Knowledge in Microbiology
Biology Questions 4
Biology is nothing without practice. Practice makes a man perfect. So there are ample of questions to be practiced to improve and test your preparation level. These questions are taken from various books and approved by our teachers. Will help to fetch you good marks in exam.
Deepjyoti Ray
HEMATOPOIESIS
In humans, hematopoiesis, the formation and development of red and white blood cells from stem cells, begins in the yolk sack in the first week of embryonic development. Here yolk sac stem cells differentiate into primitive erythroid cells containing embryonic hemoglobin. In the the third month of gestation, the stem cells migrate from the yolk sac to the fetal liver and then to the spleen; these two organs have the major role in hematopoeisis from the third to the seventh months of the gestation. As gestation continues, the bone marrow becomes the major hematopoietic organ; by birth hematopoeisis has ceased within the liver and spleen. Every mature blood cell is derived from a common stem cell.In contrast to a uni-potent cell, which differentiates into a single type, a hematopoietic stem cell is pluripotent, able to differentiate along a number of pathways and there by generate erythrocytes, granulocytes, monocytes, mast cells, lymphocytes,and megakaryocytes.A pluripotent stem cell differentiate among among one of two pathways, giving rise to either a a lymphoid stem cell or a myeloid stem cell.Lymphoid and myeloid stem cells differentiate into progenitor cells, which have lost the capacity of self renewal and are committed to a given cell lineage. The lymphoid stem cell generates T and B lymphocytes. The myeloid stem cell generates progenitor cells for red blood cells (erythrocytes), the various white blood cells ( neutrophils, eosinophils, basophils, monocytes, mast cells), and platelets. Progenitor commitment depends on the acquisition of responsiveness to particular growth factors.The heamatopoietic cells grow and mature on a meshwork of stromal cells which are nonhematopoietic cells that support the growth and differentiation of the hematopoietic cells. Stromal cells include fat cells, endothelial cells, fibroblasts and macrophages. Stromal cells influence hematopoetic stem-cell differentiation by providing a hematopoetic inducing microenvironment consisting of a cellular matrix and either membrane bound or diffusible growth factors. As hematopoetic stem cells differentiate in this microenvirenment, their membranes acquire deformability, allowing the mature cells to pass through the sinusoidal wall into the sinuses of the bone marrow, where the enter the circulation.
Yamini Chandru
PROGRAMMED CELL DEATH
In order for steady-state levels of the various hematopoietic cells to be maintained, cell division and differentiation in each of the lineages is balanced by a process called programmed cell death. Cells undergoing programmed cell death often exhibit distinctive morphologic changes, collectively referred to as apoptosis. These changes include a pronounced decrease in cell volume, modification of the cytoskeleton-resulting inpronounced membrane blebbing, a condensation of the chromatin, and degradation of the DNA into oligonucleosomal fragments. Following these morphologic changes, an apoptotic cell sheds tiny membrane-bound apoptoticbodies containing intact organelles. Macrophages quickly phagocytosis apoptotic bodies, ensuring that their intracellular contents, including proteolytic and other lytic enzymes, cationic proteins, and oxidizing molecules are not released into the surrounding tissue. In this way apptosis occur without inducing a localized inflammatory response. Apoptosis differs markedly from necrosis, the changes associated with cell death arising from injury. In necrosis the injured cell swells and bursts, releasing its intracellular contents, which are cytotoxic to other cells in the tissue; as a result, an inflammatory response develops.Each of the cells produced by hematopoiesis has a characteristic life span and then dies by programmed cell death. In the adult human, for example, there are about 5 X 1010 neutrophils in the circulation. These cells havea life span of only 1 day and then die by programmed cell death. This death, coupled with constant neutrophil production, maintains steady-state levels of these cells. If programmed cell death fails to occur, a leukemic state may develop. Programmed cell death also plays a role in maintaining proper levels of hematopoietic progenitor cells.For example, when colony-stimulating factors are removed, progenitor cells undergo programmed cell death.The expression of several genes has been associatedwith the regulation of apoptosis in hematopoietic cell lineages. Some of these gene products induce apoptosis, whereas other gene products inhibit apoptosis.The bcl-2 (B-cell lymphoma 2) gene, for example, encodes a protein product that inhibits apoptosis.Bcl-2 levels have been found to play an important role in regulating the normal life span of various hematopoietic cell lineages, including lymphocytes. Activated lymphocytes have been found to express lower levels of Bcl-2 and therefore are more susceptible to apoptotic death than native lymphocytes or memory cells.
