Chapter 3
Which class(es) of amino acids possess side chains that would be unable to form hydrogen bonds with water?
amino acids with nonpolar side chains
By convention, biologists write the sequence of amino acids in a polypeptide in which direction?
amino- to carboxyl- terminus
The helical foldings in proteins ...
are kept folded by hydrogen bonds
A certain protein is not sensitive to pH. It may have many side chains with ________ groups.
-CH2OH
Which factor is most important in determining a protein's optimum pH?
The locations of side-chain carboxyl groups.
Proteins are polymers of
amino acids
Among the forces that stabilize protein tertiary structure, hydrogen bonds are especially important because they are ...
more numerous than the other forces.
Which monomers make up RNA?
nucleotides
An amino acid residue in a protein differs from a free amino acid in having ...
one less H and/or OH
Which of the following is not attached to the central carbon atom in an amino acid?
oxygen
What type of bond joins the monomers in a protein's primary structure?
peptide
The alpha-helix is a component of __________ protein structure
secondary
____ structure describes the alpha-helices and beta-sheets that are formed by hydrogen bonding between backbone atoms located near each other in the polypeptide chain
secondary
What is an active site?
the position in an enzyme where substrates bind
In proteins, secondary, tertiary, and quaternary levels of structure depend on primary structure. Which of the following most accurately lists elements of any protein's primary, secondary, tertiary, and quaternary structure, in that order?
Amino acid sequence, hydrogen bonding between backbone groups, overall shape of a single polypeptide, and combinations of tertiary structures
Which of the following correctly orders amino acids Asp, Tyr, and Val from most hydrophobic (on the left) to most hydrophilic (on the right)?
Val, Tyr, and Asp
Which fact results from the presence of both polar and nonpolar side chains in a protein?
Water has a strong effect on tertiary structure.
A biochemist modified a protein so the amino acid lysine occurred where the amino acid aspartic acid previously occurred. This change could ...
alter the protein's tertiary structure
What two functional groups are present on every amino acid?
an amino group and a carboxyl group
A hydrocarbon skeleton is covalently bonded to an amino group at one end and a carboxyl group at the other end. When placed in water this molecule would function
as an acid and a base
acidic side chains
aspartate (D), Glutamate (E)
Which of the following types of amino acids would you predict to be present in the DNA binding sites of these proteins?
basic amino acids
Which of the following is NOT true of protein quaternary structure? a) Hydrogen bonds may hold the polypeptides in contact. b)The same kinds of stabilizing forces are involved as in tertiary structure. c)A single polypeptide may have quaternary structure. d)A quaternary protein cannot have fewer than two carboxyl groups. e)Disulfide bridges may hold the polypeptides in contact.
c)A single polypeptide may have quaternary structure.
Which of the functional groups below acts most like an acid in water?
carboxyl
Which two functional groups are always found in amino acids?
carboxyl and amino groups
Which part of an amino acid is always acidic?
carboxyl functional group
Amino acids are called "acids" because they ...
contain carboxyl groups in the backbone part.
Which of the following statements about the formation of polypeptides from amino acids is true? a) Polypeptides form by condensation or hydrolysis reactions. b) The reaction occurs through the addition of a water molecule to the amino acids. c) A bond can form between any carbon and nitrogen atom in the two amino acids being joined. d) A bond forms between the carboxyl functional group of one amino acid and the amino functional group of the other amino acid.
d) A bond forms between the carboxyl functional group of one amino acid and the amino functional group of the other amino acid.
Which of these does NOT contain a structural protein? a)spider silk b)muscles c)tendons d)ovalbumin e)ligaments
d)ovalbumin
When a protein has been unfolded enough to lose its function, the protein has been ...
denatured.
The secondary structure of proteins results because of _____ bonding between atoms in the protein's backbone.
hydrogen
The amino acid lysine has an amino group in its side chain. In a protein, a scientist replaced every lysine with serine (side chain -CH2OH). The alteration made the protein's folding ...
less sensitive to pH.
