Collaboration Teams - Members share responsibility for posting refined answers to the guided readings - succinct, relevant, clear, and with pictures or a video to compliment.
When contributing to the reading guide, follow these steps:
1) First complete the reading guide on your own from the DNA unit page.

2) Write your response to a question in word and then copy it. Be sure to upload pictures and/or video for each question.
3) Click on the edit button and then go to the appropriate question and paste your answer below it.
Sign your contribution with your first name and last initial and TEAM COLOR
4) Scroll to the very bottom and in the Optional comment box, place a summary of what you did and sign it (e.g. "I answered chp 26 question 3" - Tom S.) Th en click Save.
14-15, 20
Remember to include pictures and or video for all answersSmiley-02-june.gif

1. Explain Griffith’s experiment and the concept of transformation in detail.

Frederick Griffith, A British medical officer, was studying Streptococcus pneumonia, a bacterium that causes pneumonia in mammals. Griffith had two strains of the bacterium, a pathogenic one and a nonpathogenic strain. He was surprised to find that when he killed the pathogenic bacteria with heat and then mixed the cell remains with living bacteria of the nonpathogenic strain, some of the living cells became pathogenic. Furthermore, this new trait of pathogenicity was inherited by all the descendants of the transformed bacteria. Clearly, some chemical component of the dead pathogenic cells caused this heritable change, although the identity of the substance was not known. Griffith called the phenomenon transformation, now defined as a change in genotype and phenotype due to the assimilation of external DNA by a cell.

external image Streptococcus%20pneumoniae%20fig11.jpg

2. What did Avery, MacLeod and McCarty contribute to this line of investigation?

Avery purified various types of molecules from the heat-killed bacteria, then tried to transform nonpathogenic bacteria with each type. Only DNA worked. Finally, in 1944, Avery and his colleagues McCarty and MacLeod announced that the transforming interest was DNA.
external image 05_04_Avery_MacLeod.jpg

3. What is a bacteriophage?
A bacteriophage i​s a virus that infects bacteria, and only infects a specific host cell.Smiley-02-june.gif

external image BacteriophageCartoon.jpgexternal image bacteriophage_jpg.jpg

4. Label the diagram below and explain the Hershey Chase experiment.Smiley-02-june.gif
They devised an experiment showing that only one of the two components of T2 actually enters the E. coli cell during infection. First they grew T2 with E. coli in the presence of radioactive sulfur. The DNA of a separate batch of T2 was labeled with atoms of radioactive phosphorus. Then both batches infected separate samples of nonradioactive E. coli cells. They then put the mixtures into a blender to shake loose the phages. Then they placed the mixtures into a centrifuge, and forced the bacteria cells to the bottom of the test tubes. After testing the bacteria, the radioactive DNA ones were found to have radioactive material inside the cell, and the radioactive protein ones were found to have radioactive material outside the cell.

5. How did Chargraff’s work contribute to understanding the structure of DNA?Smiley-02-june.gif
He reported that DNA composition varies from one species to another, which accounts for the genetic variation found between different species. He also found a peculiar regularity in the ratios of nucleotide bases within a single species. The DNA composition changes from species to species, but it is consistent within the same species.

6. Why was Rosalind’s Franklin’s work essential to the understanding of the structure of DNA?
How did she do it? What technique?

Franklin’s work showed DNA is a double helix.
- alyssa c.


7. Upload a labeled diagram of DNA and explain what is meant by 5’-3’

external image 08P-210-DNA-5-3.jpg
The 5' and 3' indicate the carbon numbers in the DNA's sugar backbone. The 5' carbon has a phosphate group attached to it and the 3' carbon has a hydroxyl group. This asymmetry gives a DNA strand a "direction".

