DNA Structure and RNA Comparison

DNA Structure

• DNA is a double helix, with two strands twisted like a spiral ladder
• The strands are anti-parallel, meaning they run in opposite directions
• The backbone of the helix is made up of sugar-phosphate groups, linked by covalent bonds
• Nitrogenous bases point inward from the backbone and form hydrogen bonds between complementary bases
• Adenine pairs with Thymine (A=T)
• Guanine pairs with Cytosine (G≡C)
• The diameter of the DNA helix is 2 nm and completes one turn every 10 base pairs
• The helix has a major and a minor groove, which are important for interactions with other molecules
• The sugar is deoxyribose

DNA vs. RNA

• DNA is double-stranded, while RNA is single-stranded
• DNA contains deoxyribose as its sugar, while RNA contains ribose
• Thymine is found in DNA, while Uracil is found in RNA
• DNA primarily exists in the nucleus, while RNA can be found in the cytoplasm and nucleus
• DNA contains A, B, and Z forms, while RNA exists primarily as mRNA, rRNA, and tRNA

Gene Structure

• A Gene is a segment of DNA containing regulatory regions, exons, and introns.
• Exons contain the coding sequences for proteins, while introns are non-coding regions.
• Regulatory regions, such as promoters, control when and how a gene is expressed.

Chromosome Packing

• Chromatin is the name for nuclear material containing genetic code
• DNA is organized into chromosomes, which are packaged within the nucleus
• The process of chromosome packaging involves multiple levels of organization:
  • Nucleosomes: DNA wraps around histone proteins, forming nucleosomes. Histone proteins contain a core particle with 8 histones (2 each of H2A, H2B, H3, and H4)
  • Chromatin Fibers: Nucleosomes are linked by linker DNA, forming a "beads-on-string" structure, which coils further to form a 30 nm chromatin fiber
  • Chromatin Looped Domains: 30 nm chromatin fibers fold into loops attached to scaffold/matrix proteins in the nucleus.
  • Metaphase Chromosomes: During cell division, chromatin loops condense further, forming visible metaphase chromosomes

Heterochromatin

• Heterochromatin is a highly condensed form of chromatin, often associated with gene silencing.

Cell Division

• Just before cell division, chromatin condenses into metaphase chromosomes.
• Each chromosome consists of two sister chromatids, held together at the centromere.

Types of RNA

• mRNA (messenger RNA): Carries genetic information from DNA to ribosomes for protein synthesis.
• rRNA (ribosomal RNA): Found in ribosomes, the site of protein synthesis.
• tRNA (transfer RNA): Carries amino acids to the ribosomes for protein synthesis.

RNA Structure

• RNA is a single-stranded molecule that can fold into complex structures due to base pairing within the strand.
• RNA consists of ribonucleotides, each containing a ribose sugar, a phosphate group, and a nitrogenous base (A, U, G, or C).