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Midterm

LIFESCI 3 Study Guide - Midterm Guide: Deoxyribose, Northstar Engine Series, Histone H2BExam


Department
Life Sciences
Course Code
LIFESCI 3
Professor
All
Study Guide
Midterm

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LS3 MIDTERM I
INSTR: L. JOHNSON Friday, Feb 3, 2012
NAME:_________________________________
(last) (first)
I.D. #__________________________________
INSTRUCTIONS
1. This exam is 7 pages long. Page Value Score
Before starting make sure
you have all the pages. 2 14
2. WRITE YOUR NAME ON EVERY PAGE. 3 16
3. No credit will be given for an 4 15
illegible answer. 5 19
4. WRITE ONLY IN THE SPACE PROVIDED.
NO OTHER ANSWER WILL BE GRADED. 6 18
7 18
Total 100
KEY
1

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(6 pts) 1. Suppose you were studying a new bacteriophage and decided to label it in
vivo with either 14C-leucine, 14C-uracil or 14C-thymine. After growing the phage
for 2 hours, you isolate the progeny phage and measure the radioactivity.
a) You find that 14C is incorporated into the phage when grown in the presence
of 14C-leucine or 14C-uracil, but not 14C-thymine. What does this tell you
about this new bacteriophage? (2 pts)
The bacteriphage is composed of protein and RNA.
b) What is another choice of label you could use instead of 14C-leucine? (2 pts)
35SO4, 35S-methionine, etc
c) You use your 14C-uracil labeled phage and infect bacteria that are unlabeled.
You allow the phage to grow for an hour and then isolate the bacteria. You
find that the 14C is now contained in the bacterial DNA. How can you explain
this? (2 pts)
The bacteriophage is a retrovirus and the RNA genome was converted
into DNA.
(8 pts) 2. The structure of DNA is critical to its function.
a) Describe in words what makes up the backbone of DNA. (2 pts)
Sugar phosphate backbone made up of alternating deoxyribose and
phosphate connected through phosphodiester bonds between the 3’ position
and the 5’ position.
b) What holds the two strands of DNA together? (2 pts)
Hydrogen bonds between the bases and stacking interactions between the
bases.
c) What is the name of the compound shown below? Is it a nucleotide or a
nucleoside? (4 pts) deoxycytosine diphosphate (dCDP), nucleotide
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(9 pts) 3. RNA is similar yet distinct from DNA
a) Name three features that distinguish RNA from DNA. (3 pts)
RNA has ribose instead of deoxyribose, uracil instead of thymine and is single
stranded instead of double stranded.
(Could also say RNA has complex secondary structures, alternative base
pairing and is made in short segments compared to DNA)
b) What is it about RNA that allows it to form unusual base pairs, whereas DNA
is restricted to the traditional base-pairing? (2 pts)
RNA is not confined to forming a double helix like DNA. It can twist in all
directions allowing non-traditional base pairs to form.
c) RNA double helices are more stable than DNA double helices and yet RNA
itself is less stable than DNA. What single feature can explain both these
observations? How? (4 pts)
The 2’ OH makes RNA less stable, particularly in alkali, but it stabilizes the RNA
double helix because it contributes an additional hydrogen bonding group which
adds to the stability of helical regions.
(7 pts) 4. The chart below shows the OD 260 for two DNAs at increasing temperatures.
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