Genetics Chapter 9
In nucleic acids, the nitrogenous base is attached to the _______ carbon of the sugar.
1'
A double-stranded DNA molecule is 5,000 base-pairs long. How many complete turns are present in this molecule?
500
Ribonucleosides lack a
5′ phosphate group.
The DNA double helix resembles the structure of a spiral staircase. Which DNA component is analogous to the spiral staircase's banister (side rails)?
the sugar-phosphate backbone
A nucleic acid molecule that has 20% A, 30% C, 20% G and 30% T is most likely
single-stranded DNA
The bond that covalently links two DNA nucleotides is
the phosphodiester bond.
In the B-form of DNA, how far apart are two nucleotides?
3.4 Å
3'
Attached to a hydroxyl group
The form of DNA found in living cells is
B-DNA
What are the names of the different types of nucleic acid?
DNA and RNA
How can nucleotides found in DNA be discriminated from those found in RNA?
DNA nucleotides may contain thymine, DNA nucleotides contain deoxyribose and DNA nucleotides never contain uracil.
What statements correctly describe the structure of a DNA double helix?
DNA strands are wrapped around one another to form a helical structure. Bases on opposite strands are hydrogen bonded together.
What is Chargaff's rule?
In double-stranded DNA, A=T and C=G
Which of the following statements about Z-DNA is FALSE?
Its strands are not antiparallel
Z DNA
Left-handed twist
dCTP
Nucleotide found in DNA with three phosphate groups
What is the sugar found in nucleotides used to make RNA?
Ribose
What does it mean for two strands of DNA to be complementary?
The bases of one strand can base-pair with the bases of the other strand.
Which two main structural features result in complementary sequences of DNA forming a double helix?
The bases stack on top of one another. Hydrogen bonding between the bases.
A double-stranded DNA molecule is 5,000 base-pairs long. How long is this molecule?
1.7 um
If R = any purine, Y = any pyrimidine, and N = any nucleotide, what is the probability of finding the sequence 5′ GRANTY 3′ in any molecule of DNA? Assume nucleotides are in equal percentages.
1/256
How many hydrogen bonds would connect the DNA sequence CATG and its complement on the other strand in a double helix?
10
The X-ray diffraction data collected by Rosalind Franklin predicted that the DNA double-helix contains ____ base pairs per complete turn of the helix.
10
When was the structure of the DNA double-helix discovered?
1953
In nucleic acids, the difference between deoxyribose and ribose lies at carbon
2'
In the B-form of DNA, how wide is the major groove?
22 Å
Deoxyribonucleotides lack a
2′ hydroxyl group.
If one strand of DNA has the sequence 5'-ATGCTACATA-3', what would be the complementary sequence.
3'-TACGATGTAT-5'
A single turn of the DNA double helix has a length of
3.4 nm
The percentage of cytosine in a bacterial genome was determined to be 20 %. What is the percent of adenine?
30
A radioactive isotope that can be used to label proteins and NOT nucleic acids is
35S
Which of the following DNA molecules is the most thermodynamically stable?
5'GCATCGAGGCCGGCTG 3' 3'CGTAGCTCCGGCCGAC 5'
The double-stranded DNA molecule of the newly discovered Elradicus libanii was found by electron microscopy to have a length of 17 micrometers. How many complete turns of the helix are present in this molecule?
5,000
The double-stranded DNA molecule of the newly discovered Elradicus libanii was found by electron microscopy to have a length of 17 micrometers. How many base pairs are present in this molecule?
50,000
Consider a piece of double stranded DNA in which each strand of the helix has 1800 nucleotides. If the piece of double-stranded DNA had a total of exactly 600 deoxycytidine monophosphate nucleotides, how many deoxyguanosine monophosphate nucleotide would be present?
600
What are the three parts of a nucleotide?
A pentose sugar, a nitrogenous base, and at least one phosphate group.
Under certain in vitro conditions, triplex DNA can form. What is triplex DNA?
