This lecture provides an in-depth examination of DNA, including its structure, function, and historical discovery. It covers the basic chemical composition, including nucleotides and base pairing rules, as well as the significant contributions made by early scientists to our understanding of DNA's role in heredity.
Introduction to DNA: Structure and Function
DNA stands for deoxyribonucleic acid.
DNA is the molecule that carries genetic instructions for life.
It is found in the nucleus of most cells.
DNA determines the traits and functions of living organisms.
DNA can replicate itself for cell division and inheritance.
Key terms: DNA, Gene
Historical Background of DNA Discovery
DNA was first identified by Friedrich Miescher in 1869.
In the early 20th century, scientists began understanding its role in heredity.
Erwin Chargaff discovered base composition rules in the 1950s.
Rosalind Franklin and Maurice Wilkins used X-ray diffraction to study DNA structure.
James Watson and Francis Crick proposed the double helix model in 1953.
Key terms: Base Pairing, Double Helix
Chemical Composition of DNA
DNA is composed of nucleotides as the basic units.
Each nucleotide consists of a phosphate group, a sugar molecule, and a nitrogenous base.
Nitrogenous bases include adenine (A), thymine (T), cytosine (C), and guanine (G).
The sugar molecule in DNA is deoxyribose.
Phosphate groups link nucleotides via phosphodiester bonds.
Key terms: Nucleotide, Purines, Pyrimidines
The Genetic Code: Understanding Codons
DNA contains instructions to build proteins.
A codon is a sequence of three nucleotides.
Each codon specifies an amino acid.
The genetic code is nearly universal across organisms.
Redundancy exists due to multiple codons for the same amino acid.
Key terms: Codon, Start Codon, Stop Codon
Mutations: Types and Effects on DNA
Mutations refer to alterations in genetic sequences.
Types include point mutations, insertions, deletions, and frameshifts.
Mutations can be silent, missense, or nonsense.
Silent mutations do not affect the protein outcome.
Missense mutations change one amino acid in the protein.