome) RNA
(rRNA)
RECAP
-> amino acids are used in every cell of your body to build the proteins you need to
survive.
Basically, they are the chemical building blocks.
RECAP 2
-> ribosomes are the

protein assemblers
in a cell.
They
bind
messenger RNA and
transfer
RNA to
synthesize
(join together)
polypeptides

and
proteins
.
Ribosomes are made of
two
parts or subunits:
a
large
subunit
and
small subunit
.
The large and small subunit
combine.



a.k.a ->
protein synthesis
NOTE:
these ribosomes are "translators" -> they
translate
the
protein-coding genes
in
mRNA
into
proteins
.
Think of ribosomes as translators who make an English speaker understand Chinese!
REPLICATION
Cell division
is a
huge
part of organism survival, and DNA must
replicate
(make copies)
of itself for cells to divide.
Replication happens in
interphase
.
RECAP 3 ->
interphase
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
DNA HELICASE
unzips
the double strand into
two single strands
.
*It's a helix breaker.
How does it unzip it? By
breaking the
H-bonds
(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
DNA strands
.
Another enzyme called
DNA POLYMERASE
makes sure that an exposed Adenine from the
original strand
is paired with a
new Thymine

(A & T)
, an exposed Guanine from the original strand is paired with a
new Cytosine
, and so on.
New DNA nucleotides
(which include the
new complementary bases
) move into the nucleus.
The

green arrows
show the new bases.

NOTE:
taking a more advanced look, DNA is
anti-parallel
because each original strand contains
OPPOSITE
nucleotides
(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:
SUGAR
+
PHOSPHATE
+
BASE

(A, G, C, T)
*In RNA, the sugar is ribose.
DNA HELICASE
breaks the helix open
The strands

are
OPPOSITES
of
each other.


- Bottom to top is 5' - 3'

or sugar to phosphate ->.

- Top to bottom is 3'- 5' or phosphate to sugar ->).
And because DNA is
anti-parallel
, the
5' - 3' strand
will always have nucleotides
added
to its

3' end
(the opposite of its 3' is
5'
).

5'
3'
5'
3'
5'
3'
original strand
new strand with added nucleotides
A
T
G
C
C
G
T
A
this new strand is being built in a
continuous straight line
in the
5' to 3' direction
. We call it the
LEADING STRAND
.
The opposite strand, the
3' - 5' strand
, is called the
LAGGING STRAND
. Nucleotides
CAN'T
be added to its
5'
end because it would mean the DNA is being built in
the
3'
- 5' direction
(we don't read books from right to left)
. Remember that...
Therefore:
Again, this shows how DNA is
anti-parallel
!
DNA is
always BUILT
or
READ
in the
5' - 3' DIRECTION.
Top of the strand is 3'.
Bottom of the strand is 5'.
3 prime to 5 prime
DNA is
always BUILT or READ
in the
5'- 3' DIRECTION
(like we read books from left to right)
This process continues along the DNA strands and forms
TWO
separate, IDENTICAL
DNA molecules
.
Each DNA molecule will have
one original strand
and
one new strand
(a.k.a
1 "parent" strand
and
1 "daughter" strand
).
TRANSCRIPTION
Transcription lets the instructions of DNA be used. During transcription, the gene is rewritten into
messenger RNA
(mRNA).
mRNA holds the
genetic information
the cell needs to make a
specific type of protein
.
Think of mRNA as a
"revised edition"
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
second
passes.
DNA
a billion mRNA = a billion proteins being produced
A
gene
is a
section of DNA
that codes for a certain protein.
First, the gene is also unzipped and split apart - like in
DNA replication
- by the enzyme
RNA POLYMERASE
(sibling of DNA polymerase but for RNA):
Again, basically DNA is
transcribed
in order to make
RNA.
RECAP 5 ->
RNA is a
single strand
in which
Uracil
pairs with Adenine
(A + U)
instead of Thymine
(A + T)
. Thymine exists only in DNA.

