chapter 4

If one strand of a DNA molecule has the sequence of bases 5'ATTGCA3', the other complementary strand would have the sequence _____.

5'TGCAAT3'

Which of the following pairs of base sequences could form a short stretch of a normal double helix of DNA?

5'-ATGC-3' with 5'-GCAT-3'

What is the difference (if any) between the structure of ATP and the structure of the precursor of the A nucleotide in RNA?

there is no difference

A double-stranded DNA molecule contains a total of 120 purines and 120 pyrimidines. This DNA molecule could be composed of _____.

120 thymine and 120 adenine molecules

If a DNA sample were composed of 10% thymine, what would be the percentage of guanine?

40

Which of the following statements best summarizes the differences between DNA and RNA?

DNA nucleotides contain a different sugar than RNA molecules

If 14C-labeled uracil is added to the growth medium of cells, what macromolecules will be labeled?

RNA

Why do researchers think the first self-replicating molecule was RNA?

RNA can carry information and catalyze chemical reactions

Which of the following is a difference between RNA and DNA?

RNA has ribose sugar and DNA has deoxyribose sugar

What is the difference between a ribonucleotide and a deoxyribonucleotide?

Ribonucleotides have a hydroxyl group on the 2 carbon of their sugar subunit.

DNAase is an enzyme that catalyzes the hydrolysis of the covalent bonds that join nucleotides together. What would first happen to DNA molecules treated with DNAase?

The phosphodiester bonds between deoxyribose sugars would be broken.

When nucleotides polymerize to form a nucleic acid _____.

a covalent bond forms between the sugar of one nucleotide and the phosphate of a second

Which of the following descriptions best fits the class of molecules known as nucleotides?

a nitrogenous base, a phospate group, and a sugar

The work of Bartel's group on the ribozyme RNA replicase supports which conclusion?

an RNA world could produce molecules that could self-replicate

both DNA and RNA _____

are information-containing molecules

Compare proteins to nucleic acids. Which of the following is true?

both have primary and secondary structure

What is the structural feature that allows DNA to replicate?

complementary pairing of the nitrogenous bases

The difference between the sugar in DNA and the sugar in RNA is that the sugar in DNA _____.

contains one less oxygen atom

Which of the following are pyrimidine nitrogenous bases?

cytosine and uracil

Which of the following includes all of the pyrimidines found in RNA and DNA?

cytosine, uracil, thymine

Which of the following best describes DNA's secondary structure?

double antiparallel helical strands

One of the primary functions of RNA molecules is to _____.

function in the synthesis of proteins

If cells are grown in a medium containing radioactive 32P-labeled phosphate, which of these molecules will be labeled?

glucose

Which of the following are purine nitrogenous bases?

guanine and adenine

RNA and proteins combine in cells to form structures called ribosomes. Ribosomes contain the active site for peptide bond formation. Based on their chemical structures, do you think protein or RNA molecules actually form the active site within the ribosome?

it could be either, because both molecules have catalytic properties

DNA is the main hereditary material of all life. However, DNA lacks one important characteristic for the first forms of life. Why have researchers rejected the idea that DNA was found in the first life form?

it does not function as a catalyst

In the acid-base reaction described in the preceding paragraph about Nakano's research on RNAs, a proton (H+) is being transferred. What is acting as the proton acceptor?

magnesium hydroxide

Refer to Nakano's quote from Science. If the cytosine is positively charged (+) before self-cleavage, what would its charge be after self-cleavage?

negative (-)

Nucleic acids are polymers made up of which of the following monomers?

nucleotides

Nucleic acids have a definite polarity, or directionality. Stated another way, one end of the molecule is different from the other end. How are these ends described?

one end has an unlinked 3 carbon; the other end has an unlinked 5 carbon

Which of the following chemical bonds do you think Nakano is referring to in his quote?

phosphodiester

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 _____.

phosphorous

Which of the following did Watson and Crick already know when they were trying to determine the structure of DNA? The number of _____.

purines is always the same as pyrimidines

Bartel's research group showed that an RNA replicase ribozyme could be created by _____.

starting with random components and allowing selection to result in molecules that were better and better at replicating

Recall the Bartel lab group experiment to create a ribozyme from scratch. If they had created exact copies of each ribozyme (rather than creating copies with a few differences), the ribozymes would have _____.

stayed the same with each round of selection

Which of the following statements about the 5' end of a polynucleotide strand of RNA is correct?

the 5' end has a phosphate group attached to the number 5 carbon of ribose

DNA double helices are soluble in water but insoluble in alcohol. How do these physical properties reflect the chemical structure of the DNA molecule?

the charge phosphate groups and sugars of DNA are hydrophilic

Enzymes that break down DNA catalyze the hydrolysis of the covalent bonds that join nucleotides together. What would happen to DNA molecules treated with these enzymes?

the phosphodiester linkages of the polynucleotide backbone would be broken

In the context of chemical evolution, DNA's structure is interesting because it suggests a possible copying mechanism. What about DNA's structure facilitates copying?

the strands of the double helix are complementary

What is/are the variable structure(s) of a nucleotide?

the sugar and the base

Why is it that RNA can catalyze reactions but DNA cannot?

the sugar of RNA is much more reactive than the sugar of DNA

You have a polymer of DNA with 10 adenine bases followed by 10 cytosine bases. If that strand bonded to a strand of 20 thymine bases, how would the double helix shape vary from a typical DNA double helix?

the width of the double helix would vary along the length of the strand

What feature of single nucleotides provides the energy needed for polymerization when nucleic acids are formed?

their phosphate group

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?

these numbers tell us there are ten rungs, or steps, on the DNA "ladder" for every turn of the helix

Is Nakano's quote from Science consistent with the textbook's claim that RNA is a good candidate for the first life form?

yes