DNA and Protein
Synthesis
1)DNA is capable of replicating itself.
Every time a cell divides, each DNA strand
makes an exact copy of itself.
 2)DNA directs the production of proteins
in the cell. DNA contains the instructions
on how to make proteins.

DNA Does 2 Important Things in a
Cell:
Proteins are the workhorses of the cell.
They build all of the important structures
and carry on most of the important
cellular functions.
 What types of proteins are made
determine everything about the organism
and how it functions.

The Importance of Proteins
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Proteins are large
polymers made of
long chains of amino
acids.
Amino Acids bind
together with peptide
bonds.
A protein’s final
shape determines its
function. This shape
is determined by its
amino acid sequence.
Review of Protein Structure
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Proteins are made by
ribosomes.
Amino acids are put
together in a long
chain which then
folds and bends to
determine the final
shape.
Remember: Shape
equals function!
So, it is VERY
important that the
amino acid sequence
is correct!
Protein Structure
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The DNA in a cell
determines the
sequence of amino
acids in a protein.
The DNA sequence
is a code that
determines which
amino acid is first,
which is second,
etc.
DNA determines protein:
What determines the correct
amino acid sequence in a protein?
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The DNA in a cell’s
nucleus determines
the sequence of
amino acids that
are put together at
the ribosome.
Yet, the DNA never
leaves the nucleus!
How does the DNA
do this?
DNA leads from afar…..
Chromosomes to Genes
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DNA is able to “tell”
the ribosome how
to build the protein
by sending a
messenger….
This comes in the
form of an RNA
molecule.
Therefore, this is
called messenger
RNA, or mRNA.
Messenger RNA (mRNA)
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Protein Synthesis has
2 main processes:
1) Transcription (“to
write”) –making a
mRNA molecule
2) Translation – (“to
read”) making the
protein, using the
mRNA as a guide.
Together, these are
called Gene
Expression
From DNA to Protein
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Three types of RNA are
used in protein building
mRNA=messenger RNA
(made in nucleus—
carries the genetic
code)
tRNA=transfer RNA
(brings amino acids to
the ribosome)
rRNA=ribosomal RNA
(what ribosomes are
made of)
Ribonucleic Acid
RNA: A Major Player
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RNA differs from
DNA in 3 ways:
RNA is singlestranded; DNA is
double-stranded
RNA has Ribose;
DNA has
Deoxyribose
RNA has Uracil;
DNA has Thymine
RNA Vs. DNA
Uracil is found
in RNA only
RNA Vs. DNA
During transcription, the information in a
particular segment of DNA (a gene) is
copied into mRNA
 Step 1:
 RNA polymerase binds to a specific
sequence of bases on the DNA called the
Promoter. This is the start code.

Transcription: Reading the Gene
Step 2: Helicases unwind the DNA strand
in front of the promoter region.
 Step 3: RNA polymerase adds and links
complementary RNA bases on one side of
the DNA, following base pairing rules.
(Exception: Adenine in DNA bonds to
Uracil)

Transcription: Reading the Gene
The RNA polymerase eventually reaches a
“stop” location in the DNA.
 This stop signal is a sequence of bases
that marks the end of each gene.
 The result is a single strand of RNA
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Transcription
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To make a correct
protein, the amino acids
must be put in the
proper sequence.
Each segment of 3
nucleotides in DNA
codes for 1 amino acid.
Each triplet of DNA
bases makes a triplet of
mRNA bases—called a
Codon.
The Genetic Code
Codons of mRNA
What amino acid comes from
the code AUC? GGG? CGA?
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Translation is the
process of
converting the
“language” of RNA
into the “language”
of proteins (amino
acid sequences.)
Translation involves
mRNA, tRNA, and
rRNA.
Translation: RNA to Proteins
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Each tRNA is folded
into a compact shape.
There are 2 important
places on each tRNA:
Terminal end—has 3
bases which match up
to mRNA. This is the
Anticodon.
Amino Acid attachment
site
tRNA: Transfer RNA
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After leaving the
nucleus, the mRNA
joins with a
ribosome and tRNA.
The mRNA start
codon, AUG, signals
the beginning of a
protein.
The tRNA carrying
Methionine binds to
the start codon.
Translation, Step 1: Start Codon
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A new tRNA arrives
and binds to the next
codon on the mRNA.
A peptide bond forms
between the first
amino acid and the
second amino acid.
The first tRNA
detaches and leaves
its amino acid behind.
Translation Step 2:A new tRNA
arrives.
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The ribosome moves
one codon down the
mRNA strand.
Because the anticodon
(on the tRNA) is
attached to the codon,
they move together as a
unit.
The amino acid chain
grows as each new one
binds.
The Ribosome Moves down the
mRNA
The process ends when a stop codon is
reached.
 The amino acid chain is released, the
ribosome complex and mRNA strand fall
apart.
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Translation, Step 3: Releasing the
protein
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http://bioweb.uwlax.edu/genweb/molecul
ar/theory/translation/trans1.swf

http://www.youtube.com/watch?v=983lh
h20rGY&feature=related

http://www.youtube.com/watch?NR=1&fe
ature=endscreen&v=Ikq9AcBcohA
Protein Synthesis Animations