Download Chemistry 11 Fall 2009 Examination #5

Chemistry 11 Fall 2009
Examination #5 ANSWER KEY
For the first portion of this exam, select the best answer choice for the questions below
and mark the answers on your scantron. Then answer the free response questions that
follow (100 pts. total; multiple choice 2 pts. each).
For questions 1-4, match the carbohydrate with its size/functional group name:
A.
B.
polysaccharide
monosaccharide, aldohexose
C.
D.
1.
sucrose
C
2.
starch
A
3.
D-fructose
D
4.
maltose
C
5.
The order of amino acids in a peptide or protein
A.
B.
C.
D.
E.
6.
is critical to its structure.
is critical to its structure and function.
is critical to its function.
is critical to neither structure nor function.
can be ignored as long as all the amino acids are present.
Which of the following about lipids is NOT TRUE?
A.
B.
C.
D.
E.
7.
disaccharide
monosaccharide, ketohexose
Lipids are soluble in liquid ammonia.
Lipids are classified based on their property of solubility rather than their
structure.
Lipids are soluble in CCl4.
Lipids form an integral part of the cell membrane.
Lipids store energy within fat cells.
What is the result when a polysaccharide undergoes a hydrolysis reaction?
A.
B.
C.
D.
E.
The product is starch.
The polysaccharide breaks down into smaller sugars.
Two smaller sugars are joined to make a larger carbohydrate.
The product forms Benedict’s reagent.
The products are generally glucose, fructose, and/or galactose.
8.
At physiological pH, the NET charge on an amino acid with no ionizable side chain is:
A.
B.
C.
D.
E.
9.
Which fatty acid has the highest expected melting point?
A.
B.
C.
D.
E.
10.
resonance
a hemiacetal
hydrolysis
mutarotation
a glycoside
Which functional group is involved in donating a proton to form the zwitterion in
aqueous amino acid solutions?
A.
B.
C.
D.
E.
12.
18:0
16:0
16:1
18:2
18:3
The term used in carbohydrate chemistry to describe a ring opening, closing, and
interconverting between its anomeric forms is called:
A.
B.
C.
D.
E.
11.
+1
0
+2
–1
–2
amine
amide
carboxylic acid
peptide linkage
amino acids exist as neutral un-ionized molecules
Soaps are:
A.
B.
C.
D.
E.
sodium or potassium salts of glycerol
sodium salts of fatty acids
derivatives of carbohydrates
triglycerides
made from hydrogenated oils
13.
In its chair conformation, β-D-glucopyranose is the most widely occurring form of
glucose in nature with the following characteristics EXCEPT:
A.
B.
C.
D.
E.
14.
Which of the following descriptions about amino acids is CORRECT?
A.
B.
C.
D.
E.
15.
monosaccharides
disaccharides
polysaccharides
reducing sugars
non-reducing sugars
Fatty acids typically contain:
A.
B.
C.
D.
E.
17.
Amino acids are covalent compounds.
Amino acids are ionic compounds.
Amino acids are solids with low melting points.
both B and C
All the amino acids of all the proteins in the body are D-isomers.
Starch, sucrose and cellulose are all examples of:
A.
B.
C.
D.
E.
16.
it forms a six-membered ring.
carbon-6 is above the plane of the chair.
all of the hydroxyl groups are equatorial.
the anomeric carbon has a hydroxyl group that is below the plane of the
chair.
all axial positions are occupied by hydrogen.
12 – 20 odd number of carbons with a carboxylic acid
12 – 20 even number of carbons with an ester
branched carbon substituents that extend from the saturated or unsaturated main
chain
triple bonds surrounded by single bonds
None of the above
Which of the following is an anomeric pair?
A.
B.
C.
D.
E.
D-glucose and L-glucose
D-glucose and D-fructose
α-D-glucose and β-D-glucose
α -D-glucose and β-L-glucose
D-glucose and L-fructose
18.
The dipeptides Ser-Thr and Thr-Ser:
A.
