EXAM 4 Flashcards
(81 cards)
DNA is more resistant to hydrolysis than RNA.
What feature of DNA is responsible for this characteristic?
the absence of a 2′‑hydroxyl group in deoxyribose
The difference between a nucleoside and a nucleotide is that
nucleotides contain one or more phosphate groups, whereas nucleosides have none.
The major interaction stabilizing the double helical structure of DNA is
hydrogen bonds between bases on opposite strands.
An important key to understanding the structure and function of DNA was the observation that the amount of A equaled the amount of T and the amount of G equaled the amount of C.
Erwin Chargaff
Which compound is found in DNA but not in RNA?
thymine
Write the complementary sequence for TCGAAC. Write the new sequence in the standard 5′→3′ notation.
5’ GTTCGA 3’
Biochemist Erwin Chargaff was the first to discover that, in DNA, [A]=[T] and [G]=[C]. These equalities are now known as Chargaff’s rule.
Using Chargaff’s rule, determine the percentages of all of the bases in DNA that is 14% thymine.
Adenine =14%
Cytosine =36%
Guanine =36%
How many hydrogen bonds exist between this DNA strand and its complementary strand?
A:T = 2
G:C = 3
The composition, in mole‑fraction units, of one of the strands of a double helical DNA molecule is [A]=0.30 and [G]=0.24. This strand is the reference strand.
What is the total [T] and [C] for the reference strand?
[T+C] R: 0.46
[A+G] C: 0.46
[T] C: 0.3
[C] C: 0.24
Bacteria and other microbes can be used to “clean up” an oil spill by breaking down oil into carbon dioxide and water. Two samples isolated from the Deepwater Horizon leak in the Gulf of Mexico were labeled A and B. The DNA of each was isolated and the percent thymine measured in each sample. Sample A contains 17.7 % thymine and sample B contains 28.9 % thymine. Assume the organisms contain normal double‑stranded DNA and predict the composition of the other bases.
percent adenine in sample A:
17.7%A
percent guanine in sample A:
32.3%G
percent cytosine in sample A:
32.3%C
percent adenine in sample B:
28.9%A
percent guanine in sample B:
21.1%G
percent cytosine in sample B:
21.1%C
How is circular DNA compacted within the nucleoid of a cell?
supercoiling
What is the term for two circular DNA molecules that differ only in the number of helical turns, also called linking number?
topoisomerS
Which factor accounts for the increased rate of DNA synthesis necessary for replication in eukaryotic cells as compared to that in prokaryotes?
the presence of multiple origins at which replication can take place at the same time
During the replication of DNA,
one strand is synthesized continuously and the other is synthesized in short segments.
DNA replication in E. coli begins at a unique site called the
origin of replication
Arrange the steps of DNA replication in the order that they occur.
FIRST STEP
helicase unwinds the DNA double helix
single-stranded DNA binding proteins bind to each template strand
RNA primers are added
DNA polymerase synthesizes DNA
RNA primers are removed
DNA ligase joins DNA fragments together
LAST STEP
DNA replication involves multiple steps that require different enzymes. Which process does primase catalyze in DNA replication?
Synthesis of a short RNA sequence that initiates DNA synthesis
Match each protein to its role in DNA replication
DNA topoisiomerase: relaxes the supercoiled DNA
helicase: unwinds the DNA double helix
SSB protein: prevents the reannealing of the DNA strands
DNA polymerase I: replaces the RNA primers with DNA
primase: synthesizes RNA primers
As DNA is replicated, both continuous and discontinuous replication occur. Discontinuous replication is the result of which specific feature of DNA?
antiparallel strands
Identify each characteristic as belonging to the leading strand or the lagging strand in DNA synthesis.
Leading strand: synthesized continuously, 5’»3’
Lagging strand: Okazaki fragments, 3’»5’, forms loo[s during replication
One of the biologically harmful effects of ultraviolet (UV) light is its action on DNA.
How does UV light alter DNA?
covalent formation of pyrimidine dimers involving adjacent pyrimidines along a DNA strand
If a DNA molecule is damaged, it
is possible to repair the damage in the site where it occurs.
Which process is NOT a possible type of damage to DNA?
formation of more than three hydrogen bonds in a Watson–Crick base pair
What generally causes thymine dimers to form in a strand of DNA, and why are thymine dimers a problem?
Ultraviolet light can cause thymine dimers, potentially creating a mutation that could lead to cancer.