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Summary BIO 181 - FULL WRITTEN NOTES | LATEST UPDATE | GRADED A+
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BIO 181 - FULL WRITTEN NOTES | LATEST UPDATE | GRADED A+
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BIO 181Important info
Definitions
Lecture Notes
11/15: DNA Replication and Repair (5.1)
Learning Objectives:
- Analyze the results of key experiments that demonstrated that DNA, and not
protein, functions as the hereditary material in living organisms
- Explain the semi-conservative nature of DNA replication and relate it to your
understanding of the properties of double-stranded DNA molecules
- Describe in the context of leading and lagging strand synthesis and the function of
key DNA replication factors (helicases, single-stranded binding proteins, primases,
polymerases, ligases, and topoisomerases)
- Evaluate the purposes of various DNA repair mechanisms for correcting sequence
alterations that occur before and during DNA replication
DNA as Hereditary Mat’l
- Today, we take it for granted that DNA is the hereditary material is passed from one
generation to the next
- History shows us that this was regarded as silly by many researchers until the mid 1900s
- DNA was determined to be the hereditary information based on the results of several
classic molecular biological experiments
- 1928: Griffith
- 1940s: Avery, MacLeod, and McCarty
- 1940s: Hershey and Chase
DNA as Hereditary Mat’l - Griffith
- One of the first studies that indicated that DNA is the hereditary material was Griffith’s
discovery of transformation in bacteria called Streptococcus pneumoniae
- Griffith worked with two strains of S. pneumoniae (a “strain” of bacteria is a population
of genetically identical cells).
- One was nonvirulent (benign), and one was virulent (caused disease).
- Saw smooth colonies that were encapsulated. Sugary layer that goes on the outside of a
cell for protection
- Had individuals that had pneumonia and survived
- Two strains of bacteria, same for the most of the genetics, different in that one was
encapsulated and one was rough
- Griffith found that heat-killed virulent S. pneumoniae cells could transform a nonvirulent
rough strain into a smooth virulent strain. He called this process transformation
- Griffith took the R strain, injected the bacteria into the lungs of a mouse. Mouse
continued to live and recovered.
- Took the encapsulated strain and injected the bacteria into the lungs of a mouse and the
mouse died
, - Two strains of bacteria, same for the most of the genetics, different in that one was
encapsulated and one was rough
- Griffith found that heat-killed virulent S. pneumoniae cells could transform a nonvirulent
rough strain into a smooth virulent strain. He called this process transformation
- Griffith took the R strain, injected the bacteria into the lungs of a mouse. Mouse
continued to live and recovered.
- Took the encapsulated strain and injected the bacteria into the lungs of a mouse and the
mouse died
- Griffith wanted to find a vaccine
- You could heat up the microbes and kill them
- The toxins are heat tolerant
- Take some of the strain, the bacteria that encapsulates the cell, heats it up, and injects it
into the mouse
- Mouse lives
- Killed S-strain cells are benign
- Take R strain, S strain that is dead, and combine that and inject that into the mouse
- Mouse dies
- Live R-strain cells were transformed to S-strain cells
- Griffith tries again and heats up the bacteria again and there is the same result
- Transformation: when the heat-killed virulent cells could transform an R strain into a S
strain
- R strain does not have the ability to produce the capsule
DNA as Hereditary Mat’l - Avery
- Griffith’s experiment failed to identify the biological molecule(s) responsible for
transforming nonvirulent R cells into S cells
- However, biologists knew that at the time that chromosomes were a complex mixture of
both protein and DNA
- Therefore, Griffith’s transforming factor had to consist of either protein or Rna
- Avery, Macleod, and McCarty set out to determine if protein, DNA, or RNA was responsible for
the transformations observed by Griffith
- Even when heated up, DNA and RNA will withstand
- When we heated up the cell producing capsule, released molecules
- Set up an experiment where we take the heat treated S-strain and add the enzyme to reduce the
Protein, DNA, and RNA
- Take extract and degrade the protein into RNA and DNA then expose that to the R strain
- Gets an encapsulated cell
- Take another mixture of the S strain and heated it up, and add the RNA extract
- RNA is degraded and exposes protein and DNA to the R strain
- Add the enzyme to degrade the DNA and expose the Protein and RNA and there was no
transformation
- It is the DNA that changes the rough cell into the smooth encapsulated cell
- Avery et al. found that extracts with intact DNA were the only ones that could transform
cells to become virulent. Their results support the hypothesis that DNA is the hereditary
material, not RNA or protein
DNA as Hereditary Mat’l - Hershey
- Critics of the work of Avery et al. argued that the group’s enzyme treatments of
heat-killed virulent S. pneumoniae cells may have been incomplete
Hershey and Chase used a new experimental system to address the same questions as
, g g p
- Avery et al. found that extracts with intact DNA were the only ones that could transform
cells to become virulent. Their results support the hypothesis that DNA is the hereditary
material, not RNA or protein
DNA as Hereditary Mat’l - Hershey
- Critics of the work of Avery et al. argued that the group’s enzyme treatments of
heat-killed virulent S. pneumoniae cells may have been incomplete
- Hershey and Chase used a new experimental system to address the same questions as
Avery
- Do viral genes consist of DNA or protein?
