chapter 17

A gene is the basic unit of heredity transferred from parent to offspring, defined as a DNA sequence producing a functional product, either a polypeptide or an RNA molecule. Genes determine traits and characteristics in organisms, such as physical properties and disease susceptibility. The genetic code is nearly universal, shared among all life forms, highlighting common ancestry.

The central dogma of biology outlines the flow of genetic information: DNA to RNA to protein, involving three steps: replication (copying DNA), transcription (synthesizing mRNA from DNA), and translation (synthesizing polypeptides from mRNA). Each step is essential for cell function and environmental response.

Gene expression encompasses transcription and translation. Messenger RNA (mRNA) transports amino acid codes from the nucleus to ribosomes for protein synthesis. Ribosomal RNA (rRNA) forms a structural component of ribosomes, while transfer RNA (tRNA) brings amino acids based on mRNA codons.

Transcription occurs in the eukaryotic nucleus and prokaryotic cytoplasm, facilitated by RNA polymerase, which unwinds the DNA and synthesizes mRNA. During translation, ribosomes read mRNA codons and match them with corresponding tRNA anticodons.

There are 64 codons coding for 20 amino acids, with multiple codons specifying the same amino acid, allowing redundancy in the genetic code. Codons are read in triplets to ensure correct amino acid sequence, and a codon chart shows the amino acid for each codon.

Mutations in DNA can produce genetic variation, vital for evolution and adaptation. Types of mutations include point mutations (single nucleotide changes) and larger insertions or deletions that can cause significant protein synthesis alterations. Notably, sickle-cell anemia is caused by a point mutation in the hemoglobin gene. Mutations can be permanent if occurring in germ cells, contributing to heritable traits in future generations.