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52 Cards in this Set

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Who WHo is Frederick Griffith?
bacteriologist, injected mice with
vaccine
A substance that is prepared from killed or weakened microorganisms and is introduced into the body to protect the body against future inferctions by microrganisms.
Explain the first strain.
S strain. It is enclosed in a capsule made of polysachaarides, and is a virulent (disease causing) strain of bacteria. Because of the capsule, the body defense system cannot fight against the bacteria.
Explain the second strain.
It does not have the polysaccaride capsule and is therefore not virulent. It is rough.
What did Griffith do to determine whether the capsule had anything to do with the mice deaths?
injected the mice with dead S-bacteria and the mice remained healthy. he then injected heat-killed (no longer able to reproduced) weakened s-bacteria.
what happened then?
the mice lived-(heat killed S). thus griffith knew it was not the capsule on the S bacteria that killed the mice.
next step in griffs experiment was......?
he mixed harmless LIVE
what was the next step in griffie's experiment?
he mixed the harmless LIVE r bacteria with the harmless HEAT KILLED s-bacteria.
what was the result of this fascinating step in griffs experiemnet?
meese injected with this PREVIOUSLY HARMLESS (duh duh duh dum) mixture.....died. (yeah thats right)
what cause did griffie attribute to these deaths of these meese?
first he examined the blood of the DEAD miceiemoo and found that the live R BACTERIA had aquired the POLYSACCARIDE CAPSULES (capsules how couldyou? soap opera music...) somehow, the harmless r bacteria had changed and became virulent S BACTERIA!! MORE DRAMATIC MUSIC
Griffie then discovers transformation. WHAT IS THAT?????? :-)
it is a change in phenotype caused when bacterial cells (like R) take up foreign (thats S) genetic material.
what did AVERY do??? (elegent experiments)
avery (hes pretty cool) demonstrated that DNA is the material responsible for that griffith crap called transformation. EXPLAIN-DNA had the instructiones for the making of the capsules in the S strain
What was known at this time?
It was known that viruses,which are much asimpler than cells, arem ade of DNA surrounded by a protective protein coat. Bacteriphage, are viruses that infect bacteria, wheh phage does so, the phage are able to produce more viruses, which are releases when the bacterial cells rupture.
What was not known at this time?
IT wawas not known how the phage reporgrammed the baccterial cell to make vriuses. Was it the phage DNA, the protein, or both, that issued the instructions to bacteria during infection?
Why did Hershey and Chase use t2 to determine an answer for the experiment?
They knew that the only molecule in this phage that contained phosphurus was DNA. Liewise, the only phage molecules that contained sulfur were in the protein coat.
What was the first step?
1. THey first gre t2 with e coli bacteria in a medium that contained radiocative sulfur.(35s). THe protein coat of the virus would incrporate the 35s.
2.They grew a second patch of phage that contained phospurus(32p)The radioactive phosphurus would become part of the phages' DNA.
What was the second step?
The two different pahges were used to infect two seperate batches of e coli. BEcuae radioactive elements release particles that can be detected by machines, they can be traced. THis way, scientists can determine how bacterial cells are reprogrammed.
Step 3.
1. After a few minutes, the scientists tore open the 35s phages with the help of a blender, and then they did the same thing to the 32p. Then they used a centrifuge to seperate the bacteria and the phages. The bacterial sunk to bottom, viral floated at top.
2. When the layers of the 35s bateria were examined, they found that most of the 35s still part of the phage, meaning that the protein was not injected in the bacteria.
3. WHen 32p was examined, they found that the bacteria had most of the 32p, meaning that the DNA had been injected into the hosts. The new generation of phages that was produced by these bacteria also contained radioactive DNA.
Conclusion
The DNA of the viruses is injected into the bacterial cells while most of the proteins remain outsideThe injected DNA molecueles caused the bacterial cells to produce more viral DNA and proteins. THis meant, that the DNA, rahter than proteins, was hereditary material, at least in virusses.
What has this shown?
THat the DNA is the molecule that stores genetic info in living cells.
Who determined the structure of DNA?
Jmes Watson, Francis Crick,
Why was this imporatnt?
IT clarified how DNA can serve as teh genetic material.
Step 3.
1. After a few minutes, the scientists tore open the 35s phages with the help of a blender, and then they did the same thing to the 32p. Then they used a centrifuge to seperate the bacteria and the phages. The bacterial sunk to bottom, viral floated at top.
2. When the layers of the 35s bateria were examined, they found that most of the 35s still part of the phage, meaning that the protein was not injected in the bacteria.
3. WHen 32p was examined, they found that the bacteria had most of the 32p, meaning that the DNA had been injected into the hosts. The new generation of phages that was produced by these bacteria also contained radioactive DNA.
