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Questions and Answers
What type of bond connects a nucleobase to the sugar in a nucleoside?
What type of bond connects a nucleobase to the sugar in a nucleoside?
What is a nucleotide composed of?
What is a nucleotide composed of?
Which of the following correctly describes the sugar found in RNA?
Which of the following correctly describes the sugar found in RNA?
Which type of nucleic acid does not contain a phosphate group?
Which type of nucleic acid does not contain a phosphate group?
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What type of linkage occurs during the polymerization of nucleotides to form nucleic acids?
What type of linkage occurs during the polymerization of nucleotides to form nucleic acids?
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What is the primary function of Class I topoisomerases?
What is the primary function of Class I topoisomerases?
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What structure is formed when DNA is wrapped around histones?
What structure is formed when DNA is wrapped around histones?
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Which statement about DNA denaturation is true?
Which statement about DNA denaturation is true?
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Which component is associated with the stabilization of supercoiling in chromatin?
Which component is associated with the stabilization of supercoiling in chromatin?
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What effect does an increased percentage of G-C pairs have on Tm?
What effect does an increased percentage of G-C pairs have on Tm?
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What type of DNA structure is circular DNA?
What type of DNA structure is circular DNA?
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Which class of topoisomerase is DNA gyrase classified as?
Which class of topoisomerase is DNA gyrase classified as?
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What is hyperchromicity in the context of DNA denaturation?
What is hyperchromicity in the context of DNA denaturation?
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What is the primary structure of DNA comprised of?
What is the primary structure of DNA comprised of?
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How many hydrogen bonds are present in a G-C base pair?
How many hydrogen bonds are present in a G-C base pair?
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Which type of DNA is considered the physiological form?
Which type of DNA is considered the physiological form?
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Which of these forms of DNA is left-handed?
Which of these forms of DNA is left-handed?
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Which of the following base pairs forms two hydrogen bonds?
Which of the following base pairs forms two hydrogen bonds?
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What defines the secondary structure of nucleic acids?
What defines the secondary structure of nucleic acids?
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What is supercoiling in the context of DNA?
What is supercoiling in the context of DNA?
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Which sugar is found in DNA as opposed to RNA?
Which sugar is found in DNA as opposed to RNA?
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What type of sugar is found in RNA?
What type of sugar is found in RNA?
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Which statement is true regarding tRNA?
Which statement is true regarding tRNA?
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What is the primary function of mRNA?
What is the primary function of mRNA?
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Which of the following is not a type of RNA mentioned?
Which of the following is not a type of RNA mentioned?
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Which of the following describes ribosomal RNA (rRNA)?
Which of the following describes ribosomal RNA (rRNA)?
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What is the significance of snRNA in eukaryotic cells?
What is the significance of snRNA in eukaryotic cells?
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What aspect differentiates RNA from DNA?
What aspect differentiates RNA from DNA?
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Which component of ribosomes is analyzed by analytical ultracentrifugation?
Which component of ribosomes is analyzed by analytical ultracentrifugation?
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Study Notes
Nucleic Acids
- Nucleic acids are biopolymers composed of monomers containing three molecular components: a base (purine or pyrimidine), a monosaccharide (D-ribose or 2-deoxy-D-ribose), and phosphoric acid.
- There are two primary types of nucleic acids: RNA (Ribonucleic Acid) and DNA (Deoxyribonucleic Acid).
Pyrimidine & Purine Bases
- Pyrimidine and purine are the building blocks of nucleic acids.
- Pyrimidines include cytosine, thymine (DNA only), and uracil (RNA only).
- Purines include adenine and guanine.
Other Bases
- There are less common bases found primarily in transfer RNAs (tRNAs).
Nucleosides
- Nucleosides are composed of a D-ribose or 2-deoxy-D-ribose sugar covalently bonded to a nucleobase via a β-N-glycosidic bond.
- Nucleosides lack phosphate groups.
Nucleotides
- Nucleotides are nucleosides with a phosphate group esterified to the monosaccharide's 3'-OH or 5'-OH.
- They are named after the parent nucleoside, followed by "monophosphate".
- Polymerization of nucleotides leads to nucleic acids.
DNA - 1° Structure
- DNA is a biopolymer with a backbone of alternating 2-deoxy-D-ribose and phosphate units.
- The 3'-OH of one 2-deoxy-D-ribose is linked to the 5'-OH of the next 2-deoxy-D-ribose by a phosphodiester bond.
- The primary structure is the sequence of bases along the pentose-phosphodiester backbone.
- The sequence is read from the 5' end to the 3' end.
- DNA strands are often denoted using single-letter abbreviations (A, G, C, T, and U).
DNA differs from RNA
- DNA contains the sugar 2'-deoxyribose, while RNA contains ribose.
