Blinn BIOLOGY 204 – DNA structure depends on base pairing

DNA structure depends on base pairing of its four nucleotides, A, C, T, and G. Nucleotide A pairs with T and nucleotide C pairs with G. This forms a four-letter DNA “alphabet.” Because DNA codes for amino acids in sets of three nucleotides, there are 4 cubed (43), or 64 possible combinations, coding for 20 different amino acids. What is the best explanation for why there is no selective advantage for DNA to have five nucleotides (e.g., A, C, T, G, and E) with C pairing with either G or functionally equivalent E?

There would be a five-letter alphabet with 125 combinations, which is too numerous.
Because G and E have the same role, there would still be four functional letters of the alphabet.
It would be impossible to form the DNA molecule because it must have an equal number of C’s and G’s.
It is impossible, because there are not five known nucleotides in the cell.
Replication would be inaccurate because sometimes C would bond with G, and sometimes C would bond with E.
2. Which of the following correctly describes a difference between DNA and RNA?

DNA contains a ribose, whereas RNA contains a deoxyribose sugar.
DNA contains four nucleotides, whereas RNA contains three.
DNA is replicated, whereas RNA is translated.
DNA is single-stranded, whereas RNA is double-stranded.
DNA occurs in the nucleus, whereas RNA only occurs outside the nucleus.
3. Nucleotides are composed of

nucleic acids.
one or more amino acids.
one or more phosphates, a sugar, and a base.
fatty acids and a base.
a base and at least one phosphate.
4. In the double stranded structure of DNA,

the monomers in each strand are linked together by hydrogen bonds.
the two strands are held together by covalent bonds.
the two strands are held together by hydrogen bonds.
both strands run in the same direction.
the monomers in each strand are linked together by ionic bonds.
5. Yeast is cultured in the presence of radioactive phosphate, and the following biological molecules are purified from the cells. Which of the purified molecules should be most radioactive?

Amino acids
A polysaccharide
6. One function of nucleic acids is to

code for fatty acid synthesis.
catalyze all of the chemical reactions within a cell.
carry out photosynthesis.
code for protein synthesis.
form a cell membrane.
7. Replication is the synthesis of _______, while transcription is the synthesis of _______.

an exact copy of DNA; proteins
proteins; an RNA copy of DNA
an exact copy of RNA; an exact copy of DNA
an RNA copy of DNA; an exact copy of DNA
an exact copy of DNA; an RNA copy of DNA
8. The DNA sequence ATT CGT TCA is equivalent to which of the following RNA sequences?

9. Nucleotides are joined together in a single strand of DNA

by phosphodiester bonds.
by glycosidic linkages.
by carbon–carbon bonds.
through van der Waal’s interactions.
by hydrogen bonds.
10. Which of the following gasses is not thought to have been added to the atmosphere by extensive volcanic eruptions early in Earth’s history?

Hydrogen sulfide
Sulfur dioxide
Carbon dioxide
11. In 1969, Australian scientists analyzed the structure of an uncontaminated portion of a meteorite. They found a number of the molecules that are necessary for life, including purines, pyrimidines, sugars, and ten amino acids. This result supports which of the following statements?

Life on Earth may have originated from extraterrestrial molecules.
The small molecules of life occur elsewhere than Earth.
a, b, and c
The question of how life originated from nonbiological precursors remains to be answered.
a and b only
12. It is noteworthy that the Miller-Urey experiments produced ribose sugars because they are

essential monomers of all carbohydrates.
essential components of a nucleic acid.
essential components of proteins.
essential components of lipids.
vital nutrients.
13. Many organic molecules are easily destroyed by oxygen in modern Earth’s atmosphere. This finding

indicates that small biological molecules must be generating on the moon.
indicates that all life on Earth must have had an extraterrestrial origin.
indicates that an abiotic origin of small biological molecules is impossible.
explains why spontaneous abiotic synthesis of small biological molecules is not commonly seen in small pools and lakes.
indicates that life could never have originated on Earth.
14. The “cold chemistry” experiment of Miller showed prebiotic synthesis in test tubes containing ammonia gas, water vapor, and cyanide (HCN) cooled to –78oC. This is the temperature of the ice that covers Europa, one of Jupiter’s moons. This result is most consistent with which of the following statements?

Earth was at a temperature of –78oC 3.5 billion years ago.
Basic molecules of life can originate on a cold moon with water.
There is a possible extraterrestrial origin of life on Earth.
Both c and d
Life did not form on Earth until the formation of widespread glaciers.
15. It has been hypothesized that early life consisted of an “RNA world”—a world before DNA. Which of the following does not support this hypothesis?

Ribozymes catalyze formation of peptide linkages.
Protein enzymes catalyze the great majority of reactions in living cells.
Adding a short RNA sequence to a mixture of nucleotides causes formation of RNA polymers 7 million times faster than without the short sequence.
An artificial ribozyme catalyzes assembly of short RNAs into a longer molecule that is a copy of itself.
Retroviruses have an enzyme that catalyzes the synthesis of DNA from RNA.
16. Hydrothermal vents deep in the ocean, where hot water emerges from beneath Earth’s crust, lack oxygen gas and contain metals such as iron and nickel. In laboratory experiments, these metals have been shown to

spontaneously form double-layered spheres.
catalyze formation of nucleic acids.
catalyze formation of amino acids.
polymerize sugar molecules.
convert light energy into energy.
17. Fossilized remains in ancient geological formations indicate that cells first appeared

in ancient volcanoes.
before water arrived on Earth.
about 4.5 billion years ago.
about 5 thousand years ago.
about 3.5 billion years ago.
18. The cell membrane

is usually formed of protein molecules.
carries genetic information.
exists due to the specific gravity of water.
catalyzes chemical reactions.
encloses a distinct chemical environment.
19. Fatty acids have hydrophilic heads and hydrophobic tails. This allows them to

act as information carriers for proto-cells.
self-organize into a double layer surrounding a sphere of water.
act as catalysts for chemical reactions.
form a double-layered membrane with heads facing out and a layer of water between the tails.
self-organize into a single layer surrounding a sphere of water.
20. William Schopf found fossils in ancient Australian rocks with an internal structure unlikely to occur through abiotic processes. Additional evidence that these were fossil cyanobacteria includes

fossilized DNA.
fossilized RNA.
a carbon isotope ratio (13C:12C) consistent with photosynthetic activity.
a carbon isotope ratio (13C:12C) consistent with translation of DNA.

micrometeorites from Mars with amino acids.

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