Molec Biochem Chapter 6

For -sheets, the terms 'parallel' and 'anti-paralllel' refer to ___________. -the quaternary structure of the protein -the orientation of the hydrogen bonding -the orientation of the amide crosslinks -the topology of the reverse turns -the 'direction' of the associated peptide strands

the 'direction' of the associated peptide strands

Which level of protein structure is defined as "the hydrogen bonded arrangement of the polypeptide backbone"? Which level of protein structure is defined as "the hydrogen bonded arrangement of the polypeptide backbone"? Secondary Tertiary Quaternary Primary

Secondary

Which of the following statements about the -helix and β-sheet are TRUE? 1. They are both types of secondary structure. 2. They are both stabilized by hydrogen bonds between amino acid side chains. 3. The polypeptide backbone is fully extended in both structures. 4. They are both usually located in the interior of soluble globular proteins.

1 and 4

The classic experiment demonstrating that reduced and denatured RNase A could refold into the native form demonstrates that _______. -1° structure can determine 3° structure -denaturation does not disrupt protein 2° structure -disulfide bonds do not stabilize folded proteins -proteins are extraordinarly stable -none of the above

1° structure can determine 3° structure

Molecular chaperones assist proteins in the formation of ________. -aggregates -3° structure -amide bonds -1° structure -none of the above

3° structure

In an -helix, which amino acid makes a hydrogen bond to the 2nd residue? 6th. 1st. 3rd. 5th.

6th.

In an -helix, which amino acid residue makes a hydrogen bond to the 3rd residue? 1st 7th 6th 4th

7th

Which statement about the structure of collagen is FALSE? Cross-linking of collagen by Pro and Lys residues explains its low solubility. Lysyl oxidase, the enzyme that converts Lys residues to those of the aldehyde allysine, is the only enzyme implicated in this cross-linking process. The cross-links cannot be disulfide bonds, as in keratin, because collagen is almost devoid of Cys residues. Cross-linking of collagen involves Lys residues being converted to the allysine, where the lysine side chain amino group is converted to an aldehyde. Cross-linking of allysine residues in collagen occurs via an aldol condensation between two allysine side

Cross-linking of collagen by Pro and Lys residues explains its low solubility.

Which statement about disulfide bonds is false? -Disulfide bonds can occur between two different polypeptide chains. -Disulfide bonds help stabilize extracellular proteins. -Disulfide bonds are rare in intracellular proteins because the cytoplasm is a reducing environment. -Disulfide bonds can occur between either Cys or Met residues. -Disulfide bonds are not essential for stabilizing a folded protein -Can be reductively cleaved by 2-mercaptoethanol. -Disulfide bonds can occur within a polypeptide chain.

Disulfide bonds can occur between either Cys or Met residues.

Which statement below does not describe fibrous proteins? -The proteins are usually water soluble. -Domains are compact and globular. -These proteins usually perform a protective, connective, or supportive role in the organism. -These proteins are usually dominated by a single type of secondary structure. -Domains are usually stiff and elongated

Domains are compact and globular

Which of the following is not a disease that is caused by protein misfolding? Down's syndrome. Bovine spongiform encephalopathy. Alzheimer's disease. Creutzfeldt-Jakob disease.

Down's syndrome.

Which of the following statements about the peptide bond is FALSE? -It is a bond that displays resonance. -It is a phosphodiester bond. -It exhibits partial double bond character. -Atoms of the peptide bond are located in a single plane. -It is formed when water is released from the condensation of an amino group and a carboxylic acid.

It is a phosphodiester bond.

You have been shown the detailed 3-D structure of an unknown protein. The information indicates that the protein's non-polar amino acid side chains are all exposed on the surface, whereas its polar side chains are all "buried" in the interior. What can you conclude about this protein? -It is likely to be a peripheral membrane protein -It is likely to be a lipid-linked membrane protein. -It is likely to be a soluble cytosolic protein. -It is likely to be an integral membrane protein.

It is likely to be an integral membrane protein.

The short amino acid sequence shown below occurs within the longer amino acid sequence of a large protein. This specific portion of the amino acid sequence adopts an -helical conformation. ............Ala-Val-Ala-Val-Ala-Val-Ala-Val-Ala-Val............... When the protein has adopted its tertiary conformation, which of the following hydrogen bonds are most likely to be formed by groups on the amino acid residues in this short segment? -Hydrogen bonds with residues in a neighbouring -helix. -Hydrogen bonds with water molecules at the surface of the protein. -None, because Ala and Val side chains are unable to form hydrogen bonds. -Hydrogen bonds with other residues in the same -helix.