Conclusion
The DNA of the viruses is injected into the bacterial cells while most of the proteins remain outsideThe injected DNA molecueles caused the bacterial cells to produce more viral DNA and proteins. THis meant, that the DNA, rahter than proteins, was hereditary material, at least in virusses.
What has this shown?
THat the DNA is the molecule that stores genetic info in living cells.
Who determined the structure of DNA?
Jmes Watson, Francis Crick,
Why was this imporatnt?
IT clarified how DNA can serve as teh genetic material.
Double Helix
Two strands twistd around each other , like a winding staircase. Each strnd is made of linked nucleotides.
Nucleotides
the subunits that make up DNA. Made up of three parts.
1. Nitrogen containing base
2. 5 carbon sugar
3. phosphate group
Deoxyribose
the fivve carbon sugar
What are the four types of nitrogen bases?
Guanine/Adenine-classified as purines
Thyamine/Cytosine- classified as pyrimidians
Pyrimidians/Purines
Purines: 2 rings of carbon, and nitrogen atoms.
Pyrimidians:Made up of 1 ring of carbon and nitrogen atoms.
Explain the phosphate groups visually.
The sugar-phosphate backbonesare similar to the side rails of a ladderand the paired nitrogen are similar to the rungs of a ladder. THe nitrogen bases face each other. The double helix is held together by weak hydrogen bonds between the pairs of the bases.
Who was Erwin Chargaff?
A biochemist tha made an interesting observation abot DNA. THe amount of a=t and the amount of g=c. But amounts are varied between organisms.
What was the signifigance of Chargaff's data?
It became signifigant wen the began using xray defraction to study the structure of molecules. IN an xray dereaction, a beam of xrays is directed at an object, the xray bounces off teh object and is scattered on the film.
WHo were Wilkins and Franklin?
They developed high quality xray defraction photos of fibers in the DNA molecule. These photos suggested that the DNA molecule resembled a tightly coiled helix and was composed of 2 or 3 chains of nucleotides.
Describe Watson's and Crick's DNA model.
With tin and wire models of molecules, they built a model of DNA with the configuration of a double helixof two strands of nucleotides twisting around a central axis.
State the theory of base pairing rules.
a=t and g=c are on opposte strnads, and only allows these two pairs ebcuase of structure and size.
HOw many bonds do they form?
a=t, 2 hydrogen bonds.
g=c, 3 hydrogen bonds.
complementary
The sequence of bases on one strand are complementary(determines) to the sequence on the other side.
What did scientsist predict about specific DNA structure?
That eh complementary structure was used as a basis to make exact copies of the DNA each time the cell divided.
When dos replication occur?
S phase
Step 1.
1. BEofre it begins, the DNA helix begins to unwind.
2. THis is done by enzymes, called DNA helicases, ehich open the double helix by breaking the hydogen bonds.
3. Once the 2 strands are seperated, additional prteoins are attached to each strand, holding them apart and preventing them from twisting bsck.
3. Replication forks are the two areas on either end of the DNA, where the double helix seperates.
Step 2.
At replication fork, enzymes known as DNA polymerases move along each of the DNA strands, adding nucleotides to the exposed nitrogen bases, according to the base pairing rules. As the ploymerases move along, two new double helixes are formed.
Step 3.
ONce a DNA piolymerase has begun adding nucleotides to the growing double helix, the enzyme remains attached until all the DNA has been copied then is signaled to detach. This process produces two DNA molecuele, composed a new and original strand. Each DNA is exactly replicated.
Describe Mutations.
-wrong nucleotide asses to new strnad-prevented by the polymerases to have a proofreading role-add nucleotides to growing strand, only if the previous one is right.
*Also able to backtrack and remove incorrect and replace.
Multiple Replication Forks INcrease the Speed of REplication
~all the boxes caried in one trip, rather than one at a time.
Step 1.
1. BEofre it begins, the DNA helix begins to unwind.
2. THis is done by enzymes, called DNA helicases, ehich open the double helix by breaking the hydogen bonds.
3. Once the 2 strands are seperated, additional prteoins are attached to each strand, holding them apart and preventing them from twisting bsck.
3. Replication forks are the two areas on either end of the DNA, where the double helix seperates.
Step 2.
At replication fork, enzymes known as DNA polymerases move along each of the DNA strands, adding nucleotides to the exposed nitrogen bases, according to the base pairing rules. As the ploymerases move along, two new double helixes are formed.
Step 3.
ONce a DNA piolymerase has begun adding nucleotides to the growing double helix, the enzyme remains attached until all the DNA has been copied then is signaled to detach. This process produces two DNA molecuele, composed a new and original strand. Each DNA is exactly replicated.
Describe Mutations.
-wrong nucleotide asses to new strnad-prevented by the polymerases to have a proofreading role-add nucleotides to growing strand, only if the previous one is right.
*Also able to backtrack and remove incorrect and replace.
Multiple Replication Forks INcrease the Speed of REplication
~all the boxes caried in one trip, rather than one at a time.