The central dogma of molecular biology is the backbone of genetic information flow. It explains how DNA instructions are converted into RNA messages, which are then translated into functional proteins that drive cellular processes.

Understanding this fundamental concept is crucial for grasping how genes influence traits and biological functions. It sets the stage for exploring the intricate mechanisms of transcription, translation, and protein synthesis in living organisms.

Nucleic Acids

Structure and Function of DNA and RNA

• DNA consists of two complementary strands forming a double helix structure
• DNA strands composed of nucleotides containing deoxyribose sugar, phosphate group, and nitrogenous bases (adenine, thymine, cytosine, guanine)
• RNA typically exists as a single-stranded molecule
• RNA nucleotides contain ribose sugar instead of deoxyribose and uracil replaces thymine
• DNA primarily stores genetic information in the nucleus
• RNA plays various roles in gene expression and protein synthesis (messenger RNA, transfer RNA, ribosomal RNA)

Genetic Information Flow

• Central dogma of molecular biology describes the flow of genetic information
• DNA serves as the template for RNA synthesis through transcription
• RNA carries genetic information from DNA to ribosomes for protein synthesis
• Genetic information flows from DNA to RNA to proteins in most cases
• Exceptions to the central dogma include reverse transcription in retroviruses (HIV)
• Epigenetic modifications can influence gene expression without altering DNA sequence (DNA methylation, histone modifications)

DNA Processes

Transcription: DNA to RNA

• Transcription involves copying genetic information from DNA to RNA
• RNA polymerase enzyme catalyzes the formation of RNA molecules
• Process begins with the binding of RNA polymerase to the promoter region of a gene
• RNA polymerase moves along the DNA template strand, synthesizing complementary RNA
• Transcription terminates when RNA polymerase reaches a termination sequence
• Primary transcript undergoes processing to form mature mRNA (5' capping, splicing, 3' polyadenylation)

DNA Replication and Maintenance

• DNA replication ensures accurate transmission of genetic information to daughter cells
• Process begins at specific DNA sequences called origins of replication
• DNA helicase unwinds the double helix, creating replication forks
• DNA polymerase synthesizes new DNA strands in the 5' to 3' direction
• Leading strand synthesis occurs continuously, while lagging strand synthesis involves Okazaki fragments
• DNA ligase joins Okazaki fragments to form a continuous strand
• Telomerase maintains chromosome ends to prevent loss of genetic information during replication

Reverse Transcription in Retroviruses

• Reverse transcription converts RNA to DNA, opposite of normal transcription
• Process utilized by retroviruses like HIV to integrate their genetic material into host genome
• Reverse transcriptase enzyme catalyzes the synthesis of complementary DNA from viral RNA
• Resulting DNA can integrate into the host cell's genome, allowing viral replication
• Reverse transcription also occurs in some eukaryotic cells (telomere maintenance, retrotransposons)

Protein Synthesis

Translation: RNA to Protein

• Translation converts genetic information from mRNA into amino acid sequences
• Process occurs on ribosomes in the cytoplasm or on the rough endoplasmic reticulum
• Initiation involves the assembly of the ribosome, mRNA, and initiator tRNA
• Elongation phase adds amino acids to the growing polypeptide chain
• Termination occurs when a stop codon is reached, releasing the completed protein
• tRNA molecules act as adapters, bringing specific amino acids to the ribosome
• Genetic code determines the correspondence between mRNA codons and amino acids

Protein Structure and Function

• Proteins consist of amino acid chains folded into specific three-dimensional structures
• Primary structure refers to the linear sequence of amino acids
• Secondary structure includes common patterns like alpha helices and beta sheets
• Tertiary structure describes the overall three-dimensional shape of a single protein molecule
• Quaternary structure involves the interaction of multiple protein subunits
• Protein folding crucial for proper function (enzymes, structural proteins, signaling molecules)
• Post-translational modifications can alter protein function (phosphorylation, glycosylation)
• Misfolded proteins can lead to various diseases (Alzheimer's, Parkinson's, cystic fibrosis)