Term
| What enzyme is responsible for adding sequences to the ends of linear chromosomes (to prevent it from shortening after DNA replication)? |
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Definition
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Term
| What functional group is needed at the 3' carbon for the polymerizing replication reaction to proceed? |
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Definition
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Term
| Model of DNA replication where the old DNA helix is completely conserved and a totally new helix is produced. |
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Definition
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Term
| Short strand of DNA or RNA that binds to an original DNA template to initiate replication. |
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Definition
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Term
| Who discovered the crystal structure of DNA and had her work stolen by Watson and Crick? |
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Definition
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Term
| Radioactive material used to label proteins. |
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Definition
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Term
| DNA ___________ is the enzyme responsible for adding nucleotides to a growing strand of DNA. |
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Definition
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Term
| Specific type of primer needed to begin DNA replication by DNA polymerase. |
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Term
| The linking of thymine nucleotides together, usually caused by ultra violet light. |
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Definition
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Term
| Radioactive material used to label DNA. |
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Definition
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Term
| Model where DNA replicates by forming a completely new strand from an existing strand. The new helix is half new and half old DNA. |
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Definition
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Term
| Type of reaction that must occur for nucleotides to be covalently linked together. |
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Definition
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Term
| Model of DNA replication where original DNA template is mixed with both old and new nucleotides forming a mixed helix. |
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Definition
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Term
| Who examined the ratios of bases in DNA and found that A was the same as T and G the same as C? |
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Definition
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Term
| DNA __________ is the enzyme responsible for repairing DNA damage caused by thymine dimers. |
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Definition
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Term
| Type of nucleotides added to a growing DNA strand. Also the source of the energy for the replication reaction. |
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Definition
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Term
| Short DNA fragments + RNA primers synthesized on the lagging DNA strand during replication. |
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Definition
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Term
| Enzyme that initially opens the DNA at the origin of replication. |
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Definition
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Term
| DNA ___________ is the enzyme responsible for fusing the gaps in the phosphodiester backbone together via covalent bonding. |
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Definition
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Term
| A replication _______ is formed where the DNA is opened to allow for the enzymes to enter and initiate replication. |
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Definition
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Term
What did the Griffith experiment do?
How did it support the discovery of the genetic material? |
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Definition
He took two different strains of Streptococus pneumonia: S formed capsules and by-passed the immune system to cause disease; R could not form capsules and were easily phagocytosed by white blood cells.
Injections in mice -
S strain: die
R strain: live
Heat-killed S strain: live
Heat-killed S mixed with R: die
Some genetic "material" from the dead S strain was being transferred to the R strain "transforming them into S again. |
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Term
What did the Hershey/Chase experiments do?
How did it support the discovery of the genetic material? |
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Definition
Showed DNA was the genetic material of the phage T2 (virus). The T2 phage is composed of both DNA and proteins. When it attacks E. coli it injects material turning the bacteria into a T2-producing factory releasing phages when it ruptures.
Injected labeled proteins of one phage strain using radioactive sulfur and the DNA in another using radioactive Phosphorous.
Using centrifugation, whatever was left behind in the bacteria was the genetic material. The supernatant was radioactive with proteins while the pellet was radioactive with DNA. |
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Term
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Definition
| In all organisms, the # of adenines was approx. equal to the # of thymines (%T=%A) and the # of guanines was approx. equal to the # of cytosines (%G=%C) |
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Term
| How do you think Chargaff's rule helped Watson and Crick with their model of a DOUBLE helix? |
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Definition
| Since according to Chargaff's rule %T=%A and %C=%G, the adenine was always connected to thymine and guanine was always connected to cytosine. |
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Term
Who was Rosalind Franklin?
What did Franklin do that was important for the discovery of the double helix? |
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Definition
Franklin started working as a research associate at King's College London in the Medical Research Council's (MRC) Biophysics Unit.
Franklin is best known for her work on the X-ray diffraction images of DNA which led to discovery of DNA double helix. Her data, according to Francis Crick, was "the data we actually used" to formulate Crick and Watson's 1953 hypothesis regarding the structure of DNA. |
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Term
| What is x-ray crystallography? |
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Definition
| Method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. |
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Term
| What is the conservative model of DNA replication? |
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Definition
| The original two templates are passed to one daughter cell and the copied two templates are passed to the other daughter cell. |
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Term
| What is the semi-conservative model of DNA replication? |
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Definition
| The original template combines with a new template. Each is passed to daughter cells. Together they form the helix. |
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Term
| What is the dispersive model of DNA replication? |
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Definition
| The original template is mixed with new nucleotides and passed to the daughter cells. |
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Term
| What did Watson and Crick think was the correct method of DNA replication? |
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Definition
| From their DNA model, they came up with a possible method of replication for DNA in which DNA unwinds to form two single strands and free nucleotides pair with each strand forming two new helices (semi-conservative). |
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Term
What experiment did Meselson and Stahl do?
