1. Nucleic Acid

2. DNA RNA protein The Central Dogma Replication Transcription
Translation
The flow of genetic information is unidirectional, from DNA to protein with messenger RNA as an intermediate.

3. DNA Replication
- the process of making new copies of the DNA molecules
Potential mechanisms:
organization of DNA strands
Conservative old/old + new/new
Semiconservative old/new + new/old
Dispersive mixed old and new on each strand

4. Meselson and Stahl’s replication experiment

5. Replication as a process
1. Double-stranded DNA unwinds.
2. The junction of the unwound
molecules is a replication fork.
3. A new strand is formed by pairing
complementary bases with the
old strand.
4. Two molecules are made.
Each has one new and one old
DNA strand.

6. Enzymes in DNA replication
Primase adds
short primer
to template strand
Helicase unwinds
parental double helix
Binding proteins
stabilize separate
strands
DNA polymerase
binds nucleotides
to form new strands
Exonuclease removes
RNA primer and inserts
the correct bases
Ligase joins Okazaki
fragments and seals
other nicks in sugar-phosphate backbone

8. Replication Helicase protein binds to DNA sequences called
Primase protein makes a short segment of RNA
complementary to the DNA, a primer. 5’ 3’
Binding proteins prevent single strands from rewinding. 3’ 5’
Helicase protein binds to DNA sequences called
origins and unwinds DNA strands.

9. Replication DNA polymerase enzyme adds DNA nucleotides
Overall direction
of replication 5’ 3’
DNA polymerase enzyme adds DNA nucleotides
to the RNA primer.

10. Replication Leading strand synthesis continues in a5’ 3’
Overall direction
of replication
Leading strand synthesis continues in a
5’ to 3’ direction.

11. Replication Leading strand synthesis continues in a3’ 5’
Overall direction
of replication
Okazaki fragment
Leading strand synthesis continues in a
5’ to 3’ direction.
Discontinuous synthesis produces 5’ to 3’ DNA
segments called Okazaki fragments.

12. Replication Leading strand synthesis continues in a
Overall direction
of replication 3’ 3’ 5’ 5’
Okazaki fragment 3’ 5’ 3’ 5’ 3’ 5’
Leading strand synthesis continues in a
5’ to 3’ direction.
Discontinuous synthesis produces 5’ to 3’ DNA
segments called Okazaki fragments.

13. Replication Leading strand synthesis continues in a3’ 3’ 5’ 5’ 3’ 5’ 3’ 5’ 3’ 3’ 5’ 5’
Leading strand synthesis continues in a
5’ to 3’ direction.
Discontinuous synthesis produces 5’ to 3’ DNA
segments called Okazaki fragments.

14. Replication Leading strand synthesis continues in a5’ 3’ 3’ 3’ 5’
Leading strand synthesis continues in a
5’ to 3’ direction.
Discontinuous synthesis produces 5’ to 3’ DNA
segments called Okazaki fragments.

15. Replication 3’ 5’ 5’ 5’ 3’
Exonuclease enzymes remove RNA primers.

16. Replication Exonuclease enzymes remove RNA primers.3’ 5’
Ligase forms bonds between sugar-phosphate
backbone.
Exonuclease enzymes remove RNA primers.

17. Replication 5’ 3’ 5’ 3’ 5’ 3’ 5’ 3’ 5’ 3’ 3’ 5’ 3’ 5’

18. Transcription

19. Prokaryotic Gene Structure
Promoter CDS Terminator
UTR UTR
Genomic DNA
transcription
mRNA
translation
protein

20. Eukaryotic Gene Structure
5’ - Promoter Exon Intron Exon Terminator – 3’
UTR splice splice UTR
transcription
Poly A
translation
protein

21. Transcription initiation and elongation
1. Genes need to be expressed to be “genes”
2. Transcription is directed to specific locations (promoters)
3. RNA is elongated in the 5’-to-3’ direction

22. Promoter Promoter determines: Which strand will serve as a template.
Transcription starting point.
Strength of polymerase binding.
Frequency of polymerase binding.

23. Prokaryotic Promoter One type of RNA polymerase.
Pribnow box located at –10 (6-7bp)
–35 sequence located at -35 (6bp)

24. Eukaryote Promoter
3 types of RNA polymerases are employed in transcription of genes:
RNA polymerase I transcribes rRNA
RNA polymerase II transcribes all genes coding for polypeptides
RNA polymerase III transcribes small cytoplasmatic RNA, such as tRNA.

