Nucleic Acids and the Central Dogma

Nucleic acids are polymers of nucleotides; nucleotides consist of a pentose sugar, a phosphate group, and a nitrogenous base.

Nucleic acids form via phosphodiester bonds between the phosphate group of one nucleotide and the sugar of another.

Adenine (A) pairs with Thymine (T), and Cytosine (C) pairs with Guanine (G) during DNA synthesis.

The DNA double helix is antiparallel because the strands run in opposite directions (5' to 3' and 3' to 5').

RNA types and functions:

• mRNA (messenger RNA): Carries genetic information from DNA to ribosomes.
• tRNA (transfer RNA): Transports amino acids to the ribosome for protein synthesis.
• rRNA (ribosomal RNA): A structural component of ribosomes.

Differences between RNA and DNA

• DNA: Double-stranded, contains deoxyribose sugar and thymine.
• RNA: Single-stranded, contains ribose sugar and uracil.

The central dogma of molecular biology describes the flow of genetic information: DNA → RNA → Protein.

Gene: A specific sequence of DNA that codes for a functional product.

Genotype: The genetic makeup of an organism.

Phenotype: The observable characteristics of an organism, resulting from the interaction of its genotype with the environment.

Semiconservative DNA replication means each new DNA molecule consists of one original (template) strand and one newly synthesized strand.

DNA replication is bidirectional and includes leading and lagging strands:

• Bidirectional: Replication proceeds in both directions from the origin of replication.
• Leading strand: Synthesized continuously in the 5' to 3' direction.
• Lagging strand: Synthesized discontinuously in Okazaki fragments, also in the 5' to 3' direction.

Process of DNA replication and enzymes involved:

• Helicase unwinds the DNA double helix.
• Primase synthesizes RNA primers.
• DNA polymerase adds nucleotides to the growing strand.
• Ligase joins Okazaki fragments on the lagging strand.

Differences between DNA replication in bacteria and eukaryotes:

• Bacteria: Single origin of replication, circular chromosome.
• Eukaryotes: Multiple origins of replication, linear chromosomes.

Plasmid replication: Plasmids replicate independently of the bacterial chromosome.

• Extrachromosomal DNA is important because it can carry genes that provide the cell with beneficial traits like antibiotic resistance.

RNA synthesis using DNA as a template is called transcription.

Differences between transcription in prokaryotes and eukaryotes:

• Prokaryotes: Occurs in the cytoplasm, single RNA polymerase.
• Eukaryotes: Occurs in the nucleus, three RNA polymerases (RNA Polymerase I, RNA Polymerase II, RNA Polymerase III).

The genetic code: A set of rules by which information encoded in genetic material (DNA or RNA) is translated into proteins.

• Considered almost universal because the same codons specify the same amino acids in nearly all organisms.

Process of translation and functions of molecular machinery:

• Ribosomes bind to mRNA.
• tRNA molecules bring amino acids to the ribosome, matching the mRNA codons.
• Peptide bonds form between amino acids, creating a polypeptide chain.

Comparison of translation in eukaryotes and prokaryotes:

• Eukaryotes: Occurs in the cytoplasm, 80S ribosomes, mRNA processing (capping, splicing, polyadenylation).
• Prokaryotes: Occurs in the cytoplasm, 70S ribosomes, no mRNA processing.