4. Prokaryotes vs Eukaryotes
Prokaryote Eukaryote
Site of DNA Replication Protoplasm Nucleus
Site of Transcription Protoplasm Nucleus
Site of RNA Splicing Rare Nucleus
Site of Translation Protoplasm Cytoplasm
Site of Recombination Protoplasm Nucleus
7. STEPS
Unwinding & Strand Separation
Helicase will unwind the parental strands
breaks the H-bonds between bases
SSBP (Single-stranded DNA-binding
proteins)
attaches to separated strands and keep
them from annealing back
9. Unwinding & STEPS
Strand
Separation
Topoisomerase
breaks and
rejoins the DNA
double helix to
relieve
twisting
forced by the
opening of the
helix
(supercoils) mol-biol4masters.masters.grkraj.org
10. STEPS
Priming
Primase catalyzes synthesis of RNA primers
RNA primers attach to specific site of DNA
strand (ORI region)
Synthesis of New Strands
Leading strand (Continuous): DNA polymerase
III catalyzes synthesis of new DNA strands
at 5’ to 3’ direction (as single polymer) and
extends the leading strand
12. STEPS
Synthesis of New Strands
Lagging strand (Discontinuous): DNA
polymerase III extends the Okazaki fragments
DNA polymerase I removes RNA primers and
replaces it with DNA
Sealing the nick
DNA Ligase forms covalent bonds from 3’ to 5’
direction to join the Okazaki fragments into a
continuous strand
17. TELOMERASE AND GENE
EROSION
TELOMERES: ends of the DNA
each chromosome is one continuous double stranded
length of DNA with 2 telomeres
The 3’ to 5’ parent strand is copied no trouble as the
leading strand BUT the lagging strand (parent 5’ to 3’) has
small primers made every so often and filled in
NOTE: no template at the end to bind to so when the
primers are removed there is an overhang and exposes the
DNA to digestion which would eventually eat into the
genes at the end (gene erosion)
24. TRANSCRIPTION
Process of copying DNA to RNA
NOTE: only one strand of DNA, the template strand,
is used to make mRNA
Does not need a primer to start and can involve multiple
RNA polymerases
Divided into 3 stages
Initiation
Elongation
For VIDEOS: https://
Termination
www.youtube.com/watch?
v=WsofH466lqk
28. RNA POLYMERASE
RNA polymerase only transcribes one strand of
the parental DNA molecule (the template strand)
in the 3' to 5' direction
RNA polymerase will never add a T, instead it will
add a U
Transcription ceases when RNA polymerase
encounters special DNA sequences termed
terminators that stop the process of
transcription
30. INTRONS AND EXONS
Introns
sequences in the DNA that are NOT used to
make mRNA or to make a protein
they are NOT transcribed
Exons
sequences in the DNA that are expressed or
used to make mRNA and ultimately are used to
make a protein
31. POST-TRANSCRIPTIONAL
MODIFICATION IN EUKARYOTES
RNA SPLICING
REMOVAL OF INTRONS
5’ METHYLATED CAP AND POLYADENYLATION
PREVENTS DEGRADATION DURING TRANSIT
FROM NUCLEUS TO CYTOPLASM
35. CONTROL DURING
TRANSCRIPTION
PROKARYOTES
regulating genetic expression in nearby genes
(e.g. LAC OPERON)
EUKARYOTES
involves the organization of chromatin and
specific transcription factors which function by
either changing the rate of transcription or
altering the accessibility of chromatin to
transcriptional machinery
48. THE GENETIC CODE
www.mun.ca
http://www.genome.jp/kegg/
catalog/codes1.html
49. NUCLEOTIDE
CODES
A
Adenine
G Guanine
C Cytosine
T Thymine
U Uracil
R Purine (A or G)
Y Pyrimidine (C or T)
N Any nucleotide
W Weak (A or T)
S Strong (G or C)
M Amino (A or C)
K Keto (G or T)
B Not A (G or C or T)
H Not G (A or C or T)
D Not C (A or G or T)
V Not T (A or G or C)
50. AMINO
ACID CODES
Ala A Alanine
Arg R Arginine
Asn N Asparagine
Asp D Aspartic acid
Cys C Cysteine
Gln Q Glutamine
Glu E Glutamic acid
Gly G Glycine
His H Histidine
Ile I Isoleucine
Leu L Leucine
51. AMINO
ACID CODES
Lys K Lysine
Met M Methionine
Phe F Phenylalanine
Pro P Proline
Ser S Serine
Thr T Threonine
Trp W Tryptophan
Tyr Y Tyrosine
Val V Valine
Asx B Asn or Asp
Glx Z Gln or Glu
Xle J Leu or Ile
Sec U Selenocysteine (UGA)
Pyl O Pyrrolysine (UAG)
Unk X Unknown
54. LET’S TRY…
www.wiley.com
Met M Methionine
His H Histidine
Gly G Glycine
Asn N Asparagine
Leu L Leucine
55. AMINO ACID SEQUENCE
IS…
www.wiley.com
Met M Methionine
His H Histidine
Gly G Glycine
Asn N Asparagine
Leu L Leucine
MHGNL
met-his-gly-asn-leu
56. NUCLEOTIDE SEQUENCE
IS…
www.wiley.com
from the sequence…
(AUA or AUG)-(CAU or
CAC)-(GGU or GGC or
GGA or GGG)-(AAU or
AAC)-(CUU or CUC or
CUA or CUG)
!
EXAMPLE: nucleotide
sequence may be
AUA-CAU-GGU-AAU-CUU
!
EXAMPLE: amino acid
sequence is
MHGNL or met-his-gly-asn-leu
58. FORM YOUR GROUPS
You will be given set of questions and can discuss by group
for the FINAL answer
The score of the group will be the score of each individual
for today’s QUIZ
Submission is TOMORROW, 12noon, DB (Look for ate Malou)
READY???
59. QUESTIONS
In order to properly construct a protein, which process must
occur first: transcription or translation? Why?
LAC operon: Under what conditions is the operator activated?
Under what conditions is it inactivated?
Assume that the following sequence of bases represents a
segment of DNA that is to undergo transcription. Determine the
corresponding sequence of bases in the resulting RNA molecule.
3’-TAC GGC ATT GCA CAT TTT AGG GGC AAT ATT-5’
The following mRNA segment represents three codons. In each
case determine what the anticodon would be on the appropriate
tRNA.
AAA CGA AAU