A triple-helical structure
tRNA molecules are good examples of RNA molecules that have extensive regions that are double stranded and extensive regions that are single stranded. What are the main structural features of the tRNA molecule?
An anticodon and a site for attaching an amino acid - the acceptor site.
There are two conformations of DNA: B DNA and Z DNA. What are the main structural features of B DNA?
Bases are aligned perpendicular to the central axis of the molecule. 10 base pairs per turn.
1'
Attached to the base
5'
Attached to the phosphate group
The DNA double helix can adopt two conformations. The conformation that is most abundant in living cells is called _____ DNA.
B
The DNA double helix can form two types of structures. What are those two types of structures?
B DNA and Z DNA
What are the features of the structure that forms when short regions of RNA form base-pairs?
Double-stranded and Helical
For double-stranded DNA which of the following base ratios ALWAYS equals 1?
C/G
Which of the following is NOT a difference between RNA and DNA?
Choose this answer if all of the above are differences =RNA is generally shorter than DNA =RNA is usually single-stranded whereas DNA is double-stranded =RNA contains ribose whereas DNA contains deoxyribose =RNA contains uracil whereas DNA contains thymine
Imagine you looked along the central axis of a right-handed DNA double-helix so that the spills twisted away from you. In what direction would the spirals twist as you looked along the axis of the molecule?
Clockwise
A nucleoside composed of the base cytosine attached to ribose is called
Cytidine
Molecular genetics is the study of the structure of ______ and how it functions at the molecular level.
DNA
Nucleotides are used as the fundamental repeating structural unit of ______ and ______.
DNA and RNA
What kind of sugar is found in DNA?
Deoxyribose
DNA sequences with a high proportion of base-pairs between _____ and _____ are most stable.
G and C
The correct order of base-pair strength in DNA/RNA (from strongest to weakest) is:
GC > AT > AU
Which of the following statements about RNA is TRUE?
None of the above.
Guanosine-triphosphate
Nucleotide used to make RNA that contains three phosphate groups
UMP
Nucleotide with ribose sugar and a single phosphate group
ADP
Nucleotide with ribose sugar with two phosphate groups
Second level of DNA
Nucleotides are linked together to form strands of nucleic acids
Lowest level of DNA
Nucleotides are the building blocks of nucleic acids
In a DNA double helix, where is the sugar phosphate backbone located?
On the outside of the helix
The AT/GC base-pairing rule requires that the purines (A and G) always pair with the pyrimidines (T and C). Why is this?
Pairing a purine with a pyrimidine ensures a consistent diameter of the helix.
What is the name for the type of bond connecting two sugar molecules via a phosphate group in the backbone of DNA and RNA?
Phosphodiester bond
How can nucleotides found in RNA be discriminated from those found in DNA?
RNA nucleotides never contain thymine, they may contain uracil, and they contain ribose.
In what cellular process is triplex DNA suspected to have a role?
Recombination
What is the conventional "handedness" of the spiral in the DNA double helix?
Right handed
B DNA
Right-handed twist
The data upon which Crick and Watson based their model of the DNA double helix were from X-ray diffraction patterns from wet DNA fibers. These data were collected by the scientists
Rosalind Franklin and Maurice Wilkins
RNA molecules can contain both single-stranded and double-stranded regions. In an RNA molecule with both single and double stranded regions, what is the orientation of the bases in the single and double stranded parts of the molecule?
Single-stranded region; bases project outwards. Double-stranded region; bases project towards the center of the helix.
What assumptions did Crick and Watson need to make to determine the double-stranded, helical structure of DNA?
That all nucleotides are linked together using the same kind of bond and that DNA is composed of nucleotides linked together into chains.
Charges found that double-stranded DNA contains approximately a 1:1 ratio of adenine and thymine, and approximately a 1:1 ratio of cytosine and guanine. What did he conclude from this observation?
That each adenine in DNA interacts with a thymine and that each cytosine in DNA interacts with a guanine.
Highest level of DNA
The double-helix bends and wraps to form complex structures
Due to the twisting of the two strands of DNA around each other in a DNA double helix, groves form on the surface of the molecule. What are the names of those grooves?
