Transcript The Central Dogma of Biology states that DNA codes for RNA

THE CENTRAL DOGMA OF
BIOLOGY STATES THAT DNA
CODES FOR RNA, AND RNA
CODES FOR PROTEINS
When DNA codes for RNA, the
process is called TRANSCRIPTION.
When RNA codes for proteins, the
process is called TRANSLATION.
THERE ARE 3 TYPES OF RNA, HOWEVER
ONLY MRNA IS INVOLVED IN
TRANSCRIPTION
Name
mRNA
rRNA
tRNA
Function
Carries genetic
information from
DNA during
TRANSCRIPTIO
N in the nucleus
to direct protein
synthesis
Associates with
protein to form
the ribosome
Transports amino
acids to ribosomes
during
TRANSLATION.
Example
What
is the purpose
of Transcription?
Where
does
transcription take
place?
LET’S WATCH TRANSCRIPTION
BEFORE WE EXAMINE THE STEPS!

http://highered.mcgrawhill.com/sites/0072507470/student_view0/chapter
3/animation__mrna_synthesis__transcription___
quiz_1_.html
TRANSCRIPTION STAGE 1:
INITIATION
Transcription
begins when
RNA
Polymerase
attaches to a
PROMOTER
on the DNA
strand
 The
promoter
determines which
of the two DNA
strands will serve
as the template
strand.
 The
promoter
indicates where
RNA Polymerase
can attach to the
DNA strand
A
common
promoter on the
DNA sequence is
called the TATA
Box. This is around
25 nucleotides from
where transcription
begins.
 Once
RNA Polymerase attaches to the
promoter, it unwinds the DNA template
strand.
 RNA synthesis begins moving along the
DNA template strand and RNA begins
transcribing the DNA template strand.
The new strand is created in the 5’ to 3’
direction.
 What
would RNA Polymerase transcribe
from the following promoter sequence?
ACAGGCATATA
TRANSCRIPTION STAGE 2:
ELONGATION
 RNA
Polymerase
moves along the DNA
strand and continues
to unwind the helix.
 Polymerase reads the
strand and
transcribes a
complementary
mRNA strand.
 As polymerases
passes over the strand
the mRNA peels away
and the DNA helix reforms.
STAGE 3 TRANSCRIPTION :
TERMINATION
Transcription
proceeds until after
the RNA polymerase
transcribes a
terminator sequence
in DNA.
 Shortly past the
termination signal,
the mRNA is cut from
the Polymerase.

How might
transcription take place
if your body required a
large amount of mRNA
to be made from a
particular gene?
THE MRNA SEQUENCE IS MODIFIED
BEFORE IT LEAVES THE NUCLEUS TO
ENTER THE CYTOPLASM
A 5’ CAP is added
A POLY A tail is
added
 The
 The
5’ end is
capped with a
modified guanine
nucleotide.

Reduces
degradation
3’ end received
50-250 adenine
nucleotides .
Reduces degradation
 Aids the mRNA in
exiting the nucleus

RNA IS SPLICED BEFORE IT LEAVES THE
NUCLEUS.
INTRONS

Introns are non-coding
regions in the mRNA
sequence. They are
removed before the
mRNA exits the
nucleus.
EXONS
Exons are the coding
regions in the mRNA
molecule. They are
connected to form a
complete mRNA strand.
Think: Exons exit the
nucleus
