Lecture 9: DNA Structure Flashcards
What is Genetic Material?
- Information contained in genes that gets passed onto new generation
- Source of variability among organisms
To serve as genetic material, molecules must be able to:
- Replicate
- Store Information
- Express Information
- Allow variation by mutation
What is the Central Dogma?
DNA –> RNA –> PROTEIN
Explain the Griffith Experiment and how we discovered that DNA is genetic material during the study of Bacteria and Bacteriophages
- Provided foundation for Avery, MacLeod, and McCarty’s research
- Showed avirulent strains of Streptococcus pneumoniae could be transformed to virulence
- Speculated transforming principle could be part of polysaccharide capsule or compound required for capsule synthesis
Explain Avery, MacLeod, and McCarty experiment and how we discovered that DNA is genetic material during the study of Bacteria and Bacteriophages
- 1944 publication on chemical nature of transforming principle in bacteria
- First direct experimental proof that DNA is biomolecule responsible for heredity
What did Griffith’s Transformation Experiment prove?
- Capsules are virulent factors
- Smooth cause disease since they produce capsules
Transforming Principle is DNA. How was this proved with the test tube experiment with Avery, MacLeod, and McCarty
- Treated with protease, then ribonuclease, then finally deoxyribonuclease.
- Protease and Ribonuclease still had S cells with capsule produced
- Deoxyribose only had R cells showing DNA is the genetic material
Explain the Hershey and Chase Experiment
- Used Escherichia coli and bacteriophage T2 (TRANSDUCTION!)
- Demonstrated that DNA, not protein, is the genetic material
- Used radioisotopes 32P and 35S
- Demonstrated DNA enters bacterial cell during infection an directs viral reproduction
T/F: If Sulfur is present, proteins are there
TRUE! Think of the amino acids methionine and cysteine. Sulfur is NOT found in RNA or DNA, so this is why the radioisotopes of Sulfur mean Sulfur is present
Who came up with the radioisotope labeling technique?
Hershey and Chase
32P labels what? 35S labels what?
32P: Labels DNA (especially DNA inside of bacteriophage)
35S: Labels Protein (especially the bacteriophage coat, but NOT the inside DNA material)
Define Protoplasts
- E. coli is treated with lysozyme
- Outer wall is removed without destroying bacterium - naked cell
Explain Transfection
- Infection by only viral nucleic acid
- Proves conclusively that viral DNA alone contains ALL necessary information for production of mature viruses
What UV light wavelength is the MOST mutagenic?
260 nm
Explain Mutagenesis
- UV light is MOST mutagenic at wavelength 260 nm (action spectrum aka where MOST damage was created)
- DNA/RNA absorbs UV at 260 nm
- Protein absorbs UV at 280 nm (no significant mutagenic effects observed here)
- Molecule serving as genetic material expected to absorb at mutagenic wavelength
260/280 RATIO SHOWS WHAT?
DNA/RNA to Protein Ratio. This demonstrates the purity of a sample. THIS IS WHAT WE DO IN LAB!!!
Explain Recombinant DNA technology
- Segments of eukaryotic DNA corresponding to specific genes isolated
and spliced into the bacterial DNA - Complex inserted into bacterial cell and monitored
Explain Eukaryotic DNA now being functional in bacterial cell
- Eukaryotic gene product in bacteria containing eukaryotic gene provides
direct evidence: DNA is present and functional in bacterial cell - Example: Insulin and interferon production by bacteria
Explain Transgenic animal examples
- Human DNA microinjected into fertilized mouse egg
- DNA encoded human β-globin gene
- Now present and expressed in mouse and transmitted to progeny
T/F: Some viruses have RNA core, not DNA
True!
MV: Tobacco mosaic virus (1956)
* Demonstrated RNA serves as genetic material for these viruses
Define RNA replicase
- Enzyme isolated from E. coli (1965,
Pace and Spiegelman) - Replication of the viral RNA is
dependent on RNA replicase
Define Retroviruses
- Replicate unusually
- RNA serves as template for DNA
synthesis - Complementary synthesis of DNA by RNA-dependent DNA polymerase reverse transcriptase
Define Reverse transcriptase
RNA-dependent DNA polymerase
enzyme
Define Nucleotides
Building blocks of nucleic acid/ DNA
Nucleotides consist of:
- Nitrogenous base (two kinds)
- Pentose sugar
- Phosphate group
What are the 2 kinds of Nitrogenous bases?
- Purines (nine-member ring)
- Adenine (A)
- Guanine (G)
- Pyrimidines (six-member ring)
- Cytosine (C)
- Uracil (U)
- Thymine (T)
Define Nucleoside
- Contains nitrogenous base and pentose sugar
- Molecule is composed of purine
or pyrimidine base and ribose or
deoxyribose sugar
Define Nucleotide
- Nucleoside with phosphate group added
- Phosphate ALWAYS added to 5’ Carbon
What is a triphosphate?
- Serve as precursor molecules during nucleic acid synthesis
What is important to recognize with ATP and GTP: Adenosine triphosphate and guanine triphosphate?
Large amount of energy involved in adding/removing terminal phosphate
Nucleotides are linked by what bonds? Between what positions?
Nucleotides are linked by phosphodiester bonds between phosphate group at C-5’ position and OH group on C-3’ position