The minor groove and the major groove
What makes DNA negatively charged?
The negative charge on each phosphate in the sugar-phosphate backbone.
Some proteins can interact with the major groove in the surface of a DNA double helix. What features of this iteration are responsible for the binding of these proteins to specific sequences of DNA?
The proteins bind to specific base sequences via hydrogen bonds. The proteins recognize certain sequences of bases in the groove.
Which criteria from the list can be used to discriminate between purine and pyrimidine nucleotides?
The ring structure of the nucleotide.
What are the main structural features of DNA found in the Z conformation?
There are 12 base-pairs per turn, the bases are tilted relative to the central axis of the molecule, the sugar-phosphate backbone zig-zags slightly, and the helix is left-handed.
B DNA can be converted to the Z DNA conformation under certain conditions. In what cellular process is Z DNA believed to have a role?
Transcription
Third level of DNA
Two strands of DNA can associate to form a double-helix
A nucleotide with one phosphate group, that is found only in RNA, and contains the nitrogenous base adenine is called _____ _____.
adenosine monophosphate
When one strand of DNA in a double helix has the chemical polarity 5' to 3', and the other, running in the opposite direction, has the chemical polarity 3' to 5', then it would be said that the two strands are ______.
antiparallel
When an RNA double-helix forms due to regions of complementarity in an RNA molecule, the strands of the RNA run ______ to one another, much like the strands of DNA in a DNA double-helix. Also, the twist of the helix that forms is ______-handed, and there are approximately 11 to 12 base-pairs per 360 degree turn of the helix.
antiparallel ; right
Some proteins can interact with the major groove in the surface of a DNA double helix. These proteins recognize specific sequences of _____ in the groove, and interact with the groove via the formation of _____ bonds; thus, the protein interacts very specifically with a particular region of DNA.
bases ; hydrogen
In a DNA double helix, the bases point towards the _____ of the helix
center
When DNA is ________________ hydrogen bonds are broken.
denatured
A nucleoside that is composed of the base adenine attached to a deoxyribose is called
deoxyadenosine
A large nucleic acid molecule that has 20% A, 30% C, 30% G and 20% U is most likely
double-stranded RNA
Which of the following bases has a double heterocyclic ring structure?
guanine
Although there is significant variation in the length of RNA molecules, they are generally much shorter than chromosomal sequences of DNA. In fact, they range from only a few ____ nucleotides long to several _____ nucleotides long
hundred ; thousand
Under certain conditions, B DNA can be converted to Z DNA. For example, under high _____ conditions, sequences that contain alternating purines and _____ are more likely to convert from B DNA to Z DNA. Also, under low salt conditions, the methylation of certain bases will promote Z DNA formation.
ionic ; pyrimidines
To help them understand the data that Rosalind Franklin obtained by X-ray diffraction studies, Crick and Watson used molecular ______ to develop representations of the DNA double-helix.
modeling
A sugar, such as ribose or deoxyribose, attached to a base but not to a phosphate group is called a ______.
nucleoside
The 5′ end of a nucleic acid molecule refers to the ___________ group on the 5′ carbon of the first nucleotide.
phosphate
The difference between a nucleoside and a nucleotide is that the nucleotide has a(n) ______ ______ attached to the sugar and the nucleoside does not.
phosphate molecule
The structure of DNA that Crick and Watson proposed has _____ (number) strands of DNA that are wrapped around each other to form a double helix. The DNA bases of each strand of DNA point towards the central axis of the molecule and are held together by _____ bonds.
two ; H
Which of the following bases has a single heterocyclic ring structure?
two of the above thymine, cytosine
For double-stranded DNA which of the following base ratios ALWAYS equals 1?
two of the above (A+G)/(C+T) (G+T)/(A+C)
When comparing the structural features of RNA with the structural features of DNA, there are two main differences: First, RNA used the base ______ while DNA uses the base ______; second, DNA used the sugar ______ and RNA uses the sugar ______.
uracil ; thymine ; deoxyribose ; ribose.
