Biomolecules I

Which linkage forms the backbone of a nucleic acid? 1. A sugar-phosphate linkage 2. A sugar-base linkage 3. A sugar-base-phosphate linkage 4. A base-phosphate linkage

1. A sugar-phosphate linkage All attempts used; correct answer displayed Nucleic acids have a sugar-phosphate backbone. The base is not part of the nucleic acid backbone.

Which of the following statements about nucleotide structure is false? 1. The phosphate group is bonded to the nitrogenous base. 2. The sugar can be either ribose or deoxyribose. 3. The nitrogenous base is bonded to the sugar. 4. The sugar is bonded to the phosphate group.

1. The phosphate group is bonded to the nitrogenous base. The phosphate group is bonded to the sugar, not to the nitrogenous base. This statement is true; the sugar is ribose in RNA and deoxyribose in DNA.

Which of the following is true of pleated sheet foldings within a polypeptide? 1. They depend on regular occurrence of CO and NH. 2. Its loops are held in place mainly by disulfide bridges. 3. They are part of the polypeptide's quaternary structure. 4. The side chains are parallel to the plane of the sheet. 5. All the above.

1. They depend on regular occurrence of CO and NH. Yes! Occurring at regular intervals along the backbone, these groups stabilize the sheet by forming many hydrogen bonds between neighboring segments of the polypeptide. Not so. Hydrogen bonds are the main stabilizing forces.

True or false? Guanine and uracil are examples of nitrogenous bases. 1. True 2. False

1. True Guanine and uracil are indeed examples of nitrogenous bases; adenine, thymine, and cytosine are the others.

The helical foldings in proteins ... 1. are kept folded by hydrogen bonds. 2. are kept folded by base-pairing. 3. are kept folded by forces between side chains on adjacent turns of the helix. 4. are part of the protein's primary structure. 5. None of the above.

1. are kept folded by hydrogen bonds. Yes! The hydrogen bonds form between C=O and N-H groups of the backbone. There's a good answer among the other choices. You may need to review the lessons on protein structure.

Which statement expresses a real difference between DNA and RNA? 1. (a) DNA can make a double helix; RNA cannot. 2. (b) DNA is much longer than RNA. 3. (c) DNA has more kinds of bases than RNA. 4. Both (a) and (b). 5. (a), (b), and (c).

2. (b) DNA is much longer than RNA. Good choice! RNA is made by copying short segments of DNA.

If a strand of DNA has the nitrogen base sequence 5'-ATTTGC-3', what will be the sequence of the matching strand? 1. 3'-UAAACG-5' 2. 3'-TAAACG-5' 3. 3'-GCAAAT-5' 4. 3'-TUUUCG-5' 5. 3'-ATTTGC-5'

2. 3'-TAAACG-5' Adenine pairs with thymine and guanine pairs with cytosine. This is not how the nitrogenous bases pair.

Which of the following is NOT true of protein quaternary structure? 1. A quaternary protein cannot have fewer than two carboxyl groups. 2. A single polypeptide may have quaternary structure. 3. The same kinds of stabilizing forces are involved as in tertiary structure. 4. Disulfide bridges may hold the polypeptides in contact. 5. Hydrogen bonds may hold the polypeptides in contact.

2. A single polypeptide may have quaternary structure. Correct! Quaternary structure occurs when two or more polypeptides join together. The statement is true, so it doesn't answer this question.

Which structure is not a component of a nucleotide? 1. Pentose 2. Sulfhydryl Oxygen group 3. Phosphate group 4. Nitrogen-containing base

2. Sulfhydryl Oxygen group A nucleotide does not contain an sulfhydryloxygen group.

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? 1. There will be less rotation around backbone bonds than before. 2. The altered protein will have longer helices than before. 3. The altered protein will have shorter helices than before. 4. The altered protein will have fewer hydrogen bonds than before. 5. The primary structure of the altered protein will be shorter than before.

2. The altered protein will have longer helices than before. Great! Helical segments come to an end when they meet a proline residue, because proline grips the backbone in two places. Remove proline, and the helix can continue. Right track, wrong direction. Hint: when you see proline, think "helix breaker."

The two strands of a DNA double helix are held together by _____ that form between pairs of nitrogenous bases. 1. covalent bonds 2. hydrogen bonds 3. S—S bonds 4. hydrophilic interactions 5. ionic bonds

2. hydrogen bonds Nitrogenous base pairs are joined by hydrogen bonds. DNA does not contain sulfur.

If you measure the amounts of the bases in any sample of DNA, you'll find that ... 1. the amount of A + the amount of T = the amount of G + the amount of C. 2. the amount of A + the amount of G = the amount of T + the amount of C. 3. the amount of A + the amount of C = the amount of G + the amount of U. 4. the amount of A = the amount of G; the amount of T = the amount of C. 5. None of the above.

2. the amount of A + the amount of G = the amount of T + the amount of C. Right! For every A there's a T; for every G there's a C.

