Prelim 2 Fall07 Key - 1. a. (1 point) Which one of...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
1. a. (1 point) Which one of "Chargaff's rules" was helpful to Watson and Crick for building their model of DNA structure? (Nelson & Cox, p. 281) In all cellular DNAs, the number of adenosine residues is equal to the number of thymidine residues and the number of guanosine residues is equal to the number of cytidine residues. b. (1 point) What other key observation was used to build the model? (Nelson & Cox, p. 282) the x-ray diffraction pattern c. (3 points) List three important features of the model. (Nelson & Cox, pp. 282-3) DNA forms a double helix Strands are anti-parallel sugar-phosphate backbone is on outside bases are on inside, perpendicular to main axis of helix 36 Å per turn of the helix - ~10 base pairs 3.4 Å between nucleotides helix diameter, 20 Å 2. a. (1 point) Name or briefly describe the spontaneous chemical reaction in DNA that causes the change of a G/C base pair to an A/T base pair following replication (if the error is not corrected). (Nelson & Cox, p. 294) Cytosine deamination (a cytosine is converted to uracil) b. (1 point) What feature of DNA makes it possible for cells to detect and repair instances of the reaction described in part "a" above? (Nelson & Cox, p. 294) Uracil is not normally found in DNA c. (3 points) List the four steps required to correct the above error. For two of the steps, name the enzyme involved. (Nelson & Cox, p. 972) 1) removal of base (uracil) - DNA glycosylase 2) cleavage of DNA strand originally containing the uracil - AP endonuclease 3) removal and replacement of the nucleotides including the AP nucleotide - DNA pol I 4) repair of the nick - DNA ligase
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Answer Key 2 3. a. (2 points) Using the replication bubble below, draw in and label the newly synthesized leading and lagging strands. Use a squiggled line to represent primers. Label the 5' and 3' ends of the strands and include arrows to indicate the direction of replication. 5' 3' 5' 3' 3' 5' 5' 5' 3' 3' 5' 5' 3' 3' 5' 5' 5' 3' 3' 3' b. (2 points) Linear DNA molecules cannot be completely copied using the mechanism depicted in part "a" above. Circle the part of each strand that cannot be completely copied. In the space below, explain why not. (Nelson & Cox, pp. 1025-7) The 3' end of each strand should be circled. As the 3' end is being replicated, when the 5' primer is removed via the 5' to 3' exonuclease activity of DNA pol I there is no 3' end onto which the replacement deoxynucleotides can be added. As a result, chromosomes shorten in this region each time they are replicated. c. (Nelson & Cox, pp. 1025-7) (1 point) Name the enzyme that solves this problem in eukaryotes. telomerase (1 point) What class of enzyme is this an example of? reverse transcriptase
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This test prep was uploaded on 04/06/2008 for the course BIOBM 3300 taught by Professor Blankenshi during the Fall '08 term at Cornell University (Engineering School).

Page1 / 11

Prelim 2 Fall07 Key - 1. a. (1 point) Which one of...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online