Biomolecules, Genetics, and Chromosomal Variations

Biomolecules and Genetic Information

Biomolecules form long chains, such as in genetic information storage. These chains consist of repeating nucleotides. A nucleotide is composed of a nitrogenous base, a pentose sugar (like am5C), and a phosphate group. A nucleoside is simply a base plus a pentose sugar.

Nitrogenous bases include adenine (A), thymine (T), uracil (U), and guanine (G). Purine bases (A and G) have a two-ring structure, while pyrimidine bases (C, T, and U) have a single-ring structure. These bases contain the genetic code necessary for protein synthesis. Approximately 3000 base pairs are needed to code for a single protein. The human genome contains 46 chromosomes (23 pairs), with 22 pairs being autosomes and one pair being sex chromosomes (heterochromosomes).

Genes are located in specific regions of chromosomes and are responsible for modifying characteristics. A locus is a specific location on a chromosome, and an allele is a variant of a gene at that locus. Genetics studies heredity and the mechanisms of transmission of biological information from one generation to the next. DNA is responsible for transmitting genetic information, while RNA decodes the information encoded in DNA.

DNA Replication and Cell Division

DNA is a unique molecule capable of self-replication through a process directed by DNA polymerase. DNA duplication occurs during mitosis (cell division), which includes prophase, metaphase, anaphase, and telophase. This process results in two daughter cells with the same genetic makeup as the original cell. During interphase, the cell duplicates its DNA and performs other tasks. Meiosis, a type of cell division, results in gametes (sperm and egg cells) with half the number of chromosomes.

Protein Synthesis

The process of translating the information encoded in DNA into proteins involves RNA. Messenger RNA (mRNA) carries information from the nucleus to the cytoplasm, where proteins are synthesized by ribosomes. Transcription, mediated by RNA polymerase, creates mRNA from a DNA template. Transfer RNA (tRNA) transports amino acids to the ribosome, and ribosomal RNA (rRNA) is a component of ribosomes. During translation, mRNA interacts with ribosomes, and tRNA delivers amino acids to form proteins. The process involves three types of RNA.

Mutations and Chromosomal Variations

DNA molecules can undergo mutations, which can alter characteristics. Mutations include deletions (loss of a base), insertions (addition of a base pair), and substitutions (replacement of a base pair). Chromosomal mutations include deletions (loss of a chromosome segment, as seen in cat cry syndrome), duplications (repetition of a chromosome segment, as seen in Pallister-Killian syndrome), and translocations (exchange of segments between different chromosomes, as seen in myeloid leukemia).

Variations in Chromosome Number

Errors in chromosome duplication and distribution during meiosis can lead to variations in chromosome number. Trisomy involves an extra chromosome in a pair, affecting autosomes, sex chromosomes, or both. Monosomy affects the X chromosome, resulting in conditions like Turner syndrome (XO). Polyploidy involves a multiplication of the total number of chromosomes, often seen in plants.