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Protein Synthesis

Protein Synthesis. Unit Objectives (Chapter 12-3). By the end of this unit you will: know what transcription is know what translation is understand how proteins are made. Big picture. DNA contains the genetic code which controls the production of proteins, but it is stuck in the nucleus.

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Protein Synthesis

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  1. Protein Synthesis

  2. Unit Objectives (Chapter 12-3) By the end of this unit you will: • know what transcription is • know what translation is • understand how proteins are made.

  3. Big picture • DNA contains the genetic code which controls the production of proteins, but it is stuck in the nucleus. • Proteins are produced at the ribosomes in the cytoplasm. Houston: We Have a Problem! • There are two important events which must happen in order to make a protein; transcription and translation

  4. Transcription • Transcribing or copying the coded message of DNA onto a single stranded nucleic acid called mRNA • DNA’s code is contained in groups of 3 nitrogen bases called DNA triplets • One side of DNA is considered the coding side, or template, and the other side is considered the complimentary side. • Left side – coding side • Right side – complimentary strand

  5. To begin transcription, Helicase causes the molecule to split or “unzip”. • This exposes the nitrogen bases of the coding side • Free floating mRNA nucleotides attach to the coding side of DNA • The whole mRNA strand is removed from the coding side of DNA • The mRNA strand then moves out of the nucleus and heads for a ribosome. • The DNA strand then can re-attach with the complementary side of DNA

  6. Transcription Transcription and the TATA's

  7. mRNA • Each group of 3 nitrogen bases of mRNA are called codons.

  8. Codon Wheel

  9. Summary • Transcription is copying the DNA code onto a mRNA molecule. • mRNA leaves the nucleus and moves to the ribosome where the message is translated • AUG is called the “Initiation Codon” . It begins the process and always codes for Methionine • “Termination Codons” indicate the end of the process. UAG,UAA, and UGA are termination codons and don’t code for any amino acids

  10. Let’s try Transcription: • Assume the following sequence represents the coding side of DNA • ATG GCA TAC. • Assuming the coding side of DNA is the left side, transcribe a mRNA molecule. Draw the molecule horizontally. • Use your codon wheel to figure the sequence of amino acids.

  11. Look like this?

  12. Transcription Review • DNA contains the genetic code for the production of __________. • Each group of 3 nitrogen bases in DNA is called a __________. • The genetic code of _____ is trapped inside the nucleus because it is ____________ to fit through the pores in the nuclear envelope. • __________ is the process of copying the genetic code of _____ onto a single strand of _____. • The single stranded _____ molecule falls on it’s side with it’s nitrogen bases pointing _____ and moves out of the nucleus to find a __________. • Each group of 3 nitrogen bases in mRNA is called a __________. • AUG is a special codon that is called an ________________. It always codes for the amino acid __________. • Check you codon wheel and identify the amino acids that the following codons code for: • GGC - __________ • UUU - __________ • CAU - __________ • GUA - __________

  13. Transcription Review • Another special codon found in mRNA stops the chain of amino acids and indicates the protein is complete. These codons are called ________________. There are only 3 of the codons: _______; ________ and _______. • We are always going to assume that the coding side of DNA will be the __________ side. • Opposite the coding side is called the __________ side. • Two enzymes play a role in transcription: ____________ unzips the DNA molecule and __________________ helps attach the free-floating mRNA nucleotides to the coding side of DNA.

  14. Translation • The process where the message of mRNA is translated into sequences of amino acids. • Translation happens on the surface of ribosomes. • 3 codons can fit on the ribosome at one time. • Remember tRNA?

  15. tRNA  amino acid (specific to tRNA)  tRNA molecule  nitrogen bases called anticodons Serine

  16. tRNA cont… • Each tRNA molecule with one specific anticodon sequence can carry only one specific amino acid. • If the anticodon of tRNA is complimentary to the codon of mRNA the amino acid carried by that tRNA is dropped off. • Protein Synthesis PH

  17. Translation Animations • Translation • Translation 2 • Translation 3

  18. Activity • Use your codon chart to complete the following table:

  19. A few things we need to know… • Gene A • Gene B • Exons – translatable seqments of a chromosome • Introns – segments of DNA that do NOT code for proteins • Nonsense DNA • AUG – intiation codon • Codes for methionine • UAA, UAG, and UGA are all termination codons

  20. Protein Synthesis

  21. Protein Synthesis • Another look at Protein Synthesis

  22. Activity: Protein Synthesis • Assume the strand of DNA nucleotides below represents the coding side • ACT CCA CGA TAC • Transcribe a mRNA molecule using the coding side. Detach it and draw it hortizontally. • Draw the three tRNA molecules that would be complimentary to the mRNA molecule you created. Make sure the appropriate amino acid and anti-codon are positioned on the tRNA drawings. • Using you amino acid chart, draw the reactants and products of this synthesis.

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