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What experiment did Frederick Griffith perform?
He injected mice with the two strands of Streptococcus pneumoniae bot the “S” smooth and the “R” rough
Explain Frederick Griffiths experiment.
- He injected two different Streptococcus pneumoniae strands into the mice.
- He injected Living S (Control cells) into a group, living R cells into a group, then he injected heat-killed S cells into another group. He then mixed the heat killed S cells and the living R cells into a final group. The result of the final group was that living S cells were found in the blood stream.
What was Freserick Griffith’s conclusion from his experiment?
He concluded that the living R bacteria had been transformed into pathogenic S bacteria by an unknown, heritable substance from the dead S cells.
What was Frederick Griffiths Transforming principle?
- Living cells can be transformed by a substance from dead cells to take on the traits of the dead cells.
- This substance is the genetic material.
- Griffith believed this substance was a protein.
When did Griffith discover The transforming principle?
What experiment did Oswald T Avery, Colin M Macleod and Maclyn McCarthy perform?
They experiment to see what substance was the transforming Substance
How did Oswald T Avery, Colin M Macleod and Maclyn McCarthy perform their experiment?
They removed Protein, RNA and DNA independently and observed to see if the Pneumococcus cells still transformed from R to S cells.
What did Oswald T Avery, Colin M Macleod and Maclyn McCarthy discover?
- After removing protein the R cell still transformed
- After removing RNA the cells still transformed
- After removing the DNA the cells DID NOT transform.
What was the conclusion of Oswald T Avery, Colin M Macleod and Maclyn McCarthy experiment?
They concluded that DNA was The transforming substance.
What experiment did Alfred D Hersey and Martha Chase perform?
They determined what material was needed for a Bacteriophage to inter the cell to reproduce, DNA or protein.
What is a Bacteriophage?
- They are viruses that infect bacteria.
- They can not reproduce on their own so they infect bacteria and reproduce inside of them
When did Oswald T Avery, Colin M Macleod and Maclyn McCarthy perform their experiment?
What process did Alfred D Hersey and Martha chase perform?
they used radioactive sulfur and phosphorus to trace the fates of the protein and DNA, respectively, of T2 phages that infect bacterial cells.
What was the 1st step in Alfred D Hersey and Martha chase experiment?
1. They mixed radioactively labeled phages with bacteria. The phages infected the bacterial cells.
What was the 2nd step in Alfred D Hersey and Martha chase experiment?
They agitated in a blender to separate phages outside the bacteria from the bacterial cells.
What was the 3rd step in Alfred D Hersey and Martha chase experiment?
The Centrifuged the mixture so that bacteria formed a pellet at the bottom of the test tube
What was the 4th step in Alfred D Hersey and Martha chase experiment?
They Measured the radioactivity in the pellet and the liquid to determine the radioactive substance in the liquid of inside the cell.
What was the conclusion of the 1st batch that Alfred D Hersey and Martha chase performed?
- In batch one the phages were grown with radioactive sulfur S35 which was incorporated into phage protein (pink)
- After the experiment process they discovered the radioactive sulfur in the liquid and extracellular.
What was the conclusion of the 2nd batch that Alfred D Hersey and Martha chase performed?
- They grew the phages with radioactive phosphorus P32 which was incorporated into the phages DNA
- They discovered the radioactive phosphorus intracellular and none in the liquid.
What was the conclusion of the entire experiment of Alfred D Hersey and Martha chase?
That DNA was the substance that Bacteriophages needed to infect bacteria and duplicate.
when did Alfred D Hersey and Martha chase perform their experiment?
What research did Erwin Chargaff perform?
He determine the difference between species in the quantities of the four nucleotides that make up DNA
What did Erwin Chargaff conclude?
He determine that organisms had equal amounts of Adenine and Thymine, and equal amount of Cytosine and Guanine
Who was Rosalind Franklin?
She performed an X-ray Diffraction photo of DNA which contributed to determining the structure of DNA
What base pairing in DNA is stronger?
- The Hydrogen bonds between Guanine and Cytosine because there are three Hydrogen bonds
- For Adenine and Thymine there are only two Hydrogen bonds
Who were Watson and Crick?
They determined the structure of DNA using Rosaline Franklins X-ray.
When did Watson and Crick release their conclusion?
Who stated “it has not escaped our notice that the specific pairing that we have postulated immediately suggests a copying mechanism for the genetic material”?
Watson and Crick in 1953
What are the initial steps for DNA replication?
- 1- the parent Molecule has two complementary strands of DNA. Each bases paired by hydrogen bonding with its specific partner, A with T and G with C.
- 2- The first step in replication is the separation of the two strands of DNA.
- 3 - Each parental strand now serves as a template that determines the order of nucleotides along a new complementary strand.
- 4 - The nucleotides are connected to form the sugar-phosphate backbones of the new strands. Each “daughter” DNA molecule consists of one parental strand and one new strand
What are the Three alternative models of DNA replication?
- Conservative model
- Semiconservative model
- Dispersive model
What is the Conservative Model for DNA replication?
The two Parental strands reassociate after acting as templates for new strands, thus restoring the parental double helix.
