Genetics
Chapter 9
Paragraph 1- identification of DNA as the genetic material
• Genetic material of all living organisms is composed of DNA (deoxyribonucleic acid )
- The DNA stores all the information required to synthesize all cellular components
- The ability of DNA to store genetic information is based on its sequence and
structure
Friedrich Miescher discovered the DNA> isolated an organic acid from the nuclei of white
blood cells that was rich in Phosphorus, Nitrogen, but no sulfur.
Identification of DNA as genetic material must meet several criteria:
1. Information (to make an entire organism )
2. Transmission (parents > Offspring )
3. Replication (increase population)
4. Variation (must be capable of changing )
To account for the known phenotypic variation in each species
Allow adaptation and evolution
Some mutations start to introduce
3 key experiments: could be used to identify the genetic material
• Griffith (bacteria): transforming principle.
The bacterium comes in 2 strains: type S= smooth and type R= rough
- Type S: secrete a polysaccharide capsule > mouse died
Protects bacterium from the immune system of animals
Produce smooth colonies on solid media
When heat killed > mouse survived
- Type R: unable to secrete capsule > mouse survived.
Produce colonies with a rough appearance.
- Concluded that something form the dead S bacteria was transforming type R
bacteria into type S
Injects mouse with live R + heat killed S type > mouse died.
Something from the dead type S bacteria was transforming type R bacteria into type S
The substance that allowed this to happen was termed the transforming principle. Griffith
didn’t know what type of substance it was.
• Avery, Macleod and McCarthy (bacteria) : knew it was DNA
- They tried several extracts: DNA, proteins and RNA. Only DNA converted type R
bacteria into type S
- They also treated the DNA extracts with DNase, RNase and protease. When treated
with RNase and protease they still converted type R into type S. when treated with
DNase, it didn’t convert anymore.
RNase and protease were added to DNA extract to rule out the possibility that small amount
of contamination RNA or protein were responsible for converting the type R bacteria into
type S.
, • Hershey and Chase (virus): provided evidence that DNA is the genetic material of T2
bacteriophage, which is a type of virus that infects bacteria.
- The phage is very simple because it is made of only DNA and proteins.
- After infection of bacterium, the cell bursts and releases many viruses
- It injects the genetic material into bacteria without entering in the cell.
Researchers used radioisotopes to distinguish DNA from proteins: 32P labels DNA and 35S
labels proteins.
The residual phage particles were washed away and most of the 32P had entered the
bacterial cells (DNA), most of the 35S remains outside of the cells (proteins.)
All living organisms use DNA as genetic material, however some viruses can use RNA
instead.
During infection, the RNA code is first transcribed back to DNA, then to RNA to protein.
Paragraph 2- overview of DNA and RNA structure
• Later research showed that DNA and RNA release hydrogen ions in water and have a
net negative charge at neutral PH and therefore are acids. > nucleic acids.
DNA and RNA are large polymer macromolecules with several levels of complexity:
1. Nucleotides form the repeating unit of nucleic acids
2. nucleotides are linked to form a linear strand
3. strands interact to from a double helix.
4. The 3D structure of DNA results from folding and bending.
Paragraph 3- nucleotide structure
• The nucleotide is the repeating structural unit of DNA and RNA
It has 3 components:
1. phosphate group ( always negatively charged) > always attached to 5’
2. pentose sugar > carbons atoms are numbers in a clockwise manner.
- ribose in RNA and deoxyribose in DNA, deoxyribose contains less oxygen in the molecule.
3. nitrogen containing base > always attached to 1’
• 5 bases exist:
- DNA: A, G, T, C
- RNA: A, G, U. C
Purines ( double ring structure, bases are given numbers 1- 9 ): A and G
Pyrimidines ( single ring structure, bases are given number 1 – 6 ): C, T and U
- Nucleoside= base + sugar
Adenine + ribose= adenosine
Adenine + deoxyribose= deoxyadenosine
- Nucleotide= phosphate + sugar + base.
Adenine + ribose + 1 phosphate= adenosine monophosphate (AMP)
Adenine + deoxyribose + 2 phosphates = deoxyadenosine diphosphate (dADP)
! attachment to cytosine, thymine and uracil > cytidine, thymidine and uridine.
- Proteins isn’t genetical material, because it cannot have reproduction.
