6. The Tetranucleotide
hypothesis
Up to 1940 researchers were convinced
that hydrolysis of nucleic acids yielded the
four bases in equal amounts.
Nucleic acid was postulated to contain
one of each of the four nucleotides, the
tetranucleotide hypothesis.
Takahashi (1932) proposed a structure of
nucleotide bases connected by
phosphodiester linkages.
11. Avery, MacLeod, and Mc
Carty in 1944
demonstrate DNA could “transform”
cells.
Supporters of the tetranucleotide
hypothesis did not believe nucleic acid
was variable enough to be a molecule
of heredity and store genetic
information.
12. The Avery, MacLeod, and
McCarty Experiment
Mice injected with virulent bacteria die
13. The Avery, MacLeod, and McCarty
Experiment
Mice injected with nonvirulent bacteria live
14. The Avery, MacLeod, and McCarty Experiment
Mice injected with heat-killed virulent bacteria live
15. The Avery, MacLeod, and McCarty
Experiment
Mice injected with a mixture of nonvirulent bacteria
and heat-killed virulent bacteria die
16. The Avery, MacLeod, and McCarty
Experiment
Mice injected with a mixture of nonvirulent bacteria
and DNA from heat-killed virulent bacteria die
17. Erwin Chargaff in late
1940s
used paper chromatography for
separation of DNA hydrolysates.
Amount of adenine is equal to amount
of thymine and amount of guanine is
equal to amount of cytosine.
25. Important Developments
1972 – First recombinant DNA molecule
constructed Lambda phage DNA
inserted into SV40 virus
- Restriction enzyme EcoRI used to
create a recombinant plasmid
containing penicillin and
tetracycline resistance
1982 – Tetrahymena ribosomal RNA
splicing shown to be self- splicing
26. Important Developments
1986 – RNA is shown to act as an enzyme
- The polymerase chain reaction
(PCR) was developed by
Kari Mullis at Cetus Corporation.
1995 – First complete genome
sequenced of the bacterium
Haemophilus influenzae at TIGR
2001 – Human genome sequenced by
NIH and Celera Genomics
27. Nucleic Acids
• Nucleic Acids are very long, thread-like
polymers, made up of a linear array of monomers
called nucleotides.
• Nucleic acids vary in size in nature
• tRNA molecules contain as few as 80 nucleotides
• Eukaryotic chromosomes contain as many as
100,000,000 nucleotides.
28. Two types of nucleic acid
are found
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
29. DNA and RNA
DNA
deoxyribonucleic acid
nucleic acid that stores genetic information
found in the nucleus of a mammalian cell.
RNA
ribonucleic acid
3 types of RNA in a cell
Ribosomal RNAs (rRNA) are components of ribosomes
Messenger RNAs (mRNA) carry genetic information
Transfer RNAs (tRNA) are adapter molecules in translation
30. The distribution of nucleic
acids in the eukaryotic
cell is found in the nucleus
DNA
with small amounts in mitochondria and
chloroplasts
RNA is found throughout the cell
35. DNA as genetic material:
The circumstantial evidence
1. Present in all cells and virtually restricted to the nucleus
2. The amount of DNA in somatic cells (body cells) of any
given species is constant (like the number of
chromosomes)
3. The DNA content of gametes (sex cells) is half that of
somatic cells.
In cases of polyploidy (multiple sets of chromosomes)
the DNA content increases by a proportional factor
4. The mutagenic effect of UV light peaks at 253.7nm. The
peak for the absorption of UV light by DNA
36. NUCLEIC ACID STRUCTURE
Nucleic acids are polynucleotides
Their building blocks are nucleotides
40. Spot the difference
RIBOSE DEOXYRIBOSE
CH2OH CH2OH
O OH O OH
C C C C
H H H H H H H H
C C C C
OH OH OH H
41. Chemical Structure of DNA vs RNA
Ribonucleotides have a 2’-OH
Deoxyribonucleotides have a 2’-H
42. P
THE SUGAR-PHOSPHATE
BACKBONE P
The nucleotides are all
orientated in the same P
direction
The phosphate group joins the P
3rd Carbon of one sugar to the
5th Carbon of the next in line. P
P
43. P
G
ADDING IN THE BASES
P
C
The bases are
P
attached to the 1
st
C
Carbon
Their order is P
important A
It determines the P
genetic information of T
the molecule
P
T
44. Hydrogen bonds
DNA IS MADE OF P
G
TWO STRANDS OF C
P
POLYNUCLEOTIDE P
C G
P
P
C G
P
P
A T
P
P
T A
P
P
T A
P
45. DNA IS MADE OF TWO STRANDS OF
POLYNUCLEOTIDE
The sister strands of the DNA molecule run in opposite
directions (antiparallel)
They are joined by the bases
Each base is paired with a specific partner:
A is always paired with T
G is always paired with C
“Purine with Pyrimidine”
The sister strands are complementary but not identical
The bases are joined by hydrogen bonds, individually
weak but collectively strong
There are 10 base pairs per turn
48. 5’ End
Nucleotides
are
linked by
phosphodies
ter
bonds
3’ End
49. Three-dimensional structure of B
DNA
NMR solution structure of a 12 nucleotide fragment of DNA
5’- C G C G A A T T C G C G –3’
3’- G C G C T T A A G C G C –5’
Total of 32 hydrogen bonds.
Reading Assignment:
Tjandra et al
Journal of the American Chemical Society (2000) 122, 6190
50. Cellular Processes
replication
DNA
transcription
RNA (mRNA)
translation
Proteins
51. RNA and Transcription
DNA is in the nucleus
Proteins are synthesized on ribosomes in the
cytoplasm
RNA carries the genetic information from the
nucleus to the cytoplasm
This RNA is called messenger RNA (mRNA)
52. RNA Structure
Transcription of a DNA molecule results in a mRNA
molecule that is single-stranded.
RNA molecules do not have a regular structure like DNA.
The structures of RNA molecules are complex and unique.
RNA molecules can base pair with complementary DNA
or RNA sequences.
G pairs with C, A pairs with U, and G pairs with U.
The nucleus contains the cell’s DNA, which makes up the genome. The nucleus is surrounded by a nuclear envelope, two membrane bilayers Molecules come into and out of the nucleus through nuclear pores The inside of the nucleus is called the nucleoplasm. Chromatin is the name given to DNA complexed with proteins (histones) The nucleolus is a region where the DNA is concentrated for replication
The nucleus contains the cell’s DNA, which makes up the genome. The nucleus is surrounded by a nuclear envelope, two membrane bilayers Molecules come into and out of the nucleus through nuclear pores The inside of the nucleus is called the nucleoplasm. Chromatin is the name given to DNA complexed with proteins (histones) The nucleolus is a region where the DNA is concentrated for replication