Wednesday, November 8, 2017
Genetic material is the substance that carries the biological information regarding the structural, functional, developmental and behavioural properties of organisms. It also serves as the agent that transfers or transmits biological information from parent to progeny. In most organisms, DNA is the genetic material. But, in some viruses, RNA serves as the genetic material.
Properties of the genetic material
Some of properties are the following:
(i)Genetic material should be present in every cell.
(ii) Ability to store and transmit biological information in a stable form.
(iii) Ability to replicate with high fidelity to produce identical functional copies.
(iv) Ability to distribute its copies equally from parent cells to daughter cells with extreme accuracy and minimal error.
(v) High physical and chemical stability to prevent the loss of information and also to ensure genetic constancy in organisms.
(vi) Potentiality to generate variations (through mutation, recombination and minor errors in replication and distribution) in order to promote genetic diversity.
(vii) Ability to act and express itself for controlling the inheritance of characters specified by it.
Sunday, November 5, 2017
bacterium, the ability of purified polysaccharide to transform was also tested, but no transformation
Avery, MacLeod and McCarthy repeated Griffith's expts in vitro in a much refined way. Culture of live IIR cells produced typical IIR cell colonies, while a culture of heat-killed III s cell or a a culture of the DNA isolated from IIIS cells produced no colony. At the same time. of IIR cells, mixed either with heat-killed IIIS cells or with the DNA isolated from lllS on a medium containing antibodies for IIR cells (Ab IIR), produced some colonies of III s cells. AbIlR was used for inactivating some llR cells so that the number of IIR cells may not exceed the number of IIIS cells. These findings reveal that DNA can be the transforming Since DNA preparations often contain traces of RNA and proteins. this conclusion is not beyond doubt. In order to establish beyond doubt that DNA alone is the transforming principle, Avery and associates conducted two separate experiments, using the DNA isolated from lllS cells.In one of them, the DNA isolated from lllS cells was treated with the enzyme RNAse (to digest RNA if any), and in the other with the enzyme protease (to digest protein), before it was mixed with live llR cells. ln both these expts, some IllS cell colonies were fomied. This clearly shows that RNA and Proteins are not responsible for the transformation of III R cells to lllS cells.In another expt DNA was treated with the enzyme DNAase before it was mixed with live IIR cells.This did not yield a III S colony.This confirms that DNA is the transforming principle.
Sunday, September 17, 2017
Hemoglobin is a globular heme protein in vertebrate red blood cells and in the plasma of many invertebrates that carries oxygen and carbon dioxide; heme group binds oxygen and carbon dioxide and as well as imparts red color to the blood; also spelt as hemoglobin.Red colored conjugated protein (made up of heme and Globin) present inside the RBCNormal Hb% in adult male is 14 to 16 gm.Approximately 6.25 gm of Hb are synthesized and destroyed every day.Heme structure does not vary from species to species.It is the basic protein globin that varies in amino acid composition and sequence in different species.Globin is rich in Histidine and lysine.
Structure of Hemoglobin: Hemoglobin is a conjugated protein. It consists of a
protein combined with an ironcontaining pigment. The protein part is globin and the iron containing pigment is heme. Heme also present in the structure of myoglobin ie oxygenbinding pigment in muscles and neuroglobin ie oxygenbinding pigment in brain. Heme is iron porphyrin compound.Iron is present in ferrous (Fe2+) form. It is in unstable or loose form. In some abnormal conditions,the iron is converted into ferric (Fe3+) state, which is a stable form.The pigment part of heme is called porphyrin. It is formed by four pyrrole rings (tetrapyrrole) called, I, II, III and IV. The pyrrole rings are attached to one another by methane (CH4) bridges.The iron is attached to ‘N’ of each pyrrole ring and ‘N’ of globin molecule.Globin contains four polypeptide chains. Among the four polypeptide chains, two are βchains and two are α-chain /α-chain is made up of 141 aminoacids β-chain is made up of 146 aminoacids.
Varieties of normal human Hb are
HemoglobinA1 (two α-chains and β-chains)
HemoglobinF (two α-chains and ¥-chains)
HemoglobinA2 (two α-chains and delta-chains)
Embyonic Hemoglobin (two α-chains and €-chains)
Hemoglobin-A3 (Altered from Hb-A found in old red cells)
HemoglobinA1C (Glycosylated Hb, present in concentration of 3-5% of total Hb). In diabetes mellitus it is increased to 6 to 15%.
1 Hemoglobin as oxygen carrier:The main function of hemoglobin is to carry oxygen from the lungs to all the tissues of the body. This is due to the affinity of hemoglobin for oxygen. When hemoglobin comes in contact with oxygen, it combines with it and form oxy-hemoglobin. This is a week bond. When blood reaches to tissues, where oxygen is deficient, the bond is broken and oxygen diffuses out to tissues.
2.Hemoglobin as carbon dioxide carrier:Some of carbon dioxide is transported from tissues to lungs through hemoglobin. Although the majority of it is transported via plasma but still it carries some of CO2 to lungs.
3.Give color of blood:The red color of blood is due to hemoglobin. When red blood cells are separated from the blood, the red color disappears. This means that the red color of blood is due to red blood cells. Hence the name red blood cells is given to it. And as we know that hemoglobin is present inside red blood cells, therefore it gives red coloration to RBCs
4.Buffering action:Hemoglobin also acts as a buffer.Buffer means to resist change in pH.Blood has 7.4 pH and it remains in the narrow range.Because, if it changes the life of the person may be endangered.Therefore, hemoglobin plays very important role in keeping the pH of blood constant.
5.Erythrocyte metabolism:Hemoglobin plays an important role in the modulation of erythrocyte metabolism.
6.Interaction with drugs:Not only for oxygen, but hemoglobin act a very important role the transport of various drugs to their site of action.
7. Physiological active catabolites:Hemoglobin is a source of various physiological active catabolites.