What is the complementary DNA sequence to 5' ATGCATGTCA 3'? 1. 5' TACGTACAGT 3' 2. 5' ATGCATGTCA 3' 3. 5' TGACATGCAT 3' 4. 5' ACTGTACGTA 3'

3. 5' TGACATGCAT 3' This sequence is complementary and in the correct orientation.

If a DNA double helix is 100 nucleotide pairs long and contains 25 adenine bases, how many guanine bases does it contain? 1. 200 2. 75 3. 50 4. 25 5.150

3. 50 The sum of adenine and thymine bases equals 50.

The helical foldings of proteins are stabilized mainly by bonds between ... 1. S and S. 2. ionic groups. 3. CO and NH. 4. side chains. 5. water molecules.

3. CO and NH Right! Hydrogen bonds between these groups keep the helix coiled.

A nucleotide is composed of a(n) _____. 1. phosphate group, a nitrogen-containing base, and a hydrocarbon 2. amino group, a nitrogen-containing base, and a five-carbon sugar 3. phosphate group, a nitrogen-containing base, and a five-carbon sugar 4. sulfhydryl group, a nitrogen-containing base, and a five-carbon sugar 5. glycerol, a nitrogen-containing base, and a five-carbon sugar

3. phosphate group, a nitrogen-containing base, and a five-carbon sugar These are the components of a nucleotide

The protein shown here has ... http://session.masteringbiology.com/problemAsset/1323171/6/P-Levels_of_Structure-A.jpg 1. primary structure. 2. secondary structure. 3. tertiary structure. 4. All of the above. 5. All of the above, plus quaternary structure.

4. All of the above. Correct! All proteins have primary structure; the compact overall folding is tertiary, and the corkscrews and parallel strands are secondary.

If you were to analyze a DNA sample from a eukaryotic cell, you would find that: 1. (a) the number of purines equals the number of pyrimidines. 2. (b) the number of adenines equals the number of uracils. 3. (c) the number of guanines equals the number of cytosines. 4. Both (a) and (c). 5. (a), (b), and (c).

4. Both (a) and (c). Correct! These are consequences of the base-pairing rules, which are fundamental to life.

What holds the strands of the DNA double helix together? 1. Attractions between the ionized phosphates. 2. Covalent bonds between A and T, and between C and G. 3. Attractions between polar sugars. 4. Hydrogen bonds between purines and pyrimidines. 5. Proteins that bind to DNA bases.

4. Hydrogen bonds between purines and pyrimidines. Yes! A and G are purines; C and T are pyrimidines. Hydrogen bonds link them.

Which of the following statements about DNA structure is true? 1. The arrangement of the sugar-phosphate groups determines the genetic code. 2. Phosphodiester bonds form between the phosphate group of one nucleotide and the 5' carbon of the adjacent nucleotide. 3. DNA is always synthesized in the 3' to 5' direction. 4. The nucleic acid strands in a DNA molecule are oriented antiparallel to each other.

4. The nucleic acid strands in a DNA molecule are oriented antiparallel to each other. The 5' end of one strand in a DNA molecule is oriented opposite the 3' end of the other strand, making the strands antiparallel.

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. (a) Disulfide bridges bind the proteins together. 2. (b) Each protein is a single long alpha helix. 3. (c) Hair is another example. 4. Both (a) and (b). 5. (a), (b), and (c).

5. (a), (b), and (c). Right. An excellent way to end the quiz! Keratin is a versatile structural protein.

This ribbon diagram represents a protein in water. Even without showing the side chains, it's clear that the protein's quaternary structure ... http://session.masteringbiology.com/problemAsset/1323171/6/P-Levels_of_Structure-B.jpg 1. is stabilized by hydrogen bonds. 2. is weaker than that of entirely helical proteins. 3. is stabilized by forces between backbone groups. 4. consists of helices. 5. None of the above. There's no quaternary structure.

5. None of the above. There's no quaternary structure. Right! Quaternary structure requires at least two polypeptide chains. There's only one chain here.

The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic. Nonpolar:hydrophobic

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http://session.masteringbiology.com/problemAsset/1091057/16/1091057_001.jpg Every amino acid has a carboxylic acid group, an amino group, an α-carbon, and an R group. Look at the R group to classify the amino acid. Acidic R groups contain a carboxylic acid functional group, -COOH. Basic R groups contain an amino functional group (not amide), -NH2 (which attracts a proton to form -NH3). Neutral polar R groups are neither acidic nor basic, but contain a highly electronegative atom such as oxygen, nitrogen, or sulfur. Neutral nonpolar R groups contain mostly carbon and hydrogen (alkyl groups). They may also contain nitrogen or sulfur, but the effect of these atoms is diminished due to the size of the alkyl portion.

if R group contains either a polar,acidic, basic and a nonpolar, nonpolar loses -Amino acids w/ -CH2, -CH3 or a carbon ring in R group are nonpolar -amino acids with a negative charged R group are acidic - amino acids w/ a postive charged R group are basic -amino acids with O, H, or OH are polar?