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1. Introduction
2. The DNA is the material of inheritance
3. Replication
4.Repair
5.Genetic code
6. Mutation
The function of DNA
1. Transmission of genetic information (inheritance):
- mediated by germ cells
2. Control of cell function: in each cell(in embryogenesis and adult body)
1
The DNA is the material of inheritanceAugust Weismann
Localization:
The big question: DNA or protein?
Chemical nature
- In the nucleus- Weismann (1890): materials in the nucleus controls the cell function
- In the chromosomes
2
Stadler and Über:The absorption spectrum of DNA and the effective spectrum of mutagenesis coincide (260 nm)
- the maximal absorption of proteins is at 280 nm
The DNA is the material of inheritance
Wavelength (nm)
Mu
tati
on
eff
icie
ncy
Absorption spectrum (DNS)
Absorption spectrum (protein)
ma
x
ma
x
Mutagenezis
3
The DNA is the material of inheritance
Griffith: genetic transformation of nonvirulent pneumococci
Frederick Griffith
4
The DNA is the material of inheritance
The Herschey and Chase experiment
Martha Chase Alfred Hershey
Bacteriophage T2
attaches to the
surface of a bacterium
and injects its DNA.
Viral genes take over
the host’s machinery
and synthesizes new
viruses.
The bacterium bursts,
releasing about 200 viruses.
6
Chargaff’s rule
A = T; G = C Contradicts to Leven’s tetranucleotide hypothesis (A=T=C=G)
Erwin Chargaff
The structure of DNA9
Alexander Todd
deoxyribose ribose
ester bond
phosphate
deoxyribose
base
5’
5’
3’
3’
Todd: phosphodiester bond – nucleotides form polymers
The structure of DNA10
Alexander Todd
Todd: phosphodiester bond – nucleotides form polymers
The structure of DNA
Sugar-phosphate backbone
Bases
10
The structure of DNARosalind Franklin
Franklin: X-Ray crystallography helped reveal the structure of DNA
11
Base pairing in DNA is complementary
5′ end
3′ end
TA pairs have two
hydrogen bonds.
CG pairs have three
hydrogen bonds.
3′ end
The structure of DNAJames Watson Francis Crick
12
X
H
N
N
NN
H
H
NH
A
O
O
H
HN
N
H
H
H
T
O
H
N
N
NN
H
G
NH H
O
HN
N
C
N
H H
H
deoxyribose
deoxyribose
deoxyribose
deoxyribose
The structure of DNA
thymine (T) adenine (A) cytosine (C) guanine (G)
13
James Watson Francis Crick
Characteristics of the genetic material
and the DNA structure
(1) The genetic material stores an organism’s genetic information
- the combination of the bases can produce it
(2) The genetic material is capable for mutation
- changing of base pair sequences can produce it
(3) The genetic material is precisely replicated
- it is accomplished by the complementary base pairing
(one DNA strand contains the information of the other strand
14
Nobel Prize in Physiology or Medicine (1962)
J.D.Watson F.H.Crick M.H.F. Wilkins
What about R. Franklin?
15
Kornberg: in vitro DNA replication
Arthur Kornberg
3 subtances are needed :
(1) DNA polymerase (isolated by Kornberg)
(2) dNTPs: dATP, dCTP, dGTP, dTTP
(3) DNA template
DNA replication
16
DNA replication
The three possible models for DNA replication
Conservative
Semiconservative
Dispersive
Matthew Meselson Frank Stahl
17
DNA replicationMeselson and Stahl’s experiment: semiconservative DNA replication
N15
N14
Heavy N
Light N
17
DNA replication
lagging strand
leading strand
leading strand
parent strand
leading strand
lagging strand
Okazaki fragments
20
Genetic code
(1) The genetic code is composed of triplets: one triplet encode one amino acid
(2) The genetic code is redundant: many amino acids are encoded by more than one triplets
(3) The genetic code is „comma-free”: the triplets are not isolated units
(4) The genetic code is universal: every living being is descended from a single common ancestor
The genetic code is composed of triplets
Start codon: AUG
Stop codons: UAA, UAG, UGA
Code: in DNA
Codon: in mRNA
Anticodon: in tRNA
--------
Few exception: mitochondria, chloroplasts, protistas - in 1-1 codons
23
Mutation
Somatic mutations occur in somatic (body) cells. Mutation is passed to daughter cells,
but not to sexually produced offspring
Germ line mutations occur in cells that produce gametes. Can be passed to next generation
Point mutations: change in a single base pair—loss, gain, or substitution of a base (can
result from replication and proofreading errors, or from environmental mutagens)
Chromosomal mutations: change in segments of DNA—loss, duplication, or rearrangement
alterations of the nucleotide sequence
----------
----------
Spontaneous mutations
- occur with no outside influence. Several mechanisms:
Induced mutation
- due to an outside agent, a mutagen
24
- Sickle allele for human β-globin is a missense mutation: glutamic acid valine at 6th position
- Individuals that are homozygous have sickle-cell disease
Missense mutation27
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