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VII. DNA and Genome Structure
VII. DNA and Genome Structure
A. Search for the Genetic Information
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
a. Miescher – 1868 – isolated nuclein from
the nucleus of cells. An acidic, nitrogen rich material.
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
a. Miescher – 1868 – isolated nuclein from
the nucleus of cells. An acidic, nitrogen rich material.
b. Levene - 1910 – Chromosomes consist of
DNA and proteins. DNA was very simple (4 nucleotides)
whereas proteins were very complex (21 amino acids).
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
a. Miescher – 1868 – isolated nuclein from
the nucleus of cells. An acidic, nitrogen rich material.
b. Levene - 1910 – Chromosomes consist of
DNA and proteins. DNA was very simple (4 nucleotides)
whereas proteins were very complex (21 amino acids).
Levene found that these nucleotides were in
approximately an even ratio, and he hypothesized a
very simple “tetranucleotide” structure that was similar
over it’s length.
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
a. Miescher – 1868 – isolated nuclein from
the nucleus of cells. An acidic, nitrogen rich material.
b. Levene - 1910 – Chromosomes consist of
DNA and proteins. DNA was very simple (4 nucleotides)
whereas proteins were very complex (21 amino acids).
Levene found that these nucleotides were in
approximately an even ratio, and he hypothesized a
very simple “tetranucleotide” structure that was similar
over it’s length.
Given that the genetic system must encode the
diversity of life, it seemed likely that the more complex
molecule (proteins) was responsible.
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
a. Miescher – 1868 – isolated nuclein from
the nucleus of cells. An acidic, nitrogen rich material.
b. Levene - 1910 – Chromosomes consist of
DNA and proteins. DNA was very simple (4 nucleotides)
whereas proteins were very complex (21 amino acids).
Levene found that these nucleotides were in
approximately an even ratio, and he hypothesized a
very simple “tetranucleotide” structure that was similar
over it’s length.
Given that the genetic system must encode the
diversity of life, it seemed likely that the more complex
molecule (proteins) was responsible.
c. Chargaff – 1940’s – [A] = [T], [C] = [G];
disproving Levene’s model.
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
2. Major Experiments
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
2. Major Experiments
a. Griffiths – 1927
Streptococcus pneumoniae
causes pneumonia, meningitis, sepsis
Virulent strain has a polysaccharide
capsule that protects the cell from being
engulfed by white blood cells… and it
makes them appear smooth (IIIS).
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
2. Major Experiments
a. Griffiths – 1927
Streptococcus pneumoniae
causes pneumonia, meningitis, sepsis
Non-virulent strain has no capsule and are
killed by the immune system; they are
‘rough’ (IIR).
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
2. Major Experiments
a. Griffiths – 1927
Streptococcus pneumoniae
causes pneumonia, meningitis, sepsis
If virulent IIIS are killed by heat, they can
be injected without causing disease.
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
2. Major Experiments
a. Griffiths – 1927
Streptococcus pneumoniae
causes pneumonia, meningitis, sepsis
If virulent IIIS are killed by heat, they can
be injected without causing disease.
Griffith found that a combination of LIVE
IIR and DEAD IIIS, both non-virulent
independently, would kill the mouse.
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
2. Major Experiments
a. Griffiths – 1927
Streptococcus pneumoniae
causes pneumonia, meningitis, sepsis
If virulent IIIS are killed by heat, they can
be injected without causing disease.
Griffith found that a combination of LIVE
IIR and DEAD IIIS, both non-virulent
independently, would kill the mouse.
Concluded that the IIR received a
HERITABLE ‘transforming factor’ from
dead IIIS cells, and turned into live IIIS
cells.
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
2. Major Experiments
a. Griffiths – 1927
Streptococcus pneumoniae
causes pneumonia, meningitis, sepsis
Thought it was a chemical that induced
capsule formation.
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
2. Major Experiments
a. Griffiths – 1927
b. Dawson – 1931
Transformation in vitro (test
tube)
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
2. Major Experiments
a. Griffiths – 1927
b. Dawson – 1931
Transformation in vitro (test
tube)
c. Alloway – 1933
Transformation with an extract
from hk-IIIS – don’t even need the intact
cells to cause a HERITABLE change in the
live IIRIIIS
What causes this heritable change: DNA,
RNA, or protein?
