Exam 3: 29 Nucleic Acids (2/3 complete) Flashcards
- For a circular double-stranded DNA, which of the following quantity is not going to change unless a strand is broken?
A) Its linking number
B) Its twisting number
C) Its writhe number
D) All the above
A) Its linking number
Lk is always an integer and, importantly, it remains constant for a closed circular DNA molecule unless a strand is broken!!
Linking number (Lk): This represents the number of times one DNA strand winds around the other in a right-handed direction. Imagine holding one strand and tracing its path; Lk is how many times you completely encircle the other strand. Lk is always an integer and, importantly, it remains constant for a closed circular DNA molecule unless a strand is broken.
Linking number in DNA supercoiling means…
A) the number of times the long axis of the double helix crosses over itself
B) the number of times that a strand of DNA winds in the right-handed direction around the helix axis when the axis lies in a plane
C) the number of times one strand completely wraps around the other strand
B) the number of times that a strand of DNA winds in the right-handed direction around the helix axis when the axis lies in a plane
Writhing number in DNA supercoiling means…
A) the number of times the long axis of the double helix crosses over itself
B) the number of times that a strand of DNA winds in the right-handed direction around the helix axis when the axis lies in a plane
C) the number of times one strand completely wraps around the other strand
A) the number of times the long axis of the double helix crosses over itself
Twisting number in DNA supercoiling means…
A) the number of times the long axis of the double helix crosses over itself
B) the number of times that a strand of DNA winds in the right-handed direction around the helix axis when the axis lies in a plane
C) the number of times one strand completely wraps around the other strand
C) the number of times one strand completely wraps around the other strand
If DNA appears as a simple, planar circle, so there is no supercoiling; what will the Writhe number be?
A) will equal zero
B) will equal the number of times the DNA crosses over itself
A) will equal zero
Wr = 0: If the DNA appears as a simple, planar circle, there’s no supercoiling, and Wr is 0.
If DNA displays supercoiling; what will the Writhe number be?
A) will equal zero
B) will equal the number of times the DNA crosses over itself
B) will equal the number of times the DNA crosses over itself
Wr ≠ 0: If the DNA crosses over itself, count the number of times the long axis crosses. Right-handed supercoils are assigned negative Wr values, while left-handed supercoils have positive values.
Are right-handed supercoils assigned positive or negative Wr values?
Right-handed supercoils are assigned negative Wr values,
Are left-handed supercoiling assigned positive or negative Wr values?
Left-handed supercoils have positive values.
Which is more stable?
A) A=T
B) C (tripple bond) G
C (3x=) G most stable hydrogen bonds
Sugar+Base =
A) Nucleoside
B) Nucleotide
A) Nucleoside
Sugar+Base+Phosphate=
A) Nucleoside
B) Nucleotide
B) Nucleotide
What kind of Nitrous base are: Adenine and Guanine
A) Pyrmindes
B) Purines
B) Purines
What kind of Nitrous base are: Cytosine, Uracil, Thymine?
A) Pyrmindes
B) Purines
A) Pyrmindes
How do you distinguish Ribose sugar from Deoxyribose sugar?
Ribose sugar: OH at 2’
Deoxyribose: H at 2’
What is an ester- linkage?
Monophosphate group (AMP)
What is an anhydride- linkage?
Diphosphate group (ADP)
or
Triphosphate group (ATP)
How many rings do Pyrmindes (Cytosine, Uracil, Thymine) have?
Single rings
How many rings do Purnines (Adenine, Guanine) have?
Double rings
True or False:
Nucleosides contain a phosphate group.
False,
Sugar + Base = Nucleoside
Sugar + Base + Phosphate = Nucleotide
Clicker:
In proteins, amino acids are linked by peptide bonds; in nucleic acids, nucleotides are linked by
A. N-glycosidic bonds
B. Phosphodiester bonds
C. Hydrophobic interactions
D. None of the above
B. Phosphodiester bonds
Nucleotides are joined together in nucleic acids through phosphodiester bonds. In this linkage, the OH group of the sugar acts as a nucleophile and attacks the phosphate group of another nucleotide.
Clicker:
For a circular double-stranded DNA, which
of the following quantities is not going to
change unless a strand is broken?
A. Its linking number
B. Its twisting number
C. Its writhe number
D. All of the above
A. Its linking number
Endonuclease…
A) cut at the ends of nucleic acid strands, removing nucleotides one by one
B) cut within a strand of DNA as specific sequences of nucleotides
B) cut within a strand of DNA as specific sequences of nucleotides
Endonucleases, on the other hand, cut within a strand of DNA. They can recognize specific sequences of nucleotides and cleave the DNA at those sites.
Exonuclease….
A) cut at the ends of nucleic acid strands, removing nucleotides one by one
B) cut within a strand of DNA as specific sequences of nucleotides
A) cut at the ends of nucleic acid strands, removing nucleotides one by one
Exonucleases cut at the ends of a nucleic acid strand. They can cut at either the 5’ end or the 3’ end of the strand, removing nucleotides one by one.
(Question from discussion)
Which of the following is a reason why DNA serves as a more suitable form of genetic material (compared to RNA)?
A)It lacks a 2OH
B)It is double stranded
C)DNA polymerase’s proofreading ability
D)All of the above
D)All of the above
(Question from discussion)
Which form is found in most cellular DNA?
A)B-DNA
B)A-DNA
C)Z-DNA
A)B-DNA
- Most cellular DNA is in the B-DNA form.
- A-DNA is found in double-stranded RNA or DNA/RNA hybrids.
- Z-DNA is based on the crystal structure of CGCGCG.