How did it contribute to proving Watson and Crick correct? |
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Definition
They used heavy Nitrogen (N 15) to determine the correct model of DNA replication.
Using centrifugation, they saw after two generations that the DNA replicated semi-conservatively. |
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Term
| What free functional group is required to initiate DNA replication by DNA polymerase? |
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Definition
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Term
| What is DNA polymerase and what does it do? |
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Definition
A DNA polymerase is an enzyme that catalyzes the polymerization of deoxyribonucleotides into a DNA strand.
Links the nucleotides together into growing strands via hydrolysis using the energy released by the removal of the two phosphates. |
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Term
| What is helicase and what does it do? |
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Definition
Helicase is the enzyme that untwists the DNA double helix, separating it so the replication machinery can access it.
Opens the ORI |
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Term
| What are single stranded binding proteins and what do they do? |
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Definition
| Proteins that bind to the ORI forcing the helix to stay open while polymerases read the templates |
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Term
| What is primase and what does it do? |
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Definition
| Enzyme that adds RNA primer to each strand of DNA |
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Term
| What is DNA ligase and what does it do? |
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Definition
Enzyme that catalyzes the linkage between two free ends of double-stranded DNA chains by forming a phosphodiester bond between them
Fuses the gaps between Okazaki fragments in DNA backbone back together |
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Term
| What is telomerase and what does it do? |
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Definition
| Telomerase extends the 3’ end of the chromosome using a movable RNA template. This allows DNA polymerase to completely copy the other sequence from the end of the other strand. |
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Term
| What is an okasaki fragment? |
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Definition
| Short, newly synthesized DNA fragments that are formed on the lagging template strand during DNA replication |
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Term
| What is the difference between leading and lagging strands? |
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Definition
Leading strands are in the necessary 5'-3' direction and make DNA from a single primer.
Lagging strands are in the opposite 3'-5' direction and require DNA polymerase to run in short stretches in the opposite direction using multiple primers |
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Term
| What is always the direction of DNA replication? |
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Definition
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Term
| What does continuous and discontinuous DNA replication refer to? |
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Definition
Continuous replication refers to the leading strand which continues to make DNA from a single primer.
Discontinuous replication refers to the lagging strand which requires DNA polymerase to run in short stretches in the opposite direction requiring multiple primers. |
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Term
| Why is it not possible to copy the end of a linear chromosome? |
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Definition
| The RNA template that is laid into place must be removed and since the DNA polymerase needs the RNA template to add nucleotides onto a free 3'-OH, each successive chromosome becomes shorter |
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Term
| What enzyme proofreads DNA during replication? |
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Definition
DNA polymerase can check for mistakes while it is adding nuccleotides.
It rarely makes a mistake. |
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Term
| What enzyme proofreads DNA after replication? |
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Definition
| The 3' to 5' proof-reading exonuclease works by scanning along directly behind as the DNA polymerase adds new nucleotides to the growing strand. |
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Term
| What is a thymine dimer and what usually causes it to be formed? |
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Definition
| Thymine dimer is a distortion in the DNA molecule that usually is formed from exposure to UV light |
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Term
| How is a thymine dimer recognized? |
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Definition
| Ultraviolet light can form crosslinks between adjacent Thymine bases in DNA causing a kink which is easily detected by the endonuclease as it scans along the DNA helix |
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Term
| How is a thymine dimer repaired? |
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Definition
| A DNA nuclease removes all the nucleotides on each side of the damaged area and DNA polymerase I replaces the gap with the correct bases. DNA ligase then seals the backbone nicks. |
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Term
| Name the enzyme responsible for this type of repair (thymine dimer repair). |
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Definition
DNA nuclease removes damaged area
DNA polymerase I replaces it
DNA ligase seals it |
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Term
| Where does the energy come from to join nucleotides together? |
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Definition
| Via hydrolysis using the energy released by the removal of two phosphates |
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Term
| What are these types of nucleotides called? |
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Definition
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Term
| What enzyme removes the RNA primer? |
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Definition
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Term
| Why does DNA replication require an RNA primer to start? |
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Definition
| RNA primer provides the double stranded molecule required for initiation by DNA polymerase III |
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Term
| What is the origin of replication? |
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Definition
| DNA replication starts at a site on the DNA called the origin of replication. In higher organisms, replication begins at multiple origins of replication and moves along the DNA in both directions outward from each origin, creating two replication “forks.” |
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Term
| How many origins of replication are in eukaryotes? |
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Definition
| Eukaryote linear chromosomes have multiple ORIs |
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Term
| How many origins of replication are in prokaryotes? |
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Definition
| Prokaryotes only have one ORI (binary fission) |
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