Overview
This lecture introduces the basic structure, location, and function of DNA as the code of life, highlighting key terminology and the importance of DNA in heredity and protein synthesis.
What is DNA?
- DNA is a nucleic acid that stores information to control cellular activity and protein synthesis.
- The full name of DNA is deoxyribonucleic acid, referring to its molecular structure.
Location and Forms of DNA
- DNA is found in the nucleus of almost every cell.
- Most of the time, DNA exists as a loose chromatin network, not condensed chromosomes.
- DNA condenses into chromosomes only during cell replication or repair.
Chromosomes, Genes, and Heredity
- Chromosomes are condensed pieces of DNA; humans have 46 chromosomes (23 from each parent).
- Each chromosome is made of DNA wound around histone proteins.
- Genes are short DNA segments that carry hereditary information and code for specific proteins.
- Chromosomes may be replicated, featuring two identical chromatids joined by a centromere.
DNA Structure and Components
- The basic shape of DNA is a double helix, discovered by Watson and Crick.
- DNA is composed of nucleotides, which are its monomers or building blocks.
- Each nucleotide has three parts: a phosphate group, a deoxyribose (pentose) sugar, and a nitrogenous base.
Nitrogenous Bases and Base Pairing
- Four nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C).
- Adenine pairs with thymine (A-T), and guanine pairs with cytosine (G-C) via weak hydrogen bonds (complementary base pairing).
- Adenine and guanine are purines (double ring); thymine and cytosine are pyrimidines (single ring).
DNA's Genetic Code and Function
- All organisms use the same four bases; differences lie in their sequence.
- The DNA sequence functions as a code for protein synthesis and controls organism development.
- DNA's key functions: carries hereditary information (genes), codes for proteins, and replicates for inheritance.
Key Terms & Definitions
- DNA — Deoxyribonucleic acid; molecule storing genetic information.
- Nucleotide — The monomer/building block of DNA, consisting of a phosphate, sugar, and base.
- Chromosome — Condensed DNA structure within the nucleus, carries genes.
- Gene — Segment of DNA coding for a specific protein or trait.
- Chromatin — Spaghetti-like network of DNA in the nucleus.
- Histone — Protein that DNA wraps around in chromosomes.
- Double Helix — Twisted ladder shape of DNA.
- Purine — Nitrogen base with a double-ring structure (adenine, guanine).
- Pyrimidine — Single-ring nitrogen base (thymine, cytosine).
- Complementary Base Pair — A-T and G-C pairing by hydrogen bonds.
- Centromere — Region joining two chromatids in a chromosome.
Action Items / Next Steps
- Memorize the key terminology and DNA structure.
- Review the base pairing rules (A-T, G-C).
- Prepare for upcoming lessons on DNA replication and protein synthesis.