1 Review How does a cell interpret the genetic code
Explain What are codons and anticodons
2 Review What happens during translation
Compare and Contrast How is protein synthesis
different from DNA replication
3 Review Why is the genetic code considered universal
Infer In what way does controlling the proteins in an
organism control it’s characteristics
4 Choose one component of translation. Write a
question about that component and use it to form a
hypothesis that could be tested in an experiment
CH 13 RNA AND PROTEIN SYNTHESIS
13.2 Ribosomes and Protein Synthesis
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Proteins are made from long chains of amino acids
or polypeptides
20 different amino acids
Order of amino acids make proteins different.
Codon
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Each three-letter “word” in mRNA
Consists of three consecutive bases that specify a
single amino acid.
How to Read Codons
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Four different bases in RNA, so 64 possible threebase codons (4×4×4 = 64)
To read a codon, start at the middle of the circle
and move outward.

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Starts with AUG
Has three stop codons.
Translation
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Decoding of an mRNA message into a protein
From RNA to protein
Different languages.
Translation Steps

mRNA is transcribed in the nucleus and then enters
the cytoplasm for translation.

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Ribosome attaches to
an mRNA molecule
Ribosome reads each
codon of mRNA
Directs tRNA to bring
the specified amino acid
Ribosome then attaches
each amino acid to the
growing chain.
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tRNA has three unpaired bases or anticodon which
is complementary to one mRNA codon
Codon AUG
Anticodon UAC.


Next codon is UUC
tRNA molecule with an AAG anticodon brings the
amino acid to ribosome.

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Ribosome helps form a peptide bond between 1st
and 2nd amino acid
Bond between tRNA molecule and amino acid is
broken
tRNA shifts to 3rd site.

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Ribosome moves over one codon
New tRNA enters ribosome
Process repeats itself.

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Translation continues until a stop codon
Ribosome release polypeptide and mRNA.
Molecular Basis of Heredity

Most genes contain instructions for assembling
proteins.
Proteins Can


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
Be enzymes
Produce pigment or odor
Regulate growth
Trigger development
Operate cell parts.
Gene Expression


What DNA actually ends up doing
How the genes gets expressed or shown.

Genetic code is nearly universal in all living
organisms.
1.
2.
3.
4.
5.
A certain gene has the following base sequence
GACAAGTCCACAATC
Write this sequence down
From left to right, write the sequence of mRNA
molecule transcribed from this gene
Using the figure on pg. 311, read the mRNA from
left to right and write down the amino acid
sequence
Repeat step 3 reading the codons from right to
left.
Analyze and Conclude
1.
2.
Apply Concepts Why did steps 3 and 4 produce
different polypeptides
Infer Do cells usually decode nucleotides in one
direction only or in either direction