Keely B

8. Why does adenine always pair with thymine and guanine with cytosine in DNA?
Adenine and thymine form 2 hydrogen bonds, and guanine and cytosine form 3 hydrogen bonds. Adenine does not pair with guanine or cytosine because its pairing with thymine makes these 2 DNA bases stable. Adenine does not bond with guanine and cytosine because they prefer to bond with 3 hydrogen bonds.

Keely B

9. What is meant by the term that DNA replication is semiconservative?Smiley-02-june.gif
DNA replication is semiconservative meaning that the replicated DNA consists of one old strand (derived from the old molecule) and one new strand.—Jackie H. Pink Team


Zack B.

Adam A.

10. Detail the Meselson and Stahl experiment concerning DNA replication.Smiley-02-june.gif

Meselson and Stahl tested the conservative, semiconservative, and dispersive models of DNA. Their experiments supported the semiconservative model in which the two parental strand of DNA are templates for new, complementary strands and each replicated DNA molecule consists of one old strand and one new strand. –Jackie H. Pink Team

Zack B.

11. How is bacterial DNA replication accomplished?
Bacterial DNA replication is accomplished with remarkable speed and accuracy. It takes more than a dozen proteins and enzymes to replicate. It starts at a site called the origins of replication that’s where the strands are separated.

--Brian N

Emily A-green team​

12. What are DNA polymerases?Smiley-02-june.gif
DNA polymerases's role is in DNA replication . Polymerase reads DNA strands as a template and uses it to synthesize the new strand. This process copies a piece of DNA. The newly-polymerized molecule is complementary to the template strand and identical to the template's original partner strand. Steph A-Green Team

13. In your own words, what is meant by the term – DNA is antiparallel in arrangement”?

DNA is antiparallel in arrangement; they are oriented in opposite directions to one another. The new strands formed during DNA replication must also be antiparallel to their template strands.
Steph and Emily I need some help on this question.

--Brian N

14. Define the following terms:
pictures of some of these would help

a. Leading strand- The new DNA strand synthesized along the template strand in the 5’ – 3’ direction. Elongates continuously.
b. Lagging strand- Discontinuously synthesized DNA strand. Grows in an overall 3’-5’ direction by adding short segments, called Okazaki fragments.
c. Okazaki fragments- segments of the lagging strand. Made up of nucleotides.
d. DNA ligase- joins, or ligates, the sugar-phosphate backbones of the Okazaki fragments, forming a single new DNA strand.
e. Primer- initial nucleotide chain. Consist of either DNA or RNA. Initiates the replication of cellular DNA in the form of a short stretch of RNA with an available 3’ end.

external image 500px-Leading_strand_replication.png
Laura C, purple

15. Upload a video of DNA replication and explain what happens on the 2 antiparallel strands.

16. List the functions of the following enzymes:Smiley-02-june.gif

a. Helicase
An enzyme that untwists the double helix at the replication forks
b. Single stranded binding protein
Bind to the unpaired DNA strands stabilizing them until they serve as templates.
c. Topoisomerase
Helps to relieve the stress ahead of the replication fork.
d. Primase
Joins RNA nucleotides together one at a time, making a primer complementary to the template strand.
e. DNA Polymerase III

For the leading strand they synthesize the leading strand, adding on to the primer. Function for lagging strand it elongates each Okazaki fragment.

f. DNA Polymerase I
For the leading and lagging strand removes primer from the 5’ end of the leading strand and replaces it with DNA.
g. DNA Ligase
This joins Okazaki fragments by forming a bond between their free ends creating a continuous strand.
Martin A.

18. What is mismatch repair?Smiley-02-june.gif
It is when an enzyme is used to correct mismatched base pairs. These nucleotides sometimes evade proofreading by a DNA polymerase or arise after DNA synthesis is completed. Then, the enzyme is used to fix those errors.

19. Why is there a short section of a cell’s DNA that cannot be repaired or replaced? upload a video or diagram explaining the problem. It is very important that you understand this conceptually.

20. What are telomeres and why are they important? How does telomerase play a role in aging?