Nucleotides: structure and function Flashcards
The amino acid sequence of every protein in a cell and the nucleotide sequence of every RNA is specified by what?
The nucleotide sequence of the cell’s DNA
A segment of a DNA molecule that contains the information required for the synthesis of a functional biological product, whether protein or RNA
Gene
The only known functions of DNA
Storage and transmission of biological information
The three characteristic components of nucleotides
A nitrogenous base, a pentose, a phosphate
What is the difference between a nucleotide and a nucleoside?
The nucleoside does not have a phosphate group; the nucleotide has
The nitrogenous bases of nucleic acids are derivatives of which parent compounds?
Purines and pyrimidines
Compound composed of a nitrogenous base and a pentose
Nucleoside
The nucleotide base is joined covalently to the C-1 of the pentose at which point of pyrimidines?
N-1
The nucleotide base is joined covalently to the C-1 of the pentose at which point of purines?
N-9
The phosphate group of the nucleotide is bonded where?
To C-5 of the pentose
The bond formed between the nitrogen base and the pentose is called what?
N-β-glycosyl bond
How is an N-β-glycosyl bond formed?
By dehydration; removal of an OH from the pentose and of an H from the nitrogenous base
Purine bases
Adenine (A) and Guanine (G)
Pyrimidine bases
Uracil (U), Thymine (T) and Cytosine (C)
Which pyrimidine base occurs in DNA?
T, C
Which pyrimidine base occurs in RNA?
U, C
Two kinds of pentoses in nucleic acids
Deoxy-D-ribose and D-ribose
Which pentose is in DNA?
Deoxy-D-ribose
Which pentose is in RNA?
D-ribose
Which part of the nucleic acid determines if it is DNA or RNA?
The pentose
If a nucleic acid contains deoxy-D-ribose and uracil, is it DNA or RNA?
DNA
If a nucleic acid contains D-ribose and thymine, is it DNA or RNA?
RNA
The deoxyribonucleosides of A,G, C, T
Deoxyadenine, deoxyguanine, deoxycytosine, deoxythymine
The bonds formed by the dehydration of two nucleotides
Phosphodiester bond
In the phosphodiester linkage of dinucleotides, which part of the nucleotides are bound to each other?
The phosphate of one nucleotide binds to the 3’-hydroxyl group
The phosphate of a nucleotide is connected to a pentose on which carbon?
5’-carbon of the pentose
Which of the following will differentiate GDP from dGDP?
A. dGDP has an extra amino group attached to carbon 6 in the purine ring
B. dGDP has an extra phosphate attached to the 2’-carbon of the ribose
C. dGDP is reduced at the 2’-carbon of the ribose
D. dGDP is a purine nucleotide while GDP is a pyrimidine nucleotide
C
Which of the following is/are FALSE?
A. Every DNA contains deoxyribose and every RNA contains ribose
B. Every DNA contains thymine and every RNA contains uracil
C. In DNA, each nitrogenous base is covalently linked to a phosphate
C
Which of the following is false?
A. Sugar groups attached to the nucleotide are positive in charge in neutral ph
B. Sugar groups attached to the nucleotide are negative in charge in neutral ph
C. Phosphate groups attached to the nucleotide are negative in neutral ph
D. Both A and B
D
Backbones of DNA and RNA: hydrophobic or hydrophilic?
Hydrophilic
Charge of the phosphate groups of nucleotides at pH 7
Negative
Charge of sugar groups of nucleotides at pH 7
0
Why are the backbones of DNA and RNA hydrophilic?
At pH 7, the sugar groups are neutral, while the phosphate groups are negative. But the negative charges are generally neutralized by ionic interactions with positive charges on proteins, metal ions, and polyamines.
All the phosphodiester linkages in DNA and RNA have the same orientation along the chain. T/F
T
Orientation of DNA and RNA chains
5’ to 3’
Purine and pyrimidine bases are hydrophobic or hydrophilic?
Hydrophobic
What is the primary structure of nucleic acid?
Its covalent structure and nucleotide sequence
Adenine: purine or pyrimidine?
Purine
Thymine: purine or pyrimidine?
Pyrimidine
Cytosine: purine or pyrimidine?
Pyrimidine
Guanine: purine or pyrimidine?
Purine
Uracil: purine or pyrimidine?
Pyrimidine
Base pair of A
T (DNA) or U (RNA)
Base pair of G
C
Base pair of T
A
Base pair of U
A
Base pair of C
G
Formation of base pairs can occur between residues lying on two separate nucleotide sequences. T/F
T
Which bond forms between base pairs?
H-bonds
How many H-bonds can form between G and C?
3
How many H-bonds can form between A and T?
2
What is the orientation of two DNA strands to each other?
Anti-parallel
The two DNA strands of a double-helix are identical to each other. T/F
F
They are complementary.
Which of the following is CORRECT?
A. Uracil resembles thymine more than cytosine in a base pair
B. Adenosine typically forms 3 hydrogren bonds in a base pair
C. Guanine is a pyrimidine base
D. Base stacking is mediated by hydrogen bonding
A
Which if the following BEST distinguishes DNA from RNA?
A. DNA is double stranded while RNA is single stranded
B. DNA is helical while RNA is linear
C. DNA contains thymine while RNA contains uracil
D. DNA contains deoxyribose while RNA contains ribose
D
DNA usually exists in which conformation: A, B, Z
B form
Which form is in left-handed conformation: A, B, or Z
Z form
Which form is relatively devoid with water: A, B, or Z
A form
What is the secondary structure of DNA?
Double helix
Which of the following statements is/are TRUE regarding nucleic acid primary structure?
(a) Adenine and guanine are purine-like nitrogenous bases.
(b) RNA is more resistant to hydrolysis than DNA.
(c) RNA typically contains thymine rather than uracil.
(d) All of the above
(e) (a) and (b) only
e
Which of the following statements is/are TRUE regarding nucleic acid secondary structure?
(a) Guanine typically forms base pairs with cytosine via three hydrogen bonds.
(b) The A form of the DNA double helix predominates in biological systems.
(c) The transition form double helix to random coil is known as annealing.
(d) All of the above
(e) (a) and (b) only
a
The process of formation of a double helix between complementary sequences is referred to as annealing. T/F
T
Which of the following statements is/are TRUE regarding nucleic acid tertiary structure?
(a) It is defined by the overall three-dimensional arrangement of elements of nucleic acid secondary structure.
(b) It involves interactions between bases and the sugar-phosphate backbone.
(c) It involves formation of hydrogen bonded triplets of bases.
(d) All of the above
(e) (a) and (b) only
d
What happens when DNA is denatured?
The hydrogen bonds are disrupted, the double helix unwinds to form two separate single strands, but no covalent bonds in the DNA are broken
DNA denaturation is reversible. T/F
T
What is the hypochromic effect?
Nucleic acid’s decrease of absorption of UV light due to close interaction in base stacking, and further decrease when two complementary nucleic acid strands are paired.
What is the hyperchromic effect?
Nucleic acid’s increase in absorption of UV light due to denaturation.
The higher content of G-C base pairs, the lower the melting point of DNA. T/F
F
The higher content of G-C base pairs, the higher the melting point, because G-C forms 3 H-bonds, requiring more heat to dissociate.
Aside from being units of nucleic acids, which of the
following are functions of nucleotides?
a. Structural component of CoEnzymes
b. Cellular secondary mesenger
c. Carriers of activated intermediates
d. All of the above
e. A and B
e
