Biochemistry Chapter 6

Which of the following is CORRECT when considering the tertiary structure of globular proteins? A) All parts of the proteins can be classified as helix, β sheet or turns. B) The amino acid proline never occurs in a region where the polypeptide chain bends or turns. C) Hydrophobic residues are normally on the inside and hydrophilic residues are on the outside. D) β sheets cannot be twisted or wrapped into barrel structures. E) None of the above.

Which of the following statements about protein quaternary structure are correct? 1) It involves a complex of two or more proteins interacting with each other. 2) The subunits of the structure can be either identical or different. 3) The interactions between subunits can give rise to indefinite growth of polymeric complexes. 4) Most assemblies of protein subunits have one or more defined axis of rotation.

Which of the following statements regarding the folding of proteins is NOT true? 1) Hydrophobic residues pack together because the side chains are attracted to each other through weak Van der Waals interactions. 2) Van der Waals interactions have a stabilizing, cumulative effect. 3) Internal H bonds stabilize the fold. 4) Salt bridges stabilize the fold.

T or F Protein folding is a random process, whereby a vast number of possible conformations are tested to find the desired most stable state.

T or F Proteins cannot self-assemble into a functional conformation after they have been denatured.

T or F Proteins have an asymmetrical tertiary structure, while multisubunit proteins can exhibit several types of symmetry.

What type of bond is responsible for the primary structure of a protein?

List the two common secondary protein structures.

Which of the following forces are responsible for the tertiary structure of a protein? 1) peptide bond 2) ionic bond 3) hydrogen bond 4) disulfide bond

Where in a globular protein is the amino acid alanine likely to be located? 1) the hydrophilic interior 2) the hydrophobic interior 3) the hydrophilic exterior 4) the hydrophobic exterior

Classify alanine based on its R group. 1) acidic 2) basic 3) neutral polar 4) neutral nonpolar

Protein folding is a thermodynamically favorable process under physiological conditions because: 1) no intermediate stage disulphide bonds form during the folding process. 2) there is a decrease in entropy of the solvent by burying hydrophobic groups within the molecule. 3) there is an increase in entropy associated with protein folding. 4) of the large negative enthalpy change associated with many noncovalent interactions. 5) all of the above.

T or F Fibroin is a β-sheet protein, with a high proportion of glycine.

T or F Tropocollagen is a double helix of two left-handed polypeptide chains.

Consider a small protein containing 101 amino acid residues. The protein will have 200 bonds about which rotation can occur. Assume that three orientations are possible about each of these bonds. Based on these assumptions, about how many random-coil conformations will be possible for this protein?

Please match the correct term on the left with the appropriate structural feature of proteins listed on the right. 1) primary structure 2) secondary structure 3) tertiary structure 4) quaternary structure A) the interaction between two separate protein strands B) the sequence of AA C) small sections of organized protein structure, such as helices D) the overall fold of a single protein strand, such as the globulin fold

Which of the following statements about α-keratins is FALSE? 1) Individual molecules are α-helical. 2) They include a major class of protein that comprises hair, fingernails and animal skin. 3) There is a strip of contiguous hydrophobic surface making a shallow spiral around the helix. 4) Pairs of α-helices twist about each other in a coiled-coil structure held together entirely by hydrophobic interactions. 5) They include a small globular regions covalently linked to the surface.

Proteins are polymers of _____. 1) hydrocarbons 2) glycerol 3) nucleotides 4) CH2O units 5) amino acids

What type of bond joins the monomers in a protein's primary structure? 1) hydrophobic 2) hydrogen 3) S - S 4) peptide 5) ionic

The secondary structure of a protein results from _____. 1) hydrogen bonds 2) ionic bonds 3) bonds between sulfur atoms 4) peptide bonds 5) hydrophobic interactions

Tertiary structure is NOT directly dependent on _____. 1) bonds between sulfur atoms 2) hydrophobic interactions 3) peptide bonds 4) hydrogen bonds 5) ionic bonds

Which of the following statements is NOT true? 1) An intact protein, complete with its cofactor or metal ion, is known as a holoprotein. 2) A protein stripped of its cofactor or metal ion is known as a holoprotein. 3) A cofactor usually refers to a metal ion required for activity by a protein. 4) A prosthetic group is usually a small organic molecule required for activity by a protein.

Which statement correctly describes amphipathic (or amphiphilic) helices and sheets? 1) Helices are typically hydrophilic on one surface, whereas sheets usually have both hydrophilic and hydrophobic residues evenly distributed throughout their structure. 2) Amphipathic helices and sheets have hydrophilic and hydrophobic residues evenly distributed throughout their structure. 3) Amphipathic helices and sheets have predominantly hydrophilic (or hydrophobic) residues on one face. 4) Sheets are typically hydrophilic on one surface, whereas helices usually have both hydrophilic and hydrophobic residues evenly distributed throughout their structure.

Which of the following statements regarding Anfinsen's denaturing experiments with ribonuclease A are valid? 1) Exposing the denatured protein to air oxidation and then dialysis to remove urea restored the protein to its original functionality. 2) Removing urea by dialysis and then allowing air oxidation of the denatured protein restored the protein to its original functionality. 3) Denaturing the protein with both urea and β-mercaptoethanol yielded an inactive protein. 4) Protein folding is determined by its primary sequence.

T or F The interactions that stabilize multisubunit complexes are different to those that stabilize tertiary structure.

The protein that makes up about a third of the total protein mass in animals is: 1) hemoglobin. 2) collagen. 3) myoglobin. 4) α-keratin. 5) β-keratin.

Which of the following statements about globular proteins are true? 1) The protein folds to make itself as compact as possible. 2) The packing of the protein is such that hydrophilic residues appear on the surface where they can interact with an aqueous environment. 3) Irregularities of the protein's surface allow for the formation of clefts, which are often where the protein promotes a chemical transformation. 4) Regions of secondary structures folding on one another are examples of the protein's tertiary structure.

At what level of protein structure do β-sheets of amino acids and α-helices, located at a distance from each other along the length of a polypeptide chain, come together to form a globular protein?

What level of protein structure describes an amino acid sequence such as Ala-Gly-Ser-Val-Glu-Glu-Glu-Ala-His...?

At what level of protein structure do the α and β protein subunits come together to catalyze the hydrolysis reaction?

At what level of protein structure do the chains of amino acids fold into an α-helical structure?

In the protein adenylate kinase, the C-terminal region has the sequence Val-Asp-Asp-Val-Phe-Ser-Gln-Val-Cys-Thr-His-Leu-Asp-Thr-Leu-Lys- The hydrophobic residues in this sequence are presented in boldface type. Suggest a possible reason for the periodicity in their spacing. 1) Each residue that is hydrophobic lies on one side forming amphipathic α-helix. 2) Hydrophobic residues give rise to a helical dipole moment and partial (-) charge of the C-terminus. 3) Active site of the adenylate kinase is formed by packed together hydrophobic residues. 4) Localization of hydrophobic residues on the one side of β-strand mediates the interactions with other one of the polypeptide chain.

T or F The amino acid side chain residues in an α helix point outwards away from the center of the helix.

T or F The folded conformation of proteins can be stabilized by the binding of a metal ion or cofactor.