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Protein Synthesis
Making Proteins from DNA
DNA & the Nucleus
• DNA cannot leave the nucleus!
• So how can we get the information for
making proteins out of the nucleus?
What is RNA?
• Ribonucleic acid
– A nucleic acid
• Made up of repeating
nucleotides
– Backbone
• Sugar = Ribose
• Phosphate
– Nitrogen bases
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Adenine
Uracil
Cytocine
Guanine
Nitrogenous Base Pairs
• Adenine pairs with
Uracil
– A-U
• Cytosine pairs with
Guanine
– C-G
Differences between DNA & RNA
• Different Sugars
– DNA = deoxyribose
– RNA = ribose
• Different Nitrogen
Base Pairs
– DNA = thymine
– RNA = uracil
Single (RNA) .vs
Double (DNA)
Stranded
Types of RNA
• Messenger RNA (mRNA)
– Single chain that carries genetic information from DNA in
nucleus to the cytosol
• Transfer RNA (tRNA)
– Single chain of abt 80 nucleotides folded into a cross
shape that binds amino acids together
• Ribosomal RNA (rRNA)
– RNA in globular form. It makes up the ribosomes where
proteins are made
TRANSCRIPTION
• Process where
genetic information
is copied from DNA
into RNA
• RNA Polymerase
binds to promoters
and makes RNA
copies of a specific
sequence of DNA
PROTEIN SYNTHESIS
• Is the production of
proteins
• Remember proteins are
made up of polypeptides
• Polypeptides are
sequences of amino
acids linked together by
peptide bonds
Amino Acids
• There are 20 different
amino acids
• Proteins are made of
specific sequences of
these 20 amino acids
• The sequence
determines how the
proteins twist and fold
into a 3-D shape
Codons
• A combination of 3 mRNA nucleotides
• Codes for a specific amino acid
• Important Codons
– Start codon = AUG
– Stop codons = UAA, UAG, or UGA
TRANSLATION
• Assembling
polypeptides from info
encoded in mRNA
• mRNA leaves the
nucleus and goes to a
ribosome in the cytosol
where protein synthesis
happens
tRNA & Anti-Codons
• tRNA transports amino
acids that are in the cytosol
to the ribosome
• tRNA has a section that
carries an anti-codon
– Anti-codon is
complementary to the
corresponding mRNA
Protein Assembly
• Begins with start codon AUG
• tRNA anti-codon is UAC, which is the amino acid
methionine
• Ribosome moves along mRNA to the next codon, the
anti-codon binds to the codon and the new amino acid
attaches to the first amino acid forming a polypeptide
chain until a stop codon occurs