Disclaimer: This is not my own Powerpoint Presentation. Credits to Mindanao State University - General Santos City - College of Natural Science and Mathematics.

2.  Organelles
 nucleus
 ribosomes
 endoplasmic reticulum
(ER)
 Golgi apparatus
 vesicles
Making proteins
small
ribosomal
subunit
large
ribosomal
subunit
cytoplasm
mRNA
nuclear pore

3. The “Central Dogma”
 Flow of genetic information in a cell
 How do we move information from DNA to proteins?
transcription
translation
replication
proteinRNADNA trait
DNA gets
all the glory,
but proteins do
all the work!

5. DNA Replication
 semiconservative
 Watson and Crick base
pairing maintained
 Synthesis in 5’ to 3’ direction
 A primer is needed for
initiation
 a complex process involving
several enzymes and
proteins (Replisome)

6. Copying DNA
 Replication of DNA
 base pairing allows
each strand to serve
as a template for a
new strand

7. Models of DNA Replication
 Alternative models
 so how is DNA copied?
conservative semiconservative dispersive

9. Proteins and Enzymes
DNA polymerase I – 5’ to 3’ polymerization
– 3’ to 5’ proofreading
– 5’ to 3’ exonuclease activity
DNA Polymerase II – DNA Repair functions
DNA Polymerase III – primary replication enzyme
Helicase
Single-strand Binding Proteins
Primase
Ligase
Topoisomerase

11. Transcription
from
DNA language
to
RNA language

12. Transcription in Eukaryotes
Protein
RNA Processing
Translation
Transcription
Psssst…
DNA can’t
leave nucleus!

13. Transcription in Eukaryotes
 3 RNA polymerase enzymes
 RNA polymerase 1
 only transcribes rRNA genes
 makes ribosomes
 RNA polymerase 2
 transcribes genes into mRNA
 RNA polymerase 3
 only transcribes tRNA genes
 each has a specific promoter sequence
it recognizes

14. Transcription in Eukaryotes
 Initiation complex
 transcription factors bind
to promoter region
upstream of gene
 suite of proteins which bind
to DNA
 turn on or off transcription
 TATA box binding site
 recognition site for
transcription factors
 transcription factors
trigger the binding of RNA
polymerase to DNA

15.  Initiation
 Assembly of initiation complex
 Elongation
 adding N-bases bases
 Termination
 Rho-dependent
 Rho-independent (GC-rich)
Building mRNA

16. A A A
A
A3' poly-A tail
mRNA
5'
5' cap
3'
GP
PP
50-250 A’s
Post-transcriptional processing
eukaryotic DNA
exon = coding (expressed) sequence
intron = noncoding (inbetween) sequence
primary mRNA
transcript
mature mRNA
transcript
pre-mRNA
spliced mRNA
 Primary transcript (pre-mRNA)
 eukaryotic mRNA needs work after transcription
 mRNA processing (making mature mRNA)
 mRNA splicing = edit out introns
 protect mRNA from enzymes in cytoplasm
 add 5′ cap
 add polyA tail
~10,000 bases
~1,000 bases

17. Splicing must be accurate
 No room for mistakes!
 splicing must be exactly accurate
 a single base added or lost throws off the
reading frame
AUG|CGG|UCC|GAU|AAG|GGC|CAU
AUGCGGCTATGGGUCCGAUAAGGGCCAU
AUGCGGUCCGAUAAGGGCCAU
AUG|CGG|GUC|CGA|UAA|GGG|CCA|U
AUGCGGCTATGGGUCCGAUAAGGGCCAU
AUGCGGGUCCGAUAAGGGCCAU
Met|Arg|Ser|Asp|Lys|Gly|His
Met|Arg|Val|Arg|STOP|

18. Splicing enzymes
snRNPs
exonexon intron
snRNA
5' 3'
spliceosome
exon
excised
intron
5'
5'
3'
3'
3'
lariat
exon
mature mRNA
5'
No,
not smurfs!
“snurps”
 snRNPs
 small nuclear RNA
 proteins
 Spliceosome
 several snRNPs
 recognize splice
site sequence
 cut & paste

19. Prokaryote vs. Eukaryote genes
 Prokaryotes
 DNA in cytoplasm
 circular
chromosome
 naked DNA
 no introns
 Eukaryotes
 DNA in nucleus
 linear
chromosomes
 DNA wound on
histone proteins
 introns vs. exons
eukaryotic
DNA
exon = coding (expressed) sequence
intron = noncoding (inbetween) sequence
introns
come out!