Hydrogen bonds with other residues in the same -helix.

Which of the following stabilizes the folding of a polypeptide backbone into regular secondary structure? Disulphide bridges. Hydrogen bonds. Covalent bonds. Electrostatic interactions. Hydrophobic interactions.

Hydrogen bonds.

Where are irregular secondary structures (loops) generally found in soluble globular proteins and why? -On the surface so that they can interact with the solvent. -On the surface because they are less compact. -In the core of the protein so that they can interact with hydrophobic groups. -In the core of the protein because they connect β-strands and -helices.

On the surface so that they can interact with the solvent.

Which of the following pairings of a supersecondary structure / motif and a statement describing it is INCORRECT: -immunoglobulin fold: two beta-alpha-beta-alpha-beta units that combine to form a dinucleotide-binding site. -beta-hairpin motif: two anti-parallel beta-strands connected by a tight turn. -beta-barrels: beta-sheets that are rolled-up to form a continuous, circular sheet, with the first strand adjacent to the last strand. -alpha-alpha motif: two successive antiparallel alpha-helices packed against each other with their axes slightly inclined. -beta-alpha-beta- motif: an -helix connecting two parallel strands of a beta -sheet.

immunoglobulin fold: two beta-alpha-beta-alpha-beta units that combine to form a dinucleotide-binding site.

In a Ramachandran diagram, ______ of the area represents allowed conformations of a polypeptide chain. more than 90% more than 50% about 50% less than 25% none of the above

less than 25%

The low pH found in the gut can enhance the digestibility of dietary protein by causing _____. -prion formation -protein denaturation -amide hydrolysis -cysteine oxidation -disulfide reduction

protein denaturation

Which one of the following statements about the -helix is FALSE? -Side chains are located on the outside of an -helix. -The -helix contains hydrogen bonds between the carbonyl oxygen of one residue and an amide hydrogen that is four residues closer to the carboxy terminus of the helix. -The -helix has a right handed twist. -The -helix is a type of secondary structure that fulfills the hydrogen bonding requirements of amino acid side chains. -The -helix is a type of regular secondary structure.

The -helix is a type of secondary structure that fulfills the hydrogen bonding requirements of amino acid side chains.

Which statement about the structure of collagen is FALSE? -Collagen has the general repeating sequence (Gly-X-Y)n, where X is often Pro and Y is often 4-hydroxyproline (Hyp). -Collagen is formed by three left-handed helices. -Glycine is essential at every third position in collagen polypeptides, because the third position passes through the center of the triple helix- this location is so crowded that only a Gly side chain can fit there. -Mutations of Type I collagen in which glycine is replaced at the third position by another amino acid result in diseases like osteogenesis imperfecta (brittle bone disease). -In the collagen repeating sequence (Gly-X-Y)n, 5-hydroxylysine (Hyl) sometimes appears at the Y position -The three helices of collagen form a left-handed superhelix.

The three helices of collagen form a left-handed superhelix.

Which of the following is NOT a feature of the -keratin coiled-coil? -The two coils are held together by hydrogen bonds. -A seven-residue pseudo-repeat occurs, with contact between coils mediated by residues at positions a and d. -The two coils have a slight left-handed twist, resulting in a 3.5 residue repeat. -The predominant secondary structure is -helical.

The two coils are held together by hydrogen bonds.

What is the major role played by prosthetic groups in proteins? -They provide reactive groups not found in amino acid side chains. -They bind to the enzyme, participate in the catalytic reaction, and then leave the active site. -They are required to promote induced-fit by substrates. -They provide flexibility in the enzyme structure. -They maintain protein solubility.

They provide reactive groups not found in amino acid side chains.

Which one of the following statements about peptide bonds is FALSE. Peptide bonds are: -charged. -covalent. -involved in forming the primary structure of proteins. -amides. -rigid and planar, with partial double-bond character.

charged.

