DNA Structure:
* Double helix: DNA is a double helix, two strands of nucleotides twisted around each other like a spiral staircase.
* Nucleotides: Each strand is composed of repeating units called nucleotides. Each nucleotide consists of:
* A sugar molecule (deoxyribose)
* A phosphate group
* A nitrogenous base: Adenine (A), Guanine (G), Cytosine (C), or Thymine (T)
* Base pairing: The two strands are held together by hydrogen bonds between complementary bases: A always pairs with T, and G always pairs with C. This base pairing is crucial for DNA replication and gene expression.
How DNA functions in heredity:
1. Replication: When a cell divides, its DNA replicates, creating two identical copies. This ensures that each daughter cell receives a complete set of genetic instructions.
2. Gene expression: DNA contains the instructions for building and maintaining an organism. These instructions are encoded in genes, specific segments of DNA.
3. Transcription: Genes are transcribed into RNA (ribonucleic acid), a molecule similar to DNA.
4. Translation: The RNA is then translated into proteins, which perform a wide variety of functions in the cell.
5. Inheritance: During sexual reproduction, offspring inherit half of their DNA from their mother and half from their father. This mixing of genes is the basis of genetic diversity.
Key concepts related to DNA and heredity:
* Chromosomes: DNA is organized into structures called chromosomes. Humans have 23 pairs of chromosomes.
* Genotype: The genetic makeup of an organism.
* Phenotype: The observable characteristics of an organism, determined by its genotype and environmental factors.
* Mutations: Changes in the DNA sequence that can alter gene expression and potentially lead to new traits.
In summary: DNA acts as the blueprint for life, carrying the genetic instructions that determine an organism's traits and are passed on to its offspring. The complex process of DNA replication, gene expression, and inheritance ensures the continuity of life and the diversity of living organisms.