What is the Semiconservative model for DNA replication?
The two strands of the parental molecule separate, and each function as a template for synthesis of a new, complementary strand.
What is the Dispersive Model for DNA replication?
Each strand of both daughter molecules contains a mixture of old and newly synthesized DNA.
Who performed the experiment to determine which Model for DNA replication was correct?
Matthew Meselson and Franklin Stahl
What was the experiment Matthew Meselson and Franklin Stahl perform?
They cultured E. coli bacteria for several generations on a medium containing nucleotide precursors labeled with a heavy isotope of nitrogen, N15. The bacteria incorporated the heavy nitrogen into their DNA. The scientists then transferred the bacteria to a medium with only N14, the lighter, more common isotope of nitrogen. Any new DNA that the bacteria synthesized would be lighter than the parental DNA made in the N15 medium. They could distinguish DNA of different densities by centrifuging DNA extracted from the bacteria.
What did Matthew Meselson and Franklin Stahl find after their experiment?
After determining the weight of nitrogen they found both the lighter and the heavier lines.
What did Matthew Meselson and Franklin Stahl conclude?
That DNA replication follows the semiconservative model by comparing their result to the results predicted by each of the three models. The first replication in the N14 medium produced a band of hybrid (N15, N14) Dna. This result eliminated the conservative model. A second replication produced both light and hybrid DNA, a result that eliminated the dispersive model and supported the semiconservative model.
Where does DNA replication start?
At a site called the origin of replication
What is the Replication terminus?
Where the Replication forks meet
What is the Replication fork?
The point where the two strands of DNA are separated and replicating
How are the strands of the double helix separated?
by the enzyme helices
What is Topoisomerase?
It is an enzyme that relaxes the overwound DNA by cutting and unraveling then reattaching.
What does the Single-strand binding protein (SSBP) do?
It prevents the separated parental strands from recombining.
In what direction is DNA replicated?
5’ to 3’ direction
What is the Enzymes that replicates DNA?
What is needed to start DNA synthesis?
Single strand with a 3’ end and a primer. then Polymerase can come in to initiate the pairing.
For E. Coli how many main DNA polymerases are there?
They have two main, DNA polymerase I and DNA polymerase III
How many main Polymerases do Eukaryotes have?
For E. Coli, what does DNA Polymerase III do?
Replicates that leading Strand
What is the leading strand? the strand that is replicated continuously as the replication fork moving along the DNA molecule
What is the lagging strand?
Is it the strand that has to be replicated in the opposite direction of the replication fork. It is replicated in pieces called Okizaki Fragments.
What is an Okizaki fragment?
Segments of replicated DNA on the lagging strand
What does the enzyme Primase do?
Initiates the synthesis of the new strand by making a short nucleotide chain called a primer
What does the primer do?
It is made of RNA and initiates the synthesis of the new DNA strand
Summarize the replication of DNA in bacteria.
- 1- Helicase unwinds the parental double helix.
- 2 - Molecules of single strand binding protein stabilize the unwound template strands to prevent them from recombining.
- 3 - The leading strand is synthesized continuously in the 5’-3’ direction by DNA Pol III
- 4- Primase begins synthesis of RNA primer for fifth Okazaki fragments
- 5- DNA Pol III is completing synthesis of the fourth fragment, when it reaches the RNA primer on the third fragment. it will dissociate, move to the replication fork, and add DNA nucleotides to the 3’ end of the fifth fragment primer.
- 6- DNA pol I removes the primer form the 5’ end of the second fragment, replacing it with DNA nucleotides that it adds one by one to the 3’ and of the third fragment. The replacement of the last RNA nucleotide with DNA leaves the sugar-phosphat backbone with a free 3’ end.
- 7- DNA ligase bonds the 3’ end of the second fragment to the 5’ end of the first.
What is Helicase’s function?
Catalyzes the breaking of hydrogen bonds between base pairs and the opening of the double helix
What id the function of the Single-strand DNA-binding proteins?
They Stabilize single-stranded DNA to prevent the strand from reforming
What is the function of Topoisomerase?
Breaks and rejoins the DNA double helix to relieve twisting forces caused by the opening of the helix.
What does Primase do on the leading strand?
Catalyzes the synthesis of the RNA primer
What does DNA polymerase III do on the leading strand?
Extends the leading strand
What does the sliding clamp do on the leading strand?
Holds DNA polymerase in place during extension
What does Primase do on the lagging strand?
Catalyzes the synthesis of the RNA primer on the Okazaki fragments.
What does DNA Polymerase III do on the Lagging strand?
Extends an Okazaki fragments.
What does the sliding clamp do no the lagging strand?
Hold DNA polymerase in place during strand extension
What does DNA polymerase I do on the lagging strand?
Removes the RNA primer and replaces it with DNA
What does DNA ligase do on the lagging strand?
Catalyzes the joining of Okazaki fragments into a continuous strand
What are the telomeres?
- the ends of the chromosome, they become shorter and shorted with replication generations.
- They contain no genes.
What is the Telomere sequence in humans?
How is the telomere shortened?
