1. The structure of DNA is a double helix composed of nucleotides. Each nucleotide contains three major components: a sugar molecule (deoxyribose), a phosphate group, and a nitrogenous base. The sugar and phosphate molecules form the backbone of the DNA strand, while the nitrogenous bases (adenine, thymine, cytosine, and guanine) pair up in the center of the helix to form base pairs.
2. The four nitrogenous bases are adenine (A), thymine (T), cytosine (C), and guanine (G). They are related because A always pairs with T, and C always pairs with G. This is known as complementary base pairing.
3. Purines and pyrimidines are two types of nitrogenous bases found in DNA. Purines include adenine and guanine and have a double-ring structure, while pyrimidines include thymine and cytosine and have a single-ring structure.
4. Complementary base pairing is the specific pairing of nitrogenous bases in DNA. Adenine (A) always pairs with thymine (T) through two hydrogen bonds, while cytosine (C) always pairs with guanine (G) through three hydrogen bonds. This base pairing creates the ladder-like structure of the double helix.
5. From smallest to largest: base pair, DNA strand, nucleus, chromosome. A base pair is a pair of nitrogenous bases (such as AT or CG) that form a rung on the DNA ladder. A DNA strand is a single chain of nucleotides that make up one half of the DNA double helix. The nucleus is a membrane-bound organelle that contains the cell's genetic material, including chromosomes. A chromosome is a condensed, tightly coiled structure made of DNA and protein that contains many genes.
6. In body cells, chromosomes are distributed in pairs called homologous chromosomes. These pairs line up during cell division, and each daughter cell receives one chromosome from each pair. In sex cells (sperm and egg cells), chromosomes are distributed singly. During meiosis, the process of cell division that produces sex cells, homologous chromosomes separate, resulting in each sex cell receiving one chromosome from each pair.
7. Nuclear DNA is the genetic material found in the nucleus of cells and is inherited from both parents. It contains the majority of an organism's genetic information, including all the genes that determine physical traits. Mitochondrial DNA is the genetic material found in mitochondria, small organelles in the cell that are involved in energy production. Mitochondrial DNA is inherited only from the mother and is much smaller than nuclear DNA, containing only a few genes.