18 Questions
What is the direction of the sugar-phosphate backbone in a nucleic acid?
5' → 3' direction
What type of bond forms between nucleotides during polymerization?
Phosphodiester bond
Which of the following is a characteristic of a nucleic acid strand?
It has a directional sugar-phosphate backbone
What is the result of phosphodiester linkages joining ribonucleotides together?
Formation of RNA
How are the primary structures of DNA and RNA typically written?
By listing the sequence of bases using single-letter abbreviations
What is the function of condensation reactions in nucleic acid synthesis?
To synthesize nucleic acids
What is the role of enzymes in nucleic acid polymerization?
To create nucleoside triphosphates
What is the nature of the sugar-phosphate backbone in DNA?
It forms the ladder side rails
What is the significance of the equal number of purines and pyrimidines in DNA?
It indicates that the number of T's equals the number of A's, and the number of C's equals the number of G's
What technique was used to measure the distances between atoms in DNA?
X-ray crystallography
What is the role of hydrophobic interactions in DNA?
They cause DNA to twist into a helix
What is the term for the sugar-phosphate backbone strands in DNA?
Antiparallel
What is the primary function of DNA as a molecule?
To contain information needed for the cell's functions
What is the result of complementary base pairing during DNA replication?
Two identical daughter molecules
What is the difference between the sugar molecules found in DNA and RNA?
DNA has deoxyribose, while RNA has ribose
What is the role of phosphodiester linkages during DNA replication?
They form to create the new complementary strand
What is unique about the 2′ group on the ribose molecule in RNA?
It is more reactive than the 4′ group
What is the primary structure of RNA?
A single strand with four types of nitrogenous bases
Study Notes
Nucleotide Structure
- A deoxyribonucleotide consists of a 5-carbon sugar (deoxyribose), a phosphate group, and a nitrogenous base.
- The sugar molecule has a 5' carbon, a 1' carbon, a 4' carbon, a 3' carbon, and a 2' hydroxyl group.
Nucleic Acid Polymerization
- Nucleic acids polymerize via condensation reactions, forming phosphodiester linkages between nucleotides.
- Phosphodiester linkages occur between the phosphate group on the 5' carbon of one nucleotide and the hydroxyl group on the 3' carbon of another nucleotide.
- The polymer produced is RNA.
Directionality of Nucleic Acids
- Phosphodiester linkages form a sugar-phosphate backbone that is directional (5' → 3' direction).
- One end of the backbone has an unlinked 5' phosphate group, and the other end has an unlinked 3' hydroxyl group.
- The primary structure of DNA is written by listing the sequence of bases using single-letter abbreviations.
Energy Requirements for Polymerization
- Nucleic acid polymerization requires an energy source, which is provided by adding two additional phosphate groups to create nucleoside triphosphates (activated nucleotides).
- Energy is released when activated nucleotides polymerize, making the reaction spontaneous.
DNA Secondary Structure
- Early data suggested that DNA has a double helix structure, with antiparallel sugar-phosphate backbones and bases attached to sugars forming ladder rungs.
- Hydrophobic interactions (stacking) cause double-stranded DNA to twist into a helix, stabilized by van der Waals interactions.
- DNA has two different-sized grooves: a major groove and a minor groove.
DNA Replication
- DNA replication has three steps: separation of strands, formation of hydrogen bonds between free deoxyribonucleotides and complementary bases, and formation of phosphodiester linkages to create a new strand.
- Complementary base pairing allows each strand to be copied exactly, producing two identical daughter molecules.
RNA Structure and Function
- The primary structure of RNA differs from DNA: RNA contains ribose instead of deoxyribose, uracil instead of thymine, and has a more reactive 2' group on ribose.
- RNA is less stable than DNA due to the 2' group on ribose.
This quiz covers the process of nucleic acid polymerization, including the role of enzymes, energy sources, and activated nucleotides. It also explains how energy is released during the polymerization reaction.
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