1. DNA and Genes
• DNA contains genes, sequences of
nucleotide bases
• These genes code for polypeptides
(proteins)
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2. Protein Synthesis (Gene Expression)
Proteins (Review)
•Proteins make up all living materials

3. • Proteins are composed of amino acids – there are 20
different amino acids
• Different proteins are made by combining these 20
amino acids in different combinations
• Amino acid chains are called polypeptides.

4. • Proteins are manufactured (made) by the ribosomes

5. • Function of proteins:
1.Help fight disease
2.Build new body tissue
3.Enzymes used for digestion and other chemical reactions
are proteins
(Enzymes speed up the rate of a reaction)
4. Component of all cell membranes

6. Making a Protein—Transcription
•First Step: Copying of genetic information from DNA to RNA called
Transcription
Why? DNA has the genetic code for the protein that needs
to be made, but proteins are made by the ribosomes—ribosomes
are outside the nucleus in the cytoplasm.
DNA is too large to leave the nucleus (double stranded), but
RNA can leave the nucleus (single stranded).

7. The enzyme RNA polymerase binds to DNA and part of
DNA temporarily unzips and is used as a template to
assemble complementary nucleotides into messenger
RNA (mRNA). mRNA copies the template strand

8. • mRNA then goes through the pores of the nucleus with
the DNA code and attaches to the ribosome.

9. Making a Protein—Translation
•Second Step: Decoding of mRNA into a
protein/polypeptide chain is called Translation.
•Transfer RNA (tRNA) carries amino acids from the
cytoplasm to the ribosome.

10. These amino acids come from the food we eat. Proteins
we eat are broken down into individual amino acids and
then simply rearranged into new proteins according to the
needs and directions of our DNA.

11. • A series of three adjacent bases
in an mRNA molecule codes for
a specific amino acid—called a
codon.
• A triplet of nucleotides in tRNA Amino acid
that is complementary to the
codon in mRNA—called an
anticodon.
• Each tRNA codes for a different
amino acid.
Anticodon

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13. • mRNA carrying the DNA instructions and tRNA carrying
amino acids meet in the ribosomes.

14. • Amino acids are joined together to make a protein.
Polypeptide = Protein

15. Ribosomes
• Made of a large and small
subunit
• Composed of rRNA (40%) and
proteins (60%)
• Have two sites for tRNA
attachment --- P and A
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16. Step 1- Initiation
• mRNA transcript
start codon AUG
attaches to the
small ribosomal
subunit
• Small subunit
attaches to large
ribosomal subunit
mRNA transcript
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17. Ribosomes
Large
subunit
P A
Site Site
mRNA
Small subunit
A U G C U A C U U C G
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18. Step 2 - Elongation
• As ribosome moves, two tRNA with their
amino acids move into site A and P of the
ribosome
• Peptide bonds join the amino acids
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19. Initiation
aa2
aa1
2-tRNA
1-tRNA
anticodon
G A U
U A C
hydrogen A U G C U A C U U C G A
bonds codon mRNA
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20. Elongation
peptide bond
aa3
aa1 aa2
3-tRNA
1-tRNA 2-tRNA G A A
anticodon
U A C G A U
hydrogen A U G C U A C U U C G A
bonds codon mRNA
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21. aa1 peptide bond
aa3
aa2
1-tRNA
3-tRNA
U A C
(leaves)
2-tRNA G A A
G A U
A U G C U A C U U C G A
mRNA
Ribosomes movecmassengale one codon
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22. peptide bonds
aa1 aa4
aa2 aa3
4-tRNA
2-tRNA 3-tRNA G C U
G A U G A A
A U G C U A C U U C G A A C U
mRNA
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23. peptide bonds
aa1 aa4
aa2
aa3
2-tRNA
4-tRNA
G A U
(leaves) 3-tRNA G C U
G A A
A U G C U A C U U C G A A C U
mRNA
Ribosomes movecmassengale one codon
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24. peptide bonds aa5
aa1
aa2
aa4
aa3
5-tRNA
U G A
3-tRNA 4-tRNA
G A A G C U
G C U A C U U C G A A C U
mRNA
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25. aa1 peptide bonds aa5
aa2
aa3
aa4
5-tRNA
3-tRNA U G A
G A A 4-tRNA
G C U
G C U A C U U C G A A C U
mRNA
Ribosomes movecmassengale one codon
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26. aa5
aa4 aa199
Termination
aa200
aa3 primary
structure
aa2 of a protein
aa1
terminator
200-tRNA
or stop
codon
A C U C A U G U U U A G
mRNA
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27. End Product –The Protein!
• The end products of protein synthesis
is a primary structure of a protein
• A sequence of amino acid bonded
together by peptide bonds
aa5
aa3 aa4
aa2 aa199
aa1 aa200
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28. Messenger RNA (mRNA)
start
codon
A U G G G C U C C A U C G G C G C A U A A
mRNA
codon 1 codon 2 codon 3 codon 4 codon 5 codon 6 codon 7
protein methionine glycine serine isoleucine glycine alanine stop
codon
Primary structure of a protein
aa1 aa2 aa3 aa4 aa5 aa6
peptide bonds
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29. Use one of the codon charts on the next page to find the amino acid
sequence coded for by the following mRNA strands.
CAC/CCA/UGG/UGA
GUG GGU ACC ACU
___________/___________/___________/____________
AUG/AAC/GAC/UAA
UAC UUG CUG AUU
___________/___________/___________/____________

30. CAC/CCA/UGG/UGA
Histidine Proline Tryptophan Stop
___________/___________/___________/____________
2nd Base
1st Base
3rd Base

31. AUG/AAC/GAC/UAA
Methionine Asparagine Aspartic Acid Stop
___________/___________/___________/____________

32. Protein Synthesis

33. Protein Synthesis videos
• http://www.youtube.com/watch?
v=983lhh20rGY
• http://www.youtube.com/watch?
v=erOP76_qLWA

34. Movie about translation at bottom of webpage. Click on hyperlink in picture above.