2. Major Experiments
d. Avery, McCarty, and MacLeod - 1944
1) Took hk-IIIS extract and
added live IIR – got
transformation (control).
2. Major Experiments
d. Avery, McCarty, and MacLeod - 1944
1) Took hk-IIIS extract and
added live IIR – got
transformation (control).
2) Took hk-IIIS and added
proteases that destroy
proteins – got
transformation;
Transforming factor is
NOT a PROTEIN
2. Major Experiments
d. Avery, McCarty, and MacLeod - 1944
1) Took hk-IIIS extract and
added live IIR – got
transformation (control).
2) Took hk-IIIS and added
proteases that destroy
proteins – got
transformation;
Transforming factor is
NOT a PROTEIN
3) Took this solution, added
RNAases – got
transformation;
Transforming factor is
NOT an RNA
2. Major Experiments
d. Avery, McCarty, and MacLeod - 1944
1) Took hk-IIIS extract and
added live IIR – got
transformation (control).
2) Took hk-IIIS and added
proteases that destroy
proteins – got
transformation;
Transforming factor is
NOT a PROTEIN
3) Took this solution, added
RNAases – got
transformation;
Transforming factor is
NOT an RNA
4) Added DNAases – NO
TRANSFORMATION;
transforming factor is
DNA.
2. Major Experiments
d. Hershey and Chase - 1952
1) Viruses replicate within a
bacterium… requiring the
replication of the genetic
information.
2. Major Experiments
d. Hershey and Chase - 1952
1) Viruses replicate within a
bacterium… requiring the
replication of the genetic
information.
2) Viruses are about 50%
DNA and 50% protein.
Which goes inside the
cell to cause change?
2. Major Experiments
d. Hershey and Chase - 1952
1) Viruses replicate within a
bacterium… requiring the
replication of the genetic
information.
2) Viruses are about 50%
DNA and 50% protein.
Which goes inside the
cell?
3) Labelled proteins with
radioactive sulfur and
DNA with radioactive
phosphorus by growing
virus on labelled bacteria
for one generation.
2. Major Experiments
d. Hershey and Chase - 1952
4) Then, they exposed
normal bacteria to these
differentially labelled
viruses.
2. Major Experiments
d. Hershey and Chase - 1952
4) Then, they exposed
normal bacteria to these
differentially labelled
viruses.
5) Then they shook the
solutions, separating the
viral component from
the bacterial component.
2. Major Experiments
d. Hershey and Chase - 1952
4) Then, they exposed
normal bacteria to these
differentially labelled
viruses.
5) Then they shook the
solutions, separating the
viral component from
the bacterial component.
6) Both replicates
confirmed that only DNA,
and not protein, entered
the cell and must be
responsible for
orchestrating viral
reproduction. DNA is
the genetic information.
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
2. Major Experiments
3. Other Evidence
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
2. Major Experiments
3. Other Evidence
a. Mutagenesis
The wavelengths of radiation
that cause damage to the
genetic information are the
wavelengths absorbed by
DNA, not proteins.
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
2. Major Experiments
3. Other Evidence
a. Mutagenesis
b. Recombinant DNA Technology
1986 – gene for luciferase (from fireflies) was
transferred to plant embryos. When they
grew, and then were injected with luciferin
(the enzymes substrate), the action of the
enzyme (oxidation of luciferin) releases light.
VII. DNA and Genome Structure
A. Search for the Genetic Information
1. Early Work
2. Major Experiments
3. Other Evidence
a. Mutagenesis
b. Recombinant DNA Technology
c. RNA is the genetic information in
some viruses
RNA injected by virus can act directly (TMV),
or can be copied into DNA (retroviruses) and
inserted into the hosts genome and inherited
during host cell replication (HIV).
