lOMoARcPSD|251 697 7
Lecture 4 – Nucleic Acids, DNA Structure and DNA replication
• Nucleic Acids
- Macromolecules composed of chains of nucleotides.
- Found in all cells.
- Most well known are:
, lOMoARcPSD|251 697 7
➢ DNA (deoxyribonucleic acid) – Contains genetic information of the
cell.
➢ RNA (Ribonucleic Acid) – Plays roles in translating the genetic
information in the DNA into proteins.
• Frederick Griffith
- Studied Streptococcus pneumonia, a pathogenic bacterium causing
pneumonia.
- 2 strains of streptococcus:
➢ S strain is virulent
➢ R strain is novirulent
- Infected mice with each of the 2 strains to understand the difference
between the strands.
- Conclusions:
➢ Information specifying virulence was passed from the dead S strain
cells into the live R strain cells.
➢ Griffith called the transfer of this information transformation (it
transformed cells from being non-virulent to being virulent)
• Avery, Macleod and McCarty
- Repeated Griffith’s experiment but used purified cell extracts (DNA and
protein)
- They discovered:
➢ Removal of all protein from the transforming material did not
destroy its ability to transform R strain cells.
, lOMoARcPSD|251 697 7
➢ DNA-digesting enzymes destroyed all transforming ability.
➢ Transforming material is DNA.
• Structure of DNA
Building blocks of DNA (and RNA) are nucleotides, each composed of:
➢ A 5-carbon sugar
➢ A phosphate group (PO-4)
➢ A nitrogen-containing base that may be a purine (Adenine or
guanine) or a pyrimidine (thymine or cytosine)
-
Structure of Nucleotides:
➢ Nitrogenous base attached to the 1’ carbon deoxyribose.
➢ Phosphate group attached to the 5’ carbon of deoxyribose.
➢ Free hydroxyl group (-OH) at 3’ carbon of deoxyribose.
Structure of DNA:
➢ Nucleotides are connected to each other to
form a long chain (polymer)
➢ Phosphodiester bond. Formed between the
5’phosphate group and the 3’-OH of the
next in a 5’ to 3’ orientation.
Determining the structure of DNA
➢ Chargaff’s Rules: Amount of adenine =
amount of thymine. Amount of cytosine =
amount of guanine.
➢ Franklin and Wilkins: Franklin performed
X-ray diffraction to identify the 3-D
structure. Discovered DNA is helical.
Diameter of 2nm, complete turn of helix
every 3.4nm.
➢ Watson and Crick: Deduced the structure of DNA using others
evidence. Proposed a double helical structure.
Structure
➢ 2 sugar phosphate backbones.
Lecture 4 – Nucleic Acids, DNA Structure and DNA replication
• Nucleic Acids
- Macromolecules composed of chains of nucleotides.
- Found in all cells.
- Most well known are:
, lOMoARcPSD|251 697 7
➢ DNA (deoxyribonucleic acid) – Contains genetic information of the
cell.
➢ RNA (Ribonucleic Acid) – Plays roles in translating the genetic
information in the DNA into proteins.
• Frederick Griffith
- Studied Streptococcus pneumonia, a pathogenic bacterium causing
pneumonia.
- 2 strains of streptococcus:
➢ S strain is virulent
➢ R strain is novirulent
- Infected mice with each of the 2 strains to understand the difference
between the strands.
- Conclusions:
➢ Information specifying virulence was passed from the dead S strain
cells into the live R strain cells.
➢ Griffith called the transfer of this information transformation (it
transformed cells from being non-virulent to being virulent)
• Avery, Macleod and McCarty
- Repeated Griffith’s experiment but used purified cell extracts (DNA and
protein)
- They discovered:
➢ Removal of all protein from the transforming material did not
destroy its ability to transform R strain cells.
, lOMoARcPSD|251 697 7
➢ DNA-digesting enzymes destroyed all transforming ability.
➢ Transforming material is DNA.
• Structure of DNA
Building blocks of DNA (and RNA) are nucleotides, each composed of:
➢ A 5-carbon sugar
➢ A phosphate group (PO-4)
➢ A nitrogen-containing base that may be a purine (Adenine or
guanine) or a pyrimidine (thymine or cytosine)
-
Structure of Nucleotides:
➢ Nitrogenous base attached to the 1’ carbon deoxyribose.
➢ Phosphate group attached to the 5’ carbon of deoxyribose.
➢ Free hydroxyl group (-OH) at 3’ carbon of deoxyribose.
Structure of DNA:
➢ Nucleotides are connected to each other to
form a long chain (polymer)
➢ Phosphodiester bond. Formed between the
5’phosphate group and the 3’-OH of the
next in a 5’ to 3’ orientation.
Determining the structure of DNA
➢ Chargaff’s Rules: Amount of adenine =
amount of thymine. Amount of cytosine =
amount of guanine.
➢ Franklin and Wilkins: Franklin performed
X-ray diffraction to identify the 3-D
structure. Discovered DNA is helical.
Diameter of 2nm, complete turn of helix
every 3.4nm.
➢ Watson and Crick: Deduced the structure of DNA using others
evidence. Proposed a double helical structure.
Structure
➢ 2 sugar phosphate backbones.
