Unlocking Protein Synthesis: Transcription & Translation

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. 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

4. 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. Here is how we will “do it”! • DNA Coding Triplet: • ATA CGA • mRNA Codons that would be transcribed: • UAU GCU • Amino Acids: Tyrosine + Alanine

10. 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

11. Let’s try Transcription: • Assume the sequence of nitrogen bases below represents the coding side of DNA. • ACT CCC CGA TAC • Transcribe the DNA triplets into mRNA codons • Draw the mRNA molecule that would be produced during Transcription. • Translate the mRNA molecule into the amino acids it represents. Use your codon wheel.

12. Look like this?

13. 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 - __________

14. 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.

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

16. Transcription Review • Another special codon found in mRNA stops the chain of amino acids and indicates the protein is complete. These codons are called Termination codons. There are only 3 of the codons: UGA; UAA and UAG. • We are always going to assume that the coding side of DNA will be the left side. • Opposite the coding side is called the complimentary side. • Two enzymes play a role in transcription: Helicase unzips the DNA molecule and RNA polymerase helps attach the free-floating mRNA nucleotides to the coding side of DNA.

17. 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?

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

19. 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 • Let’s go back to our mRNA molecule. Draw the respective tRNA molecules that would be involved in Translation.

20. Translation Animations • Translation • Translation 2 • Translation 3

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

22. A few things we need to know… • Gene A • Gene B • Exons – translatable segments 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

23. Ribosome Structure • “A” Site • Arrival Site • First tRNA arrives • “P” Site • Peptidyl Site • Amino Acids bond together • “E” Site • Exit site • Naked tRNA goes to find another amino acid “A” Site “P” Site “E” Site

24. Protein Synthesis

25. Protein Synthesis • Another look at Protein Synthesis

26. Quiz: Protein Synthesis • Assume the strand of DNA nucleotides below represents the coding side . • ACT CCA CGA TAC • Draw the mRNA molecule that would be transcribed.(Value: 4) • 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. (Value: 3) • Using you amino acid chart, draw the polypeptide that would be created. (Value:3)

27. Mutations • Point Mutation: A change in one nitrogen base in DNA. • EX: DNA AAA TCT CGA • mRNAUUU AGA GCU • Amino AcidsPhen-Arg-Ala • Point Mutation • DNA AAA TGT CGA • mRNA UUU ACA GCU • Amino AcidsPhen-Thre- Ala

28. ``Lucky`` Point Mutation • DNAAAA TCT CGA • mRNA UUU AGA GCU • A.A. Phen-Arg-Ala • DNA AAA TCC CGA • mRNAUUU AGG GCU • A.A.Phen – Arg - Ala

29. Frame shift Mutations • - Mutation that deletes or adds a nitrogen base pair. • - The result impacts the rest of the amino acids in the chain • DNA AAA TCT CGA • mRNA UUU AGA GCU • A.A. Phen – Arg- Ala • (Deletion) AA ATC TCG_ • mRNA • A.A. YIKES!