1. Nucleic Acid Chemistry
Where the info is…interpreting the blueprint

2. Central Dogma DNA ---------------- RNA-------------- protein
Replication
transcription
translation

3. Central Dogma Replication Transcription Translation
DNA making a copy of itself
Making a replica
Transcription
DNA being made into RNA
Still in nucleotide language
Translation
RNA being made into protein
Change to amino acid language

4. Replication Remember that DNA is self complementary
Replication is semiconservative
One strand goes to next generation
Other is new
Each strand is a template for the other
If one strand is 5’ AGCT 3’
Other is: ’ TCGA 5’

5. Replica
Write the strand complementary to:
3’ ACTAGCCTAAGTCG 5’
Answer

6. Replication is Semiconservative

7. Replication Roles of enzymes DNA binding proteins Topoisomerases
Helicase
DNA polymerases
ligase
DNA binding proteins
DNA synthesis
Leading strand
Lagging strand

8. Replication

9. Replication Helix opens Causes supercoiling upstream
Helicase
Causes supercoiling upstream
Topoisomerases (gyrase)
DNA Binding Proteins
Prevent reannealing

10. Replication

11. Replication Leading strand 3’ end of template
As opens up, DNA polymerase binds
Makes new DNA 5’ - 3’
Same direction as opening of helix
Made continuously

12. Replication

13. Replication Lagging strand 5’ end of template RNA primer
Can’t be made continuously as direction is wrong
RNA primer
New DNA made 5’  3’
Opposite direction of replication
Discontinuous
Okazaki fragments
Ligase closes gaps

14. Transcription DNA template made into RNA copy
Uracil instead of Thymine
One DNA strand is template
Sense strand
Other is just for replication
Antisense (not to be confused with nonsense!)
In nucleus
nucleoli

15. Transcription From following DNA strand, determine RNA sequence
3’ GCCTAAGCTCA 5’
Answer

16. Transcription

17. Transcription DNA opens up RNA polymerase binds Enzymes? Which strand?
Using DNA template, makes RNA
5’-3’
Raw transcript called hnRNA

18. Transcription How does RNA polymerase know where to start?
upstream promotor sequences
Pribnow Box
TATA box
RNA polymerase starts transcription X nucleotides downstream of TATA box

19. Introns and Exons Introns Exons Intervening sequences
Not all DNA codes for protein
Regulatory info, “junk DNA”
Exons
Code for protein

20. Processing of hnRNA into mRNA
3 steps
Introns removed
Self splicing
5’ methyl guanosine cap added
Poly A tail added
Moved to cytosol for translation

21. Processing of hnRNA into mRNA

22. Translation RNA -- Protein On ribosomes Vectorial nature preserved
Change from nucleotide language to amino acid language
On ribosomes
Vectorial nature preserved
5’ end of mRNA becomes amino terminus of protein
Translation depends on genetic code

23. Genetic Code Nucleotides read in triplet “codons”
5’ - 3’
Each codon translates to an amino acid
64 possible codons
3 positions and 4 possiblities (AGCU) makes 43 or 64 possibilities
Degeneracy or redundancy of code
Only 20 amino acids
Implications for mutations

24. Genetic Code

25. Genetic Code Not everything translated AUG is start codon
Find the start codon
Also are stop codons
To determine aa sequence
Find start codon
Read in threes
Continue to stop codon

26. Translation Steps: Translate the following: Find start codon (AUG)
After start codon, read codons, in threes
Use genetic code to translate
Translate the following:
GCAGUCAUGGGUAGGGAGGCAACCUGAACCGAC
Answer

27. Translation Process
Requires Ribosomes, rRNA, tRNA and, of course, mRNA
Ribosome
Made of protein and rRNA
2 subunits
Has internal sites for 2 transfer RNA molecules

28. Ribosome
Left is cartoon diagram Right is actual picture

29. Transfer RNA Mostly double stranded Several loops
Folds back on itself
Several loops
Anticodon loop
Has complementary nucleotides to codons
3’ end where aa attach

30. Transfer RNA

31. Translation Initiation Elongation Termination
Ribosomal subunits assemble on mRNA
rRNA aids in binding of mRNA
Elongation
tRNAs with appropriate anticodon loops bind to complex
have aa attached (done by other enzymes)
Amino acids transfer form tRNA 2 to tRNA 1
Process repeats
Termination
tRNA with stop codon binds into ribosome
No aa attached to tRNA
Complex falls apart

32. Translation

33. Translation Happening of process (circa 1971)

34. Mutations Changes in nucleotide sequence
Can cause changes in aa sequence
Degeneracy in genetic code can prevent
Two types
Point mutations
Single nucleotide changes
Frame shift
Insertions or deletions

35. Point Mutations Single nucleotide changes Old sequence
AUG GGU AGG GAG GCA ACC UGA ACC GAC
aa: G R E A T
New sequence
AUG GGU AGU GAG GCA ACC UGA ACC GAC
aa: G S E A T

36. Point mutations Depending on change, may not change aa sequence
Old sequence
AUG GGU AGG GAG GCA ACC UGA ACC GAC
aa: G R E A T
New sequence
AUG GGU AGA GAG GCA ACC UGA ACC GAC
aa: G R E A T

37. Point Mutations Change could make little difference
If valine changed to leucine, both nonpolar
Change could be huge,
Could erase start codon
Old sequence
AUG GGU AGG GAG GCA ACC UGA ACC GAC
aa: G R E A T
New sequence
AUU GGU AGA GAG GCA ACC UGA ACC GAC
aa: no start codon…protein not made

38. Point Mutations Other possibilities, Bottom line, Stop codon inserted
Truncated protein
Stop codon changed
Extra long protein
Bottom line,
Depends on what change is

39. Frame Shift mutations Insertions or deletions Insertion example
Change the reading frame
Insertion example
Old sequence
AUG GGU AGG GAG GCA ACC UGA ACC GAC
aa: G R E A T
New sequence
AUG GGU AGG AGA GGC AAC CUG AAC CGA C
aa: G R R G N L N R

40. Frame Shift Mutations Deletion example Old sequence
AUG GGU AGG GAG GCA ACC UGA ACC GAC
aa: G R E A T
New sequence Delete second A (Underlined above)
AUG GGU GGG AGG CAA CCU GAA CCG AC
aa: G G R Q P G P

41. Complementary DNA Strand
Template:
3’ ACTAGCCTAAGTCG 5’
5’ TGATCGGATTCAGC 3’
Back

42. RNA Transcript
DNA 3’ GCCTAAGCTCA 5’
RNA 5’ CGGAUUCGAGU 3’
Back

43. Translation Answer Find start codon GCAGUCAUGGGUAGGGAGGCAACCUGAACCGAC
Read in threes after that:
AUG GGU AGG GAG GCA ACC UGA ACC GAC
Using Genetic code
G R E A T stop
After stop codon…rest is garbage
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