BIOS Homework 2

Which polymers are composed of amino acids?
Proteins

What is attached to the central carbon atom in an amino acid?
1.) An amino functional group
2.) A side chain (“R group”)
3.) A carboxyl functional group

What is not attached to the central carbon atom in an amino acid?
An oxygen

Which part of an amino acid is always acidic?
Carboxyl functional group

Which monomers make up RNA?
Nucleotides

What about the formation of polypeptides from amino acids is true?
A bond forms between the carboxyl functional group of one amino acid and the amino functional group of the other amino acid.

What about the formation of polypeptides from amino acids isn’t true?
1.) Polypeptides form by condensation or hydrolysis reactions.
2.) The reaction occurs through the addition of a water molecule to the amino acids.
3.) A bond can form between any carbon and nitrogen atom in the two amino acids being joined.

True or false? Enzymes in the digestive tract catalyze hydrolysis reactions.
True

What is the linking of the monomers involves the removal of water?
dehydration synthesis

What is true of polymers?
They are always made of monomers.

What isn’t true of polymers?
1.) Their synthesis generally consumes water.
2.) They are often made by a hydrolysis process.
3.) They are always made by condensation reactions.

The organic molecule called DNA is an example of what?
a polymer made of nucleotides.

Proteins are polymers of *blank*.
amino acids

What type of bond joins the monomers in a protein’s primary structure?
peptide

The secondary structure of a protein results from *blank*.
hydrogen bonds

Tertiary structure is NOT directly dependent on *blank*.
peptide bonds

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

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 20^153.

A biochemist modified a protein so the amino acid lysine occurred where the amino acid aspartic acid previously occurred. This change could what?
alter the protein’s tertiary structure

dentify the empirical formula of a free amino acid whose side chain is just H.
C2H5O2N

An amino acid residue in a protein differs from a free amino acid in having what?
1.) one less H.
2.) one less OH.
3.) one less H and one less OH.

A residue in the middle of a polypeptide has −CH3 as its side chain or R group. How many atoms does the residue contain?
10

Amino acids are called “acids” because they what?
contain carboxyl groups in the backbone part.

In a protein, peptide bonds connect what?
C=O to N-H.

What is true of the side chains that occur in proteins?
1.) Some of them contain only C and H.
2.) Some of them contain carboxyl groups.

What isn’t true of the side chains that occur in proteins?
None of them join the backbone at more than one point.

A certain amino acid side chain ionizes at low pH but not at very high pH. What else is true of this side chain?
It contains an amino group.

What isn’t true of protein quaternary structure?
A single polypeptide may have quaternary structure.

What is true of protein quaternary structure?
1.) A quaternary protein cannot have fewer than two carboxyl groups.
2.) Hydrogen bonds may hold the polypeptides in contact.
3.) Disulfide bridges may hold the polypeptides in contact.
4.) The same kinds of stabilizing forces are involved as in tertiary structure.

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?
1.) Disulfide bridges bind the proteins together.
2.) Each protein is a single long alpha helix.
3.) Hair is another example.

The helical foldings of proteins are stabilized mainly by bonds between what?
CO and NH.

What is true of pleated sheet foldings within a polypeptide?
They depend on regular occurrence of CO and NH.

What isn’t true of pleated sheet foldings within a polypeptide?
1.) They are part of the polypeptide’s quaternary structure.
2.) Its loops are held in place mainly by disulfide bridges.
3.) The side chains are parallel to the plane of the sheet.

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.

The helical foldings in proteins what?
are kept folded by hydrogen bonds.

What do the three main forces that stabilize protein tertiary structure have in common?
They involve the side chains.

Among the forces that stabilize protein tertiary structure, hydrogen bonds are especially important because they are what?
more numerous than the other forces.

What fact results from the presence of both polar and nonpolar side chains in a protein?
Water has a strong effect on tertiary structure.

What fact doesn’t results from the presence of both polar and nonpolar side chains in a protein?
1.) Proteins ionize when they are placed in water.
2.) Each protein has many functions.
3.) A protein’s folding doesn’t depend on the polarity of the environment.
4.) pH has a strong effect on secondary structure.

The sequence of polar and nonpolar side chains has a strong effect on a protein’s folding mainly because what?
water attracts polar but not nonpolar groups.

The decrease between 43∘C and 60∘C probably results from what?
breaking hydrogen bonds.

When a protein has been unfolded enough to lose its function, the protein has been what?
denatured.

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 what?
less sensitive to pH.

Which factor is most important in determining a protein’s optimum pH?
The locations of side-chain carboxyl groups.

Why don’t cells rely more on disulfide bridges to stabilize the folding of proteins?
They make the protein rigid. Many proteins change their shape as they work.

To make a disulfide bridge, it’s necessary to what?
remove two H atoms.

A certain protein is not sensitive to pH. It may have many side chains with *blank* groups.
-CH2OH