The difference between deoxyribose and ribose is that the deoxyribose has 1 less H atom.
3’ and 5’ are important for polymerization.
,Paragraph 4- structure of a DNA strand
• A phosphate group connects 2 sugars molecules via 2 ester bonds > phosphodiester
linkage.
- Covalent bond called diester bond: 2 OH groups in phosphoric acid react wit hydroxyl
groups on other molecules to form 2 ester bonds.
The backbone consists of phosphates and sugar molecules. The backbone is negatively
charged due to the negative charge on each phosphate.
• The strands contain a specific sequence of bases. The nucleotides within a strand are
covalently attached to each other via phosphodiester linkages.
It goes 5’ > 3’. This gives directionality.
Paragraph 5- discovery of the double helix.
• Discovery of the double helix was guided by work done on protein structure,
3 important scientists:
• Pauling
- Regions of protein can fold into a secondary structure called an alpha helix.
- He built ball- and stick models
• Rosalin Franklin
- The diffraction pattern she obtained suggested several structural features of DNA.:
helical, more than one strand and 10 base pairs per complete turn.
- The X rays diffracted by DNA.
- The diffraction pattern indicated that the helix contains about 10 base pairs per
complete turn.
- Strong meridional arcs come from the horizontal bases. The distance between them
and the center tells us about the interbase distance.
- Spacing between layer lines tells us about the helical pitch.
- Angle tells us about the radius.
• Chargaff
- Analyzed the base composition of DNA isolated from many different species.
- The chromosomes were extracted from cells and then treated with protease to
separate the DNA from the chromosomal proteins. The DNA was then treated with a
strong acid which cleaved the bonds between the sugar and bases, thereby releasing
the individual bases from the DNA strands.
- This mixture of bases was then subjected to paper chromatography to separate the
four types.
- He saw that the bases weren’t equally. But some bases did have the same
distribution. This gave information how the bases were organized.
- Its not super exact, because the measuring process was not very precise.
- A = T and C = G
• Watson and crick
- Solved the structure of DNA
- Didn't use any experiment but were great thinkers.
- Sugar phosphate backbone on the outside
- Bases projecting towards each other
- One strand can work as the template for the other.
, Paragraph 6- structure of the DNA double helix.
• Hydrogen bonding between bases in the base pairs and base stacking hold the DNA
strands together.
If you count the bases along one strand, once you reach 10, you have gone 360 around the
acis of the helix. The linear distance along a strand through such a complete turn is 3,4 nm.
Each base pair traverses 0,34 nm.
• If the 2 sequences are complementary, you write it to the 3’ – 5’ kind. This is called
as antiparallel arrangement.
- Base stacking= the base pairs are oriented so that the flat bodies of the bases are
facing each other.
Base stacking is a structural feature that stabilizes the double helix by excluding water
molecules, which are polar.
- A bonded to T by 2 hydrogen bonds
- C bonded to G by 3 hydrogen bonds.
• The direction of the DNA double helix spirals in a direction that is called right-
handed.
• Grooves are to describe the indentations where atoms of the bases are in contact
with the water in the surrounding cellular fluid. Certain proteins can bind within
these grooves > thus they can interact with a particular sequence of base. This is
important because it says something about the accessibility of enzymes.
- Minor groove and major groove
DNA double helix can form different types of structures
• B DNA
- Predominant form
- Right-handed helix
- Number of base pairs per 260 turn are 10
- Centrally located, hydrogen bonds between base pairs are oriented relatively
perpendicular to the central axis.
- DNA structure of chromosomes ends ( telomeres ) is an exception ( not double
stranded B DNA ).
• Z DNA
- Left-handed
- Appears to zigzag slightly
- 12 base pairs per 360 turn.
- Vases are substantially tilted relative to the central axis.
The ability of B DNA to adopt a Z DNA conformation depends on various factors.
At high ionic strength, formation of a Z DNA conformation is favored by a sequence of bases
that alternates between purines and pyrimidines.
At lower ionic strength, the methylation of cytosine bases favors Z DNA formatiom.
Cytosine methylation occurs when a cellular enzyme attaches a methyl group to a cytosine
base.
- Negative supercoiling favors the Z DNA
The biological significance of Z DNA is that it has a possible role in the process of
transcription. In addition, other research has suggested that Z DNA may play a role in
determining chromosome structure by affecting the level of compaction.