In a 12-residue -helix, how many backbone hydrogen bonds will the 5th amino acid make and how many backbone hydrogen bonds will the 10th amino acid make? 0 and 0. 1 and 1. 3 and 2. 2 and 1

2 and 1

Crystalline proteins assume nearly the same structures as the proteins in solution. Several lines of evidence support this statement; which is the most compelling? -Different crystal forms of the same protein have virtually identical conformations. -Enzymes are often catalytically active in the crystalline state. -Enzymes are often catalytically active in solution -A crystalline protein is essentially in solution, because of the waters of hydration that crystallize along with the protein. -Electron density maps can be obtained at high resolution

Enzymes are often catalytically active in the crystalline state

Lysine can form a salt bridge by associating with a nearby _____ residue. Pro Ser Glu Gln Gly

Glu

In protein X-ray crystallography, X-ray radiation is utilized because _______. -X-ray lenses are very precise -X-ray diffraction patterns are most readily interpreted -the colors of protein crystals block visible light -the wavelength of X-ray radiation is close to the observed covalent bond lengths -X-rays are effectively diffracted by the atomic nuclei

the wavelength of X-ray radiation is close to the observed covalent bond lengths

Which of the following is TRUE for a β-pleated sheet? A. There are hydrogen bonds perpendicular to the direction of the polypeptide chain. B. The polypeptide chain is almost fully extended C. The polypeptide chains may be hydrogen bonded together in parallel or anti-parallel orientation. A and C only are correct. A, B, and C are correct.

A, B, and C are correct

Which of the following series of amino acids is most likely to be buried in the center of a water-soluble globular protein? Pro, Gln, His Gly, Asn, Ser Glu, Asp, Lys Ala, Leu, Phe

Ala, Leu, Phe

Which pairs of amino acid side chains could not interact in the interior of a protein by hydrogen bonding? Asp, Asn Ala, Lys Gln, Thr Ser, His

Ala, Lys

Conformation(s) that has (have) both a favorable hydrogen bonding pattern and and values that fall within the allowed Ramachandran conformational regions is (are) helix. collagen helix. sheet. All of the above. None of the above

All of the above.

Which of the following statements is FALSE? -Both -helices and β-sheets have conformations that minimize steric strain in the polypeptide backbone. -Both -helices and β-sheets have R groups that are oriented away from the core of the structure. -Both -helices and β-sheets form only from adjacent amino acid residues in the polypeptide. -Both -helices and β-sheets are stabilized by hydrogen bonds between groups in the polypeptide backbone

Both -helices and β-sheets form only from adjacent amino acid residues in the polypeptide.

Which group of the 3rd residue is used to make its hydrogen bond in the -helix? -side chain -C-H -C=O -N-H

C=O

Which treatment is least likely to cause a protein to denature? -Temperatures approaching 100oC. -High concentrations of salts -Extremes of pH. -High concentrations of chaotropic agents like urea or the guanidinium ion -High concentrations of detergents like SDS.

High concentrations of salts

Which pair of amino acid side chains could form an ion pair? Glu, Gly Lys, Arg Asp, Gln His, Asp

His, Asp

Why does a decrease in pH alter/disrupt the tertiary structure of an enzyme? -It reduces disulphide bonds. -It promotes proteolytic cleavage of peptide bonds. -It disrupts ion pairs/salt bridges. -It reduces hydrophobic interactions. -It deprotonates prosthetic groups.

It disrupts ion pairs/salt bridges

Which of the following statements is true because of the hydrophobic effect? -Charged polar residues R, H, K, E, and D are usually found on the surfaces of proteins. -Uncharged polar residues S, T, N, Q, and Y are usually found on the surface of proteins, but may also be found in the interior. -Nonpolar residues V, L, I, M, and F are found in the interior of proteins. -The interior of proteins is packed very densely.

Nonpolar residues V, L, I, M, and F are found in the interior of proteins

What is the major factor that "drives" the folding of proteins into their tertiary structure? -Formation of the maximum number of ionic interactions. -Formation of the maximum number of hydrophilic interactions. -Placement of polar amino acid residues on the surface of the protein. -Placement of hydrophobic amino acid residues within the interior of the protein.

Placement of hydrophobic amino acid residues within the interior of the protein.

Which of the following describes the entire three-dimensional structure of a single polypeptide? Tertiary structure Quaternary structure Primary structure Secondary structure

Tertiary structure

Which of the following is not a requirement for the structural determination of a protein using two-dimensional (2D) NMR spectroscopic techniques such as NOESY? -The ability of the protein to crystallize. -Known geometric constraints such as covalent bond distances and angles. -The protein's primary amino acid sequence. -A low molecular mass no greater than ~40 kD.

The ability of the protein to crystallize.

What ultimately determines the unique three dimensional structure of soluble globular proteins? -The number of subunits. -The exact number of disulfide bonds. -The exact number of H-bonds. -The sequence of the amino acid residues. -The prosthetic groups.

The sequence of the amino acid residues.

