BIO 151 - Exam 2 Questions And Answers

Which of the following are purine nitrogenous bases? - ANS guanine and adenine If cells are grown in a medium containing radioactive 32P-labeled phosphate, which of these molecules will be labeled? - ANS nucleic acids What is the difference (if any) between the structure of ATP and the structure of the precursor of the A nucleotide in RNA? - ANS There is no difference. When nucleotides polymerize to form a nucleic acid ________. - ANS a covalent bond forms between the sugar of one nucleotide and the phosphate of a second A double-stranded DNA molecule contains a total of 120 purines and 120 pyrimidines. This DNA molecule could be composed of ________. - ANS 120 thymine and 120 adenine molecules Franklin and Wilkins analyzed DNA by bombarding DNA crystals with X-rays. Their analysis yielded two numbers that sparked interest, 3.4 nm and 0.34 nm. What is the significance of these numbers? - ANS These numbers demonstrate there are 10 rungs, or steps, on the DNA "ladder" for every turn of the helix. Which of the following did Watson and Crick already know when they were trying to determine the structure of DNA? The number of ________. - ANS purines is always the same as pyrimidines Which of the following descriptions best fits the class of molecules known as nucleotides? - ANS a nitrogenous base, a phosphate group, and a sugar Like many molecules, nucleotides have asymmetry. This gives nucleic acids a specific direction for polymerization. The 3' carbon of a nucleotide has a hydroxyl group, while the 5' carbon is covalently bonded to _____. - ANS phosphate group Nucleic acids are polymers made up of which of the following monomers? - ANS nucleotides What is the structural feature that allows DNA to replicate in anti-parallel manner? - ANS complementary pairing of the nitrogenous bases If one strand of a DNA molecule has the sequence of bases 5'ATTGCA3', the other complementary strand would have the sequence ________. Hint: you have to start in reverse because it is antiparallel. - ANS 5'TGCAAT3' What is the difference between a ribonucleotide and a deoxyribonucleotide? - ANS Ribonucleotides have a hydroxyl group on the 2 carbon of their sugar subunit. Which of the following includes all of the pyrimidines found in RNA and DNA? - ANS cytosine, uracil, and thymine What is/are the variable structure(s) of a nucleotide? - ANS sugar and base Which of the following pairs of base sequences could form a short stretch of a normal double helix of DNA? - ANS 5'-ATGC-3' with 5'-GCAT-3' Enzymes that break down DNA catalyze the hydrolysis of the covalent bonds that join nucleotides together (reverse of polymerization). What would happen to DNA molecules treated with these enzymes? - ANS The phosphodiester linkages of the polynucleotide backbone would be broken. What feature of single nucleotides provides the energy needed for polymerization when nucleic acids are formed? - ANS their phosphate groups Some viruses consist only of a protein coat surrounding a nucleic acid core. If you wanted to radioactively label the nucleic acids separately from the protein, you would use radioactive ________. (Which atom is in nucleotides but not proteins?) - ANS phosphorus Which of the following are pyrimidine nitrogenous bases? - ANS cytosine and uracil Which of the following best describes DNA's secondary structure? - ANS double antiparallel helical strands The difference between the sugar in DNA and the sugar in RNA is that the sugar in DNA ________. - ANS contains one less oxygen atom DNA double helices are soluble in water because of all the following except _____. (This has an important practical application for DNA isolation (extraction): when DNA is in alcohol, it is an insoluble, white-powder-like material that biologists and chemists call "precipitate"). - ANS hydrogen at 2' C Side chains of amino acids ________. - ANS may be polar or nonpolar Which one of the following is NOT a component of each monomer used to make proteins? - ANS a phosphorus atom, P What component of amino acid structure varies among different amino acids? - ANS the components of the R-group At about pH 7 in most cells, what happens to the amino R-group on an amino acid? - ANS It acts as a base and gains a proton, giving it a positive charge At about pH 7 in most cells, what happens to the carboxyl R-group on an amino acid? - ANS It acts as an acid and loses a proton, giving it a negative charge. Why are polymerization reactions endergonic? Polymerization reactions ________. - ANS reduce entropy Which of the following involves an increase in entropy? - ANS hydrolysis In solution, why do hydrolysis reactions occur more readily than condensation reactions? - ANS Hydrolysis increases entropy and is exergonic. Suppose you discovered a new amino acid. Its R-group contains only hydrogen and carbon atoms. Predict the behavior of this amino acid. - ANS hydrophobic A peptide bond ________. - ANS forms the primary structure of proteins The bonding of two amino acid molecules to form a larger molecule requires the ________. - ANS release of a water molecule here are 20 different amino acids. What makes one amino acid different from another? - ANS different side chains (R-groups) attached to an α carbon Upon chemical analysis, a particular polypeptide was found to contain 100 amino acids. How many peptide bonds are present in this protein? - ANS 99 which two functional groups are always found in amino acids? - ANS carboxyl and amino groups Amino acids are acids because they always possess which functional group? - ANS carboxyl 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 ________. - ANS as an acid and a base which type of interaction stabilizes the α-helix and the β-pleated sheet structures of proteins? - ANS hydrogen bonds You disrupt all hydrogen bonds in a protein. What level of structure will be preserved? - ANS primary