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36 Cards in this Set
- Front
- Back
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Chargaff's Rule |
DNA from any cell of an organism should have a 1:1 pyrimidine: purine ratio A=T and C=G |
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Which DNA Replication Model is Correct? |
Semi-Conservative (Each DNA molecule has one old and one new strand) |
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Who did the experiment that showed how DNA replicates? |
Meselson and Stahl |
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Describe the steps of Meselson and Stahl's Experiment: |
1. Grew bacteria in presence of N15 2. Switched bacteria to a plate with lighter N 3. Used centrifugation after one cell division, then after two cell divisions, and so on to see the ratio of heavy to light DNA. |
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What is the sequence of oriC in E. Coli? |
3 AT-rich 13-mer repeats & 4 9-mer repeats |
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What 2 Enzymes are involved in DNA unwinding? |
DNA Gyrase (DNAG) and Helicase (DNAB) |
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What does Helicase do? |
It unwinds DNA at the origin of replication so that the template is exposed. -Hydrolyzes ATP for energy to break H-bonds |
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What does DNA Gyrase do? |
Catalyzes negative supercoiling (which is ATP-dependent) |
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What does Single-Stranded Binding Protein do? |
Stabilizes ssDNA after it is unwound to keep it from being rewound |
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What is telomerase? |
An enzyme made of protein and RNA subunits |
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Telomere Structure and Functions |
100's of repeats of the sequence TTAGGG at the end of chromosomes (humans) Functions: -Prevents loss of genes during cell division -Prevents Fusion of chromosome ends -Protects chromosome ends from degradation |
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In what direction does DNA replication take place? |
In the 5' to 3' direction |
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Parts of a nucleotide |
-Deoxyribose sugar -Phosphate group -One of 4 Nitrogenous Bases |
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New nucleotides are added to the --- prime end of the newly forming DNA strand during replication |
3' |
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What does DNA polymerase do? |
It catalyzes new nucleotide additions to the daughter strand. |
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What do Beta Clamps and the Clamp Loader do? |
They help to hold DNA polymerase in place on the DNA. |
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DNA Polymerase can not begin adding nucleotides without: |
A Primer |
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What is a Primer? |
A short sequence of RNA |
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What does Primase do? |
Pairs primers to the template DNA strand |
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On which strand does continuous DNA synthesis occur? |
On the 3'-5' oriented parent strand. |
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On which strand does discontinuous synthesis occur? |
On the 5'-3' parent strand. (The lagging strand) |
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Lagging Strand DNA replication is completed in segments called: |
Okazaki Fragments |
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Describe what primase does on the lagging strand: |
It adds primers ahead of the 5' end. |
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What enzyme adds the okazaki fragments to primers? |
DNA Polymerase III |
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What enzyme replaces the RNA primers on the lagging strand with DNA nucleotides? |
DNA polymerase I |
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What does DNA ligase do? |
It ensures bonding between the fragments of DNA and the replaced nucleotides on the lagging strand. |
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The Methyl-Directed mismatch repair system relies on what fact? |
Methylation of a newly synthesized DNA strand does not occur until several minutes after the strand is made. |
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A sequence of DNA with only one methylated strand is said to be: |
hemi-methylated |
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What does the MutS protein do? |
It binds to a mismatched base pair in DNA and forms a complex with the protein MutL |
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The formation of the MutS and MutL complex recruits what protein to a hemi-methylated DNA strand near the site of a base pair mismatch? |
MutH |
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What are Thymine Dimers and what causes them? |
Thymine Dimers occur between adjacent thymines, weaken H bonding, and cause deformations of the double helix, leading to errors in replication. UV Light and other ionizing irradiations cause them. |
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What enzyme eliminates thymine dimers from the DNA strand? |
DNA photolyase |
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How does DNA photolyase work? |
It binds to a thymine dimer, is activated by light, and transfers an electron to the dimer, leading to the reformation of two separate thymines. |
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What enzyme eliminates methylations from guanine that can be caused by chemical agents |
methylguanine DNA- methyltransferase |
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The nucleotide excision repair process uses what enzymes? |
UVRA, UVRB, UVRC, UVRD |
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What does UVR stand for? |
Ultra Violet Light Repair |
