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The Central Dogma of Molecular
Biology:
DNA------>RNA------>Protein

The central dogma
concerns the flow of
biological information:

DNA is a selfreplicating molecule
containing genetic
information that can be
transcribed into an
RNA message that can
be translated into a
polypeptide (protein).
DNA

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The DNA molecule is a
double helix of two long
chains of nucleotide
molecules.
During DNA replication
DNA is duplicated,
producing two double
helices.
Imbedded in these long
strands of DNA are genes
that control the production
of proteins to the cell.
Transcription

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The first step in decoding
these genetic messages is to
copy part of the genetic
sequence from DNA into
RNA, or ribonucleic acid.
This is called Transcription
These RNA molecules then
carry out the process of
making proteins.
Structure of RNA

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RNA, like DNA,
consists of a long
chain of nucleotides.
The structure of RNA
and DNA nucleotides
are very similar.
Structure of RNA

There are three distinct
differences;
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The sugar in RNA is ribose (two
hydroxyl groups)
RNA is generally single stranded
RNA contains the nitrogenous
base Uracil in place of Thymine
RNA is like a copy of a master
blue print (DNA) that is used
to create the building blocks of
the cell.
Types of RNA:

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RNA molecules have many functions, but
most RNA is used in the process of protein
synthesis.
The assembly of amino acids into proteins
is controlled by RNA.
Types of RNA
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The three major types
of RNA are:
Messenger RNA
(mRNA)
Ribosomal RNA
(rRNA)
Transfer RNA (tRNA)
Messenger RNA (mRNA)
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Most genes contain
instructions for
assembling amino
acids into proteins.
The RNA molecules
that carry copies of
these instructions are
known as messenger
RNA (mRNA) because
they serve as the
messenger from DNA
to the rest of the cell.
Ribosomal RNA (rRNA)

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Proteins are
assembled on
ribosomes.
Ribosomes are made
of proteins as well as
a form of RNA
known as Ribosomal
RNA (rRNA).
Transfer RNA (tRNA)

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During the construction of
proteins, a third type of
RNA molecule transfers
each amino acid to the
ribosomes as it is specified
by coded messages in the
mRNA.
These RNA molecules are
known as Transfer RNA
(tRNA).
Transcription

RNA molecules are
produced by copying
(transcribing) part of
the nucleotide
sequence of DNA into
complimentary
sequence of RNA.
This is called
TRANSCRIPTION.
Transcription

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Transcription requires an
enzyme known as RNA
polymerase that is similar
to DNA polymerase.
During transcription, RNA
polymerase binds to DNA
and separates the DNA
strands.
RNA polymerase then uses
one strand of DNA as a
template from which
nucleotides are assembled
into a strand of RNA.
Transcription

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How does RNA
polymerase know where to
start and stop?
RNA polymerase will only
bind to DNA in an area
called the promoter region,
which have specific base
sequences.
There are also non-coding
regions of DNA called
termination sequences
which tell RNA
polymerase to stop
transcribing.
RNA Editing

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RNA requires editing,
just like most of your
papers.
Large pieces of RNA
are sometimes cut and
trimmed before they
can go into action
(only in eukaryotes).
RNA Editing
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The pieces removed
are called introns
(intervening
sequences) and are cut
out why the RNA is
still inside the nucleus.
The remaining
portions, called exons,
or expressed
sequences, are spliced
back together to form
the final mRNA.
RNA Editing

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Why do cells spend
valuable energy to
make long strands of
RNA just to cut them
up and splice them
back together?
This is done so RNA
can be cut and spliced
in different ways so a
single gene can be
used to produce many
different RNA strands.