Class average 267 ± 61 points
(min 91; max 382)
Estimated passing grade ranges A >320; B >260; C >200
For regrading please ask:
Lawrence #1,2
Nina #3,4
Philong #5
Matt #6,7
Jenn #8,9
Kris #10,11
Andrew #12
Below is the key for each question including the point break down:
Before requesting a regrade, please understand the key, and read the point distribution given by TAs to grade each question.
1. 10 for Dielectric Constant
10 for inverse relation of force and D
10 for Hydrophobic
2. 5 each for Vander Waals and H bond
10 for H bond for short distance
10 for H bond structural effects.
3A. Answer is 2. There was no partial credit given.
3B. Zero
3C. Only full names of any of the charged residues was excepted.
3D. The sequence had to be only 3 residues long. If more residues were
given, no credit was given. If there were charged residues, three points
were taken off each.
4a. The sequence had to start with S. (2pts). It had to alternate
polar-non-polar-polar. If there was a mistake in only one residue 3 points
were taken off. Some people put 5' -> 3'. These answers had 3 points taken
off.
4b. 2.1nm. No partial credit was given. The calculation was .7nm x 3 =
2.1nm. If the person used .35nm, this had to be calculated by 6. Most
people multipled this by 7. This is wrong.
Question 5:
Part I:
+10 for base pairing or AT and GC
+10 for interaction between two separate strands
+0 for saying H-bonds stabilize double helix (info already given in
the question)
Part II:
+5 for H-bonds increasing Tm or comparing 3 H-bonds in GC to 2H-bonds
in AT
+5 for GC content directly proportional to Tm
+10 for drawing correct graph
+5 for drawing %ss vs. Tm graph with two curbves, one with greater
GC content
+0 for drawing only one S curve
+0 for drawing S curve on GC content graph
(+5 if the only thing mentioned for the entire question was cooperativity,
must say "cooperativity"' for points)
question 6
- 30 points for AATS attach correct AA to tRNA
-5 for wrong wording but right idea,
-10 had right idea but no understanding of translation process, -15
for saying specificity of AATS only, -20 and
-25 for weaker varyations on the latter answer
question 7
- 5 points for a tRNA feature and 5 points for which molecule differs
from that feature
Question 8: 30 points total
Part A: 15 points total
+5 points for glycosidic bond (no points for peptide bond)
+5 points for beta(1,3)
+5 points for beta(1,4)
Part B: 15 points total
+15 points for hydrolysis or decondensation
+10 points if they say 'addition of water' because it asked specifically
for a chemical reaction
+0 for any other answer ie. methylation or hyaluronase.
Question 9: 40 points total
+10 points for 'beta glycosidic bonds lead to elongated polymers'. The important word is 'elongated' or 'extended' (anything of that sort). If it mentions just 'sheets', 'long' ('long' is close to elongated, but tended to lack further explanation), or 'linear', I gave 5 points.
+10 points for a correct example of a beta polyglucose, like cellulose. If they gave me anything that wasn't a beta polyglucose (glucose as the important part), I gave 5 points (ex. Chitin= beta(1,4) NAG, but not glucose specifically).
+10 points for alpha glycosidic bonds lead to helical polymers.
+10 points for a correct beta± polyglucose (examples would be
amylose, amylopectin, starch, glycogen). Lots of people gave 'sucrose'
as an answer. Even though sucrose is a disaccharide and not a polysaccharide
(polyglucose), I gave them full credit.
#10
+15 for knowing that the membrane was destroyed, solubilized, broken etc...with partial credit +5 points for answers that get the point by describing this process but not saying it...
+15 for saying micelle and either drawing a picture and labeling or describing what a micelle is..if they don't describe a micelle I took off -5 because it asked to in the directions
#11
+10 for labeling the phospholipid correctly...most got this
+20 for showing a monolayer with the correct orientation of the phospholipid...I took off all points for pictures with bilayers and if they had both structures I took off -5.
Question 12:
Under which circumstances?
Just mentioning that you need a pure crystal got you no points.
+7 points : X-ray crystallography requires the domain being imaged to
be in a static, regularly ordered crystal lattice.
or
+7 points : crystallography solves a time-averaged structure.
or
+ 10 points : for stating both
Why can it not solve atomic details of flexible regions?
+10 points : flexible domians result in disordered or moving regions
of the crystal lattice.
Also accepted : flexible regions generate a blurry or
blank diffraction pattern.
How can one identify flexible domains?
+10 points : the location of missing structural information (in the
electron density) identifies flexibile domains.
How would you solve the latter problem?
+10 points : use NMR to solve flexible regions.