Name:_________________________
Biochemistry Test 3
All problems are worth 14 points. YOU MAY SKIP ONE PROBLEM. If you do all the problems I
will throw out the one with the lowest point value.
1. A (5 points) Below is a disaccharide made of two sugars you should know. Since this is a sugar I
invented there is no trivial name, so your job is to name the disaccaride as completely as possible.
(Hint: If this were lactose the name I would be looking for is $-D-Galactopyranosyl-(164)$-Dglucopyroanose
CH2 OH
CH2 OH
H
O
H H
H
O
OH
H
O
OH
OH H
HO
H
H
OH
$-D-glucopyranose (163) $-D-ribofuranose
B. (4 points) Does this sugar contain end? If so, circle the carbon would be oxidized when Cu2+ is
reduced.
Yes, circle on C1 of the ribose (the rightmost C on the structure)
C. (5 points) Assume I have an enzyme that would hydrolyze this disaccharide into two
monosaccharides. What would the linear forms of the two monosaccharides be?
H
H
HO
O
OH
H
H
OH
H
OH
CH2OH
H
H
H
H
O
Note: I remember asking you to memorize the
linear configuration of glucose but not ribose.
OH Thus, on this question I took points off if the
OH OH’s were pointing in the wrong direction on
glucose but not for ribose.
OH
CH2OH
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2. (14 points) What are the three major classes of glyconjugates. Describe the general features of each
class of glycoconjugate and give an example or two.
Proteoglycans - Mostly carbohydrate with a little protein, carbohydrate is usually a simple, highly
repetitive sequence. Proteoglycans are a major component of the extracellular matrix. An
example is the proteoglycan aggramer
Glycoproteins - Mostly protein with not as much carbohydrate. Usually classed as O-linked (sugar
attached to Ser or Thr) or N-linked (sugar attached to Asn). Sugars are usually more complex
often with branching. Many integral membrane proteins and most secreted proteins are
glycoproteins.
Glycolipids - Carbohydrate attached to lipids. Carbohydrate portion is complex and branched, very
similar to carbohydrates seen glycoproteins. Seen in many biological membranes, is a major
portion of cell-cell recognition, and part of blood typing.
3. (14 points) Draw the structure of an Adenine base paired to a Uracil, and a Guanine base paired to
a Cytosine
See figure 10-11 from your text. As I graded this problem I only took off 2 points for having te base
pairs incorrect. I was surprised by the number of people who had this wrong. Since this is a very basic
property from which all of genetic flows, if I ever ask this problem again the base pairing will be worth
about 10 points!
4. (14 points) Describe the many ways that DNA can be nonenzymatically altered in the cell.
Deamination - loss of extracyclic NH2 groups. G6U occurs about 100/day/cell
also several other base conversions occuring about 100 X slower
Depurination - G or A (purines) breaking link to sugar. Occurs about 10,000/cell/day
Dimerization - UV light dimerizeses adjacent pyrimidines, primarily TT.
Alkylations - alkyl groups added by various chemicals found in the environments, examples include
dimethylsulfate, dimethylnitrosamine and nitrogen mustard.
Oxidative damage - primarily comes from free radical reactions that aren’t elimnated by various
protecting mechanisms in the cell.
X-ray and (-ray damage. Can cleave any covalent bond in a DNA molecule.
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5. (14 points) Name the three major classes of membrane lipids and briefly describe their structure.
I was looking for a diagram like figure 11-6 from your text, with a structural diagram of each
phospholipid. Here the three major classes are glycerophospholipids, phospho-sphinplipids, and
glyco-sphingo lipids. Many people did glycerophospholipids, sphingolipids and steroids. I accepted
this answer
6. (14 points) What is an isoprenoid? List at least 5 different lipids that are made from an isoprenoid
backbone.
An isoprenoid is a compound derived fro a 5C isoprene precursor
CH 3
H 2C C
H
CH 2
Isoprenoid compunds include Steroid hormones, Vitamins A, D, E, and K, and the dolichol anchor that
is used for some membrane proteins
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7. (14 points) Describe, in as much detail as possible, the fluids mosaic model of a membrane.
I was looking for a diagram similar to figure 12-3 from our text, plus a discussion that mentioned how
the lipid bilayer is made with phospholipids with the hydrophobic tails pointing into the center of the
bilayer, and the hydrophillic head on the surface of the bilayer. These lipids are very fluid and move
easily in the plane of the bildayer, but cannot flip-flop from one side to the other. In fact the lipid
composition of the inside of membrane is often different than the lipid composition of the outside of the
bilayer. Protein are thought to float freely in this surface and can also mover laterally as long as they
aren’t anchored to cytoskeleton in some way. Proteins can be wither integral membrane protein that
are buried in the membrane anc cannot be easily removed, or peripheral proteins that are associated
with the membrane through some weak interactions that can be easily broken.
8 (14 points) Describe, in as much detail as possible, the structure and function of the Na+K+ ATPase.
A figure like 12-34 from your text, Plus a discussion that included some of the following points:
the Na+K+ ATPase is a P-type ATPase, meaning its mechanism goes through a phosphorylated
intermediate and its action can be inhibited by Vanadate. It is a dimer composed of a 50,000 and a
110,000 MW subunits, both of which span the membrane. This ATPase is used to pump 3 Na+ ions
out of the cell and 2 K+ ions into the cell for every ATP hydrolyzed. The ion gradients established by
this pump are very important to the cell and this pump alone may account for as much as 25% of the
ATP hydrolysis in a resting cell. In the discussion I was also checking to be sure the ATPase was not
getting confused with the K+ channel ehat was also discussed in this chapter.
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