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Protein Synthesis:
Transcription & Translation
Unit 4: DNA
Chapter 12-3
DNA > mRNA > ribosome > protein
Learning Goals
• 1. Summarize the overall process of protein
synthesis including the “central dogma”.
• 2. Describe Transcription in detail including
where it takes places and the roles of
introns and exons.
• 3. Describe Translation in detail including
where it takes place, codons, anti-codons,
tRNA, amino acids, and protein
• 4. Explain how gene expression works.
Standards
• Standard 1d: The central dogma of
molecular biology outlines the flow of
information from transcription of ribonucleic
acid (RNA) in the nucleus to translation of
proteins on ribosomes in the cytoplasm.
•Central Dogma Rule:
•DNA > RNA > ribosome > protein
Protein Synthesis Overview
• Two processes are required:
– 1. Transcription: DNA > mRNA
– 2. Translation: mRNA > protein
Transcription: DNA > mRNA
• Process of
making
messenger RNA
(mRNA) from a
DNA template to
take the DNA info
outside of the
nucleus
• DNA can NOT leave the
nucleus (too big)
• Messenger RNA
(mRNA) carries the info
encoded in DNA out of
the nucleus to the
ribosomes located in
the cytoplasm.
• Steps of Transcription
– 1. DNA strands unwind & separate
– 2. DNA strand containing a specific gene
serves as a template strand
– 3. RNA nucleotides are matched to
complimentary DNA bases
– 4. mRNA molecule is complete and DNA
rewinds
• mRNA Processing
– Introns: the mRNA
contains extra info
(junk) that must be
removed (cut out)
– Exons: the remaining
pieces carry useful
information are
spliced (connected)
together to make the
complete mRNA
• The bases of mRNA pair with DNA
bases but RNA replaces T with U
DNA
A
T
G
C
• DNA:
• mRNA:
RNA
U
A
C
G
CTG TAC GGA
---> Transcription
GAC AUG CCU
template
strand
Now you try…
• Based on the DNA template, create the
matching mRNA strand:
• DNA: C T A T G C A A A C T A T A G
GAU ACG UUU GAU AUC
• mRNA: ______________________________
Check: Are there any T’s in your mRNA?
There shouldn’t be!!!
Translation: mRNA > protein
• Process of making
proteins from info
on mRNA
– mRNA travels out of
nucleus to the
ribosome, which
“reads” the mRNA
as a series of 3 letter
words called codons
• Codon: 3-base code on mRNA that
codes for a specific amino acid
– Ex. CGU = alanine
GUU = valine
• The sequence of bases in DNA tell
mRNA what order amino acids must
join together to make a particular
protein.
Codons
found in
mRNA
Third Base
First Base
Second Base
• Transfer RNA (tRNA) matches up with
each codon and transfers the correct
amino acid
• Each tRNA molecule has 3 unpaired
bases called the anticodon that is
complementary to one mRNA codon.
• Each amino acid is added to a growing
chain of amino acids
• Protein = peptide bonds connecting amino
acids
– Many different types of proteins exist because
the number and sequence of amino acids can
be different
Second Base
First Base
Practice translating
mRNA into amino acids:
mRNA: AUG AAA AGU UGU CUG GUU UAA
A.A:
Met - Lys – Ser - Cys – Leu – Val - Stop
______________________________________
Third Base
Codons found
in mRNA
How DNA determines proteins
• DNA molecules serve as templates for making
messenger RNA molecules
• Messenger RNA molecules move to ribosomes
• Transfer RNA molecules bring amino acids to the
ribosome
• Polypeptides (proteins) are formed as ribosomes
move along the messenger RNA strand
Gene Expression
• DNA in all of your body cells is the same!
– Ex: DNA in your eye cells is the same DNA
that is in your skin cells.
• Different types of cells express different
genes.
– Ex: Your eyes may be green, while your skin
is brown.
• Specialization of cells is due to different
patterns of gene expression, rather than
different genes themselves.
– Liver cells express different genes than blood
cells
• DNA:
TAC TCC AGC GCA ACT
----Transcription---->
• mRNA: AUG AGG UCG CGU UGA
----Translation--->
• A.A.:
met arg ser arg stop
Learning Goals
• 1. Summarize the overall process of protein
synthesis including the “central dogma
rule”.
• 2. Describe Transcription in detail including
where it takes places and the roles of
introns and exons.
• 3. Describe Translation in detail including
where it takes place, codons, anti-codons,
tRNA, amino acids, and protein
• 4. Explain how gene expression works.