- DNA uses the pyrimidine base thymine, while RNA uses uracil.
- DNA is often denoted with a "d" prefix to indicate deoxyribose.
DNA - 2° Structure
- The secondary structure of DNA involves the arrangement of nucleic acid strands.
- The most prominent structure is the double helix, proposed by Watson and Crick in 1953.
- The double helix consists of two antiparallel polynucleotide strands coiled around the same axis in a right-handed manner.
- The structure is based on X-ray crystallography.
Base Pairing: T-A and G-C
- Base pairing is complementary, with T-A and G-C pairs.
- T-A base pairs have 2 hydrogen bonds.
- G-C base pairs have 3 hydrogen bonds.
Other Forms of DNA
- A-DNA: a right-handed helix, thicker than B-DNA, with 11 base pairs per turn.
- B-DNA: the most common form in vivo, with a diameter of 11 angstroms and 10 base pairs per turn.
- Z-DNA: a left-handed double helix that may play a role in gene expression.
Comparison of A, B, and Z Forms of DNA
- A-DNA and B-DNA are right-handed helices.
- Z-DNA is left-handed and usually consists of alternating purine-pyrimidine bases.
- Methylated cytosine is also found in Z-DNA.
DNA - 3° Structure
- The tertiary structure of DNA involves the three-dimensional arrangement of all atoms, specifically supercoiling.
- Circular DNA: a type of double-stranded DNA where the 5' and 3' ends of each strand are joined by phosphodiester bonds.
- Supercoiling: further coiling and twisting of the DNA helix.
Topoisomerases
- Topoisomerase Class I: cuts one DNA strand, passes an end through, and reseals the cut.
- Topoisomerase Class II: cuts both strands, passes some of the remaining DNA helix between the cut strands, and reseals.
- DNA gyrase: a bacterial topoisomerase.
Supercoiling in Eukaryotic DNA
- Histone: a protein rich in lysine and arginine, associated with eukaryotic DNA.
- Chromatin: DNA wrapped around histone particles in a bead-like structure.
- Supercoiling is accommodated by the histone-protein component of chromatin.
- Each "bead" is a nucleosome, which consists of DNA wrapped around a histone core.
Denaturation of DNA
- Denaturation disrupts the secondary structure of DNA.
- Heat denaturation (melting) causes strands to separate.
- Increasing absorbance at 260 nm during denaturation is called hyperchromicity.
- The midpoint of the denaturation (melting) curve is designated as Tm.
- Higher G-C content results in a higher Tm.
- Renaturation is achievable by slow cooling.
Denaturation of DNA (cont.)
- The double helix unwinds during denaturation.
- The process can be reversed with slow cooling and annealing.
Principal Types of RNA
- RNA is composed of long, unbranched chains of nucleotides linked by phosphodiester bonds between the 3'-OH and 5'-OH of adjacent sugars.
- The sugar in RNA is β-D-ribose.
- RNA contains the pyrimidine bases uracil and cytosine.
- RNA is typically single-stranded.
Information Transfer in Cells
- Information encoded in DNA is transcribed into RNA.
- The RNA sequence is dictated by the DNA sequence.
- This process is known as the Central Dogma of biology.
RNA (types)
- RNA molecules are classified by structure and function.
1. tRNA
- Transfer RNA (tRNA) is the smallest type of RNA.
- It is a single-stranded polynucleotide chain with 73-94 nucleotide residues.
- tRNA carries an amino acid at its 3' end.
- Intramolecular hydrogen bonding occurs within tRNA.
2. rRNA
- Ribosomal RNA (rRNA) is found in ribosomes, where protein synthesis occurs.
- Only a few types of rRNA exist in cells.
- Ribosomes are composed of 60-65% rRNA and 35-40% protein.
- Ribosomes have two subunits with different sizes, defined by their sedimentation coefficients in Svedberg units (S).
3. mRNA
- Messenger RNA (mRNA) carries genetic information from DNA to ribosomes for protein synthesis..
- mRNA is present in small amounts and is short-lived.
- mRNA is single-stranded.
- Its biosynthesis is directed by DNA information.
- A complementary mRNA strand is synthesized along one DNA strand, starting from the 3' end.
4. snRNA
- Small nuclear RNA (snRNA) is found in the nucleus of eukaryotes.
- It is small (100-200 nucleotides long) and forms complexes with proteins called small nuclear ribonucleoprotein particles (snRNPs).
- snRNPs are involved in the processing of initial mRNA transcribed from DNA.
Biosynthesis of Nucleic Acids: Replication
- Replication is the process of duplicating DNA.
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Description
Explore the fundamental concepts of nucleic acids, including their structure and classification. This quiz covers the differences between DNA and RNA, the roles of purine and pyrimidine bases, and the essential components of nucleosides and nucleotides.