- After the DNA polymerase synthesizes the last Okazaki fragment in lagging strand
- No DNA synthesis occurs after primer is removed (no free 3’ end for DNA polymerase) chromosome is shortened.
How are telomeres replicated?
- 1- When the RNA primer is removed from the 5’ end of the lagging strand. a strand of parent DNA remains unreplicated
- 2. Telomerase binds to the “overhanging” section of single strand DNA. Telomerase adds deoxyribonucleotides to the end of the parent DNA, extending it.
- 3. telomerase moves down the DNA strand and adds additional repeats
- 4. Primase, DNA polymerase and ligase then synthesize the lagging strand in the 5’ to 3’ direction, restoring the original length of chromosome
What is Telomerase?
An enzyme that is active in the production of germ cells and adds telomeric repeats to chromosome ends
What was the first mammal cloned by humans?
- Dolly a sheep
- She showed signs of early aging.
What determines the frequency of crossing over?
the distance between the genes
How do you determine the recombination frequency?
Example: 130 recombinants/9027 total offspring = recombination frequency of 0.014 of crossing over happens 1/4% of the time
What does 1% recombination =?
1 Map unit or 1 centiMorgan (cM) so there are 1cM between these two genes or 1 M.U.
How can you determine the arrangement of alleles, Cis or Trans?
- Cis - when the alleles are homozygous
- Trans - When the alleles are heterozygous
From a two-point test cross that produces 200 offspring, 20 of the offspring are recombinant and 180 are parental types. What is the map distance between the two genes?
What are the alterations of chromosome structure?
What is the alteration of a chromosome structure that removes a chromosomal segment?
What is the alteration of chromosome structure that repeats a segment of the chromosome?
What is the alteration of chromosome structure that reverses a segment within a chromosome?
What is the alteration of chromosome structure that moves a segment from one chromosome to another non homologous one?
What can lead to duplication and deletion of chromosomal segments?
Unequal crossing over during meiosis.
What is Prader-Willi syndrome?
Deletion of part of the long arm of chromosome 15
What does Prader-willi syndrome result in?
- Poor sexual development in males
- Behavioral problems
- Mental retardation
- Compulsive eating
- Exceptionally proficient at jigsaw puzzles
When is Deletion of a chromosomal segment beneficial?
Deletion of the gene called ccr5 (chemokine receptor 5) reduces the susceptibility to HIV infection
What is an example of chromosomal duplication?
The eye of the Drosophila fly, duplication of the region 16A resiling in Bar eyes
When is duplication of a gene beneficial?
Extra copy of ccl3L1 reduces the infection rate of HIV-1 and slow the progression of AIDS in infected individuals.
What causes the Philadelphia chromosome that causes Chronic Myelogenous Leukemia?
Reciprocal translocation between the long arms of chromosome 9 and 22
What are the exceptions from Mandelian Genetics?
- The genetics of cell organelles, like mitochondria and plastids
What is Imprinting?
- When genes have different effects depending on whether they were inherited from the father or the mother
- Usually results in silencing of genes but can result in activatio og genes
How are the genetic of cell organelles like mitochondiria and plastids transferred?
Organelles are usually only inherited from one parent. Usually the mother.
What is Angelman syndrome?
A condition when a deletion inq11-13 on chromosome 15 is inherited from the mother.
What does Angelman syndrome result in?
- Mental retardation, abnormal gait
- Frequent laughing and excitability
- Extended tongue
- A silencing (by imprinting of the mothers copy of the same region can also result in Angelman syndrome
What is the Methylation of Cytosine?
- When a Methyl group is attached to the Cytosine on the 5th carbon.
- Can only happen in a 5'-CpG-3'
- 3'-GpC-5' coding of the DNA.
What does methylation cause?
- DNA methylation reduces gene expression in genes that contain methylated bases (usualy cytosine)
- The inactivated X chromosome in maals is heavily methylated.
- Methylated DNA recruits enxymes that de-acelyate histones
- DNA Methylation plays a key role in genomic imprinting.
What is Lyonization
- Proposed by Mary Lyon
- Epigenetics silencing of randomly chosen X chromosome in females
What is the Honderwinter?
- Refers to the winter of 1944-1954 in the German occupied part of the Netherlands
- Daily food rations had fallen to 580 Kcal by feb of 1945
- 4.5 Million people were affected and more then 20K people perished from starvation
- The survivors and their descendants have been intensely studied for the long term medical consequences of famine
- Occurs around day 16 in human development
- All the descendant cell from a cell that inactivated a particular X chromosome have the same X chromosome inactivated
- Females are mosaic with respect to the expression of genes on the x chromosome
What is Epigenetics?
The study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself
What is an example of Transenerational Epigenetics?
- The Igf2 gene was analyzed because it was known to differentially methylated in the maternal and paternal alleles, and because the methylation state of a gene is known to influence the growth rate of the embryo.
- The methylation state of lgf2 in the descendants of children conceived during the dutch hunger winter is still influenced by famine 60yrs earlier, this is an example of transgenerational epigenetics
What is the Maternal effects?
The phenotype of the offspring is determined by the genotype of the mother.