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
Proteins, as we have learned, do everything!
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

7. Transcription
Transcription and the TATA's

8. mRNA
Each group of 3 nitrogen bases of mRNA are called codons.

9. Codon Wheel

10. The Genetic Code
Use the code by reading from the center to the outside
Example: AUG codes for Methionine

11. Name the Amino Acids
GGG?
UCA?
CAU?
GCA?
AAA?

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

13. 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

14. 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.

15. Look like this?

16. 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 - __________

17. 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.

18. 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

19. 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.

20. 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?

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

22. 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.

23. Translation Animations

24. Activity Use your codon chart to complete the following table: Codon
Amino Acid
Anticodon
DNA triplet
AUG (initiation codon)
UCC
AAA
CGU

25. 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

26. Ribosome Structure “A” Site “P” Site “E” 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
“P”
Site
“A” Site
“E” Site

27. Protein Synthesis

28. Protein Synthesis
Another look at Protein Synthesis

29. Quiz: Protein Synthesis
Assume the strand of DNA nucleotides below represents the coding side (The Boyfriend!)
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)

30. Mutations Point Mutation: A change in one nitrogen base in DNA.
EX: DNA AAA TCT CGA
mRNA UUU AGA GCU
Amino Acids Phen-Arg-Ala
Point Mutation
DNA AAA TGT CGA
mRNA UUU ACA GCU
Amino Acids Phen-Thre- Ala

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

32. 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) AAA TCT CG_
mRNA
A.A.