Evolutionary processes have resulted in proteins having ________. -core ion-pairing -efficient folding pathways -extremely stable 3° structures -single subunits -similar 1° structures

efficient folding pathways

Chaperonins such as the GroEL/ES system function ____. -with thermophilic proteins only -at low pH -in an ATP-dependent fashion -in a non-aqueous environment -in vitro only

in an ATP-dependent fashion

Protein diseases are caused by _____. -mutations affecting the 1° structure -mutations affecting the 3° structure -changes in the post-synthetic -processing of proteins -All of the above. -None of the above.

All of the above.

Which of the following is FALSE with respect to β-sheets? -β-sheets may be parallel or anti-parallel. -Strands in a β-sheet are connected by irregular loops. -β-sheets are stabilized by non-covalent forces. -Amino acid side chains protrude from one side of the β-sheet.

Amino acid side chains protrude from one side of the β-sheet.

Which of the following amino acid residues form hydrogen bonds with Ala residues located in an alpha-helix? -Polar residues involved in the stabilization of tertiary structure. -Residues located within the same -helix. -Residues in a neighbouring -helix. -None, because Ala is unable to form hydrogen bonds.

Residues located within the same -helix.

Which statement about the structure of collagen is FALSE? The introduction of vitamin C containing limes to the diet of the British navy alleviated scurvy and led to the nickname "limey" for the British sailor. The modified prolines found in collagen are synthesized from proline post-translationally by an enzyme called prolyl hydroxylase. Prolyl hydroxylase requires ascorbic acid (vitamin C) to maintain its activity. Scurvy is a disease caused by vitamin C deficiency that results in weak collagen Collagen includes nonstandard residues like 4-hydroxyproline (Hyp) and 3-hydroxyproline. Collagen include the nonstandard residue 3-hydroxylysine (Hyl)

Collagen include the nonstandard residue 3-hydroxylysine (Hyl)

Which of statements in the following list pairing a term / structure / chemical with its definition or an effect it has on protein tertiary structure is INCORRECT: -Hydrophobic effect: In proteins, the tendency of nonpolar side chains to minimize their contacts with water. -Metal ion: Can stabilize folded proteins, e.g. by the tetrahedral coordination of Zn2+. -Hydropathy value: A measure of the combined hydrophobicity and hydrophilicity of an amino acid residue. -Ribonuclease A: A protein that can rapidly renature spontaneously. -Ion pairs: Electrostatic interactions that usually occur on the surfaces of proteins -Hydrogen bonds: They fine-tune tertiary structure by selecting a unique conformation among many hydrophobically-stabilized ones. -Detergent: Interferes with the hydrophobic interactions responsible for a protein's native structure. -Cosmotropic agent: Denatures proteins by increasing the solubility of nonpolar groups in water (e.g.'s include urea and the guanidinium ion)

Cosmotropic agent: Denatures proteins by increasing the solubility of nonpolar groups in water (e.g.'s include urea and the guanidinium ion)

Which one of the following sequences of five amino acids would most likely be located on the surface of a soluble globular protein? Glu-Asn-Ser-Thr-Gln Val-Thr-Val-Glu-Val Tyr-Phe-Glu-Asn-Leu Met-Phe-Pro-Ile-Leu

Glu-Asn-Ser-Thr-Gln

Which of the following sequences of amino acids is most likely to be at the surface of a water-soluble globular protein? Pro-Phe-Thr Ala-Leu-Phe Gly-Tyr-Val Glu-Asp-Lys Ile-Ser-Met

Glu-Asp-Lys

Which of the following pairings of an item related to protein folding and a descriptive statement about it is INCORRECT: -Molecular chaperones : Essential proteins that bind to unfolded and partially folded polypeptide chains to prevent the improper association of exposed hydrophobic segments that might lead to non-native folding as well as polypeptide aggregation and precipitation. -GroEL and GroES: Highly symmetrical multi-subunit chaperonin complex that is essential for the survival of E. coli; GroEL resembles a hollow cylinder/barrel that is capped by GroES. (Chaperonins are a large multisubunit class of chaperones.) -Molten globule: A collapsed state of a protein in which nonpolar groups are largely buried, but they are not well packed. -Heat shock proteins (Hsp) : Catalyze the formation of native disulfide bonds. -Molecular chaperone: Binds to unfolded and partially folded proteins to prevent improper association of exposed hydrophobic segments.

Heat shock proteins (Hsp) : Catalyze the formation of native disulfide bonds.

Who is credited with the discovery of the -helix secondary structure of proteins? Watson and Crick. Linus Pauling. Robert Corey. Chou and Fasman.

