The Phosphodiester Bond

Nucleic acids (RNA and DNA):

formed by the condensation of nucleotides, catalyzed by polymerases.

The bond:  a phosphodiester bond.

The bond is shown in figure a display of a trinucleotide DNA fragment.



A couple of shorthand notations to designate nucleic acid polymers:
vertical lines represent the sugars
diagonal lines represent the phosphodiester bonds.



More commonly: only indicate the order of bases and the direction of the polymer chain. For instance:

5' - AGTCCGATGCAAGCTCG - 3'

The complementary sequence:

5'-AGTCCGATGCAAGCTCG-3'
3'-TCAGGCTACGTTCGAGC-5'


proposed by James Watson and Francis Crick.

Serebellum

It's related with muscle motor function. If the serebellum is removed surgically, cordinated muscle contraction is disturbed and maintanence of body posture disappear. The serebellar structure is similar to the cortex cerebri. There are gray matter on the surface but white matter in the inner side. The surface have many small invagination that is called as gyri as like cerebri. Serebellum receives impulses from the perphery by the sipinocerebellar tract and from some nuclei from brain stem and also fibers from motor cortex.

Nervous system animation

Detailed animations about nervouse system and cell singaling, brain signals, central nervous system.

Forebrain


Forebrain is divided into the diencephelon and thelencephelon. the dorsal portion of the diencephelon is the epithalamus, the lateral portion the thalamus and the ventral portion is the hypothalans.

The epithalamus contains a small nucleus that transmits olfactory information to the brain stem, the pineal and parapineal bodies, and the anterior choroid plexus.

In lower vertebrates epithalamus is well developed and importantt for the transmission of impulses from periphery to cerebral cortex, but in mammales most of sensory information is transferred to the cerebral cortex via thalamus.

properties of excitable cell

Rheobase is the lowest current that will initiate an action potential. the chronaxie is the maximum stimulus duration when the current is 2X reheobase. Rheobase and chronaxie define the shape of the strength-duration relationship. A slowly inceasing depolarizing current may not initiate an action potential even though it may rise to an intensity much greater than threshold level. A maintained depolarization causes the threshold to rise towards 0 mV. This called as accomadation.

It is not possible to elicit a second action potential after brief period of first action potential. This period is called as absolute refractory period. in this period all Na channels again can be aplicable for activation, this period is called as relative refractory period.

myelination

first one, in the central nervous system, myelin is formed by the oligodendrocytes. One oligodendrocyte can contribute to the myelin sheath of several axons.

myelination II: in the peripheral nervous system, myelin is formed by Schwann cells. Each Schwann cell associates with only one axon, when forming a myelinated intermode.

vertebrate nervous system

The organization of the vertebrate nervous system is different from invertebrates. Vertebrates have a well-organized hollow dorsal nervous system. The central nervous system included a brain and spinal cord. The peripheral nervous system comprise peripheral nerves extending from spinal cord and peripheral ganglia. nervous