PROTEIN
SYNTHESIS
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Protein Synthesis
• DNA ‘s code must be copied
and taken to the ribosomes.
• In the ribosomes, this code
must be read so amino acids
can be assembled to make
proteins.
• This process is called
PROTEIN SYNTHESIS
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RNA
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Roles of RNA and DNA
• DNA is the MASTER
PLAN
• RNA is the
BLUEPRINT (copy) of
the Master Plan
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RNA Differs from DNA
• RNA has a sugar ribose
DNA has a sugar deoxyribose
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Other Differences
•
•
RNA contains the
base uracil (U)
DNA has thymine
(T)
RNA molecule is
single-stranded
DNA is doublestranded
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DNA
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Structure of RNA
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Remember the
Complementary Bases
On DNA:
A-T
C-G
On RNA:
A-U
C-G
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.
Three Types of RNA
• Messenger RNA (mRNA) copies
DNA’s code & carries the
genetic information to the
ribosomes
• Ribosomal RNA (rRNA), along
with protein, makes up the
ribosomes
• Transfer RNA (tRNA) transfers
amino acids to the ribosomes
where proteins are synthesized
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Messenger RNA
• Long Straight chain
of Nucleotides
• Made in the Nucleus
• Copies DNA &
carries info to
ribosomes.
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Ribosomal RNA (rRNA)
• Globular in shape
• Are part of the
ribosomes actual
structure.
• Site of protein
Synthesis (where
the proteins are
made)
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Transfer RNA (tRNA)
• Clover-leaf shape
• Single stranded molecule.
• Attachment site at one end
for an amino acids.
• Opposite end has three
nucleotide bases called the
anticodon.
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Transfer RNA
amino acid
attachment site
U A C
anticodon
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Codons and Anticodons
• The 3 bases of an
anticodon are
complementary to
the 3 bases of a
codon
• Example: Codon ACU
Anticodon UGA
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UGA
ACU
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Transcription
and
Translation
(The actual making of a protein.)
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Protein Synthesis
 The production or
synthesis of proteins.
 Two phases:
Transcription & Translation
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Transcription
• The process of copying
the sequence of one
strand of DNA, the
template strand.
• mRNA copies the template
strand.
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Transcription
• During transcription, RNA
polymerase binds to DNA and
separates the DNA strands
• RNA Polymerase then uses
one strand of DNA as a
template to assemble
nucleotides into RNA
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Transcription
• Promoters are regions on
DNA that show where RNA
Polymerase must bind to
begin the Transcription of
RNA Called the TATA box.
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Transcription
• Specific base sequences act
as signals to stop Called the
termination signal.
• Once the Polymerase is done
it falls off, the DNA re-zips
up and the mRNA escapes
out the nucleus.
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mRNA Transcript
•mRNA leaves the nucleus
through its pores and goes to
the ribosomes.
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Translation
• Translation is the process
of decoding the mRNA
into a protein.
• Ribosomes read mRNA
three bases or 1 codon at
a time and construct the
proteins
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Step 1- Initiation
• mRNA enters the
ribosome and
attaches to the
tRNA.
The tRNA has an
anticodon that
matches with the
three “start”
nucleotides.
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Initiation
amino
aa2
2-tRNA
1-tRNA
anticodon
hydrogen
bonds
U A C
A U G
codon
G A U
C U A C U U C G A
mRNA
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Step 2 - Elongation
• The ribosome moves down the mRNA
strand.
• The first tRNA detaches and leaves
it’s amino acid.
• Two new tRNA with their amino acids
move into position (positions are called
A and P)
• The new tRNAs have the correct amino
acid for that specific codon. Each
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amino Acid forms
a bond.
Amino
1
peptide bonds
Amino
4
Amino
2
Amino
3
4-tRNA
2-tRNA
A U G
3-tRNA
G C U
G A U G A A
C U A C U U C G A A C U
mRNA
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Amino
1
peptide bonds
Amino
5
Amino
2
Amino
3
Amino
4
5-tRNA
U G A
3-tRNA
4-tRNA
G A A G C U
G C U A C U U C G A A C U
mRNA
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Termination
• tRNA’s will continue to read
mRNA and hook up amino acids
until “stop” codon is reached.
• A “stop” codon is three
nucleotides on the mRNA that
tRNA does not have an
anticodon for.
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Dissaembly
• When the stop codon is reached
the ribosome falls off, the
protein goes into the body, and
the tRNAs go out to find more
amino acids.
• The ribosome will go find
another strand of mRNA and the
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whole process starts over.
End Product –The Protein!
• The end products of protein
synthesis is a primary structure
of a protein
• A sequence of amino acid
bonded together by peptide
bonds
2
1
3
4
5
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