Chapter 9
Paragraph 1- identification of DNA as the genetic material
• Genetic material of all living organisms is composed of DNA (deoxyribonucleic acid )
- The DNA stores all the information required to synthesize all cellular components
- The ability of DNA to store genetic information is based on its sequence and
structure
Friedrich Miescher discovered the DNA> isolated an organic acid from the nuclei of white
blood cells that was rich in Phosphorus, Nitrogen, but no sulfur.
Identification of DNA as genetic material must meet several criteria:
1. Information (to make an entire organism )
2. Transmission (parents > Offspring )
3. Replication (increase population)
4. Variation (must be capable of changing )
To account for the known phenotypic variation in each species
Allow adaptation and evolution
Some mutations start to introduce
3 key experiments: could be used to identify the genetic material
• Griffith (bacteria): transforming principle.
The bacterium comes in 2 strains: type S= smooth and type R= rough
- Type S: secrete a polysaccharide capsule > mouse died
Protects bacterium from the immune system of animals
Produce smooth colonies on solid media
When heat killed > mouse survived
- Type R: unable to secrete capsule > mouse survived.
Produce colonies with a rough appearance.
- Concluded that something form the dead S bacteria was transforming type R
bacteria into type S
Injects mouse with live R + heat killed S type > mouse died.
Something from the dead type S bacteria was transforming type R bacteria into type S
The substance that allowed this to happen was termed the transforming principle. Griffith
didn’t know what type of substance it was.
• Avery, Macleod and McCarthy (bacteria) : knew it was DNA
- They tried several extracts: DNA, proteins and RNA. Only DNA converted type R
bacteria into type S
- They also treated the DNA extracts with DNase, RNase and protease. When treated
with RNase and protease they still converted type R into type S. when treated with
DNase, it didn’t convert anymore.
RNase and protease were added to DNA extract to rule out the possibility that small amount
of contamination RNA or protein were responsible for converting the type R bacteria into
type S.
, • Hershey and Chase (virus): provided evidence that DNA is the genetic material of T2
bacteriophage, which is a type of virus that infects bacteria.
- The phage is very simple because it is made of only DNA and proteins.
- After infection of bacterium, the cell bursts and releases many viruses
- It injects the genetic material into bacteria without entering in the cell.
Researchers used radioisotopes to distinguish DNA from proteins: 32P labels DNA and 35S
labels proteins.
The residual phage particles were washed away and most of the 32P had entered the
bacterial cells (DNA), most of the 35S remains outside of the cells (proteins.)
All living organisms use DNA as genetic material, however some viruses can use RNA
instead.
During infection, the RNA code is first transcribed back to DNA, then to RNA to protein.
Paragraph 2- overview of DNA and RNA structure
• Later research showed that DNA and RNA release hydrogen ions in water and have a
net negative charge at neutral PH and therefore are acids. > nucleic acids.
DNA and RNA are large polymer macromolecules with several levels of complexity:
1. Nucleotides form the repeating unit of nucleic acids
2. nucleotides are linked to form a linear strand
3. strands interact to from a double helix.
4. The 3D structure of DNA results from folding and bending.
Paragraph 3- nucleotide structure
• The nucleotide is the repeating structural unit of DNA and RNA
It has 3 components:
1. phosphate group ( always negatively charged) > always attached to 5’
2. pentose sugar > carbons atoms are numbers in a clockwise manner.
- ribose in RNA and deoxyribose in DNA, deoxyribose contains less oxygen in the molecule.
3. nitrogen containing base > always attached to 1’
• 5 bases exist:
- DNA: A, G, T, C
- RNA: A, G, U. C
Purines ( double ring structure, bases are given numbers 1- 9 ): A and G
Pyrimidines ( single ring structure, bases are given number 1 – 6 ): C, T and U
- Nucleoside= base + sugar
Adenine + ribose= adenosine
Adenine + deoxyribose= deoxyadenosine
- Nucleotide= phosphate + sugar + base.
Adenine + ribose + 1 phosphate= adenosine monophosphate (AMP)
Adenine + deoxyribose + 2 phosphates = deoxyadenosine diphosphate (dADP)
! attachment to cytosine, thymine and uracil > cytidine, thymidine and uridine.
- Proteins isn’t genetical material, because it cannot have reproduction.
