Portage Biochem Module 6
What is the difference between a nucleoside and nucleotide? - CORRECT
ANSWER-A nucleoside is formed from the covalent bonding of a base (purine or
pyrimidine) to either ribose (RNA) or 2-deoxyribose (DNA). Nucleotides are built from
a nitrogen-containing organic base, a monosaccharide, and phosphate.
What characteristic makes purines and pyrimidine heterocyclic? - CORRECT
ANSWER-Each has a ring with nitrogen in the ring instead of all carbon atoms in the
ring.
Is this molecule ribose or 2-deoxyribose? Briefly explain what structural information
was used to determine this. - CORRECT ANSWER-Ribose. This molecule contains
an -OH on carbon 2. 2-deoxyribose has an -H atom on the second carbon.
Is the following a pyrimidine or purine? Provide the name and one-letter symbol. -
CORRECT ANSWER-Pyrimidine. It is thymine (T).
What is the difference between thymine and uracil? - CORRECT ANSWER-These
two bases differ by a methyl group. Thymine has an extra methyl group on the ring.
From the course and module information, where in a eukaryotic or prokaryotic cell, is
the DNA located? How about the RNA? - CORRECT ANSWER-DNA is located in
the nucleus of a eukaryotic cell or the nucleoid of a prokaryotic cell. RNA is found in
the nucleus, on the ribosome, and in other parts of the cell.
Which DNA and RNA bases contain a carbonyl group? - CORRECT
ANSWER-Guanine, cytosine, thymine, and uracil all contain C=O group attached to
the rings. Adenine is the only base that does not.
What constitutes the backbone of DNA? - CORRECT ANSWER-In DNA, this
consists of the alternating deoxyribose and phosphate groups linked together
through covalent bonds.
How many hydrogen bonds form between A and T? - CORRECT ANSWER-Two
hydrogen bonds are formed between these two bases. G and C form three H-bonds.
Which nucleic acid is single-stranded? - CORRECT ANSWER-RNA. RNA forms
single strands. (Particularly, this was noted in this module for tRNA.) DNA forms a
double helix.
What interactions stabilize the DNA double helix? - CORRECT ANSWER-Hydrogen
bonds stabilize the helix. Each AT pair and form two hydrogen bonds, and each GC
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