Overview
This lecture introduces DNA and RNA structure, key terminology, and the foundational concepts needed to understand genetic disorders, which will be explored further in future lessons.
DNA Structure and Composition
- DNA (deoxyribonucleic acid) consists of 46 molecules in the nucleus of most cells.
- DNA and RNA are polymers made of nucleotide building blocks.
- Each nucleotide includes a sugar, a phosphate group, and a nitrogenous base.
- DNA uses the sugar deoxyribose in its nucleotides.
Nitrogenous Bases and Base Pairing
- Nitrogenous bases are divided into purines (double ring: adenine, guanine) and pyrimidines (single ring: cytosine, thymine, uracil).
- DNA contains adenine (A), thymine (T), cytosine (C), and guanine (G); RNA replaces thymine with uracil (U).
- DNA forms a double helix with a sugar-phosphate backbone and hydrogen-bonded nitrogenous bases inside.
- A purine always pairs with a pyrimidine; A pairs with T (2 hydrogen bonds), C pairs with G (3 hydrogen bonds).
- The law of complementary base pairing means each DNA strand determines the sequence of the other.
Chromatin, Chromosomes, and Genes
- Chromatin is DNA complexed with histone proteins, which help organize and protect the DNA.
- Genes are specific DNA segments coding for proteins.
- The genome is all the genes (about 20,000) in a person; most DNA is non-coding.
- DNA is highly compacted in the nucleus and doubles before cell division.
- During cell division, DNA is tightly coiled into chromosomes visible under a microscope.
- Duplicated chromosome copies are called sister chromatids, which separate during division.
RNA Structure and Function
- RNA (ribonucleic acid) assists in protein synthesis and acts as a messenger between the nucleus and cytoplasm.
- Three types of RNA: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).
- RNA is single-stranded, uses ribose sugar, and contains uracil instead of thymine.
- RNA mainly functions in the cytoplasm, while DNA stays in the nucleus.
Key Terms & Definitions
- Nucleotide — building block of DNA/RNA; contains a sugar, phosphate, and nitrogenous base.
- Purine — double-ring nitrogenous base (adenine, guanine).
- Pyrimidine — single-ring nitrogenous base (cytosine, thymine, uracil).
- Chromatin — DNA wrapped around histone proteins for structural support.
- Gene — DNA segment that codes for a protein.
- Genome — total genetic content (all genes) of an organism.
- Chromosome — coiled, condensed DNA structure visible during cell division.
- Sister chromatids — identical copies of a chromosome joined together before cell division.
- mRNA — messenger RNA, carries genetic code from DNA to ribosome.
- rRNA — ribosomal RNA, component of ribosomes.
- tRNA — transfer RNA, brings amino acids for protein synthesis.
Action Items / Next Steps
- Review the chart comparing DNA and RNA differences.
- Prepare for the next lecture on protein synthesis.