Protein properties are determined by the number and order of bases on the DNA molecule. If the number or sequence of bases in a DNA molecule changes, the structure of the protein it encodes changes accordingly. Gene mutations lead to abnormalities in the quality and quantity of protein molecules, which cause dysfunction of the body. These diseases are called molecular diseases.
There are many types of molecular diseases.According to the functions of various proteins, molecular diseases can be divided into transport protein diseases, coagulation and anticoagulation factor deficiency, immune protein deficiency diseases, membrane protein diseases, receptor protein diseases, etc.
1. Hemoglobin disease
Hemoglobinopathy (hemoglobinopathy) refers to diseases caused by abnormal globin molecular structure or synthesis. It is the most thoroughly and thoroughly studied molecular disease in human Mendel or genetic diseases. It is a representative of transport protein diseases and the best model for studying human genetic mechanisms. It is estimated that more than 100 million people worldwide carry the gene for hemoglobin disease, and the incidence is high in southern China. Therefore, hemoglobin disease is one of the most common inheritances.
(1) Composition, structure and genetic control of normal hemoglobin
1. The composition and development of human hemoglobin Each red blood cell contains about 280 million hemoglobin molecules, each molecule is composed of four subunits, each unit is composed of a globin peptide chain and a heme prosthetic group, namely hemoglobin The molecule is a spherical tetramer composed of two pairs of globin chains (Figure 4-10). One pair is the α-like chain (α chain and ξ chain), which is composed of 141 amino acids; the other is the β-like chain (ε, β, γ, and δ chain), which is composed of 146 amino acids. These 6 different globin chains are combined into 6 different human hemoglobins, namely Hb Gower1 (ξ2ε2), HbGower2, (α2ε2), Hb Portland (ξ2γ2), HbF (α2γ2), HbA (α2β2) and HbA2 ( α2δ2). There are two subtypes of γ chain, namely Gγ2 and Aγ2. Therefore, there are two types of HbF: α2Gγ2 and α2Aγ2. The 136th amino acid of the former is glycine and the latter is alanine.
Gene mutations cause abnormal protein synthesis The various blood proteins mentioned above appear alternately at different stages of development (Figure 4-11). During early embryonic development, embryonic hemoglobin HbGowerl, HbGower2 and HbPortland are synthesized. The fetal period (from 8 weeks to birth) is mainly HbF. Adults have three types of hemoglobin: HbA, accounting for more than 95%; HbA2, accounting for 2% -3.5%; HbF, less than 1.5%.
2. Human globin genes Human globin genes are divided into two categories: one is the α-like globin gene cluster (α-like globin gene cluster), including ξ and α genes; the other is the β globin gene cluster (β -like globin gene cluster), including ε, γ (Gγ and Aγ), δ and β genes.
(1) Alpha-globin-like gene: The human alpha-globin gene cluster is located at 16p13, and there are two alpha-globin genes on each chromosome. Therefore, there are 4 alpha genes in diploid cells, and each alpha gene is almost The same amount of alpha globin chain. In addition, the α-globin-like gene cluster also includes two ξ genes and a pseudogene Ψα. These genes are closely linked and their arrangement order is shown in Figure 4-12.
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