Medical Genetics - V. M. Zaporozhan 2005

Introduction to Medical Genetics
Molecular Basis of Heredity
Gene

In the strict sense of the word, a gene is defined as a region of a DNA molecule that carries information about The Structure of a single polypeptide, tRNA molecule, or rRNA molecule. In the broad sense, a gene is a Structural and functional unit of heredity that contains a specific amount of Genetic information.

According to their function, genes are divided into several groups (Table 1.2).

1. Structural genes carry information regarding the structure of Polypeptides, rRNA, tRNA, and other RNAs. So-called "housekeeping genes" are expressed in all Cells because their products are essential for maintaining the viability of any Cell type. Examples include rRNA and tRNA genes, as well as histone genes. Terminal differentiation genes

("luxury genes") are tissue-specific genes that function only in certain cell types or at specific stages of ontogenesis, such as immunoglobulin genes.

2. Regulatory genes are DNA nucleotide sequences (functional regions) that regulate the reading of genetic information from structural genes (i.e., they regulate structural Gene Expression). A promoter is a DNA nucleotide sequence at the 5' end of a gene to which the RNA polymerase enzyme binds to initiate METABOLISM/31.html">Transcription of the structural gene; a terminator is the region where transcription ends. Enhancers are DNA regions that enhance transcription by binding to specific transcription factors that facilitate the attachment of RNA polymerase to the promoter. Silencers are DNA sequences that repress transcription, also by binding to transcription factors.