B.
C.
D.
E.
19.
The number of fatty acids that make up a triglyceride is/are:
A.
B.
C.
D.
E.
20.
amylose
glycogen
cellulose
lactose
sucrose
The interaction that forms between the ionized side chains of amino acids with opposite
charges is called:
A.
B.
C.
D.
E.
22.
One
Two
Three
either A, B or C
Fatty acids are not part of a triglyceride molecule.
Human beings don’t have the enzymes necessary for the hydrolysis of the β (1→4)
glycosidic linkages between molecules of glucose. That is why we cannot digest this
compound, a component of certain laxatives. The compound described is:
A.
B.
C.
D.
E.
21.
are stereoisomers
are constitutional isomers
have different properties
both A and C
both B and C
a salt bridge
a hydrogen bond
a hydrophobic interaction
an α-helix
an antiparallel β-pleated sheet
Hydrogenation involves which of the following?
A.
B.
C.
D.
E.
removing hydrogen from fatty acids and forming more double bonds
adding hydrogen to fatty acids and reducing double bonds
raising the melting point of the fat or oil
both A and C
both B and C
END OF MULTIPLE CHOICE
23.
(17 pts. total) This section involves a series of questions dealing with amino acids and
proteins.
A.
(4 pts.) Amino acids are generally classified on the basis of their side-chain
chemical properties. Your textbook classifies glycine as a polar amino acid when
its side chain is nonpolar. Explain why.
Glycine as a unit behaves like a polar amino acid as there is only a
small amount of nonpolar character from the sidechain compared to the
large influence of the α-amino and α-COOH groups.
B.
(2 pts.) Is it possible to have an enantiomer of glycine? If possible, draw the
enantiomer and indicate if it is a D- or L- form. If not possible, indicate why
glycine does not have an enantiomer.
No because glycine does not contain a chiral center, which means it cannot
possess an enantiomer.
C.
(5 pts.) Write the names of two amino acids that have more than one stereocenter?
Draw the structures and indicate the stereocenters with an asterisk (*).
The two amino acids are isoleucine and threonine as shown below:
OH
H
*
H3N
*
COO
Isoleucine
D.
H
*
H3N
*
COO
Threonine
(6 pts.) In heavy metal poisoning, one of the antidotes prescribed is raw egg
whites and milk. The type of noncovalent interaction formed between proteins in
egg white and the heavy metal is -----S- Hg2+ -S----- (where ----- represents the
understood remainder of the protein chain).
1)
(2 pts.) Identify the amino acid that is involved in this interaction. Cys
2)
(2 pts.) What is this interaction called? metal-ion coordination
3)
(2 pts.) Does this interaction affect the primary, secondary, tertiary, or
quaternary structure of a protein? Briefly explain.
This interaction affects the tertiary structure of a protein. (Refer to
your course guide for descriptions of the 4 types of protein structure.)
24.
(12 pts. total) Questions 24 and 25 involve carbohydrates.
For #24 (A – D), consider the hydrolysis of lactose.
A.
(5 pts.) Draw the structure of lactose. Does your drawing represent a reducing or
non-reducing sugar? Make certain to draw all the possible anomers of your
structure (if applicable).
Reducing sugar because the cyclic hemiacetal of the D-glucopyranose unit is
in equilibrium with its open-chain form and can be oxidized to a carboxyl
group.
CH2OH
O
CH2OH
OH
O
O
OH
OH
OH +
OH
CH2OH
OH
O
CH2OH
O
O
OH
OH
OH
OH
OH
OH
B.
(2 pts.) What is the molecular formula for lactose? C12H22O11
C.
(1 pt.) Identify the products for the hydrolysis of lactose by drawing Fischer
projections of the sugar(s) below. Can you name the sugar(s)? If so, label your
drawing(s). D-galactose and D-glucose, shown respectively below:
H
HO
HO
H
D.
