Overview
This lecture introduces the structure and function of DNA, covering its key components, basic terminology, and the essential roles DNA plays in heredity and protein synthesis.
What is DNA?
- DNA (deoxyribonucleic acid) is a nucleic acid molecule storing all necessary information to control cellular activity.
- It directs cell specialization, tissue formation, and protein synthesis.
DNA Location and Forms
- DNA is located in the cell nucleus, mostly as a loose chromatin network.
- During cell reproduction or repair, chromatin condenses to form chromosomes.
- Humans have 46 chromosomes, receiving 23 from each parent.
- Genes, segments of DNA, carry hereditary information.
Chromosome Structure
- Chromosomes are condensed DNA strands wrapped around histone proteins.
- Replicated chromosomes have two identical chromatids joined by a centromere.
- The p arm is the short arm; the q arm is the long arm of a chromosome.
Structure of DNA
- DNA is composed of nucleotides, which are its building blocks or monomers.
- Each nucleotide has a phosphate group, a deoxyribose (pentose) sugar, and a nitrogenous base.
- The four nitrogenous bases are adenine (A), thymine (T), guanine (G), and cytosine (C).
- A pairs with T, and G pairs with C—these are complementary base pairs.
DNA Double Helix
- The shape of DNA is a double helix, discovered by Watson and Crick.
- The double helix is a twisted ladder formed by the sugar-phosphate backbone and base pairs connected by weak hydrogen bonds.
Nitrogenous Bases and Pairing
- Adenine and guanine are purines (double-ringed).
- Thymine and cytosine are pyrimidines (single-ringed).
- Base pairs are held together by weak hydrogen bonds, important for DNA replication and protein synthesis.
Functions of DNA
- DNA stores hereditary information in genes, determining organism characteristics.
- DNA provides the code for protein synthesis, guiding growth and development.
- DNA replicates during cell division, passing genetic information to the next generation.
Key Terms & Definitions
- DNA (Deoxyribonucleic Acid) — molecule carrying genetic information for cell activities.
- Chromatin — loose, thread-like DNA in the nucleus.
- Chromosome — condensed DNA structure formed during cell division.
- Gene — segment of DNA coding for proteins or traits.
- Nucleotide — DNA building block with a phosphate, sugar, and nitrogenous base.
- Double Helix — spiral structure of DNA strands.
- Complementary Base Pair — specific pairing of A with T and G with C.
- Purine — double-ringed nitrogenous base (adenine, guanine).
- Pyrimidine — single-ringed nitrogenous base (thymine, cytosine).
Action Items / Next Steps
- Memorize DNA structure, terminology, and complimentary base pairing rules.
- Learn the names and contributions of Watson and Crick.
- Review the difference between chromatin, chromosomes, genes, and nucleotides.