Linus Pauling.

Which one of the following sequences of five amino acids would most likely be located in the interior of a water soluble globular protein? Tyr-Phe-Glu-Asn-Leu Met-Phe-Pro-Ile-Leu Glu-Asn-Ser-Thr-Gln Val-Ala-Val-Glu-Val

Met-Phe-Pro-Ile-Leu

Which statement is not a consequence of the hydrophobic effect? -The entropy of water increases when proteins fold. -Metal ions can function to stabilize folded proteins. -The folding of proteins is generally a favorable process. -Nonpolar side chains are buried in the interior of a protein.

Metal ions can function to stabilize folded proteins.

Which of the following is TRUE about prosthetic groups? -Prosthetic groups are bound and released by the protein as needed. -Prosthetic groups are an integral part of the three dimensional structure of the protein. -Prosthetic groups are amino acids with additional reactivity. -Prosthetic groups are inorganic.

Prosthetic groups are an integral part of the three dimensional structure of the protein

Which of the following statements about prosthetic groups is INCORRECT? -Heme is an example of a prosthetic group. -Prosthetic groups increase the inherent chemical reactivity of proteins. -Prosthetic groups are not amino acids. -Prosthetic groups form an integral part of the secondary structure of proteins.

Prosthetic groups form an integral part of the secondary structure of proteins.

Which is NOT a conclusion drawn from the experiments of Christian Anfinsen about renaturation of Ribonuclease A? -A protein's primary structure can determine its tertiary structure. -A protein can fold spontaneously to its native structure without the -presence of other factors. -A protein can fold rapidly to its native structure. -Proteins are marginally stable in solution

Proteins are marginally stable in solution

Which of the following statements about quaternary structure is FALSE? -Quaternary structure is fine-tuned by ion pairs, disulfide bonds, and hydrogen bonds. -Quaternary structure is defined as the arrangement of polypeptide backbones in proteins with four subunits -Quaternary structure exists only in proteins containing more than one polypeptide. -Quaternary structure is stabilized primarily by hydrophobic interactions

Quaternary structure is defined as the arrangement of polypeptide backbones in proteins with four

Which of the following statements about quaternary structure is FALSE? -Quaternary structure is defined as the arrangement of polypeptide backbones in proteins with four subunits -Quaternary structure exists only in proteins containing more than one polypeptide -Quaternary structure is fine-tuned by ion pairs, disulfide bonds, and hydrogen bonds. -Quaternary structure is stabilized primarily by hydrophobic interactions.

Quaternary structure is defined as the arrangement of polypeptide backbones in proteins with four subunits

Which of the following statements about quaternary structure is TRUE? -Quaternary structure is defined as the 3D structure of proteins with four subunits. -Quaternary structure requires covalent interactions between polypeptide chains. -Quaternary structure is stabilized by the same types of noncovalent interactions as tertiary structure. -Quaternary structure exists only in proteins containing prosthetic groups.

Quaternary structure is stabilized by the same types of noncovalent interactions as tertiary structure.

Which of the following statements about quaternary structure is TRUE? -Quaternary structure is stabilized by the same types of noncovalent interactions as tertiary structure. -Quaternary structure is defined as the 3D structure of proteins with four subunits. -Quaternary structure exists only in proteins containing prosthetic groups. -Quaternary structure requires covalent interactions between polypeptide chains.

Quaternary structure is stabilized by the same types of noncovalent interactions as tertiary structure.

Which of the following statements about quaternary structure is TRUE? -Quaternary structure is stabilized by the same types of noncovalent interactions as tertiary structure. -Quaternary structure is defined as the precise, 3-D arrangement of polypeptide backbones in proteins with more than one subunit. -Quaternary structure exists in monomeric proteins. -Quaternary structure requires covalent interactions between polypeptide chains

Quaternary structure is stabilized by the same types of noncovalent interactions as tertiary structure.

What is the primary driving force in the formation of protein tertiary structure? -The formation of van der Waals interactions between neighbouring groups. -The exclusion of non-polar substances from aqueous solution. -Energy released when additional hydrogen bonds are formed. -Energy released when additional ion pairs are formed

The exclusion of non-polar substances from aqueous solution.

Compare the -helix with the structure of double-stranded DNA. Which statement is TRUE for both structures? -The backbones are on the outside of the helix. -The hydrogen bonds are perpendicular to the axis of the helix. -Hydrogen bonds are the primary determinant of stability. -The helices are right handed.