25. Eukaryote Promoter Goldberg-Hogness or TATA located at –30
Additional regions at –100 and at –200
Possible distant regions acting as enhancers or silencers (even more than 50 kb).

26. RNA Synthesis DNA template: 3’-to-5’
RNA synthesis: 5’-3’; no primer needed

28. Termination Sites
The newly synthesized mRNA forms a stem and loop structure (lollipop).
A disassociation signal at the end of the gene that stops elongating and releases RNA polymerase.
All terminators (eukaryotes and prokaryotes) form a secondary structure.

29. Termination Sites
The terminator region pauses the polymerase and causes disassociation.

30. Splice Sites Eukaryotics only
Removing internal parts of the newly transcribed RNA.
Takes place in the cell nucleus (hnRNA)

31. Splice Sites
Conserved splice sites are shared by both the exon and the intron.
Different signals on the donor site (3’) and on the acceptor site (5’).

32. Translation

33. Genetic Terminology Chromosome
- threadlike structures in the nucleus that carry genetic information
Gene
- fundamental unit of heredity
- inherited determinant of a phenotype
- sequence of DNA that instructs a cell to produce a
particular protein
DNA
- deoxyribonucleic acid,
- the genetic material
- the biochemical that forms genes

34. Open Reading Frames (ORF)

35. TRANSCRIPTION TRANSLATION Unwinding of gene regions of a DNA molecule
Pre mRNA Transcript Processing
mRNA
rRNA
tRNA
protein subunits
Mature mRNA transcripts
ribosomal subunits
mature tRNA
Convergence of RNAs
TRANSLATION
Cytoplasmic pools of amino acids, tRNAs, and ribosomal subunits
Synthesis of a polypetide chain at binding sites for mRNA and tRNA on the surface of an intact ribosome
FINAL PROTEIN
Destined for use in cell or for transport

36. PROTEIN TRANSLATION m-RNA GOES THRU RIBOSOME.
RIBOSOME IS r-RNA,CODE THREADS THRU RIBOSOME.
AREA OF RIBOSOME BOUND TO tRNA
20 TYPES OF AA
ANTICODON ON ONE END OF t-RNA.
AA ON OTHER END OF t-RNA
AA ATTACH TO EACH OTHER IN PEPTIDE BOND
FORM PROTEINS

37. The triplet code

39. Role of Ribosome 70S ribosome 50S subunit 30S subunit 16S rRNA
34 proteins
21 proteins
23S rRNA
5S rRNA

40. mRNA  Ribosome mRNA leaves the nucleus via nuclear pores.
Ribosome has 3 binding sites for tRNAs:
A-site: position that aminoacyl-tRNA molecule binds to vacant site
P-site: site where the new peptide bond is formed.
E-site: the exit site
Two subunits join together on a mRNA molecule near the 5’ end.
The ribosome will read the codons until AUG is reached and then the initiator tRNA binds to the P-site of the ribosome.
Stop codons have tRNA that recognize a signal to stop translation. Release factors bind to the ribosome which cause the peptidyl transferase to catalyze the addition of water to free the molecule and releases the polypeptide.

41. Purpose of tRNA
The proper tRNA is chosen by having the corresponding anticodon for the mRNA’s codon.
The tRNA then transfers its aminoacyl group to the growing peptide chain.
For example, the tRNA with the anticodon UAC corresponds with the codon AUG and attaches methionine amino acid onto the peptide chain.

42. tRNAs are specific carriers of amino acids
Aminoacyl-tRNA synthetases attach specific amino acids to heat-stable tRNA molecules
ATP +
Amino
acid
Amino
acid 3’ 5’
aminoacyl-tRNA
synthetase
tRNA
e.g. tRNAPhe
aminoacylated tRNA
e.g. Phe-tRNAPhe

43. RNA  Protein: Translation
Ribosomes and transfer-RNAs (tRNA) run along the length of the newly synthesized mRNA, decoding one codon at a time to build a growing chain of amino acids (“peptide”)
The tRNAs have anti-codons, which complimentarily match the codons of mRNA to know what protein gets added next
But first, in eukaryotes, a phenomenon called splicing occurs
Introns are non-protein coding regions of the mRNA; exons are the coding regions
Introns are removed from the mRNA during splicing so that a functional, valid protein can form

44. Translation, continued
Catalyzed by Ribosome
Using two different sites, the Ribosome continually binds tRNA, joins the amino acids together and moves to the next location along the mRNA
~10 codons/second, but multiple translations can occur simultaneously

46. See you later。。。。。。