- During replication, cells will fill up with new viruses
- Protein coat, DNA inside the virus
- Radio Label: protein with radioactive sulfur, DNA with radioactive phosphorus
- All of the viruses that made in the presence of both radioactive phosphorus and sulfur
- Track the DNA and the protein
- Take the DNA and allow them to infect the e coli cells
- Allow the injection of virus into the E. coli, but stop the experiment
- Used a blender to knock the viruses off the e-coli
- Supernate: where all the viruses are going to be
- If it is the DNA that is in the e coli, we will see the phosphorus in the pellet
- The radioactive protein was found in the supernatant and the radioactive DNA was found
in the pellet
- It was the DNA that was being taken up by the nonencapsulated cell, the DNA was
transcribed, read, and produced the capsule
-
DNA as Hereditary Mat’l - Conclusion
- DNA is being passed from the F1 generation to F2
- It was the DNA that were made up of the sister chromatid
- These ideas of hereditary comes back to Mendel and his ideas
DNA Replication:
- Two crucial questions were raised by the finding that DNA is the hereditary material:
- How did the simple primary and secondary structure of DNA hold the information
required to make life possible
- How is DNA copied so that genetic information is passed faithfully from one cell
to another during growth, and from parents to offspring during reproduction
- The answers to these questions were found in the double helix structure of the DNA
molecule
DNA Replication - Structure Review
- DNA is a linear polymer made up of monomers called nucleotides. Each nucleotide is
composed of deoxyribose, a phosphate group, and a nitrogenous base
- Deoxyribonucleotides are joined at the phosphate group attached to the 5’ carbon of
deoxyribose and the hydroxyl group attached to the 3’ carbon of deoxyribose
- Carbon 1 is always linked to the base
- Carbon 3 will have a hydroxyl group
- This is where you will attach a new nucleotide
Carbon 5 is always attached to the phosphate group
, - DNA is a linear polymer made up of monomers called nucleotides. Each nucleotide is
composed of deoxyribose, a phosphate group, and a nitrogenous base
- Deoxyribonucleotides are joined at the phosphate group attached to the 5’ carbon of
deoxyribose and the hydroxyl group attached to the 3’ carbon of deoxyribose
- Carbon 1 is always linked to the base
- Carbon 3 will have a hydroxyl group
- This is where you will attach a new nucleotide
- Carbon 5 is always attached to the phosphate group
- This gives the nucleotide orientation
- Each nucleotide has 3 pieces to it
- Base is always bonded to carbon 1
- 3 contains the hydroxyl group
- 5 has a phosphate group
- Carbon #2 is where we find the difference between DNA and RNA
- If there is an OH on carbon 2, RNA NUCLEOTIDE
- If there is just a hydrogen on carbon 2, DNA NUCLEOTIDE
- We are always going to link nucleotides from 5’ to 3’ carbons
- This primary structure gives DNA directionality - one end has an exposed hydroxyl
group on the 3’ carbon of deoxyribose, and the other end has an exposed phosphate group
on the 5’ carbon
- The two strands run opposite of each other
- Hydroxyl group is what attaches the phosphate group from 5’ carbon to the 3’ carbon
- Phosphodiester linkage = linkage between two nucleotides
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