1. Chapter 17
Protein Synthesis

2. I. Big Picture DNA →mRNA→protein
Transcription – synthesis of RNA using DNA
Translation – actual production of protein
Figure 17.3

3. II. Transcription Occurs – In nucleus
Need – DNA, RNA polymerase, RNA nucleotides, transcription factors

4. II. Transcription - Initiation
Transcription factors attach to the promoter (TATA Box) which causes RNA polymerase II to attach creating a transcription initiation complex.

5. II. Transcription - Initiation

8. II. Transcription - Elongation
2. RNA polymerase unwinds the DNA and begins to match free-floating RNA nucleotides to the template strand in a 3’→5’ direction.
3. RNA polymerase continues down the template strand. As it does the RNA is kicked out and the DNA zips back up.

10. II. Transcription - Termination
4. This continues passing a terminator (TTATTT) and then it goes nucleotides past and cuts off the mRNA.

11. MOVIE!

12. III. RNA Processing 5’ cap added - Guanine (modified) added to 5’ end
- Attach here sign for ribosome
- Protects end
Poly (A) tail
adenines
- Keeps from breaking down
- Facilitates export of mRNA out of the nucleus

14. III. RNA Processing RNA Splicing
- average pre mRNA 8,000 bp / average processed mRNA 1,200 / average protein 400 A.A.
- removal of part of the RNA molecule
- Introns – non coding segments
- Exons – coded sections (expressed)
- snRNP – small nuclear ribonucleoproteins / recognize splice sites at ends of introns / made of snRNA and proteins

16. III. RNA Processing
Spliceosome – several snRNP and other proteins / cut out introns and put exons together
Ribozymes – RNA molecules that function as enzymes
Why have introns? Regulate passage of RNA from the nucleus / alternative RNA splicing, different polypeptides based on exons

18. IV. Translation Occurs: In the cytoplasm
Need: mRNA, tRNA, Ribosome, aminoacyl-tRNA synthetase, ATP, GTP, release factor, initiation factor, A.A.

19. IV. Translation - tRNA Transfer RNA / moves AA to ribosome
45 different tRNA molecules
Has the anti codon that matches up w/ the codon on the mRNA
3rd base in the anti-codon is flexible / U in the codon can match with A or G from the anti-codon / I (inosine - like A) can match with U,C,or A / wobble
Aminoacyl-tRNA synthetase – adds AA to tRNA / uses ATP / 20 different ones

23. IV. Translation - Ribosome
Allows tRNA to match to mRNA codons
Larger in eukaryotic cells than in prokaryotic cells
Large and small subunits / 2/3 rRNA, 1/3 protein / made in nucleolus
P site – holds tRNA carrying the growing polypeptide
A site – holds tRNA with next AA
E site – Exit of tRNA

24. IV. Translation - Initiation
Small ribosome unit attaches after the 5’ cap and the initiator tRNA matches to the start codon AUG.
The large ribosome unit attaches forming the translation initiation complex. AUG is found in the P site.
Initiation factors and GTP (energy) are used to do this.

26. IV. Translation - Elongation
A tRNA w/ matching anti-codon matches up in the A site. A elongation factor moves the tRNA into the A site.
rRNA molecule in the large ribosome unit catalyzes (ribozyme) a bond between the AA and the whole polypeptide is attached to the tRNA in the A site.
The A site moves to the P site and the P site exits from the E site. This takes GTP. mRNA moves 5’→3’ through the ribosome.

28. IV. Translation - Termination
7. A stop codon reaches the A site and a release factor binds to the codon which causes water to bond to the end of the polypeptide. Everything releases.

29. MOVIE!

30. V. Where do Proteins Go?
Ribosomes are found in the cytosol, some free some bound to the outside of the ER.
Signal Peptide – sequence of AA targeting polypeptide for ER
Signal-recognition Particle (SRP) – identifies the signal peptide and moves to a translocation complex (hole in the ER).

32. VI. Prokaryotic vs. Eukaryotic
Eukaryotic RNA polymerase depends on transcription factors
Transcription is terminated differently
Ribosomes are different
Pro can transcribe and translate at the same time
Eu process their RNA
Eu have ways to target proteins to organelles

33. VII. Point Mutations Mutation – change in DNA
Point Mutation – change in one base pair / can be passed down if gamete is effected
1. Substitution
- base pair sub – replacement of a base pair / can have no effect or major effects
- missense mutations – mutation still codes for an AA just not the right one
- nonsense mutation – change AA to stop

35. VII. Point Mutations Insertion and Deletion
- addition or loss of base pair
- disastrous
- Frameshift mutation – lead to nonsense

36. VII. Point Mutations Mutagens
- Errors during replication, repair, or recombination
- Spontaneous mutations
- UV radiation / thymine dimers
- Base Analogues / look like nucleotides
- change bases
- insert during replication

37. Want to see a movie about protein Synthesis?