DNA Replication Basics

DNA Replication

• Chargaff's rules dictate that in DNA, the amount of adenine is equal to thymine, and the amount of guanine is equal to cytosine; these rules are applicable in determining the composition of DNA.
• DNA has a double helix structure.
• The antiparallel nature of DNA refers to the strands running in opposite directions.
• Adenine and guanine are purines.
• Cytosine, thymine, and uracil are pyrimidines.
• A nucleotide consists of a nitrogenous base, a phosphate group, and a sugar (deoxyribose in DNA, ribose in RNA).
• Nitrogenous bases include adenine, guanine, cytosine, thymine (in DNA), and uracil (in RNA).
• Nucleotides contain a phosphate group.
• The sugar in DNA is deoxyribose.
• The sugar in RNA is ribose.
• Hydrogen bonds hold the two DNA strands together.
• Covalent bonds link the nucleotides within a single strand.

DNA Replication Process

• DNA replication follows a semiconservative model, where each new DNA molecule contains one original and one new strand.
• Replication begins at the origins of replication.
• A replication fork is a Y-shaped region where the parental DNA strands are being unwound.
• Helicase unwinds the double helix at the replication fork.
• Single-strand binding proteins stabilize single-stranded DNA to prevent re-pairing.
• Topoisomerase relieves the strain ahead of the replication fork by breaking, swiveling, and rejoining DNA strands.
• A primer is a short RNA sequence that starts DNA synthesis.
• Primase synthesizes the RNA primer.
• DNA polymerase adds nucleotides to the growing DNA strand.
• The leading strand is synthesized continuously in the 5' to 3' direction.
• The lagging strand is synthesized in short fragments (Okazaki fragments).
• Okazaki fragments are short DNA fragments synthesized on the lagging strand.
• Ligase joins Okazaki fragments to form a continuous DNA strand.
• Mismatch repair corrects errors that occur during DNA replication.
• Nuclease cuts out damaged DNA.
• Nucleotide excision repair replaces damaged DNA segments.

Genetic Engineering

• Genetic engineering involves manipulating genes for practical purposes.
• Plasmids are small, circular DNA molecules in bacteria, often used as vectors.
• Recombinant DNA contains DNA from two or more sources.
• Gene cloning produces multiple copies of a gene.
• Restriction enzymes cut DNA at specific sequences.
• A restriction site is a specific DNA sequence recognized by a restriction enzyme.
• Restriction fragments are DNA segments resulting from cutting DNA with restriction enzymes.
• Gel electrophoresis separates DNA fragments by size.
• Polymerase chain reaction (PCR) amplifies specific DNA segments.
• DNA sequencing determines the nucleotide sequence of DNA.

Understand the fundamentals of DNA replication. Explore Chargaff's rules, the double helix structure, and the components of nucleotides. Learn about the semiconservative model of DNA replication and the roles of key enzymes like DNA polymerase.