Download DNA replication

DNA
Content
1. Introduction
2. The DNA is the material of inheritance
3. Replication
4. Repair
5. Genetic code
6. Mutation
DNA determines who we are
DNA determines who we are
DNA and behavior
DNA: our robotic self
Brain: our free self
….or?
The age of DNA
Medicine and Biotechnology
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)
The DNA
August Weismann
is the material of inheritance
Localization:
- In the nucleus
- Weismann (1890): materials in the nucleus controls the cell function
- In the chromosomes
Chemical nature
The big question: DNA
or protein?
The DNA
is the material of inheritance
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
Mutagenezis
max
Absorption spectrum (protein)
max
Mutation efficiency
Absorption spectrum (DNS)
Wavelength (nm)
The DNA
Frederick Griffith
is the material of inheritance
Griffith: genetic transformation of nonvirulent pneumococci
The DNA
Oswald T. Avery
is the material of inheritance
Avery: genetic transformation by DNA
The DNA
Martha Chase Alfred Hershey
is the material of inheritance
The Herschey and Chase experiment
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.
The RNA
can also be the genetic material
The Tobacco mosaic virus (TMV) experiment:
The structure of DNA
The structure of DNA
Erwin Chargaff
A = T; G = C
Contradicts to Leven’s tetranucleotide hypothesis (A=T=C=G)
Chargaff’s rule
The structure of DNA
Alexander Todd
Todd: phosphodiester bond – nucleotides form polymers
The structure of DNA
Alexander Todd
Todd: phosphodiester bond – nucleotides form polymers
deoxyribose
ribose
base
ester bond
3’
5’
3’
5’
phosphate
deoxyribose
The structure of DNA
Alexander Todd
Todd: phosphodiester bond – nucleotides form polymers
Bases
Sugar-phosphate backbone
The structure of DNA
Rosalind Franklin
Franklin: X-Ray crystallography helped reveal the structure of DNA
The structure of DNA
James Watson Francis Crick
DNA is a double helix
Model building
The structure of DNA
3′ end
James Watson Francis Crick
TA pairs have two
hydrogen bonds.
CG pairs have three
hydrogen bonds.
Base pairing in DNA is complementary
5′ end
3′ end
The structure of DNA
thymine (T)
adenine (A)
cytosine (C)
guanine (G)
H
H
N
H
N
T
H
N
N
A
X
H
H
N
C
H
N
deoxyribose
deoxyribose
N
H
N
N
H
O
O
N
O
H
N
H
N
H
H
H
deoxyribose
G
N
H
deoxyribose
N
N
H
O
H
Characteristics of the genetic material
and the DNA structure
James Watson Francis Crick
(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
Nobel Prize in Physiology or Medicine (1962)
J.D.Watson
F.H.Crick
M.H.F. Wilkins
What about R. Franklin?
DNA replication
Arthur Kornberg
Kornberg: in vitro DNA replication
3 subtances are needed :
(1) DNA polymerase (isolated by Kornberg)
(2) dNTPs: dATP, dCTP, dGTP, dTTP
(3) DNA template
DNA replication
Matthew Meselson Frank Stahl
The three possible models for DNA replication
Semiconservative
Conservative
Dispersive
DNA replication
Meselson and Stahl’s experiment: semiconservative DNA replication
N15
Heavy N
N14
Light N
DNA replication
The direction of new strand synthesis is 5’  3’
DNA replication
RNA primer is needed for chain initiation
DNA replication
Okazaki fragments
leading strand
parent strand
leading strand
lagging strand
leading strand
lagging strand
DNA replication
Repair
Genetic code
The genetic code is composed of triplets
Code: in DNA
Codon: in mRNA
Anticodon: in tRNA
-------Start codon: AUG
Stop codons: UAA, UAG, UGA
(1)
(2)
(3)
(4)
The genetic code is composed of triplets: one triplet encode one amino acid
The genetic code is redundant: many amino acids are encoded by more than one triplets
The genetic code is „comma-free”: the triplets are not isolated units
The genetic code is universal: every living being is descended from a single common ancestor
Few exception: mitochondria, chloroplasts, protistas - in 1-1 codons
Genetic code
M.W. Nirenberg
Two methods
R.W. Holley
1968
for their interpretation of the genetic code and its function in protein synthesis"
H.G. Khorana
Mutation
alterations of the nucleotide sequence
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
---------Spontaneous mutations
- occur with no outside influence. Several mechanisms:
Induced mutation
- due to an outside agent, a mutagen
Silent mutation
- no change in amino acid sequence
Missense mutation
- base substitution results in amino acid substitution
Missense mutation
- Sickle allele for human β-globin is a missense mutation: glutamic acid  valine at 6th position
- Individuals that are homozygous have sickle-cell disease
Nonsense mutation
- base substitution results in a stop codon
Frame-shift mutation
- single bases inserted or deleted—usually leads to nonfunctional proteins
Chromosomal mutations
Deletions
Translocations
Insertions
Mutation
Mutation provides the raw material for evolution in the form of genetic diversity.
Mutations can harm the organism, or be neutral.
Occasionally, a mutation can improve an organism’s adaptation to its environment,
or become favorable as conditions change.