Unit Objectives (Chapter 12-3)
By the end of this unit you will:
 know what transcription is
 know what translation is
 understand how proteins are made.
Transcription
•
Transcribing or copying the coded message
of DNA onto a single stranded nucleic acid
called mRNA
• DNA’s code is contained in groups of 3
nitrogen bases called DNA triplets
• One side of DNA is considered the coding
side, or template, and the other side is
considered the complimentary side.
• Left side – coding side
• Right side – complimentary strand
To begin transcription, Helicase causes the
molecule to split or “unzip”.
 This exposes the nitrogen bases of the
coding side
 Free floating mRNA nucleotides attach to the
coding side of DNA
 The whole mRNA strand is removed from the
coding side of DNA
 The mRNA strand then moves out of the
nucleus and heads for a ribosome.
 The DNA strand then can re-attach with the
complementary side of DNA

Transcription
Transcription and the TATA's
mRNA

Each group of 3 nitrogen bases of mRNA are
called codons.
Codon Wheel
Here is how we will “do it”!
DNA Coding Triplet:
 ATA CGA
 mRNA Codons that would be
transcribed:
 UAU GCU
 Amino Acids:
Tyrosine + Alanine

Summary
Transcription is copying the DNA code onto
a mRNA molecule.
 mRNA leaves the nucleus and moves to
the ribosome where the message is
translated
 AUG is called the “Initiation Codon” . It
begins the process and always codes for
Methionine
 “Termination Codons” indicate the end of
the process. UAG,UAA, and UGA are
termination codons and don’t code for any
amino acids

Let’s try Transcription:
Assume the sequence of nitrogen bases
below represents the coding side of DNA.
 ACT CCC CGA TAC
 Transcribe the DNA triplets into mRNA
codons
 Draw the mRNA molecule that would be
produced during Transcription.
 Translate the mRNA molecule into the
amino acids it represents. Use your codon
wheel.

Look like this?
Transcription Review
DNA contains the genetic code for the production of __________.
Each group of 3 nitrogen bases in DNA is called a __________.
The genetic code of _____ is trapped inside the nucleus because
it is ____________ to fit through the pores in the nuclear
envelope.
__________ is the process of copying the genetic code of _____
onto a single strand of _____.
The single stranded _____ molecule falls on it’s side with it’s
nitrogen bases pointing _____ and moves out of the nucleus to
find a __________.
Each group of 3 nitrogen bases in mRNA is called a __________.
AUG is a special codon that is called an ________________. It
always codes for the amino acid __________.
Check you codon wheel and identify the amino acids that the
following codons code for:












GGC - __________
UUU - __________
CAU - __________
GUA - __________
Transcription Review




Another special codon found in mRNA stops the
chain of amino acids and indicates the protein is
complete. These codons are called
________________. There are only 3 of the codons:
_______; ________ and _______.
We are always going to assume that the coding side
of DNA will be the __________ side.
Opposite the coding side is called the __________
side.
Two enzymes play a role in transcription:
____________ unzips the DNA molecule and
__________________ helps attach the free-floating
mRNA nucleotides to the coding side of DNA.
Transcription Review








DNA contains the genetic code for the production of Protein.
Each group of 3 nitrogen bases in DNA is called a DNA triplet.
The genetic code of DNA is trapped inside the nucleus because it
is too big to fit through the pores in the nuclear envelope.
Transcription is the process of copying the genetic code of DNA
onto a single strand of mRNA.
The single stranded mRNA molecule falls on it’s side with it’s
nitrogen bases pointing up and moves out of the nucleus to find a
ribosome.
Each group of 3 nitrogen bases in mRNA is called a codon.
AUG is a special codon that is called an Initiation codon. It always
codes for the amino acid Methionine.
Check you codon wheel and identify the amino acids that the
following codons code for:




GGC - Glycine
UUU - Phenylalanine
CAU - Histidine
GUA - Valine
Transcription Review
Another special codon found in mRNA stops the
chain of amino acids and indicates the protein is
complete. These codons are called Termination
codons. There are only 3 of the codons: UGA; UAA
and UAG.
 We are always going to assume that the coding side
of DNA will be the left side.
 Opposite the coding side is called the complimentary
side.
 Two enzymes play a role in transcription: Helicase
unzips the DNA molecule and RNA polymerase helps
attach the free-floating mRNA nucleotides to the
coding side of DNA.

Translation
The process where the message of
mRNA is translated into sequences of
amino acids.
 Translation happens on the surface of
ribosomes.
 3 codons can fit on the ribosome at one
time.
 Remember tRNA?

tRNA
 amino acid (specific
to tRNA)
 tRNA molecule
 nitrogen bases
called anticodons
tRNA cont…
•
Each tRNA molecule with one specific
anticodon sequence can carry only one
specific amino acid.
• If the anticodon of tRNA is complimentary
to the codon of mRNA the amino acid
carried by that tRNA is dropped off.
• Protein Synthesis PH
• Let’s go back to our mRNA molecule. Draw
the respective tRNA molecules that would
be involved in Translation.
Translation Animations
Translation
 Translation 2
 Translation 3

Activity

Use your codon chart to complete the
following table:
Codon
AUG
(initiation
codon)
UCC
AAA
CGU
Amino Acid
Anticodon DNA
triplet
A few things we need to know…
← Gene A
← Gene B
•
•
Exons – translatable segments of a
chromosome
Introns – segments of DNA that do
NOT code for proteins
– Nonsense DNA
•
•
•
AUG – intiation codon
Codes for methionine
UAA, UAG, and UGA are all
termination codons
Ribosome Structure
“A” Site
• Arrival Site
• First tRNA arrives
“P” Site
“P”
Site
•Peptidyl Site
•Amino Acids bond together
“E” Site
•Exit site
•Naked tRNA goes to find
another amino acid
Protein Synthesis
Protein Synthesis

Another look at Protein Synthesis
Quiz: Protein Synthesis
Assume the strand of DNA nucleotides
below represents the coding side .
 ACT CCA CGA TAC
 Draw the mRNA molecule that would be
transcribed.(Value: 4)
 Draw the three tRNA molecules that would
be complimentary to the mRNA molecule
you created. Make sure the appropriate
amino acid and anti-codon are positioned
on the tRNA drawings. (Value: 3)
 Using you amino acid chart, draw the
polypeptide that would be created.
(Value:3)

Mutations
•
•
•
•
•
•
•
•
Point Mutation: A change in one nitrogen
base in DNA.
EX: DNA
AAA TCT CGA
mRNA
UUU AGA GCU
Amino Acids
Phen-Arg-Ala
Point Mutation
DNA
AAA TGT CGA
mRNA
UUU ACA GCU
Amino Acids
Phen-Thre- Ala
``Lucky`` Point Mutation
DNA
 mRNA
 A.A.
 DNA
 mRNA
 A.A.

AAA TCT CGA
UUU AGA GCU
Phen-Arg-Ala
AAA TCC CGA
UUU AGG GCU
Phen – Arg - Ala
Frame shift Mutations
•
•
•
•
•
•
•
•
- Mutation that deletes or adds a nitrogen
base pair.
- The result impacts the rest of the amino
acids in the chain
DNA
AAA TCT CGA
mRNA
UUU AGA GCU
A.A.
Phen – Arg- Ala
(Deletion)
AA ATC TCG_
mRNA
A.A.
YIKES!