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Protein Production
Protein Production
Overview
Structure of Proteins
Importance of Proteins
Instructions for Protein Production
Transcription
Translation
Polysome
Regulation of Protein Production
Fate of Proteins
Protein Production
Protein Structure
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Basic building blocks are
amino acids (peptides)
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20 known amino acids
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All amino acids contain a
single carbon backbone with
an amino group at one end
and a carboxyl group at the
other
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Differ from each other by their
unique 'R' group (functional
group)
Protein Production
Protein Structure
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Have 4 important levels of structure
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Primary
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Secondary
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3D structure achieved when bonds form between segments
of the growing secondary structure which fold on itself
Can be denatured
Quaternary
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Result of bonding between segments of the growing primary
structure as it folds on itself
Alpha helix or beta pleated sheet forms
Tertiary
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Simple sequence of amino acids
Bonding between several proteins in their tertiary structure to
form a large macromolecule
Hemoglobin
The sequence by which amino acids are put
together helps determine the level of structure of a
protein which then determines how the protein can
be used by the cell
Protein Production
Importance of Proteins
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Proteins are important organic compounds to
all cells
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Enzymes
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Structure & Repair
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Reproduction (Cell Division)
Protein Production
Importance of Proteins
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Proteins are important
organic compounds to
all cells
–
Enzymes
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Control the rate of
chemical reactions in
the cell
Protein Production
Importance of
Proteins
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Proteins are
important organic
compounds to all
cells
–
Structural elements
for growth and repair
of the cell
Protein Production
Importance of Proteins
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Proteins are important
organic compounds to
all cells
–
Reproduction
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For example, the
spindle fiber which
separate sister
chromatids in
karyokinesis
Protein Production
Instructions for
Protein Production
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Specific proteins are
produced from instructions
contained in genes
Genes = specific regions
along one strand of the
double-stranded DNA
molecules
Each gene can only
produce one specific
protein
Protein Production
Protein Production is a twofold process
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Transcription
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Information on the gene of
DNA is copied to a molecule of
messenger RNA (mRNA)
Preserves the integrity of the
DNA
Translation
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Copied information on mRNA
is translated into molecules
containing a specific sequence
of amino acids (proteins)
Occurs in the ribosomes
Protein Production
Protein Production
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Transcription
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3 Steps
– Initiation
– Elongation
– Termination
Protein Production
Protein Production
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Transcription
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Initiation
– RNA polymerase binds to
the promoter site
● Promoter site = part
of the DNA that
signals where to
begin transcription
● RNA polymerase =
the enzyme that
builds mRNA
– Helicase unwinds the DNA
to expose the gene
Protein Production
Protein Production
–
Transcription
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Elongation
– RNA polymerase moves
along the exposed gene
building mRNA
– mRNA will contain a base
sequence that
compliments the base
sequence on the gene
Protein Production
Protein Production
–
Transcription
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Termination
– RNA polymerase reaches
the terminator site-a
portion of the DNA at the
end of the gene that signal
the stop of transcription
– The completed mRNA
dissociates from the RNA
polymerase and DNA
molecules and is ready for
translation
Protein Production
-TranslationProtein Production
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Translation
–
mRNA leaves the
nucleus for the
cytoplasm where it finds
ribosomes
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mRNA threads
itself through
the ribosome
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Ribosome has 2 sites on it
for reading the bases on
the mRNA which are
passing through
Protein Production
-TranslationProtein Production
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Translation
–
Ribosomes expose 3
sequential mRNA bases
(triplet) at a time at each of
these sites
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Each triplet is a codon which
specifies an amino acid
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Ribosomes translate codons
into an amino acid sequence
that becomes a polypeptide
chain (protein)
Protein Production
-TranslationProtein Production
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Translation
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Translation of
codons is
achieved by tRNA &
enzymes
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tRNA contains an
anticodon which is
complementary to a
specific mRNA codon
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tRNA carries the
amino acid specified
by its anticodon
Protein Production
-TranslationProtein Production
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Translation
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In the ribosome tRNA
anticodons bind to mRNA
codons
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Amino acids on adjacent
tRNAs are brought together,
peptide bonds are created and
a polypeptide forms
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At the end of the mRNA a stop
codon is read, and the protein,
now complete, detaches
Protein Production
Translation & Polysomes
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In cytoplasm mRNA
attaches to MANY
ribosomes forming a
polysome
Translation of a single
mRNA occurs on the
polysome forming MANY
identical proteins from a
SINGLE mRNA
Protein Production
Regulation of Protein
Production
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Prokaryotic Cells
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Gene expression is
regulated primarily
during transcriptional
level
Eukaryotic Cells
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Gene expression is
regulated at the
epigenetic,
transcription, and posttranscription levels
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Epigenetic level = when the DNA
is uncoiled and loosened from
nucleosomes
Transcriptional level = during
active transcription of DNA to
mRNA
Translational level = during active
RNA translation to a protein
Post-Translational level = after
the protein has been made
Protein Production
How does Protein Production differ between
eukaryotic and prokayotic cells?
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Prokayotic Cells
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Transcription occurs in nucleoid area
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Translation occurs in the ribosome
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First amino acid in the protein is always
methionine
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Transcription & translation occur almost
simultaneously
Eukaryotic Cells
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Transcription occurs in nucleus
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Translation occurs at the ribosome
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First amino acid in the protein is always
formylmethionine
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Translation occurs only after the initial mRNA
molecule (pre-mRNA) is modified to the final
mRNA
Fate of the Proteins
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Proteins formed on
free ribosomes are
generally used by the
cell
Proteins formed on
ribosomes attached to
the ER (rough ER)
are generally
exported out of the
cell
How does this occur?
Fate of the Proteins
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Proteins to be
secreted are made
in ribosomes of
rough ER
As they are synthesized
new protein enter the
interior of the ER
Fate of the Proteins
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Proteins are packaged
into vesicles & leave
ER for the Golgi bodies
In the Golgi body the
proteins are sorted,
modified and stored
Eventually these
proteins are
repackaged into new
vesicles, leave the
Golgi body for the
cell membrane and
are released by
exocytosis
Protein Production in Action