The difference between deoxyribose and ribose is that the deoxyribose has 1 less H atom.
3’ and 5’ are important for polymerization.
,Paragraph 4- structure of a DNA strand
• A phosphate group connects 2 sugars molecules via 2 ester bonds > phosphodiester
linkage.
- Covalent bond called diester bond: 2 OH groups in phosphoric acid react wit hydroxyl
groups on other molecules to form 2 ester bonds.
The backbone consists of phosphates and sugar molecules. The backbone is negatively
charged due to the negative charge on each phosphate.
• The strands contain a specific sequence of bases. The nucleotides within a strand are
covalently attached to each other via phosphodiester linkages.
It goes 5’ > 3’. This gives directionality.
Paragraph 5- discovery of the double helix.
• Discovery of the double helix was guided by work done on protein structure,
3 important scientists:
• Pauling
- Regions of protein can fold into a secondary structure called an alpha helix.
- He built ball- and stick models
• Rosalin Franklin
- The diffraction pattern she obtained suggested several structural features of DNA.:
helical, more than one strand and 10 base pairs per complete turn.
- The X rays diffracted by DNA.
- The diffraction pattern indicated that the helix contains about 10 base pairs per
complete turn.
- Strong meridional arcs come from the horizontal bases. The distance between them
and the center tells us about the interbase distance.
- Spacing between layer lines tells us about the helical pitch.
- Angle tells us about the radius.
• Chargaff
- Analyzed the base composition of DNA isolated from many different species.
- The chromosomes were extracted from cells and then treated with protease to
separate the DNA from the chromosomal proteins. The DNA was then treated with a
strong acid which cleaved the bonds between the sugar and bases, thereby releasing
the individual bases from the DNA strands.
- This mixture of bases was then subjected to paper chromatography to separate the
four types.
- He saw that the bases weren’t equally. But some bases did have the same
distribution. This gave information how the bases were organized.
- Its not super exact, because the measuring process was not very precise.
- A = T and C = G
• Watson and crick
- Solved the structure of DNA
- Didn't use any experiment but were great thinkers.
- Sugar phosphate backbone on the outside
- Bases projecting towards each other
- One strand can work as the template for the other.
, Paragraph 6- structure of the DNA double helix.
• Hydrogen bonding between bases in the base pairs and base stacking hold the DNA
strands together.
If you count the bases along one strand, once you reach 10, you have gone 360 around the
acis of the helix. The linear distance along a strand through such a complete turn is 3,4 nm.
Each base pair traverses 0,34 nm.
• If the 2 sequences are complementary, you write it to the 3’ – 5’ kind. This is called
as antiparallel arrangement.
- Base stacking= the base pairs are oriented so that the flat bodies of the bases are
facing each other.
Base stacking is a structural feature that stabilizes the double helix by excluding water
molecules, which are polar.
- A bonded to T by 2 hydrogen bonds
- C bonded to G by 3 hydrogen bonds.
• The direction of the DNA double helix spirals in a direction that is called right-
handed.
• Grooves are to describe the indentations where atoms of the bases are in contact
with the water in the surrounding cellular fluid. Certain proteins can bind within
these grooves > thus they can interact with a particular sequence of base. This is
important because it says something about the accessibility of enzymes.
- Minor groove and major groove
DNA double helix can form different types of structures
• B DNA
- Predominant form
- Right-handed helix
- Number of base pairs per 260 turn are 10
- Centrally located, hydrogen bonds between base pairs are oriented relatively
perpendicular to the central axis.
- DNA structure of chromosomes ends ( telomeres ) is an exception ( not double
stranded B DNA ).
• Z DNA
- Left-handed
- Appears to zigzag slightly
- 12 base pairs per 360 turn.
- Vases are substantially tilted relative to the central axis.
The ability of B DNA to adopt a Z DNA conformation depends on various factors.
At high ionic strength, formation of a Z DNA conformation is favored by a sequence of bases
that alternates between purines and pyrimidines.
At lower ionic strength, the methylation of cytosine bases favors Z DNA formatiom.
Cytosine methylation occurs when a cellular enzyme attaches a methyl group to a cytosine
base.
- Negative supercoiling favors the Z DNA
The biological significance of Z DNA is that it has a possible role in the process of
transcription. In addition, other research has suggested that Z DNA may play a role in
determining chromosome structure by affecting the level of compaction.
