Protein Synthesis
A CLOSER LOOK AT
TRANSCRIPTION AND TRANSLATION
The many functions of proteins:
 1. Structural component - present in skin, hair, muscles
 2. Chemical messengers/receivers - hormones
 3. Defense against disease - antibodies
 4. Enzymes – lactase
I’m Team
Protein!
What does a protein look like?
-Proteins are long chains of amino acids.
Secondary and Tertiary Structure
 The long chains of amino acids (known as polypeptides)
coil up to create a functional (working) protein. The
protein will not work unless it is coiled up.
There are 20 different amino acids
that make up proteins
Structure of the Amino Acids
Central carbon surrounded by:
Amino group (NH2)
These are
Carboxylic acid (COOH)
the same on
Hydrogen
every amino
acid
R – functional group
 Most amino acids look exactly
R
the same except for the _____
FUNCTIONAL
group or ________________
group.
 There are 20 different
functional groups that give each
amino acid different properties.
How does a polypeptide form?
aa = amino acid
Single amino acids
aa + aa + aa + aa
polypeptide
aa – aa – aa – aa +
Connected by a peptide bond
Where do you think that we get the information
to make specific proteins?
 DNA
 DNA is the blueprint that tells your cell what protein
to make.
 This molecule can be found within the nucleus of
the cell.
 Where are proteins made?

On Ribosomes found in the cytoplasm of the cell or attached
to the rough endoplasmic reticulum.
• If the DNA instructions are inside the nucleus and the protein
makers are outside of the nucleus them the cell must use an
intermediate to get the protein message out!
DNA vs. RNA Video
DNA
RNA
•Double Stranded
•Single Stranded
•Deoxyribonucleic acid
•Deoxyribose Sugar
•Nitrogen Bases
-Adenine
-Thymine
-Cytosine
-Guanine
•Ribonucleic acid
•Nucleotides
-sugar
-phosphate
-nitrogen base
•Double strands held
together by hydrogen
bonds
•A=T
C G
•Longer than RNA
•Ribose Sugar
•Nitrogen Bases
-Adenine
-Uracil
-Cytosine
-Guanine
•A=U
C G
•Shorter than DNA
There are 3 types of RNA
Each play an essential role in protein synthesis
• messenger RNA (mRNA)
• ribosonmal RNA (rRNA)
• transfer RNA (tRNA)
What is a gene?
 A segment of DNA that codes for a specific protein.
Why Transcription?
 To transcribe means
to “rewrite”
 Transcription is
rewriting the DNA
language into RNA
language!
The beginning of Protein Synthesis
DNA
A T
 Transcription : Step 1
 Occurs in the nucleus
 RNA polymerase (an
enzyme) binds to the DNA &
unzips the DNA
T A
A T
C G
C G
G C
T A
A T
T A
A T
A T
T A
RNA polymerase
Protein Synthesis
Transcription : Step 2




RNA polymerase adds free
RNA nucleotides using the
DNA template
Follows the complementary
base paring rules:
 A = U
 C = G
Transcription uses only a
specific region of the DNA
known as a gene.
As RNA polymerase moves
past DNA rewinds
A U
T
T A
A
A U
T
C G
G
C G
G
G C
C
T A
A
A U
T
T A
A
A U
T
A U
T
T A
A
Protein Synthesis
Transcription : Step 3



RNA polymerase reaches a
specific sequence of
nucleotides that marks the
end of the gene (“stop”
signal)
RNA polymerase releases
the DNA & newly formed
mRNA.
mRNA leaves the nucleus.
A
U
T
T
A
A
A
U
T
C
G
G
C
G
G
G
C
C
T
A
A
A
U
T
T
A
A
A
U
T
A
U
T
T
A
A
RNA and Protein Synthesis
messenger RNA(mRNA)
 single stranded
 Carries the instructions
from a gene (DNA) to
make a protein
 Moves from the nucleus to
the cytoplasm.
 Each group of three bases
is known as a codon.
RNA and Protein Synthesis
ribosomal RNA(rRNA)
 is part of the structure of
ribosomes
 Ribosomes are made from
RNA & other proteins
 Ribosomes read the mRNA
and help assemble the amino
acids to make a protein.
RNA and Protein Synthesis
transfer RNA(tRNA)
 transfers the amino
acids to the ribosome to
make a protein
 Assembles the amino
acids in the correct order
based on the codonanticodon matching.
Transcription
This is a molecule of messenger RNA.
It was made in the nucleus by
transcription from a DNA molecule.
codon
A U G G G C U U AAA G C A G U G C A C G U U
mRNA molecule
Transcription
Step1:
•The mRNA attaches to a Ribosome.
•Translation will not start until the ribosome
reads a “start” codon (usually AUG)
ribosome
A U G G G C U U AAA G C A G U G C A C G U U
Amino acid
Transcription
tRNA molecule
Step 2:
•A transfer RNA molecule arrives at the ribosome.
•It brings an amino acid to the first three bases
(codon) on the mRNA.
anticodon
•The three unpaired bases (anticodon) on the tRNA
link up with the codon on the mRNA.
UAC
A U G G G C U U AAA G C A G U G C A C G U U
Transcription
Step 3:
•Another tRNA molecule comes into place,
bringing a second amino acid.
•Its anticodon links up with the second codon
on the mRNA.
UAC
A U G G G C U U AAA G C A G U G C A C G U U
Transcription
Peptide bond
•A peptide bond forms between the two amino acids.
A U G G G C U U AAA G C A G U G C A C G U U
Transcription
The first tRNA molecule releases its amino acid and
moves off into the cytoplasm.
A U G G G C U U AAA G C A G U G C A C G U U
Transcription
Step 4:
•The ribosome moves along the mRNA to the next
codon.
A U G G G C U U AAA G C A G U G C A C G U U
Transcription
•Another tRNA molecule brings the next
amino acid into place.
A U G G G C U U AAA G C A G U G C A C G U U
Transcription
•A peptide bond joins the second and third
amino acids to form a polypeptide chain.
A U G G G C U U AAA G C A G U G C A C G U U
ala
leu
Transcription
arg
pro
thr
The process continues.
The polypeptide chain gets longer.
This continues until a termination (stop) codon
is reached.
The polypeptide is then complete. It is released
from the ribosome.
A U G G G C U U AAA G C A G U G C A C G U U
How does it know
which amino acid
to bring?
Protein Synthesis: How proteins are made
Transcription