CHO
OH
H
H
OH
CH2OH
H
HO
H
H
CHO
OH
H
OH
OH
CH2OH
(4 pts.) FIGURE IT OUT! Doctors use a lactose tolerance test to determine if a
person is lactose intolerant. In this test, the person is given a solution of lactose to
drink. Blood glucose concentration levels are then measured over the next two
hours. A test was carried out on a healthy man who was lactose tolerant and on a
man who was lactose intolerant. The results for the first hour are shown below:
Blood glucose concentration in mmol/L
Healthy lactose tolerant man
Lactose intolerant man
3.8
3.8
4.7
3.9
6.1
3.8
6.6
3.9
6.2
3.9
Time in minutes
0
15
30
45
60
25.
1)
(2 pts.) The blood glucose concentration changed in the healthy man after
he had taken the test. Describe how this can be the case using appropriate
biochemical principles. The healthy man has an enzyme (i.e., lactase)
that helps in the hydrolysis of lactose into D-glucose and D-galactose,
thereby increasing the concentration of glucose in the blood.
2)
(2 pts.) Now explain the results for the lactose intolerant man using
appropriate biochemical principles. The lactose intolerant man lacks
the enzyme lactase and therefore cannot break down lactose, resulting
in a low glucose concentration.
(12 pts. total) Below is the structure of a carbohydrate. Answer all the questions that
follow regarding this carbohydrate. Numbering labels of sugars do not necessarily imply
linkage order.
OH
OH
HO
O
OH
sugar 2
sugar 1
O
HO
O
OH
OH
HO
A.
(1 pt.) Identify the type of linkage in the structure above. α (1→4) linkage
B.
(1 pt.) The covalent bond joining the two monosaccharides is known as what?
Glycosidic bond
C.
(4 pts.) Using your knowledge of organic chemistry, draw the MOST STABLE
chair conformation for each of the sugars present in this carbohydrate. Both
sugars 1 and 2 are D-glucose as shown via the chair conformation below:
CH2OH
O
HO
HO
HO
D.
(4 pts.) Convert each of the chair conformations to Fischer projections and name
each of the sugars. Both sugars 1 and 2 are D-glucose as shown below:
H
HO
H
H
26.
OH
CHO
OH
H
OH
OH
CH2OH
E.
(1 pt.) Is this carbohydrate a reducing or non-reducing sugar? Briefly explain
your identification. Reducing sugar because the cyclic hemiacetal of the Dglucopyranose unit (sugar 2) is in equilibrium with its open-chain form and
can be oxidized to a carboxyl group.
F.
(1 pt.) Finally, identify your carbohydrate based on your knowledge of structures
taught to you in class. Maltose
LAST ONE! (15 pts. total)
A.
(3 pts.) What is the difference between a fatty acid, a triglyceride, and a steroid?
Appropriate detail should accompany your response in order to receive credit.
Fatty acids consist of 12-20 even numbers of carbons (including a carboxylic
acid) that are the building blocks of fat molecules. Three fatty acids combine
with one glycerol to form a triglyceride. Steroids are compounds that
contain a four ring generic structure.
B.
(6 pts.) Give an example of a triglyceride and a fatty acid molecule by drawing
two structures using your knowledge of biochemistry. Also draw the structure of
the steroid nucleus and name the most important steroid.
An example of a fatty acid is CH3(CH2)14COOH. Several examples possible
here as long as the # of carbons is even with 12 – 20 carbons.
An example of a triglyceride is:
O
CH2OC(CH2)14CH3
O
CHOC(CH2)7CH=CH(CH2)7CH3
O
CH2OC(CH2)16CH3
The structure of a steroid is:
Most important steroid is cholesterol.
C.
(2 pts.) What is the other name for FAT? Name the functional group present in
this molecule. Triglyceride. Ester functional groups link the glycerol to the
fatty acids.
D.
(3 pts.) The reaction of a triglyceride with a strong base is called saponification
and is of commercial importance in making soap.
E.
(1 pt.) The carriers of cholesterol are called lipoproteins.