COMPLEMENT SYSTEM
The term 'complement' (C) refers to a system of factors that occur in normal serum and are activated characteristically by antigen-antibody interaction and subsequently mediate a number of biologically significant consequences.Towards the end of the nineteenth century, it was noticed that bactericidal, bacteriolytic and hemolytic actions of the appropriate antibodies required the participation of a heat labile components present in the normal sera of human beings and animals. Buchner(1889) was the first to observe that the bactericidal effect of serum was destroyed by heating at 55 °C for one hour. Pfieffer (1894) discovered the cholera vibrios were lysed when injected intraperitoneally into specifically immunised guinea pigs (bacteriolysis in vivo or Pfieffer's phenomenon). Bordet (1895) extended these observations and established that immunebacteriolysis and hemolysis required two factors the heat stable antibody and a heat labile factor, whichwas called alexine. This term has been replaced by the present name complement which was coined by Ehrlich, because this factor complemented the actionof the antibody.
COMPLEMENT COMPONENTS
The complement system consists of at least twenty chemically and immunologically distinct serum proteins comprising the complement components, the properdin system and the control proteins.Complement is a complex of nine different fractions,CI to C9. The fraction C1 occurs in serum as a calcium ion-dependent complex, which on chelation with EDTA yields three protein subunits called C1q, r, ands. Thus C is made up of a total of 11 different proteins. C fractions are named C1 to C9 in the sequence of the cascading reaction, except that C4 comes after C1 before C2The model traditionally used to explain C activity in immune cytolysis is the lysis of erythrocyte sensitised by its antibody. The erythrocyte (E) antibody (A) complex is called EA, and when C components areattached to EA, the product is called EAC, followed by the components that have reacted (for example, EAC14235 or EAC 1-5). When a C component acquires enzymatic or other demonstrable biological activity, it is indicated by a bar over the component number, for example, the enzymatically activated C1 is shown as C1. Fragments cleaved from C components during the cascade are indicated by small letters (C3a, C3b). Inactivated forms of C components are indicated bythe prefix 'i' (iC3b).
COMPLEMENT ACTIVATION
Complement is normally present in the body in an inactive form but when its activity is inducedby antigen-antibody combination or other stimuli, components react in a specific sequence as a cascade.Basically, the C cascade is a series of reactions in which the preceding components act as enzymes on the succeeding components, cleaving them into dissimilar fragments. The larger fragments usually join the cascade. The smaller fragments which are releasedoften possess biological effects which contribute to defence mechanisms by amplifying the inflammatory process, increasing vascular permeability, inducingsmooth muscle contraction, causing chemotaxis of leucocytes, promoting virus neutralisation, detoxifying endotoxins and effecting the release of histamine frommast cells.The C cascade can be triggered off by two parallel but independent mechanisms or pathways which differ only in the initial steps. Once C3 activation occurs, the subsequent steps are common in both pathwayswhich have been called the classical C pathway and the alternative or properdin pathway.The classical pathway is so called because it was the first one identified. But actually it is a more recently evolved mechanism of specific active immunity, while the alternative pathway represents a more primitive system of nonspecific innate immunity.
Biomicrofluidics
Studying is nothing without practice. Practice makes a man perfect. So there are ample of questions to be practiced to improve and test your preparation level. These questions are taken from various books and approved by our teachers. Will help to fetch you good marks in exam.
SRM BIOLOGY QUESTION BANK
SRM BIOLOGY QUESTION BANK
Anirudh Pareek
SRM BIOLOGY MCQS
SRM BIOLOGY MCQS
SRM BIOLOGY QUESTION BANK
SRM BIOLOGY QUESTION BANK
Biomechanics: principles and applications
Biomechanics is a comprehensive presentation of the current principles and applications of biomechanics integrating both systems and subsystems models.
Yimpangakum Imsong
ANTIGENS
An antigen has been defined as any substancewhich, when introduced parenterally into the body stimulates the production of an antibody with which it reacts specifically and in an observable manner. This traditional description of an antigen is no longer comprehensive enough in the light of current concepts about the immune response. Some antigensmay not induce antibodies but may sensitise specific lymphocytes leading to cell mediated immunity or may cause immunological tolerance.The word 'parenteral' (meaning, outside the intestinal tract) is used in the definition because orally administered antigens are usually denatured by digestive enzymes and their antigenicity destroyed, so that no antibodyformation takes place. When given parenterally, antigens do not undergo any such inactivation and can induce antibody production. However, there are exceptions and some antigens can be immunogenic when given orally, such as oral vaccines. The word 'specifically in the definition is important as specificity is the hallmark of all immunological reactions.An antigen introduced into the body reacts only with those particular immunocytes (B or T lymphocytes) which carry the specific marker for that antigen and which produce an antibody cells complementary to that antigen only. The antibody so produced will react only with thatparticulate antigen and with no other though immunological cross-reaction may occur between closely related antigens.The two attributes of antigenicity are1. induction of an immune response (immunogenicity),and2. specific reaction with antibodies or sensitised cells (immunological reactivity).