ANCIENT BACTERIA?
250 million years later, scientists revive life forms
Thursday, October 19, 2000
U.S. researchers say they have revived bacteria that have been dormant
for more then 250 million years, resurrecting micro-organisms that last
wriggled before dinosaurs walked the Earth.
In a paper published today in the journal Nature, scientists from West
Chester University in Pennsylvania described how they isolated bacteria
spores within 250-million- year-old salt crystals buried in a rocky deposit
in New Mexico.
ANCIENT BACTERIA?
•  "I just find it a silly and unbelievable report,"
said Dr. Tomas Lindahl, an expert on the
stability of DNA who works at the Imperial
Cancer Research Fund in London.
•  “There are no active repair enzymes in a
spore”, he said, “and radioactivity alone would
eventually break the DNA into pieces that
would make a spore no longer viable”.
ANCIENT BACTERIA?
•  “However, attempts to replicate of results
involving DNA purported to be over a million
years old have not succeeded. Theoretical
studies suggest that DNA is unlikely to survive
intact more than about 100,000 years…”
GENETIC
TRANSFORMATION
GENETIC
TRANSFORMATION
Def’n - change in genotype of one individual after exposure to another’s DNA
GENETIC
TRANSFORMATION
2 NUCLEIC ACID
CATEGORIES
A FACT
•  A DNA polymer can be made up of any
combination of nucleotides (polynucleotide)
e.g. AAA, AGC, GTC, TTG, TGT, GCG, …
•  One triplet codes (indirectly)for one amino
acid
ANOTHER FACT
•  Each nucleotide has only
one complementary base
A FACT
•  A DNA polymer can be made up of any
combination of nucleotides (polynucleotide)
e.g. AAA, AGC, GTC, TTG, TGT, GCG, …
•  One triplet codes (indirectly)for one amino
acid
HOW MANY DIFFERENT
CODONS ARE THERE?
•  ANSWER: 43 = 64
•  A doublet codon would give 42 = 16
•  Thus, a triplet code is the smallest
word that can give codes for all amino
acids
A FACT
•  DNA is not translated into amino acids.
It is transcribed into rna
RNA DIFFERS FROM DNA
•  RNA sugar (ribose) has one more oxygen than
does DNA (deoxyribose)
•  Uracil replaces thymine as the
complementary base to adenine
•  RNA is typically single-stranded
ANOTHER FACT
•  Each nucleotide has only one
complementary base
ONE GREAT
UNDERSTATEMENT
•  It has not escaped our notice that the specific
[base] pairing that we have
postulated immediately
suggests a possible
copying mechanism
for the genetic material”
SEMI-CONSERVATIVE
DNA REPLICATION
•  3 STEPS:
–  The 2 DNA strands of the parental DNA
unwind and separate
–  Each parental strand acts as a template for
production of a complementary daughter strand
–  Each new daughter strand winds together with
its mother strand
SEMI-CONSERVATIVE
DNA REPLICATION
The Critical Enzymes:
–  Helicase – breaks hydrogen bonds between
nucleotides bases (per strand)
–  Polymerase – recognizes the correct base and
bonding to the ribose – phosphate
–  Ligase – bonds together fragments
of DNA in the daughter strand
DNA REPLICATION
DNA REPLICATION
•  Fast – 50 – 500 nucleotides/sec
•  Accurate – errors at 1 x 10-6
A PROBLEM
In eukaryotic cells, DNA inhabits the
nucleus whereas the protein that it codes
for is synthesized
in
the cytoplasm.
A SOLUTION
Two step process.
GENETIC CODES
U
U
C
A
G
UUU
UUC
UUA
UUG
CUU
CUC
CUA
CUG
AUU
AUC
AUA
AUG
GUU
GUC
GUA
GUG
Phe
Leu
Leu
Ile
Val
C
UCU
UCC
UCA
UCG
CCU
CCC
CCA
CCG
ACU
ACC
ACA
ACG
GCU
GCC
GCA
GCG
A
Ser
Pro
Thr
Ala
UAU
UAC
UAA
UAG
CAU
CAC
CAA
CAG
AAU
AAC
AAA
AAG
GAU
GAC
GAA
GAG
G
Tyr UGU
UGC
UGA
UGG
His CGU
CGC
Gin CGA
CGG
Asn AGU
AGC
Lys AGA
AGG
Asp GGU
GGC
Glu GGA
GGG
Cys U
C
A
Trp G
U
Arg C
A
G
Ser U
C
Arg A
G
U
Gly C
A
G
THE GENETIC LANGUAGE
•  An example of a “genetic sentence” that
codes for a protein:
THEDOGFEDTHECATFORFUN
TRANSCRIPTION
ANOTHER PROBLEM
•  Which DNA strand should be copied –
just one or both?
YET ANOTHER PROBLEM
•  How to rapidly move polymerase
enzyme along unraveled strand
•  Nuclear molecular motors (myosin)
similar to those used in the cytoplasm
were recently discovered
TRANSLATION
•  tRNA decodes the
message carried
by the mRNA
•  Translation takes
places at
ribosomes
TRANSLATION
•  A complex series of steps:
•  http://www.dnalc.org/view/15481Translation-RNA-to-protein-3D-animationwith-no-audio.html