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LESSON- 7 and 8
THE CHEMICAL BUILDING BLOCKS OF LIFE:
B. AMINO ACIDS AND PROTEINS.
A. Objectives.
-
-
Give the basic structure of an amino acid; identify the amino group, carboxyl group and
side chain.
Explain why amino acids have different properties, what is special about the amino
acids in each group and name some amino acids of each group.
Explain and draw the peptide bond and how it relates amino acids to peptides and
proteins.
Explain in words and figure the relationship between the primary, secondary, tertiary
and quaternary structure of proteins; describe the alpha helix and beta-pleated sheet;
discuss how different amino acid sequences lead to different tertiary structures; discuss
the nature and role of disulfide bonds in tertiary and quaternary structure; describe the
quaternary structure of multimeric proteins.
Discuss the differences between globular and fibrous proteins and relate these to their
secondary and tertiary structure; what is protein conformation? protein denaturation?
and chaperones?
B. Lecture outline.
1.
AMINO ACIDS.
Read:
Proteins (SBM p59-67).
a. structure of an amino acid:
b. different classes of amino acids.
2.
PEPTIDE BOND.
Read:
3.
Figure 3.18 (SBM p63).
PROTEIN STRUCTURE.
a. primary structure:
b. secondary structure:
- alpha helix.
- beta-pleated sheet.
b. tertiary structure: disulfide bonds.
c. quaternary structure.
d. denaturation, folding, and chaperones.
C.
Study Questions.
1.
For what structural level of the protein is the peptide bond
responsible?
A.
primary structure.
B.
secondary structure.
C.
tertiary structure.
D. quaternary structure.
E.
cinquenary structure.
2.
When a protein is denatured by physical or chemical means, which structural level is least affected.
A.
primary structure.
B.
secondary structure.
C.
tertiary structure.
D. quaternary structure.
E.
cinquenary structure.
3.
What bond is vital to the primary structure of a protein?
A.
peptide bond.
B.
hydrogen bond
C.
ionic bond.
D.
glycosidic bond.
E.
phospho-di-ester bond.
4.
What type of bond is formed between the
two molecules shown during a
condensation reaction? A(n)
A.
ionic bond.
B.
hydrophobic bond.
C.
hydrogen bond.
D.
a covalent bond.
E.
a dehydration bond.
5.
An amino acid is to a protein what a
A.
monosaccharide is to a polysaccharide.
B.
fatty acid is to a lipid.
C.
nucleotide is to a nucleic acid.
D.
both A and C.
E.
all of the above.
6.
The level of protein structure which affects all the others is the
A.
primary structure.
B.
secondary structure.
C.
tertiary structure.
D.
quaternary structure.
E.
cinquenary structure.
7.
Radioactive nitrogen could be used to identify
A.
albumin (protein)
B.
cholesterol.
C.
D.
E.
corn oil.
potato starch.
cellulose.
8.
Proteins are polymers formed of structural units called.
A.
amino acids.
B.
fatty acids.
C.
nucleic acids.
D.
phosphate groups. E.
sugars.
9.
A peptide bond between two subunits might be split by the catalytic addition of
A.
a molecule of water.
B.
two amino acids.
C.
positively and negatively charged ions.
D.
simple sugars.
E.
hydrogen atoms.
10.
A chain of amino acids linked together end—to—end is
A.
a phospholipid.
B.
a nucleic acid.
C.
a polysaccharide.
D.
a polypeptide.
E.
a prostaglandin.
11.
An example of a protein whose function is structural is
A.
collagen.
B.
hemoglobin.
C.
insulin.
D. Na-K channel protein.
E.
albumin.
12.
The number of different amino acids commonly found in proteins is
A.
0
B.
2
C.
16 — 18
D. 20
E.
hundreds.
13.
What is NOT a functional class of amino acids?
A.
complex
B.
ionic
C.
polar
D. non—polar
E.
polyunsaturated.
14.
When a protein is dissolved in water, the amino acids found at the outer surface of the molecule are likely to
be
A.
aromatic
B.
hydrophobic
C.
non—polar
D. hydrophilic
E.
saturated.
15.
When a protein is dissolved in water, the amino acids found at the interior of the molecule are likely to be
A.
polar, uncharged.
B.
hydrophobic.
C.
ionic.
D.
E.
polar, charged.
unsaturated.
16.
The linear sequence of amino acids along the chain of a protein is termed the
A.
primary structure.
B.
secondary structure.
C.
tertiary structure.
D. quaternary structure.
E.
cinquenary structure.
17.
When dissolved in water, polypeptide chains tend to fold into complex globular shapes. This is the
A.
primary structure.
B.
secondary structure.
C.
tertiary structure.
D.
quaternary structure.
E.
cinquenary structure.
18.
In most proteins, sulfur containing amino acids (what is their name?) form crosslinks (disulfide bonds) which
tend to
A.
cause hydrolysis of the peptide bonds.
B.
force hydrophobic side chains to the outside.
C.
inhibit formation of new peptide bonds.
D.
increase the solubility of the protein.
E.
stabilize the structure of the protein.
