Cellular Biology: DNA, RNA, Chromosomes, and Genetics
Cellular Components and DNA
Cell: The DNA resides within the cell. During cell reproduction, DNA is maintained in both daughter cells, ensuring they inherit the same characteristics as the parent cell. A cell contains three organelles within the nucleus and two outside. Eukaryotic cells possess a nuclear envelope, while prokaryotic cells do not. The main components of a cell are the nucleus, cytoplasm, and cell membrane.
DNA: The term DNA stands for deoxyribonucleic acid. It carries all genetic information. DNA is a long chain composed of nucleotide subunits. These nucleotides are arranged in a chain, forming a double helix structure. The structure is stabilized by complementary nucleobases that join the two chains.
Genetic Code and RNA
Genetic Code: Every three nucleobases form a codon, which determines the synthesis of amino acids. There are 20 essential amino acids. The genetic code is degenerate, meaning different codons can code for the same amino acid. The genetic code and codons are universal across all living organisms.
RNA: RNA is simpler than DNA, consisting of a single chain. It contains uracil (U) instead of thymine (T) and is made of ribose nucleic acid, rather than deoxyribonucleic acid.
Chromatin, Chromosomes, and the Cell Cycle
Chromatin and Chromosomes: Chromosomes contain more compact DNA than chromatin. Chromosomes vary in shape, and DNA is located within them. Chromatins are the arms of the chromosomes. The number of chromosomes is species-specific; humans have 46 chromosomes.
The Cell Cycle: This encompasses all events during a cell’s life. The cell cycle can be very long (e.g., neurons) or short (e.g., skin cells). It is divided into two main phases: interphase and cell division/mitosis.
Meiosis and Genetic Variation
Meiosis: Meiosis results in four daughter cells from one parent cell through two divisions. The first meiotic division involves DNA duplication (similar to mitosis), while the second does not (reductive division).
Mutations and Their Impact
Mutation: A mutation is a random change in DNA, without any specific purpose.
Mutations can affect:
- Somatic cells (somatic mutations), which are generally not significant unless they cause cancer.
- Reproductive cells (germ line mutations), which are crucial as all cells in the new organism will carry the same altered information.
Mutations can occur:
- Spontaneously (natural mutations).
- Artificially (induced mutations) by radiation or mutagenic chemicals.
Gene mutations:
- Base Substitution Mutations: One nucleotide is replaced by another.
- Mutations by loss or insertion of nucleotides: These are deletions (a base is removed) or additions (a base is added).
Mendel’s Contributions
Mendel: Mendel, through his work with pea plants, investigated why offspring resemble their parents. He observed variations in pea traits, laying the foundation for understanding heredity.