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DNA and Genes DNA and Genes DNA contains genes , sequences of nucleotide bases These genes code for polypeptides (proteins) 1

Protein synthesis

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Page 1: Protein synthesis

DNA and GenesDNA and Genes• DNA contains genes, sequences of

nucleotide bases• These genes code for polypeptides

(proteins)

1

Page 2: Protein synthesis

Protein Synthesis (Gene Expression)

Proteins (Review)•Proteins make up all living materials

Page 3: Protein synthesis

• 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.

Page 4: Protein synthesis

• Proteins are manufactured (made) by the ribosomes

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•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

Page 6: Protein synthesis

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).

Page 7: Protein synthesis

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

Page 8: Protein synthesis

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

Page 9: Protein synthesis

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.

Page 10: Protein synthesis

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.

Page 11: Protein synthesis

•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 that is complementary to the codon in mRNA—called an anticodon.

•Each tRNA codes for a different amino acid.

Amino acid

Anticodon

Page 12: Protein synthesis

12copyright cmassengale

Page 13: Protein synthesis

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

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• Amino acids are joined together to make a protein.

Polypeptide = Protein

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RibosomesRibosomes

• 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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Page 16: Protein synthesis

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Step 1- InitiationStep 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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Page 17: Protein synthesis

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RibosomesRibosomes

PSite

ASite

Largesubunit

Small subunit

mRNAmRNA

A U G C U A C U U C G

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Page 18: Protein synthesis

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

18copyright cmassengale

Page 19: Protein synthesis

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InitiationInitiation

mRNAmRNA

A U G C U A C U U C G

2-tRNA

G

aa2

A U

A

1-tRNA

U A C

aa1

anticodon

hydrogenbonds codon

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Page 20: Protein synthesis

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mRNAmRNA

A U G C U A C U U C G

1-tRNA 2-tRNA

U A C G

aa1 aa2

A UA

anticodon

hydrogenbonds codon

peptide bond

3-tRNA

G A A

aa3

ElongationElongation

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Page 21: Protein synthesis

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mRNAmRNA

A U G C U A C U U C G

1-tRNA

2-tRNA

U A C

G

aa1

aa2

A UA

peptide bond

3-tRNA

G A A

aa3

Ribosomes move over one codon

(leaves)

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Page 22: Protein synthesis

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mRNAmRNA

A U G C U A C U U C G

2-tRNA

G

aa1

aa2

A UA

peptide bonds

3-tRNA

G A A

aa3

4-tRNA

G C U

aa4

A C U

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Page 23: Protein synthesis

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mRNAmRNA

A U G C U A C U U C G

2-tRNA

G

aa1aa2

A U

A

peptide bonds

3-tRNA

G A A

aa3

4-tRNA

G C U

aa4

A C U

(leaves)

Ribosomes move over one codoncopyright cmassengale

Page 24: Protein synthesis

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mRNAmRNA

G C U A C U U C G

aa1aa2

A

peptide bonds

3-tRNA

G A A

aa3

4-tRNA

G C U

aa4

A C U

U G A

5-tRNA

aa5

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Page 25: Protein synthesis

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mRNAmRNA

G C U A C U U C G

aa1aa2

A

peptide bonds

3-tRNA

G A A

aa3

4-tRNA

G C U

aa4

A C U

U G A

5-tRNA

aa5

Ribosomes move over one codoncopyright cmassengale

Page 26: Protein synthesis

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mRNAmRNA

A C A U G U

aa1

aa2

U

primaryprimarystructurestructureof a proteinof a protein

aa3

200-tRNA

aa4

U A G

aa5

C U

aa200

aa199

terminatorterminator or stopor stop codoncodon

TerminationTermination

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Page 27: Protein synthesis

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End Product –The Protein!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

aa1

aa2 aa3 aa4aa5

aa200

aa199

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Page 28: Protein synthesis

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Messenger RNA (mRNA)Messenger RNA (mRNA)

methionine glycine serine isoleucine glycine alanine stopcodon

proteinprotein

A U G G G C U C C A U C G G C G C A U A AmRNAmRNA

startcodon

Primary structure of a proteinPrimary structure of a protein

aa1 aa2 aa3 aa4 aa5 aa6

peptide bonds

codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1

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Page 29: Protein synthesis

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

___________/___________/___________/____________

AUG/AAC/GAC/UAA

___________/___________/___________/____________

GGUGUG ACC ACU

UAC UUG CUG AUU

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CAC/CCA/UGG/UGA

___________/___________/___________/____________Histidine1st

Bas

e

2nd Base

3rd Base

Proline Tryptophan Stop

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AUG/AAC/GAC/UAA

___________/___________/___________/____________Methionine Asparagine Aspartic Acid Stop

Page 32: Protein synthesis

Protein Synthesis

Page 33: Protein synthesis

Protein Synthesis videos

• http://www.youtube.com/watch?v=983lhh20rGY

• http://www.youtube.com/watch?v=erOP76_qLWA

Page 34: Protein synthesis

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