Lecture 2a Flashcards
What were the candidates for genetic material?
Protein, DNA, and RNA.
Why were protein, DNA, and RNA the only candidates for genetic material?
They were the only molecules complex/big enough to contain instructions/blueprints.
What was proposed to the be the phosphorus storage?
DNA
What did DNA just appear to be?
An inert repeating polymer of nucleotides.
In the early 1900’s what did most biologists expect to be the genetic material?
Proteins, because they seemed to have the complexity and diversity needed.
What two strains of bacterium made it possible to test whether protein or DNA is the genetic material?
R and S strains of Streptococcus pneumoniae.
What strain killed the mice?
S strain
What strain could the mice survive?
R strain
Why could the S strain kill?
It appeared to have virulence genes that the R strain lacked.
What was the process for injecting the R strain?
Living type R bacteria were injected into a mouse. After several days, the mouse survived and no living bacteria were isolated.
What was the process for injecting the S strain?
Living type S bacteria were injected into a mouse. After several days, the mouse died, and type S bacteria were isolated from the dead mouse.
What happens when we grow bacterial cells on top of bacterial food?
They form yellow colonies that we can isolate.
In 1928, who showed that the living R strain could take up the virulence genes from a dead S strain?
Frederick Griffith
What did Griffith show?
A live R strain could take up the virulence genes from a dead S strain, turning the R strain into S cells.
What was Griffith’s process with the S and R strains?
1) Living type R and heat-killed type S bacteria were injected into a mouse.
2) After several days, the mouse died.
3) Live S cells were isolated from the dead mouse.
In 1944, who showed that genes are made of DNA?
Avery, MacLeod, and McCarthy.
What did Avery, MacLeod, and McCarthy show?
Genes are made of DNA.
Describe Avery, MacLeod, and McCarthy’s process.
1) They purified protein, DNA, and RNA from S cells.
2) They mixed each preparation with R cells.
3) They watched which turned the R cells into S cells, which ended up being the DNA.
What was Avery, MacLeod, and McCarthy’s conclusion?
Genes that turn R into S are DNA.
Did people accept Avery, MacLeod, and McCarthy’s findings?
No, they resisted the idea that DNA (and not protein) was the genetic material.
In 1952, who else did experiments that confirmed DNA is genetic material?
Alfred Hershey and Martha Chase
What type of virus did Hershey and Chase use and why?
Bacteriophage T2. They were known to consist of protein and DNA, but not RNA so they could test between the two best options.
What was known in 1952 about bacteriophage T2?
The infected bacterial cell will produce more bacteriophages that will rupture the cell and infect other cells.
What did people know proteins contained?
Sulfur, but not phosphorus.
What did people know DNA contained?
Phosphorus, but not sulfur.
Describe only the radioactive aspect of the Hershey and Chase experiment.
They grew bacteria with radioactive sulfur and then infected the bacteria with bacteriophage T2. This resulted in infectious T2 bacteriophage particles with radioactive proteins, but normal DNA.
They grew other bacteria with radioactive phosphorus and then infected the bacteria with bacteriophage T2. This resulted in infectious T2 particles with radioactive DNA, but normal proteins.
Describe the overall Hershey and Chase experiment.
1) Infection of non-radioactive bacteria with the bacteriophage.
2) Blending to make the viruses let go of the bacterial cells.
3) Centrifugation to separate (and remove) the virus portions that did not enter the bacterial cells.
4) Cells rupture releasing new infectious T2 particles.
What did Hershey and Chase observe after centrifugation?
Radioactive DNA was inside of the bacterial cells, but the radioactive protein was outside of the cells. Because DNA entered the cell, it is the genetic material.
What are genes?
The blueprints to make a living organism.
What are alleles?
Different versions of the same gene.
How many copies of each gene do we have and from where?
Two copies, one from mom and one from dad.
Where are the genes?
In the sperm and egg which fuse.
What are genes?
DNA
What 3 things does DNA (genetic material) have to do?
1) Code for information
2) Be replicated
3) Be inherited by offspring
What did we need to understand in order to figure out how DNA codes for information?
The structure of DNA.
How did chemists determine the structure of nucleotides?
They discovered an enzyme that cleaved DNA into nucleotides.
What is this?
A nucleotide.
How many different bases are there for a nucleotide?
4, Adenine, Thymine, Guanine, and Cytosine.
What is the structure of each nucleotide?
Contains a base, a sugar, and a phosphate.
What remains consistent in each nucleotide and what differs?
The sugar and phosphate are the same. The base differs.
What did Edwin Chargaff discover?
When any DNA molecule was cleaved into nucleotides, [A] = [T] and [G] = [C]. However, the (G+C) always differed from the (A+T) amount.
Who determined the shape of DNA?
Roselind Franklin used x-ray diffraction pictures to show that DNA was a delix.
Who are the FUCKING RAT THIEVES who stole Franklin’s ideas?
James fucking Watson and Frances fucking Crick. Fuck them.
How did Prick Watson and Prick Crick determine the structure of DNA?
First of all, they were FUCKING THIEVES, but they had Tinkertoy-style models of the DNA nucleotides made and they used them to deduce the structure of DNA.
What was they key to Watson’s and Crick’s success in DNA structure?
They understood what a Hydrogen bond was. And apparently they knew how to steal from women. Classic.
What do covalent bonds involve?
The sharing of electrons.
Between Oxygen/Nitrogen and Hydrogen, who has the stronger pull for electrons?
Oxygen/Nitrogen. This gives them a partial negative charge and Hydrogen a partial positive charge.
What do partial positive charges do that is important for Hydrogen bonding?
They attract partial negative charges. This creates hydrogen bonds.
How many atoms are needed to make an H-bond?
3 atoms.
What is the length difference between hydrogen and covalent bonds?
Hydrogen bonds are roughly twice as long as covalent bonds.
What did James Watson notice about the bases on nucleotides?
If we rotate the A and G bases 180 degrees, they can hydrogen bond to the T and C bases.
How did Watson and Crick see the formation of the helix?
They made two strands and linked the phosphate of one nucleotide to the sugar of the next nucleotide, which formed a helix. This turned out to be the correct structure of DNA.
How do the bases appear in the double helix structure?
The bases are flat and face each other like the steps in a spiral staircase. This DNA helix is called a B helix.
After the double-stranded DNA structure was uncovered, what was then obvious?
1) DNA strands could be separated and then used as templates to assemble new polymers (how DNA is copied).
2) Instructions were in the nucleotide sequence of the DNA.
What is DNA?
Two polymers hydrogen-bonded to each other.
Why is the nucleotide sequence important?
It carries the instructions.
Why is the double-stranded nature of DNA important?
It allows for nucleotide sequences to be replicated.
