Molecular Biology
Complete Organized Study Notes
.
Includes all major topics, cleaned formatting, and exam questions.
This version is designed for revision and resale-style presentation: clearer
structure, consistent headings, easier scanning.
Made by a student-athlete
1
, Table of Contents
1. History Of Molecular Biology 18. Mutation Accumulation
2. The Chemical Structure Of DNA 19. Mitochondrial DNA And Chloroplastic DNA
3. The Physical Structure Of DNA 20. Transformation – Technique
4. Different DNA Structures 21. DNA Amplification – Technique
5. Proteins That Bind DNA 22. Spectrophotometry – Technique
6. Superstructure Of DNA 23. Genome Packaging
7. RNA Structure 24. Eukaryotic Chromosomes
8. The Central Dogma And The Genetic Code 25. Centromers And Telomers – Crucial
Chromosome Structures
9. Deciphering The Genetic Code
26. DNA Replication
10. The Genetic Code
27. DNA Polymerases
11. The Genome
28. Prokaryotic DNA Polymerase
12. The Genomic Era
29. Eukaryotic DNA Replication
13. Repetitive DNA
30. DNA Repair
14. Exons And Introns
31. Polymerase Chain Reaction – Technique
15. Genes
32. Transcription
16. Southern Blot - Technique
33. Transcription In Eukaryotes
17. Non Coding DNA
2
,1. HISTORY OF MOLECULAR BIOLOGY
Biology at the beginning of the last century included TWO important and SEPARATE areas of research:
- Biochemistry, carried out by physiologists and physicians, which was focused on chemical reactions
in living systems, proteins, catalysis and enzymes. They were concentred on studying very specific
reactions.
Timeline: 1865, GENES are particular factors; 1900, chromosomes are hereditary units;
1910; genes are located in chromosomes
- Genetics, concerning breeders and cultivators which had a practical interest in the improvement of
plant and animals. But they were focused on highly phenotypic aspects.
Timeline: 1869, DNA DISCOVERY; 1900-1910, chemical analysis and biochemical studies
of DNA.
• 1944: It was discovered that DNA IS THE GENETIC MATERIAL
• 1953: It has a helix structure
- Friedrich Miescher (physician) in 1869 identified an unknown substance
inside cells. While he was studying white blood cells, he isolated the nuclei
and found a PHOSPHORUS-RICH, acidic substance that was unlike every
other protein. He called it “nuclei” because it came from the cell nucleus.
-1910s- 1935: Phoebus Levene and Tipson discovered that DNA contains four
smaller units: A, T, C, and G. However, they made the critical mistake of
thinking that DNA was made of repeating A, T, C, G units, always in the same
order TETRANUCLEOTIDE HYPOTESIS.
He proposed a LINEAR structure model.
In the early 1950s, Takahashi was one of the several scientists who attempted to
propose a HELICAL STRUCTURE for DNA. His model was characterized by a
triple helix, with the phosphate group placed inside the helix, and the bases
oriented toward the outside, rather than the inside.
(It was wrong because: Negative phosphate groups repel each other, so putting
them inside the helix made the model chemically unstable. Having bases on the
outside would not allow proper base pairing or information encoding. Triple
helices don’t naturally form under normal cellular conditions.)
But the experiments that actually demonstrated that DNA IS THE GENETIC MATERIAL are:
1. The Bacterial “transformation” experiment, Griffith, 1929
He had two strains of Streptococcus Pneumoniae: a ROUGH colony (R), characterized by the absence of a
protective capsule. It is recognized and destroyed by the immune system. And a SMOOTH colony (S)
which is virulent due to the presence of a polysaccharide envelope \ capsule, which prevents recognition by
part of the immune system.
3
, So, the presence of the polysaccharide capsule determines that one strain is lethal and the other is not. Both
characteristics are inherited, it is something genetically encoded, a “GENE”.