In a polypeptide, what bonds are responsible for the primary structure?
peptide bonds
___ structure is the sequence of amino acids in a protein
primary
Where is the information that directs different polypeptides to fold into different shapes?
primary structure
Which polymers are composed of amino acids?
proteins
The main reason that proteins outperform other macromolecules in terms of catalytic ability is because
proteins can contain a variety of R groups
___ structure is the result of two or more protein subunits assembling to form a larger, biologically active protein complex
quaternary
To make a disulfide bridge, it's necessary to ...
remove two H atoms
___ structure is achieved when a protein folds into a compact, three dimensional shape stabilized by interactions between side-chain R groups of amino acids
tertiary
Proteins help cells with which task(s)?
transport, signaling, catalysis
The helical foldings of proteins are stabilized mainly by bonds between
CO and NH
In a protein, peptide bonds connect ...
C=O to N-H.
A residue in the middle of a polypeptide has −CH3{\rm -CH_3} as its side chain or R group. How many atoms does the residue contain?
10
How many different primary sequences can be generated by randomly assembling amino acids into peptides that are five residues long?
20^5=3,200,000
Identify the empirical formula of a free amino acid whose side chain is just H.
C2H5O2N
Some of the strongest biological structures (e.g., beaks and claws) are made of many molecules of the protein keratin. What else is true of structures made of keratin?
Disulfide bridges bind the proteins together. Each protein is a single long alpha helix. Hair is another example.
basic side chains
Lysine (K), arginine (R), Histidine (H)
nonpolar side chains
Glycine (g), alanine (a), valine (v), lecuine (L), isoleucine (I), phenylalanine (F), tryptophan (W), proline (P), methionine (M)
The human myoglobin protein contains 153 amino acids. If you take one guess at the amino acid sequence, what is your chance of being right?
One chance in 20153.
Which of the following statements about protein primary structure is true?
Primary structure is produced by the unique sequence of amino acids in a protein.
Which statement is true of the side chains that occur in proteins?
Some of them contain carboxyl groups and Some of them contain only C and H.
What will probably be the effect on a protein if you replace the amino acid proline with the amino acid glycine (side chain -H) at several points?
The altered protein will have longer helices than before.
Most protein enzymes catalyze only one specific chemical reaction effectively. What feature of protein structure is most directly responsible for this specificity?
The specific geometry and types of amino acids in the active site
Which of the following is true of pleated sheet foldings within a polypeptide?
They depend on regular occurrence of CO and NH.
What do the three main forces that stabilize protein tertiary structure have in common?
They involve the side chains
The locations of side-chain carboxyl groups.
They make the protein rigid. Many proteins change their shape as they work.
Which of the following is true of protein folding? a) Some proteins can fold spontaneously b) sfolded proteins can still function correctly. cCorrect folding is aided by high temperature d)Once protein fold, their structuree doesn't change
a) Some proteins can fold spontaneously
A certain amino acid side chain ionizes at low pH but not at very high pH. What else is true of this side chain?
contains an amino group
The secondary structure of a protein results from
hydrogen bonds
Nonpolar amino acid residues are typically found in the interior of globular proteins like trypsin. Which chemical force is most directly responsible?
hydrophobic interactions
Defensive proteins are manufactured by the _____ system.
immune
Tertiary structure is NOT directly dependent on
peptide bonds
A compound contains hydroxyl groups as its predominant functional group. Therefore, this compound _____.
should dissolve in a nonpolar solvent
Which of the following parts of an amino acid vary among different amino acids?
side chain, or R group
polar side chains
threonine (T), cysteine (C), Tyrosine (Y), asparagine (N), glutamine (Q),serine (S)
True or false? Enzymes in the digestive tract catalyze hydrolysis reactions.
true
The sequence of polar and nonpolar side chains has a strong effect on a protein's folding mainly because ...
water attracts polar but not nonpolar groups