DNA Structure and Replication

DNA Structure and Replication

• DNA is a double helix composed of nucleotides.
• Nucleotides consist of a nitrogenous base, a deoxyribose sugar, and a phosphate group.
• The four nitrogenous bases are adenine (A), thymine (T), guanine (G), and cytosine (C). A pairs with T, and G pairs with C.
• DNA replication is the process of copying DNA.
• In semi-conservative replication, each new DNA molecule consists of one original strand and one newly synthesized strand.
• DNA replication begins at specific sites called origins of replication.
• Replication forks are created at the origin, where the DNA strands separate.
• DNA polymerase synthesizes new DNA strands in the 5' to 3' direction.
• Okazaki fragments are short DNA segments synthesized on the lagging strand, which must be joined later by DNA ligase.

Gene Expression

• Gene expression is the process by which information from a gene is used to synthesize a functional gene product, such as a protein.
• The process beings with transcription, where DNA is used as a template to synthesize RNA, including mRNA.
• mRNA carries the genetic code from the DNA to the ribosomes, where protein synthesis occurs (translation).
• The process involves several steps, including: transcription initiation, elongation, and termination; mRNA processing (capping, splicing, and polyadenylation); and translation initiation, elongation, and termination.

DNA Packaging

• The length of DNA molecules is much longer than the cell.
• DNA must be packaged tightly to fit within the cell.
• Nucleosomes are the fundamental units of DNA packaging, consisting of DNA wrapped around histone proteins.
• Several levels of DNA organization exist within a chromosome, leading to increased compaction.

DNA Replication Enzymes and Proteins

• Several enzymes and proteins are involved in DNA replication.
• DnaA, DnaB, DNA primase, DNA polymerase I and III, and DNA ligase are examples of important enzymes and proteins involved.
• DNA gyrase controls the degree of Supercoiling.
• Primosomes contain DNA helicase and primase.
• These enzymes and proteins work together to replicate the DNA accurately and efficiently.

DNA Forms

• DNA exists in different forms, such as A-DNA, B-DNA, and Z-DNA, these forms differ in their structural characteristics and properties.
• The properties differ by their helix handedness, number of base pairs per turn, rise per base pair, pitch, diameter and the presence of minor and major grooves.

Ribonucleic Acid (RNA)

• RNA is a single-stranded molecule involved in various cellular processes.
• RNA contains uracil (U) instead of thymine (T) found in DNA. The sugar in RNA is ribose, not deoxyribose, and the other components are the same as DNA's.
• rRNA, tRNA, and mRNA are types of RNA involved in protein synthesis and other functions.
• Specific structures within RNA can form secondary structures like loops and stem pairs in the mRNA,