The experiment consisted of inserting a lab mouse with different Pneumococcus strains:
- S strain (virulent) mouse dies
- S strain heated (the heat kills the virulent strain) mouse lives
- R strain (not virulent) mouse lives
- R strain + HEATED S strain (killed) mouse dies and VIABLE S AND R BACTERIA ARE
EXTRACTED FROM THE MOUSE.
This means that there must be something that converts the R strain into a virulent one à A chemical
substance is GENETICALLY TRASFROMING ANOTHER CELL. Griffith called it THE
TRANSFORMING PRINCIPLE, and the transformation could be inherited.
2. The Avery, MacLeod and McCarty experiment, 1944
They also used the two different strains of Pneumococcus, but instead of mixing the whole extract with R,
they MIXED THE S STRAIN WITH ALL DIFFERENT MOLECULES FROM THE R STRAIN:
Polysaccharides, lipids, RNA, proteins and DNA. With the aim to locate the transformative molecule.
- They firstly studied if the transformative activity in S cells was destroyed by heat. They discovered
that the S cell extract, which contained mostly DNA with a little proteins and RNA, was still able,
when inserted in a culture of R cells, to give rise to a few S colonies
- Then, they studied if the transforming activity was destroyed by either protease or RNase. And
discovered that the transforming activity did not occur in the protein or RNA. (S cell extract with
inserted protease or RNase, inserted in R culture, still gives rise to a few S colonies).
- Lastly, by inserting DNase into the S cell extract, and consequently inserting it into a R culture of
cell, it gave ONLY R COLONIES, and therefore the TRANSFORMING ACTIVITY MOST
LIKELY OCCURRED IN THE DNA.
This experiment was not accepted by the scientific community because the genetic information was
considered to be in proteins.
3. The “blender” experiment, Chase and Hershey, 1952
They used a different system. They studied the T4 phage infection of E. coli. T4 phage is a virus that infects
bacterial cells by attacking the host and INJECTING GENETIC MATERIAL into the bacterial cells. They
are composed of a protein coat in the outside shell and DNA inside. The two geneticists wanted to
understand what substance they were injecting. Was it proteins or DNA?
4
Complete Organized Study Notes
.
Includes all major topics, cleaned formatting, and exam questions.
This version is designed for revision and resale-style presentation: clearer
structure, consistent headings, easier scanning.
Made by a student-athlete
1
, Table of Contents
1. History Of Molecular Biology 18. Mutation Accumulation
2. The Chemical Structure Of DNA 19. Mitochondrial DNA And Chloroplastic DNA
3. The Physical Structure Of DNA 20. Transformation – Technique
4. Different DNA Structures 21. DNA Amplification – Technique
5. Proteins That Bind DNA 22. Spectrophotometry – Technique
6. Superstructure Of DNA 23. Genome Packaging
7. RNA Structure 24. Eukaryotic Chromosomes
8. The Central Dogma And The Genetic Code 25. Centromers And Telomers – Crucial
Chromosome Structures
9. Deciphering The Genetic Code
26. DNA Replication
10. The Genetic Code
27. DNA Polymerases
11. The Genome
28. Prokaryotic DNA Polymerase
12. The Genomic Era
29. Eukaryotic DNA Replication
13. Repetitive DNA
30. DNA Repair
14. Exons And Introns
31. Polymerase Chain Reaction – Technique
15. Genes
32. Transcription
16. Southern Blot - Technique
33. Transcription In Eukaryotes
17. Non Coding DNA
2
,1. HISTORY OF MOLECULAR BIOLOGY
Biology at the beginning of the last century included TWO important and SEPARATE areas of research:
- Biochemistry, carried out by physiologists and physicians, which was focused on chemical reactions
in living systems, proteins, catalysis and enzymes. They were concentred on studying very specific
reactions.
Timeline: 1865, GENES are particular factors; 1900, chromosomes are hereditary units;
1910; genes are located in chromosomes
- Genetics, concerning breeders and cultivators which had a practical interest in the improvement of
plant and animals. But they were focused on highly phenotypic aspects.
Timeline: 1869, DNA DISCOVERY; 1900-1910, chemical analysis and biochemical studies
of DNA.
