1. The Building of Proteins from a Nucleic Acid Template
Protein Synthesis
The Building of Proteins from a Nucleic Acid Template

2. DNA Provides the Template.
Information contained in the SEQUENCE of N-bases found along the DNA molecule.
Transferring that information into an Amino Acid SEQUENCE is the trick.
A G C C T A G G G A T A G
T C G G A T C C C T A T C

3. A 2-step Process
Transcription
DNA RNA
Translation
RNA Protein

4. Transcription Production of RNA. RNA = Ribonucleic Acid. Ribose Sugar.
Single Stranded Molecule.
Uracil instead of Thymine.

5. Transcription RNA Polymerase
Attaches at a Promoter – a sequence of the DNA that indicates where a gene starts.
With the help of Transcription Factors.

6. Transcription A “window” in the DNA is opened – ultimately, a gene.
RNA Nucleotides are added (from 5’ to 3’) in accordance with the DNA parent template (which is read from 3’ to 5’).

7. Transcription Complimentary Base Pairing. DNA RNA G - C C - G T - A
A - U

8. Transcription Elongation of a single stranded RNA molecule.
The DNA window closes behind.

9. Transcription
Termination – a sequence of bases is reached signaling RNA Polymerase to release.
The “gene” closes
The RNA transcript is released.

10. In Eukaryotic cells, things get a little more complex:
RNA Processing
In Eukaryotic cells, things get a little more complex:
Several types of RNA polymerase are present – each with a slightly different function – I, II, and III.
A larger mRNA is transcribed…

11. RNA Processing
During Transcription, RNA polymerase II transcribes MORE than just the protein-encoding part of the gene.
Untranslated Regions (UTRs) are transcribed at the 5’ and 3’ ends.
The 3’ UTR is called a Polyadenylation signal.
A A U A A A
3’ UTR
5’ UTR

12. RNA Processing
AFTER Transcription is terminated, additional alterations are made to the ends of this “pre-mRNA” strand.
A 5’ cap at the leading (5’) end (composed of a Guanine-like nucleotide).
A poly-A tail at the trailing (3’) end (composed of many Adenine nucleotides).
5’cap
A A U A A A
Poly-A tail

13. 5’ Cap and Poly-A Tail These END pieces serve several functions:
1. Help “ferry” the eventual mRNA transcript out of the nucleus.
2. Protect the protein-encoding area from degradation.
3. Help attach the proper end (5’) of the transcript to the place where Translation will take place – the Ribosome.

14. Further RNA Processing
RNA splicing – removes portions of the transcript.
Removed segments are called INTRONS.
The remaining coding segments are called EXONS.
Introns
5’cap
A A U A A A
Poly-A tail
Exons

15. Further RNA Processing
INTRONS are recognized by snRNPs…
“small nuclear RiboNucleoProteins”.
snRNPs cut out INTRONS and join the adjacent EXONS.
This occurs in the nucleus.

16. Further RNA Processing
The resulting molecule is the RNA transcript proper (no longer the pre-mRNA).
5’cap
A A U A A A
Poly-A tail
A A U A A A
5’cap
Poly-A tail

17. Why? Introns may be vestigial. Introns may have regulatory roles.
Alternative RNA splicing – more than one polypeptide from a single gene.
More chances of unique Exon combinations (taking into account “crossing over” during meiosis).
(Cross-overs at introns won’t disrupt exons).

18. 3 Types of RNA mRNA = Messenger RNA rRNA = Ribosomal RNA
The “blueprint”
rRNA = Ribosomal RNA
The “workbench”
tRNA = Transfer RNA
The “truck”

19. mRNA – messenger RNA
The “message” – the blueprint for the production of a polypeptide – a protein.
But there’s only 4 N-bases, and 20 amino acids!
What’s the code?

20. The Genetic Code Triplet Base Code.
Every 3-letter word in the RNA Transcript is a CODON.

21. The Genetic Code
Each CODON codes for a single Amino Acid.

22. The Genetic Code

23. rRNA – Ribosomal RNA
The location for protein synthesis – the workbench on which a polypeptide is built.
rRNA makes up a RIBOSOME.
Ribosomes have 2 sub-units.
Large subunit
Small subunit

24. rRNA – Ribosomal RNA
The Large subunit has several binding sites:

25. tRNA – Transfer RNA
The “transfer-er” – the truck that brings individual Amino Acids to the workbench for the production of a polypeptide – a protein.
With a driver – the Anticodon.

26. tRNA – Transfer RNA
Each tRNA carries a specific Amino Acid to the Ribosome.
It “knows” when to drop this Amino Acid off by…
COMPLIMENTARY BASE PAIRING of its Anticodon with the corresponding Codon found on the mRNA.

27. tRNA – Transfer RNA
Aminoacyl-tRNA synthetase = the enzyme responsible for hooking Amino Acids to tRNAs.
Aminoacyl tRNA = truck with cargo.

28. Translation
Translating the RNA sequence data into Protein sequence data.
N-bases Amino Acids
In the cytoplasm of Eukaryotic cells.

29. Translation Initiation - All 3 types of RNA come together.
This requires some energy (provided by Guanosine Triphosphate -- GTP).

30. Translation
Elongation – Amino Acids are added with the help of elongation factors (proteins).
Codon meets Anticodon
at the ‘A’ binding site.
2. A Peptide Bond Forms
between adjacent Amino Acids

31. Translation
Then, a shift in the Ribosome (a “Translocation”) moves the empty tRNA to the exit (E-site), opening the A-site for the next tRNA.

32. Translation Termination…
Continued elongation until a “STOP” codon is reached (UAG, UAA, or UGA).
A release factor (protein) binds to this codon, effectively releasing the polypeptide.
The mRNA, tRNA, and rRNA separate.

33. Protein Synthesis
Primary Structure
Of the Protein

34. Protein Synthesis
In response to a need for a particular protein – need it NOW.
The same gene can be transcribed by several RNA polymerase molecules simultaneously…allowing faster protein production.
Polyribosomes – strings of Ribosomes translate a single mRNA simultaneously – allowing faster protein production.

35. Polyribosomes

36. Bound and Free Ribosomes
Free-floating Ribosomes are the sites for free-floating protein production.
Ribosomes bound to membranes are the sites for membrane-bound and secretory proteins.

37. Review – Fig

38. Point Mutations
Point Mutations occur at single nucleotides along DNA’s template strand.
Substitutions – the replacement of a pair of nucleotides at a particular location.
Silent Mutations.
Not-So-Silent Mutations.
Missense
Nonsense

39. Substitution Mutations
Original Sequence:
Silent Mutation:
Missense Mutation:
Nonsense Mutation:

40. Point Mutations
Insertions & Deletions – adding or removing bases along the sequence.
Results in a FRAME SHIFT because all other codons “downstream” are affected.
Can reverse if there are 3 insertions or 3 deletions.

41. Insertions & Deletions
Original Sequence:
Insertion/nonsense:
Deletion/missense:
3-Nucleotide Insertion/Deletion (missense):

42. Assignment: Review chapters 16 & 17! Transcription: Translation:
Translation:
Overall: