Chapter 3 Intro to cell quizzes

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

C2H5O2N

In a protein, peptide bonds connect

C=O to N-H.

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

The helical foldings in proteins ...

are kept folded by hydrogen bonds.

The secondary structure of proteins results because of _____ bonding between atoms in the protein's backbone.

hydrogen

A certain protein is not sensitive to pH. It may have many side chains with ________ groups.

-CH2OH

Which functional group shown above is characteristic of alcohols?

-OH

Which of the groups shown above is a functional group that helps stabilize extracellular proteins by forming covalent cross-links within or between protein molecules?

-SH

A residue in the middle of a polypeptide has −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?

205=3,200,000

Which of the following statements 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.

Which of the following is NOT true of protein quaternary structure?

A single polypeptide may have quaternary structure.

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 helical foldings of proteins are stabilized mainly by bonds between ...

CO and NH.

Which part of an amino acid is always acidic?

Carboxyl functional group

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.

Nonpolar amino acid residues are typically found in the interior of globular proteins like trypsin. Which chemical force is most directly responsible?

Hydrophobic interactions

Where is the information that directs different polypeptides to fold into different shapes?

In the primary structure

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.

Which monomers make up RNA

Nucleotides

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 polymers are composed of amino acids?

Proteins

Which statement is true of the side chains that occur in proteins?

Some of them contain only C and H. Some of them contain carboxyl groups.

Which of the following is true of protein folding?

Some proteins can fold spontaneously

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.

Which factor is most important in determining a protein's optimum pH?

The locations of side-chain carboxyl groups.

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.

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.

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

True

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.

Proteins are polymers of _____.

amino acids

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 carboxy-terminus

What two functional groups are present on every amino acid?

an amino group and a carboxyl group

Which of the following is not attached to the central carbon atom in an amino acid?

an oxygen

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

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

What is the name of the functional group shown in the figure below?

carboxyl

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

Amino acids are called "acids" because they ...

contain carboxyl groups in the backbone part.

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

denatured.

The secondary structure of a protein results from _____.

hydrogen bonds

Defensive proteins are manufactured by the _____ system.

immune

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.

Among the forces that stabilize protein tertiary structure, hydrogen bonds are especially important because they are ...

more numerous than the other forces.

Which of these does NOT contain a structural protein?

ovalbumin

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

peptide

In a polypeptide, what bonds are responsible for the primary structure?

peptide bonds

Tertiary structure is NOT directly dependent on _____.

peptide bonds

The main reason that proteins outperform other macromolecules in terms of catalytic ability is because ____.

proteins can contain a variety of R groups

To make a disulfide bridge, it's necessary to ...

remove two H atoms.

The alpha-helix is a component of __________ protein structure.

secondary

A compound contains hydroxyl groups as its predominant functional group. Therefore, this compound _____.

should dissolve in water

What is an active site?

the position in an enzyme where substrates bind

Which of the following parts of an amino acid vary among different amino acids?

the side chain, or R group

Proteins help cells with which task(s)?

transport catalysis signaling

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.