Lec.1 Molecular and genetic factors in disease

Lec:1 Dr.Mohammed Alhamdany

Molecular and genetic factors in disease
Almost all diseases have a genetic component, and many disorders that cause long-term morbidity and mortality.
All human cells are derived from the zygote (the fertilized ovum), a single totipotent stem cell capable of producing all cell types. During development, organs and tissues are formed by the integration of four closely regulated cellular processes:
1-cell division
2- migration.
3-differentiation.
4-programmed cell death.
These processes continue in adult life by small populations of stem cells capable of self-renewal. These cells can also differentiate to maintain and repair the tissues.

DNA, chromosomes and chromatin
The nucleus is a membrane-bound compartment found in all cells, with the exception of erythrocytes and platelets. In humans, the nucleus contains 46 chromosomes, each of which comprises a single linear molecule of deoxy-ribonucleic acid (DNA), which is intimately complexed with proteins in the form of chromatin. The basic (structural) unit of chromatin is the nucleosome, which is a structure of approximately 147 base pairs (bp) of DNA bound round a complex of four different histone proteins.
Each nucleus contains two copies of the genome and thus humans are diploid organisms. The diploid status is present as 22 identical chromosomal pairs—the autosomes—named 1–22 and two sex chromosomes (XX in females and XY in males). Each DNA strand consists of a linear sequence of four bases—guanine (G), cytosine (C), adenine (A) and thymine (T)—covalently linked by phosphate bonds. The sequence of on strand of double-stranded DNA determines the sequence of the opposite strand because the helix is held together by hydrogen bonds between adenine and thymine or guanine and cytosine.