• 1944: It was discovered that DNA IS THE GENETIC MATERIAL
• 1953: It has a helix structure
- Friedrich Miescher (physician) in 1869 identified an unknown substance
inside cells. While he was studying white blood cells, he isolated the nuclei
and found a PHOSPHORUS-RICH, acidic substance that was unlike every
other protein. He called it “nuclei” because it came from the cell nucleus.
-1910s- 1935: Phoebus Levene and Tipson discovered that DNA contains four
smaller units: A, T, C, and G. However, they made the critical mistake of
thinking that DNA was made of repeating A, T, C, G units, always in the same
order TETRANUCLEOTIDE HYPOTESIS.
He proposed a LINEAR structure model.
In the early 1950s, Takahashi was one of the several scientists who attempted to
propose a HELICAL STRUCTURE for DNA. His model was characterized by a
triple helix, with the phosphate group placed inside the helix, and the bases
oriented toward the outside, rather than the inside.
(It was wrong because: Negative phosphate groups repel each other, so putting
them inside the helix made the model chemically unstable. Having bases on the
outside would not allow proper base pairing or information encoding. Triple
helices don’t naturally form under normal cellular conditions.)
But the experiments that actually demonstrated that DNA IS THE GENETIC MATERIAL are:
1. The Bacterial “transformation” experiment, Griffith, 1929
He had two strains of Streptococcus Pneumoniae: a ROUGH colony (R), characterized by the absence of a
protective capsule. It is recognized and destroyed by the immune system. And a SMOOTH colony (S)
which is virulent due to the presence of a polysaccharide envelope \ capsule, which prevents recognition by
part of the immune system.
3
, So, the presence of the polysaccharide capsule determines that one strain is lethal and the other is not. Both
characteristics are inherited, it is something genetically encoded, a “GENE”.
The experiment consisted of inserting a lab mouse with different Pneumococcus strains:
- S strain (virulent) mouse dies
- S strain heated (the heat kills the virulent strain) mouse lives
- R strain (not virulent) mouse lives
- R strain + HEATED S strain (killed) mouse dies and VIABLE S AND R BACTERIA ARE
EXTRACTED FROM THE MOUSE.
This means that there must be something that converts the R strain into a virulent one à A chemical
substance is GENETICALLY TRASFROMING ANOTHER CELL. Griffith called it THE
TRANSFORMING PRINCIPLE, and the transformation could be inherited.
2. The Avery, MacLeod and McCarty experiment, 1944
They also used the two different strains of Pneumococcus, but instead of mixing the whole extract with R,
they MIXED THE S STRAIN WITH ALL DIFFERENT MOLECULES FROM THE R STRAIN:
Polysaccharides, lipids, RNA, proteins and DNA. With the aim to locate the transformative molecule.
- They firstly studied if the transformative activity in S cells was destroyed by heat. They discovered
that the S cell extract, which contained mostly DNA with a little proteins and RNA, was still able,
when inserted in a culture of R cells, to give rise to a few S colonies
- Then, they studied if the transforming activity was destroyed by either protease or RNase. And
discovered that the transforming activity did not occur in the protein or RNA. (S cell extract with
inserted protease or RNase, inserted in R culture, still gives rise to a few S colonies).
- Lastly, by inserting DNase into the S cell extract, and consequently inserting it into a R culture of
cell, it gave ONLY R COLONIES, and therefore the TRANSFORMING ACTIVITY MOST
LIKELY OCCURRED IN THE DNA.
This experiment was not accepted by the scientific community because the genetic information was
considered to be in proteins.
3. The “blender” experiment, Chase and Hershey, 1952
They used a different system. They studied the T4 phage infection of E. coli. T4 phage is a virus that infects
bacterial cells by attacking the host and INJECTING GENETIC MATERIAL into the bacterial cells. They
are composed of a protein coat in the outside shell and DNA inside. The two geneticists wanted to
understand what substance they were injecting. Was it proteins or DNA?
4
