Download Protein Synthesis: Part I: Transcription

Protein Synthesis:
Part I: Transcription
Biology
Transcription
p  A
nucleotide sequence
of DNA is copied into
a complimentary
sequence in RNA
p  Synthesis of mRNA
p  (Synthesis = making)
Transcription Overview
p  DNA
is located in the nucleus
p  mRNA copies DNA
p  mRNA leaves the nucleus and travels
through the cytoplasm to the ribosome
p  mRNA complements known as codons
n 
Only 3 nucleotide letters long
p  Remember
RNA has uracil (U) instead
of thymine (T)!
How does transcription happen?
1. 
RNA
polymerase
binds to DNA
in the
nucleus and
separates
the DNA
strands
2. 
RNA polymerase uses one strand of the
DNA as a template and complimentary
RNA nucleotides are assembled into single
stranded mRNA
Base pairing as follows:
DNA
RNA
G
C
C
G
T
A
A
U
3. 
The new strand of
mRNA separates
from the DNA
4. 
The two strands
of DNA reunite
5. 
The mRNA leaves
the nucleus,
moving into the
cytoplasm
The Genetic Code
Polypeptides:
long amino acid
chains
p  20
different
AAs that can
combine to
form a
polypeptide
The Genetic Code, cont.
p  RNA
code is written
in a language that is
four letters (A, G, C,
U)
p  Code
is read three
letters at a time, so
each word of the
coded message is 3
letters long
The Genetic Code, cont.
¨  Codon:
3
consecutive
nucleotides on
mRNA that specify
a single amino acid
¨  64
possible codons
¨  Certain
codons
code for start or
stop the protein
Transcription – Step I
A C G T A T C G C G T A
T G C A T A G C G C A T
Template DNA Strands
Transcription – Step II
A C G T A T C G C G T A
U G C A U A G C G C A U
Template DNA is Matched Up with
Complementary mRNA Sequences