DNA Structure and Replication

DNA Structure

• DNA, or deoxyribonucleic acid, is a double helix composed of two strands of nucleotides.
• Each nucleotide contains a sugar molecule (deoxyribose), a phosphate group, and one of four nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T).
• The bases pair specifically: A with T, and G with C.
• This complementary base pairing is crucial for DNA replication and gene expression.
• The sugar-phosphate backbone forms the exterior of the helix, while the bases form the internal rungs.
• DNA is typically organized into chromosomes within the cell nucleus.

DNA Replication

• DNA replication is the process of creating an identical copy of a DNA molecule.
• It's a semi-conservative process, meaning each new DNA molecule consists of one original strand and one newly synthesized strand.
• DNA polymerase enzymes are crucial for adding new nucleotides to the growing DNA strand.
• The process begins at specific points called origins of replication.
• Replication proceeds bidirectionally from these origins.
• Multiple replication forks are formed to speed up the process.
• Error correction mechanisms minimize mistakes during replication.

Gene Expression

• Gene expression is the process by which information from a gene is used to synthesize a functional gene product, typically a protein.
• This process involves two main steps: transcription and translation.
• In transcription, a messenger RNA (mRNA) molecule is synthesized from a DNA template.
• During translation, the mRNA molecule is decoded to produce a specific protein.
• The genetic code specifies which amino acids are incorporated into a polypeptide chain during translation.
• Regulation of gene expression is essential for controlling cell function and development.

The Genome

• The genome is the complete set of genetic information of an organism.
• It includes all the DNA within the chromosomes.
• The genome's organization differs among prokaryotic and eukaryotic organisms.
• Eukaryotic genomes typically contain large amounts of non-coding DNA.
• Prokaryotic genomes are generally smaller and have less non-coding DNA.
• Human genome project mapped the complete human genome.
• Genome sequencing allows for the identification of genes and variations in DNA sequences (e.g., mutations).
• Genomics is the study of genomes and their function.

DNA Types

• There are three main types of RNA: mRNA, tRNA, and rRNA.
• mRNA carries the genetic code from DNA in the nucleus to the ribosomes in the cytoplasm.
• tRNA carries specific amino acids to ribosomes during protein synthesis.
• rRNA forms part of the ribosomes, the cellular machinery that synthesizes proteins.

DNA Damage and Repair

• DNA can be damaged by various internal and external factors.
• This damage can result from exposure to radiation, chemicals, or reactive oxygen species.
• Cellular mechanisms exist to repair damaged DNA.
• Different repair pathways address different types of DNA damage, such as base excision repair, nucleotide excision repair, and mismatch repair.
• DNA repair mechanisms are vital for maintaining genomic stability.

Applications of DNA knowledge

• DNA analysis is used in various applications like forensic science, medicine (gene therapy, diagnosis), agriculture (crop improvement), and evolutionary biology.
• Genetic testing can identify genetic predispositions to diseases.
• CRISPR gene editing technology allows precise modification of DNA sequences, holding promise for treating genetic disorders.
• DNA fingerprinting utilizes individual DNA variations for identification purposes.