VII. DNA and Genome Structure
A. Search for the Genetic Information
B. Determining DNA Structure
VII. DNA and Genome Structure
A. Search for the Genetic Information
B. Determining DNA Structure
1. Background Work:
- Chargaff’s ratios
VII. DNA and Genome Structure
A. Search for the Genetic Information
B. Determining DNA Structure
1. Background Work:
- Chargaff’s ratios
- Astbury’s 3.4A periodicity
VII. DNA and Genome Structure
A. Search for the Genetic Information
B. Determining DNA Structure
1. Background Work:
2. Race for the Prize:
a. Linus Pauling (CalTech) – Nobelist
for describing helical structure of proteins,
turned his attention to DNA.
VII. DNA and Genome Structure
A. Search for the Genetic Information
B. Determining DNA Structure
1. Background Work:
2. Race for the Prize:
a. Linus Pauling (CalTech) – Nobelist
for describing helical structure of proteins,
turned his attention to DNA. He used X-Ray
crystallography, and with impure samples of
DNA, suggested DNA was a triple-helix…
VII. DNA and Genome Structure
A. Search for the Genetic Information
B. Determining DNA Structure
1. Background Work:
2. Race for the Prize:
a. Linus Pauling
b. Maurice Wilkins and Rosalind Franklin
- The King College Lab, Univ. of London.
- They had a more purified sample of DNA, but
lab tensions made their supervisor assign Wilkins the ‘B’
form and Franklin the ‘A’ form. Wilkins concluded that
the B form was helical; Franklin did not agree.
VII. DNA and Genome Structure
A. Search for the Genetic Information
B. Determining DNA Structure
1. Background Work:
2. Race for the Prize:
a. Linus Pauling
b. Maurice Wilkins and Rosalind Franklin
- However, her subsequent work and beautiful
x-rays ultimately convinced her of a double-helical
structure… submitted to journals in March 1953 but
without describing a specific model.
Critical contributions were confirming Astbury’s 3.4A
periodicity, and finding a larger periodicity at 34.0A.
VII. DNA and Genome Structure
A. Search for the Genetic Information
B. Determining DNA Structure
1. Background Work:
2. Race for the Prize:
a. Linus Pauling
b. Maurice Wilkins and Rosalind Franklin
c. Francis Crick and James Watson
- Cavendish Lab, Cambridge University.
VII. DNA and Genome Structure
A. Search for the Genetic Information
B. Determining DNA Structure
1. Background Work:
2. Race for the Prize:
a. Linus Pauling
b. Maurice Wilkins and Rosalind Franklin
c. Francis Crick and James Watson
- Cavendish Lab, Cambridge University.
- Crick was the crystallographer and a modeller.
- Were working on helical structures with the
‘backbone’ on the inside. On seeing Franklin’s picture 51
in January 1953, they changed direction and ultimately
produced a model of DNA that explained Franklin’s
regularities and Chargaff’s Ratios.
VII. DNA and Genome Structure
A. Search for the Genetic Information
B. Determining DNA Structure
1. Background Work:
2. Race for the Prize:
a. Linus Pauling
b. Maurice Wilkins and Rosalind Franklin
c. Francis Crick and James Watson
- Cavendish Lab, Cambridge University.
- Crick was the crystallographer and a modeller.
- Were working on helical structures with the
‘backbone’ on the inside. On seeing Franklin’s picture 51
in January 1953, they changed direction and ultimately
produced a model of DNA that explained Franklin’s
regularities and Chargaff’s Ratios.
d. 1958 – Franklin dies of ovarian cancer;
probably related to her x-ray work.
VII. DNA and Genome Structure
A. Search for the Genetic Information
B. Determining DNA Structure
1. Background Work:
2. Race for the Prize:
a. Linus Pauling
b. Maurice Wilkins and Rosalind Franklin
c. Francis Crick and James Watson
- Cavendish Lab, Cambridge University.
- Crick was the crystallographer and a modeller.