The helices are right handed

Which of the following is NOT a feature of the peptide bond? -As a result of the peptide bond, only two dihedral angles per residue in a polypeptide chain can vary freely. -Six atoms, including two alpha-carbons are in the plane of each peptide bond. -The peptide bond is highly polar. -The trans conformation is much more common than cis. -The peptide bond has 10% double bond character.

The peptide bond has 10% double bond character.

Which of the following statements about peptide bonds is FALSE? -Water is released when a peptide bond is formed. -The peptide bond exhibits partial double bond character -The peptide bond has restricted rotation around the bond between the carbonyl carbon and C. -The peptide bond is planar.

The peptide bond has restricted rotation around the bond between the carbonyl carbon and C.

Irregular loops of secondary structure tend to be located on the outside of folded proteins because: -The side chains in loop structures are free to form H bonds with water. -These regions of a peptide tend to contain mostly polar side chains. -The peptide bonds in loop structures are free to form H bonds with water. -alpha -helices and β-sheets are typically located towards the centre of the protein, leaving no room for the loops. -Their side chains are too bulky to fit inside the protein.

The peptide bonds in loop structures are free to form H bonds with water.

In the experiment of Christian Anfinsen, which condition permitted Ribonuclease A to renature? -The presence of O2 at pH 8.0 during renaturation. -The use of 8 M urea to denature the protein. -The presence of 2-mercaptoethanol during denaturation. -Exposure to high temperatures during renaturation

The presence of O2 at pH 8.0 during renaturation.

Which one of the following statements about the β-sheet is FALSE? -The side chains in a β-sheet alternate between the two sides of the sheet. -The β-sheet is a type of regular secondary structure. -The β-sheet is a type of secondary structure that fulfills the hydrogen bonding requirements of amino acid side chains. -The β-sheet contains hydrogen bonds between the carbonyl oxygen of one residue and an amide hydrogen of a residue on an adjacent strand. -β-sheets can be parallel or antiparallel.

The β-sheet is a type of secondary structure that fulfills the hydrogen bonding requirements of amino acid side chains.

Which one of these characteristics is not true for the helix? -Proline is typically not found in the helix. -There is a requirement for glycine every third amino acid residue. -It is right-handed. -There are 3.6 amino acids per turn. -A hydrogen bond forms between the carbonyl oxygen of the nth amino acid residue and the -NH group of the (n + 4)th amino acid residue.

There is a requirement for glycine every third amino acid residue.

Why do Tyr and/or Trp residues tend to destabilize an -helix when they occur next to each other in a protein? -The R group of neither amino acid can form a hydrogen bond. -There is steric hindrance between the bulky Tyr and/or Trp side chains. -There are possible covalent interactions between the Tyr and/or Trp side chains. -Both amino acids are highly hydrophobic. -There is electrostatic repulsion between the Tyr and Trp side chains.

There is steric hindrance between the bulky Tyr and/or Trp side chains.

Which of the following statements is TRUE regarding the R-groups of amino acid residues in an -helix? -They are found on the exterior of the helix. -They alternate between the outside and the inside of the helix. -They form the hydrogen bonds that produce the helix. -They are found in the interior of the helix. -They cause the helix to be right handed.

They are found on the exterior of the helix.

Which of the following statements about domains found in multi-domain proteins is false? -They contain 20-50 amino acids. -They are often structurally independent. -They resemble small, globular proteins. -They often have specialized functions

They contain 20-50 amino acids

Of the following, which amino acid is least likely to be found on the surface of a single-subunit protein? Trp Ser Gly Asp Lys

Trp

What BEST distinguishes irregular secondary structure from regular secondary structure? -Irregular secondary structure is disordered (random) whereas regular secondary structure is ordered. -In a given protein the conformation of irregular secondary structure is unknown whereas the conformation of regular secondary structure is known. -Unlike regular secondary structure, successive residues in irregular secondary structure do not have the same backbone configuration. -Unlike regular secondary structure, the backbone of irregular secondary structure does not form any hydrogen bonds.

Unlike regular secondary structure, successive residues in irregular secondary structure do not have the same backbone configuration.

Which pairs of amino acid side chains could interact in the interior of a protein only via van der Waals interactions? Arg, Thr. Gln, His. Val, Leu. Ser, Ser.

Val, Leu

A domain is: -a folded segment of polypeptide with -a separate hydrophobic core. -an -helix, β-sheet or irregular secondary structure. -the same as a protein's tertiary structure. -always a motif.

a folded segment of polypeptide with -a separate hydrophobic core.