20. Translation
from
nucleic acid language
to
amino acid language

21. Translation
 Codons
 blocks of 3
nucleotides
decoded into
the sequence
of amino acids

22. Translation in
Prokaryotes
Bacterial chromosome
mRNA
Cell wall
Cell
membrane
Transcription
Translation
proteinPsssst…
no nucleus!

23.  Transcription & translation are simultaneous
in bacteria
 DNA is in
cytoplasm
 no mRNA
editing
 ribosomes
read mRNA
as it is being
transcribed
Translation in Prokaryotes

24. Translation: prokaryotes vs. eukaryotes
 Differences between prokaryotes &
eukaryotes
 time & physical separation between
processes
 takes eukaryote ~1 hour
from DNA to protein
 RNA processing

25. Translation in Eukaryotes

26. mRNA
From gene to protein
DNA
transcription
nucleus cytoplasm
mRNA leaves
nucleus through
nuclear pores
proteins synthesized
by ribosomes using
instructions on mRNA
aa
aa
aa
aa
aa
aa
aa
aa
ribosome
protein
translation

27. How does mRNA code for proteins?
TACGCACATTTACGTACGCGGDNA
AUGCGUGUAAAUGCAUGCGCCmRNA
Met Arg Val Asn Ala Cys Alaprotein
?
How can you code for 20 amino acids
with only 4 nucleotide bases (A,U,G,C)?
4
4
20
ATCG
AUCG

28. AUGCGUGUAAAUGCAUGCGCCmRNA
mRNA codes for proteins in triplets
TACGCACATTTACGTACGCGGDNA
AUGCGUGUAAAUGCAUGCGCCmRNA
Met Arg Val Asn Ala Cys Alprotein
?
codon

29. Cracking the code
1960 | 1968
 Crick
 determined 3-letter (triplet) codon system
Nirenberg & Khorana
WHYDIDTHEREDBATEATTHEFATRATWHYDIDTHEREDBATEATTHEFATRAT
 Nirenberg & Khorana
 determined mRNA–amino acid match
 added fabricated mRNA to test tube of
ribosomes, tRNA & amino acids
 created artificial UUUUU… mRNA
 found that UUU coded for phenylalanine (phe)

30. The code
 Code for ALL life!
 strongest support for
a common origin for
all life
 Code is redundant
 several codons for
each amino acid
 3rd base “wobble”
 Start codon
 AUG
 methionine
 Stop codons
 UGA, UAA, UAG
Why is the
wobble good?

31. How are the codons matched to
amino acids?
TACGCACATTTACGTACGCGGDNA
AUGCGUGUAAAUGCAUGCGCCmRNA
amino
acid
tRNA
anti-codon
codon
5′ 3′
3′ 5′
3′ 5′
UAC
Met
GCA
Arg
CAU
Val

32. mRNA
From gene to protein
DNA
transcription
nucleus
cytoplasm
aa
aa
aa
aa
aa
aa
aa
aa
ribosome
protein
translation
aa

33. Transfer RNA structure
 “Clover leaf” structure
 anticodon on “clover leaf” end
 amino acid attached on 3′ end

35. Ribosomes
 Facilitate coupling of
tRNA anticodon to
mRNA codon
 organelle or enzyme?
 Structure
 ribosomal RNA (rRNA) & proteins
 2 subunits
 large
 small E P A

36. Ribosomes
Met
5'
3'
U
U
A C
A G
APE
 A site (aminoacyl-tRNA site)
 holds tRNA carrying next amino acid to
be added to chain
 P site (peptidyl-tRNA site)
 holds tRNA carrying growing
polypeptide chain
 E site (exit site)
 empty tRNA
leaves ribosome
from exit site

37. Building a polypeptide
 Initiation
 brings together mRNA, ribosome
subunits, initiator tRNA
 Elongation
 adding amino acids based on
codon sequence
 Termination
 end codon 123
Leu
Leu Leu Leu
tRNA
Met Met
Met Met
PE A
mRNA
5' 5' 5' 5'
3' 3' 3'
3'
U UA AA
AC
C
C
AU UG G
GU
U
A
AA
AC
C
C
AU UG G
GU
U
A
AA
AC
C
C
AU UG G
GU U
A
AAC
CAU UG G
G
A
C
Val
Ser
Ala
Trp
release
factor
A
A A
CC
U UGG
3'

38. Can you tell
the story?
DNA
pre-mRNA
ribosome
tRNA
amino
acids
polypeptide
mature mRNA
5' cap
polyA tail
large ribosomal subunit
small ribosomal subunit
aminoacyl tRNA
synthetase
E P A
5'
3'
RNA polymerase
exon intron
tRNA

39. 2007-2008
end