Download Protein Synthesis

PROTEIN
SYNTHESIS
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DNA
and
Genes
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Genes & Proteins
• DNA contains genes,
sequences of nucleotide
bases
• These genes code for
polypeptides (proteins)
• Proteins are used to build
cells and do much of the
work inside cells
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Genes & Proteins, cont.
• Proteins are made of
amino acids linked
together by peptide
bonds
• 20 different amino acids
exist
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Amino Acid Structure
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Genes & Proteins, cont.
• Amino acid
chains are
called
polypeptides
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Starting with DNA
• DNA is found inside the nucleus
• Proteins are made in the
cytoplasm of cells by organelles
called ribosomes
• Ribosomes may be free in the
cytosol or attached to the
surface of rough ER
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Starting with DNA, cont.
• DNA ‘s code must be copied
and taken to the cytosol
• In the cytoplasm, 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 & DNA
• DNA is the MASTER
PLAN
• RNA is the BLUEPRINT
of the Master Plan
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Roles of RNA & DNA, cont.
• RNA has a sugar ribose
• DNA has a sugar deoxyribose
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Roles of RNA & DNA, cont.
•
•
RNA contains the
base uracil (U)
DNA has thymine
(T)
RNA molecule is
single-stranded
DNA is doublestranded
DNA
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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 chain of nucleotides
• Made in the nucleus
• Copies DNA & leaves
through nuclear pores
• Carries information for a
specific protein
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Ribosomal RNA (rRNA)
• rRNA is a single
strand 100 to 3000
nucleotides long
• Globular in shape
• Made inside the
nucleus of a cell
• Site of protein
Synthesis
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Transfer RNA (tRNA)
• Clover-leaf shape
• Single stranded molecule with
attachment site at one end for
an amino acid
• Found out in the cytosol
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Transfer RNA
amino acid
attachment site
U A C
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The Genetic Code
• A codon is a set of three RNA
bases
• A codon designates a specific
amino acid
• An amino acid may have more
than one codon
• There are 64 possible codons
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The Genetic Code
•Use the code
by reading
from the
center to the
outside
•Example:
AUG codes
for
Methionine
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Name the Amino Acids
•
•
•
•
•
GGG?
UCA?
CAU?
GCA?
AAA?
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Remember the
Complementary Bases
On DNA:
A-T
C-G
On RNA:
A-U
C-G
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Transcription
and
Translation
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Pathway to Making a Protein
DNA
mRNA
tRNA to ribosomes
Protein
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Protein Synthesis
• The production or synthesis of
polypeptide chains (proteins)
• Two phases:
Transcription & Translation
• mRNA must be processed
before it leaves the nucleus of
eukaryotic cells
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DNA  RNA  Protein
Nuclear
membrane
DNA
Transcription
Eukaryotic
Cell
Pre-mRNA
RNA Processing
mRNA
Ribosome
Translation
Protein
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Transcription
• The process of copying the
sequence of one strand of
DNA
• mRNA copies the template
strand
• Requires the enzyme RNA
Polymerase
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Template Strand
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Question:
• What would be the
complementary RNA strand
for the following DNA
sequence?
DNA 5’-GCGTATG-3’
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Transcription, cont.
• 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, cont.
• Promoters are regions on DNA
that show where RNA
Polymerase must bind to begin
the Transcription of RNA
• Specific base sequences act as
signals to stop
• Called the termination signal
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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
polypeptide chain
• Ribosomes read mRNA three
bases or 1 codon at a time
and construct the proteins
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Translation, cont.
• mRNA transcript
start codon AUG
attaches to the
ribosome
mRNA transcript
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Translation, cont.
• As ribosome moves, two tRNA with
their amino acids move into
attachment sites
• Peptide bonds join the amino acids
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End Product –The Protein!
• The ribosome knows the protein is
complete when it reaches a stop
codon
• Protein - a sequence of amino acid
bonded together by peptide bonds
• Protein is released from ribosome
out into cytoplasm
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