Biology: DNA and RNA Basics

DNA and RNA

• DNA is deoxyribonucleic acid, a double-stranded molecule.
• RNA is ribonucleic acid, a single-stranded molecule.
• DNA stores genetic information.
• RNA carries instructions for protein synthesis.
• Nucleotides are the building blocks of both DNA and RNA.
• Each nucleotide comprises a pentose sugar, a phosphate group, and a nitrogenous base.
• DNA sugars are deoxyribose, and RNA sugars are ribose.
• DNA bases are adenine (A), thymine (T), guanine (G), and cytosine (C).
• RNA bases are adenine (A), uracil (U), guanine (G), and cytosine (C).
• In DNA, A pairs with T via 2 hydrogen bonds, and G pairs with C via 3 hydrogen bonds.
• In RNA, A pairs with U via 2 hydrogen bonds, and G pairs with C via 3 hydrogen bonds.

Nucleotide Structure

• DNA and RNA are made of nucleotides.
• Each nucleotide is a monomer.
• Nucleotides are formed by linking a pentose sugar (deoxyribose/ribose), a phosphate group, and a nitrogenous base together.
• Phosphate group gives DNA and RNA a negative charge.

DNA Structure

• DNA is a double helix.
• Two strands are antiparallel, meaning they run in opposite directions (5' to 3' and 3' to 5').
• Strands are held together by hydrogen bonds between complementary bases.
• A pairs with T, and G pairs with C.
• The sugar-phosphate backbone forms the outside of the double helix.
• Bases are stacked in the interior of the double helix.
• Major and minor grooves in the helix provide sites for protein interactions.

RNA Structure

• RNA is single-stranded.
• RNA is less stable than DNA.
• RNA sugar is ribose.
• RNA contains uracil (U) instead of thymine (T).
• Several types of RNA exist (mRNA, tRNA, rRNA).

DNA Replication

• DNA replication is semi-conservative.
• Each new DNA molecule consists of one original (parental) strand and one new strand.
• Enzymes like helicase unwind the DNA double helix, and enzymes like polymerase synthesize new strands using the original strands as templates.
• Okazaki fragments are short DNA fragments synthesized on the lagging strand, which is replicated in short bursts.
• Ligase seals the gaps between Okazaki fragments.

Protein Structure

• Proteins are made of amino acids.
• Primary structure: Linear sequence of amino acids.
• Secondary structure: Folding of the polypeptide chain (α-helices and β-sheets).
• Tertiary structure: 3D folding of the polypeptide chain.
• Quaternary structure: Association of multiple polypeptide chains.

Transcription

• Transcription is the synthesis of RNA from a DNA template.
• RNA polymerase binds to a promoter region on the DNA.
• RNA polymerase unwinds the DNA double helix and uses one strand as a template to synthesize a complementary RNA molecule.
• The RNA molecule detaches at the termination sequence.
• mRNA carries the genetic message from the DNA to the ribosomes
• DNA provides the template.
• RNA polymerase is the enzyme.
• mRNA is produced.

Regulation of Gene Expression

• Gene expression is the process by which genetic information is used to create functional gene products.
• Regulation of gene expression is crucial for maintaining cellular homeostasis.
• Gene regulation can occur at various stages.
• Prokaryotes use operons to simultaneously regulate multiple genes.
• Eukaryotes employ various mechanisms like transcription factors, histone modification and DNA methylation.

Mutations

• Mutations are changes in DNA sequences.
• Mutations can be spontaneous (random) or induced by environmental factors.
• Mutations can be small-scale (gene mutations—e.g., substitution, insertion, deletion) or large-scale (chromosome mutations—e.g., duplication, deletion, inversion).
• Mutations can have diverse effects, from no effect to a drastic change in the protein product, and/or cellular function.