19.
The secondary, tertiary and quaternary structure of a protein is determined by the
A.
nature of the peptide bond.
B.
primary structure.
C.
direction of the amino acids in the chain.
D.
frequency of amino acids in the polypeptide chain.
E.
presence of amino groups and carboxyl groups on a single carbon atom.
20.
The amino acid sequence of different proteins is
A. the same.
B. different.
21.
The primary difference between the amino acids commonly found in proteins is in their:
A.
R or variable groups.
B.
number of potassium groups.
C.
number of phosphate groups.
D.
number of carbonyl groups.
E.
number of asymmetric carbons.
22.
Some proteins are important biological buffers because:
A.
they react with water to produce carbon dioxide, which neutralizes acids.
B.
they contain weakly acidic and weakly basic groups.
C.
they are able to absorb great amounts of carbon dioxide during condensation reactions.
D.
they produce carbonic acid upon hydrolysis.
E.
All of these.
23. Regulatory proteins:
A.
defend against foreign invaders.
B.
store nutrients.
C.
catalyze a specific chemical reaction.
D.
control the expression of specific genes.
E.
strengthen and protect cells and tissues.
24. The following amino acid would be characterized as
__________ based on the chemical properties of its side
chain.
A.
B.
C.
D.
E.
nonpolar
acidic
basic
hydrophilic
electrically charged
25. At which level of protein structure are peptide bonds most important?
A.
primary
B.
secondary
C.
tertiary
D.
quaternary
E.
globular
26. Which of the following is responsible for the alpha-helical structure of proteins?
A.
hydrophobic interactions
B.
nonpolar covalent bonds
C.
ionic interactions
D.
hydrogen bonds
E.
polar covalent bonds
27. Proteins with alpha helical forms exhibit this property:
A.
strength
B.
elasticity
C.
heat stability
D.
rigidity
E.
All of the above.
28. If tyrosine and isoleucine undergo condensation, the new bond that is formed is between the:
A.
oxygen of the R group and the hydrogen of the amino group.
B.
carbon of the R group and the nitrogen of the amino group.
C.
carbon of the carboxyl group and the hydrogen of the R group.
D.
carbon of the carboxyl group and the hydrogen of the amino group.
E.
carbon of the carboxyl group and the nitrogen of the amino group.
29,30. Use the figure below to answer the corresponding questions.
29. In the figure, ionic attractions would form between the R groups of which amino acids?
A.
1 and 3
B.
2 and 4
C.
D.
E.
3 and 5
4 and 6
3 and 6
30. Hydrophobic interactions would occur between the R groups of which two amino acids in the accompanying
figure?
A.
1 and 4
B.
2 and 5
C.
3 and 6
D.
2 and 4
E.
3 and 5
30. The tertiary structure of proteins is typified by the:
A.
association of several polypeptide chains by weak bonds.
B.
order in which amino acids are joined in a peptide chain.
C.
bonding of two amino acids to form a dipeptide.
D.
folding of a peptide chain to form an alpha helix.
E.
three-dimensional shape of an individual polypeptide chain.
31. All of the following types of chemical bonds are
responsible for maintaining the tertiary structure of this
polypeptide except:
A.
ionic bonds.
B.
hydrogen bonds.
C.
hydrophobic interactions.
D.
disulfide bonds.
E.
peptide bonds.
32.
This functional group forms cross bridges that help stabilize protein tertiary structure:
A.
hydroxyl
B.
carbonyl
C.
amino
D.
phosphate
E.
sulfhydryl
33. Molecular chaperones are proteins that mediate the folding process of:
A.
other proteins.
B.
amino acids.
C.
lipids.
D.
DNA.
E.
sugars.
34. If the differently shaded portions of this molecule represent different polypeptide
chains, then this figure is representative of:
A.
an amino acid.
B.
the quaternary structure of a protein.
C.
a steroid hormone.
D.
cellulose.
E.
a carotenoid.
35. Which of the following statements is true of proteins?
A.
Proteins lose some or all of their normal activity if their three-dimensional structure is disrupted.
B.
Proteins are composed of ribose, phosphate, and a nitrogen-containing base.
C.
The activity of proteins is independent of temperature and pH.
D.
Denaturation is usually reversible.
E.
All proteins are enzymes.
36. Which pair of amino acid side groups would be most likely to associate with each other by an ionic bond?
1.
–CH3
2.
–CH2—COO3.
–CH2—CH2—NH3+
4.
–CH2—CH2—COO5.
–CH2—OH
A.
B.
C.
D.
E.
1 and 2
2 and 4
1 and 5
2 and 5
3 and 4
37. Which of the following levels of protein structure may be affected by hydrogen bonding?
A.
Primary and secondary
B.
Primary and tertiary
C.
Secondary, tertiary, and quaternary
D.
Primary, secondary, tertiary
E.
Primary, secondary, tertiary, and quaternary
38. Which of the following associations between R groups are the strongest?
A.
Hydrophobic interactions
B.
Hydrogen bonds
C.
Ionic bonds
D.
Peptide bonds
E.
Disulfide bridges