Transcription and
Translation
What is Transcription?
• It is a process that produces a
complementary strand of RNA by copying a
complementary strand of DNA
– DNA is copied to messenger RNA (mRNA)
– mRNA goes from nucleus to the ribosomes
that are in the cytoplasm
• Remember: A=U and C=G
How does Transcription Work?
• It requires RNA polymerase which is an
enzyme that binds to DNA and separates the
DNA strands.
• The Enzyme then uses one strand of DNA as
a template in which nucleotides are
assembled into a strand of mRNA
Transcription
Template DNA
A C G T A T C G C G T A
U G C A U A G C G C A U
mRNA
• Template DNA is Matched Up with
Complementary mRNA Sequences
Where does Transcription take
place?
In the Nucleus
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
The Genetic Code
It is the language of
mRNA that codes
for amino acids
• They are in a 3nucleotide
sequence on mRNA
called a Codon.
This 3 letter codon
codes for a specific
amino acid
The Genetic Code
–Codons code for amino acids using
the genetic code
–There are 20 amino acids
–AUG codon is the start codon
Deciphering the Genetic Code:
If the mRNA looks like:
UCGCACGGU
The codon sequence breaks down into:
UCG- CAC- GGU
Use the codon chart to find each amino acid as:
Serine- Histidine- Glycine
(the amino acid sequence)
The Genetic Code
What isTranslation?
• The decoding a mRNA message into proteins
– Also called protein synthesis (making proteins)
tRNA
– Takes place on the ribosome
• tRNA structure:
– Anticodon: group of 3 bases that are
anticodon
What are the steps to Translation?
1. mRNA is transcribed from DNA in the
nucleus and released into the cytoplasm
What are the steps to Translation?
2. mRNA in cytoplasm binds to ribosome at
the start codon (AUG)
What are the steps to
Translation?
3. tRNA binds to mRNA codon by forming
complementary base pairs with the tRNA
anticodon
 The correct
amino acid is
brought to the
ribosome by
the tRNA
What are the steps to
Translation?
4. The amino acid is transferred to the
growing polypeptide chain
What are the steps to Translation?
5. The polypeptide chain continues to grow
until the ribosome reaches a “stop” codon
What are the steps to Translation?
6. The polypeptide chain is released
 A polypeptide chain is a protein
Translation
Translation cont.