Deoxyribonucleic acid, or DNA, is a polymer of nucleotides linked together by specific bonds known as phosphodiester bridges. The phosphate group (PO3) of one nucleotide links to the hydroxyl group (OH) of the following nucleotide.Hundreds of millions of these linkages occur within the DNA polymer.he two DNA strands are held together by interchain hydrogen bonds. H-bonds pair the bases in one chain to the complementary bases in the other chain. (A/T and G/C).
The master circadian pacemaker in mammals is located in the suprachiasmatic nucleus in the rostroventral hypotha-lamus (Figure 2). Lesion studies identified it in 1972, and in vitro and in vivo functional studies, as well as transplant studies, have repeatedly corroborated the finding since then.
A pacemaker is a small device that's placed in the chest or abdomen to help control abnormal heart rhythms. This device uses electrical pulses to prompt the heart to beat at a normal rate.Pacemakers are used to treat arrhythmias (ah-RITH-me-ahs). Arrhythmias are problems with the rate or rhythm of the heartbeat.acemakers can: 1  Speed up a slow heart rhythm. 2  Help control an abnormal or fast heart rhythm. 3  Make sure the ventricles contract normally if the atria are quivering instead of beating with a normal rhythm (a condition called atrial fibrillation).