And in this case, RNA is called
"messenger"
RNA because it
CARRIES
information from DNA to the
ribosomes
.
Remember that the
ribosomes
are the sites of
protein synthesis

(a protein-making factory)
.
Yellow polymerase
After RNA polymerase unzips the gene DNA strand,
T A C
(a sequence of nucleotides/bases, or
CODON
)
ALWAYS
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
"
semi-conservative
.
A functional single strand
with the
START CODON

A U G
is made.

This is

mRNA
!
This mRNA strand can now leave the nucleus and head over to the ribosomes.

It's time to create a protein:
PROTEIN SYNTHESIS
begins ->
TRANSLATION
.
TRANSLATION
NOTE:
it's very important to understand the nature of mRNA's chemical message.
There are only
4
bases/nucleotides in RNA:
A, U, G, C
.
To make a protein, around
20 different amino acids
are needed. If there was
one base
per amino acid, it obviously wouldn't work.
If there were
two bases
per amino acid, there would be combinations
less
than 20, which still isn't enough!
So, the nucleotides/bases work in
threes
or
triplets
(the
CODON,
e.g
A U G
), resulting in 64 combinations :)
Where DNA contains a protein synthesis code,
mRNA's
version of it is a
CODON sequence
.
Translation occurs in
3 STEPS
:
INITIATION
,
ELONGATION
, and
TERMINATION
INITIATION
Once the mRNA arrives at a ribosome,
ribosomal RNA

(rRNA)
- which is the
RNA component of the ribosome
and essential for protein synthesis -
aligns
the strand into the correct position on the ribosome.
The
small subunit
of the ribosome holds the mRNA strand. The
large subunit
of the ribosome will hold the
TRANSFER RNA

(tRNA).

The first codon of mRNA is
A U G
. This codes for the amino acid
METHIONINE
. Methionine is
always
the first amino acid in any protein.
This is why
A U G
is the
START CODON.

Therefore, the mRNA strand's start codon is marked.
The ribosome is ready to translate the mRNA into a protein!
START CODON
tRNA
comes in during the second step of translation ->
ELONGATION
.
ELONGATION
This process ensures that the amino acids are put into the
RIGHT
sequence for building the protein.
tRNA
transports
[hence the name] a

specific amino acid
to the ribosome.
They have relevant features that are
IMPORTANT
to protein formation:
each has a
bonding site
for the amino acid
each has an
anticodon
on the other end.
each is the
exact same length
each is
3D
-> allows the ribosome to hold it in a position where
peptide bonds
can form between the amino acids.
An anticodon is also a
TRIPLET
or has three bases that are
complementary
to the mRNA bases
(
U A C

pairs with mRNA's
A U G
etc.)
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
amino acid
is also aligned at the
opposite end
of the tRNA.
Or, you can say each tRNA carries a
corresponding amino acid.

tRNA C U A
codes for the amino acid
aspartic acid
.
The
sequential alignment
of these amino acids lets
PEPTIDE BONDS
link them together.

This sequential alignment starts as
methionine
(the FIRST amino acid in ANY PROTEIN) bonds to the
next
amino acid after it.

A
dipeptide bond
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.
E.g methionine
A U G
------ glutamine
C A G
---- so on
The
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
another
amino acid.
tRNA is reusable and recyclable
; the process continues.
amino acid chain
TERMINATION
Termination is self-explanatory. Translation of an mRNA strand can't go on forever. So translation keeps on running until a
TERMINATOR
or
STOP CODON
is reached.
The tRNA whose bases are complementary to an mRNA's
TERMINATOR codon
=
(there are 3 terminator codons out of 64)
U A A
,
U G A
, and
U A G
does NOT carry an amino acid.
Thus, the sequence ends.
These three steps (
INITIATION
,
ELONGATION
AND
TERMINATION
) 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
SPECIFIC PROTEIN
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.
Full transcript