Download Nucleotide HW Key

Chemistry 160 DNA Homework key
1. Describe the structure of DNA.
repeating polymer of 2-deoxyribose and phosphates in a 3’, 5’ phosphodiester linkage.
nitrogenous bases (purines and pyrimidines) are attached at C-1 of the sugar. The polmers are
arranged in an antiparallel double helix with the sugar-phosphate backbone on the outside and
the bases on the inside. Bases are perpendicular to the helix giving a “twisted ladder”
arrangement
2. Draw both a GC and an AT base pair.
H
N
H
N H -- -- --O
N
N
N
O -- -- -- H
N
N
adenine
NH -- -- --
N
-- -- -- --HN
O
thymine
N
N
N
N
O
N H -- -- -H
Guanine
cytosine
3. Draw a piece of RNA with the sequence 5'--->3' U-G-C-A.
O
O
O P O
N
O
O
U
O
N
O
O
O P
N
O
O
O
N
N
O
G
N
N
N
O
O
O
O P
N
O
N
O
C
N
O
N
O
O
N
O
N
O
O P
A
N
O
O
O
4. What are three differences between DNA and RNA?
DNA is double stranded, found only in nucleus, has AGCT (v. AGCU in RNA), deoxyribose v
ribose (in RNA)
5. Why is DNA more stable than RNA?
DNA has no oxygen on C-2 of the sugar while RNA does. That oxygen on C-2 of the ribose is
where RNA’ses act to open the ring.
6. What are histones and why are they necessary?
positively charged proteins that bind to the negatively charged phosphates. Allows DNA to fold
into small space.
7. Does all DNA code for protein? If not, what else does it do?
much does not, much of it is regulatory or structural
8. What is an Okazaki fragment?
a piece of DNA on the lagging strand (the 5’ ---> 3’ end) that is made as the strand opens, but,
since DNA is made 5’-->3’, it has to be made in bits. leaves little pieces that have to be closed by
DNA ligase.
9.Describe DNA replication.
DNA is opened and DNA binding proteins prevent it from reannealing. Then DNA polymerase
attaches to the strands and starts making DNA 5’----3’. One strand is leading as it allows DNA
to be made in the right way. The other is lagging (see #8) See diagram below
10. How does RNA polymerase know where to start transcription?
TATAA box upstream, says...bind here
11. Describe translation.
See diagram below:
A piece of mRNA binds to ribosome. tRNA with an anticodon loop complimentary to the codon
binds to the ribosome. A second tRNA with an anticodon loop complimentary to the next codon
binds in the next site on the ribosome. The aa’s on the tRNA’s then bind forming a peptide
bond. This process repeats until a stop codon is encountered.
12. Given the DNA sequence below, determine the amino acid sequence.
3’A C C T T T A C G A T C C G A G A A T C C G C A T C G G A C T T C 5’
RNA: 5’U G G A A A U G C U A G G C U C U U A G G C GUA G C CU G A A G 3’
protein
start
L-------G-------S----STOP
13. What would happen to the amino acid sequence if the 15th base was changed from an A to a
G?
change below in red changes sequence to LGP
3’A C C T T T A C G A T C C G G G A A T C C G C A T C G G A C T T C 5’
RNA: 5’U G G A A A U G C U A G G C C C U U A G G C GUA G C CU G A A G 3’
protein
start
L-------G-------P----STOP
14. What would happen to the amino acid sequence if the 15th base was deleted?
change below
3’A C C T T T A C G A T C C G G A A T C C GCA T C G G A C T T C 5’
RNA: 5’U G G A A A U G C U A G C C U U A G G C GUA G C C U G A A G G 3’
protein
start
L-------A------- L---------G------V-----A-----stop