Nucleic Acids and Nucleotide Components

Nucleic Acids

• Nucleic acids, specifically DNA, are composed of three parts: a sugar, a phosphate, and a base.
• The sugar in DNA is deoxyribose; in RNA, it is ribose.
• Nucleotides in DNA and RNA are linked by covalent bonds.
• The sugar-phosphate backbone is formed by covalent bonds.

Components of Nucleotides

• DNA molecules have three parts: a pentose sugar, a negatively charged phosphate group, and a base containing nitrogen.
• The base can have one or two rings.
• 'X' in the diagram represents a hydrogen in DNA, and a hydroxyl group in RNA.

Components of Nucleotides (Continued)

• Chemical bonds in nucleotides occur at specific locations.
• All bonds within nucleotides are covalent bonds, resulting from electron sharing.

Sugar-Phosphate Bonding

• The pattern of sugar (pentose)-phosphate-pentose-phosphate is called the pentose phosphate backbone.
• Nucleotides are always added in the same way, where the phosphate of a new nucleotide links covalently to the pentose sugar of the preceding nucleotide.

A1.2.11 - DNA - Nucleotides

• DNA contains four nucleotides that differ only in their nitrogenous bases.
• All DNA bases contain nitrogen.
• Pyrimidines, like thymine and cytosine, have a single ring structure.
• Purines, like adenine and guanine, have a double ring structure.
• The pairing of purines and pyrimidines in DNA maintains the structure's stability.

Nitrogenous Base

• Any sequence of bases is possible along a DNA or RNA molecule.
• The number of potential sequences is essentially infinite.
• The sequence of bases is how information is stored in organisms.
• This forms a universal code shared by all organisms.

RNA as a Polymer of Condensation

• RNA is a single, unbranched polymer of nucleotides.
• Nucleotides are monomers of RNA.
• Nucleotides are linked through condensation reactions.

DNA - Structure

• DNA consists of nucleotide polymers.
• The sugar in DNA is deoxyribose.
• The nitrogenous base pairs are adenine, cytosine, guanine, and thymine.
• The base pairs AT and CG are consistently paired.

DNA Structure

• The two DNA strands are antiparallel. This means they run in opposite directions.
• One end will end with a phosphate group, and the other with a deoxyribose.
• If the strands were oriented the same way, the bases would not be able to create hydrogen bonds with each other.
• DNA is a double helix with a constant diameter of 2 nanometers.

Antiparallel

• The two single strands that make up the double-stranded molecule run in opposite directions.

A1.2.10 Direction of RNA and DNA

• The 3' end of a nucleotide is unlinked; carbon 3 is available for linkage to another nucleotide.
• The 5' end of a nucleotide is unlinked; the phosphate group is attached to carbon 5.
• RNA and DNA have a 5' to 3' directionality.
• In both replication and transcription, the template strand in copied 3' to 5'.
• The new strand is created 5' to 3'. During translation, the mRNA segment is copied 3' to 5', but the amino acid is constructed 5' to 3'.

A1.2.13 Nucleosomes

• DNA in eukaryotes associates with proteins to form nucleosomes.
• Nucleosomes are globular structures with a core of 8 histone proteins, and DNA coils around this core.
• Another histone protein (H1) secures the DNA to the core.
• A short segment of DNA connects each nucleosome.
• Prokaryotes do not have nucleosomes.

A1.2.14 Hershey and Chase

• Hershey and Chase studied bacteriophages, viruses that infect bacteria, to investigate genetic material.
• They labeled viral proteins with radioactive sulfur and DNA with radioactive phosphorus.
• The viral DNA entered the bacteria, proving DNA is the genetic material, while proteins did not.

A1.2.15 Chargaff's Data

• The tetranucleotide hypothesis proposed that DNA contained repeating sequences of the four bases.
• Chargaff's analysis of the composition of DNA nucleotides for various species disproved this hypothesis, showing that the base ratios varied.

DNA vs RNA

• DNA's sugar is deoxyribose, whereas RNA's sugar is ribose.
• Thymine in DNA is replaced by uracil in RNA.
• RNA typically forms single strands, unlike the double helix of DNA.

DNA Replication

• DNA replication occurs before cell division, ensuring cells inherit the same genetic information.
• The DNA strands separate, then new nucleotides are added in a complementary way to the original strand, creating two identical DNA molecules. This process is semi-conservative as each new molecule contains one old strand and one new strand.

Base pairing in Allowing Genetic Information to be Passed On

• Genes are sections of DNA containing genetic information, each gene with information for a specific purpose.
• Gene expression occurs when a gene influences a cell.
• Copying the base sequence to make RNA is the first step of this process, known as transcription.

Conservation of Genetic Code

• DNA and RNA contain information encoded in a sequence of bases.
• The sequence of bases is decoded during protein synthesis, using a system of codons.
• There are 64 codons, most coding for specific amino acids.
• One codon signifies the start and several codons signal the stop of protein synthesis.

A1.2.10 Direction of RNA and DNA (Processes)

• Directionality of RNA and DNA impacts how enzymes and ribozymes work.
• The 5' to 3' direction is important for DNA processes.
• Replication, transcription, and translation all follow the 5' to 3' direction.

Diversity of Possible DNA Base Sequences

• Genetic information is stored in the base sequence of one of the DNA strands.
• There are 4 possible bases (A, C, G, T) for each base.
• The number of possible sequences increases drastically with more bases; and is limitless.
• This limitless variability makes DNA ideal to store a large amount of information.

Explore the essential structures of nucleic acids, focusing on DNA and RNA. Learn about the components of nucleotides including sugars and phosphate groups, as well as the chemical bonds that form the sugar-phosphate backbone. This quiz will enhance your understanding of molecular biology and the fundamental aspects of genetic material.