- Were working on helical structures with the
‘backbone’ on the inside. On seeing Franklin’s picture 51
in January 1953, they changed direction and ultimately
produced a model of DNA that explained Franklin’s
regularities and Chargaff’s Ratios.
d. 1958 – Franklin dies of ovarian cancer;
probably related to her x-ray work.
e. 1962 – Nobel Prizes for Crick, Watson, and
Wilkins
VII. DNA and Genome Structure
A. Search for the Genetic Information
B. Determining DNA Structure
1. Background Work:
2. Race for the Prize:
3. The Structure of DNA
3. The Structure of DNA (and RNA)
- basic unit is a “nucleotide”, that has three
parts:
i. pentose sugar:
3. The Structure of DNA (and RNA)
- basic unit is a “nucleotide”, that has three
parts:
i. pentose sugar:
ii. Nitrogenous base:
3. The Structure of DNA (and RNA)
- basic unit is a “nucleotide”, that has three
parts:
i. pentose sugar:
ii. Nitrogenous base:
3. The Structure of DNA (and RNA)
- basic unit is a “nucleotide”, that has three
parts:
i. pentose sugar:
ii. Nitrogenous base:
iii. Phosphate group:
3. The Structure of DNA (and RNA)
- basic unit is a “nucleotide”, that has three parts:
i. pentose sugar:
ii. Nitrogenous base:
iii. Phosphate group:
- nucleotide diphosphates and triphosphates can also occur, and two of these
(ATP and GTP) are energetically important, too.
3. The Structure of DNA (and RNA)
- basic unit is a “nucleotide”, that has three parts:
- nucleotides are linked by phosphodiester bonds to form a helix:
3. The Structure of DNA (and RNA)
- basic unit is a “nucleotide”, that has three parts:
- nucleotides are linked by phosphodiester bonds to form a helix:
- typically, synthesis occurs by adding new bases to the 3’ hydroxyl
group…
3. The Structure of DNA (and RNA)
- basic unit is a “nucleotide”, that has three parts:
- nucleotides are linked by phosphodiester bonds to form a helix:
- typically, synthesis occurs by adding new bases to the 3’ hydroxyl
group…
- the helix has a 5’ to 3’ “polarity”
3’
3. The Structure of DNA (and RNA)
- basic unit is a “nucleotide”, that has three parts:
- nucleotides are linked by phosphodiester bonds to form a helix:
- DNA double-helices have helices that are ‘complementary’ (base pair pairing)
A purine (A or G) always binds with a
pyrimidine (T or C)
In fact, A with T (2 h-bonds)
And G with C (3 h-bonds)
3. The Structure of DNA (and RNA)
- basic unit is a “nucleotide”, that has three parts:
- nucleotides are linked by phosphodiester bonds to form a helix:
- DNA double-helices have helices that are ‘complementary’ (base pair pairing)
and ‘antiparallel’ (polarity is in opposite directions).
3. The Structure of DNA (and RNA)
- basic unit is a “nucleotide”, that has three parts:
- nucleotides are linked by phosphodiester bonds to form a helix:
- DNA double-helices have helices that are ‘complementary’ (base pair pairing)
and ‘antiparallel’ (polarity is in opposite directions).
VII. DNA and Genome Structure
A. Search for the Genetic Information
B. Determining DNA Structure
1. Background Work:
2. Race for the Prize:
3. The Structure of DNA
4. Function of DNA and RNA overview
4. Function of DNA and RNA overview
i. DNA is a template for RNA production (transcription)
GENE
DNA
RNA
4. Function of DNA and RNA overview
i. DNA is a template for RNA production (transcription)
ii. RNA may be functional, or may itself be a template for protein
formation (translation). DNA coding for RNA coding for proteins is called the “central
dogma” of genetics.
PROTEIN GENE
RNA GENE
DNA
RNA
M-RNA: Protein-gene transcript
Protein
Functional RNA
(r-RNA, t-RNA)
4. Function of DNA and RNA overview
i. DNA is a template for RNA production (transcription)
ii. RNA may be functional, or may itself be a template for protein
formation (translation). DNA coding for RNA coding for proteins is called the “central
dogma” of genetics.
iii. Introns are sequences in a gene (and the RNA transcript) that
are ‘cut out’ of the RNA and are not translated into protein sequence. Exons are the
coding sequences.
PROTEIN GENE
RNA GENE
DNA
exon
Initial RNA
Transcript
splicing
m-RNA
Protein
Post-translational
processing
(same process)
Functional RNA
(r-RNA, t-RNA)