Bruce effect

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• The Bruce effect was first noted by HILDA M. BRUCE in 1959.

• The Bruce effect is also known as pregnancy block, it is shown by the rodents, it refers to the tendency of the pregnant female rodents to terminate their pregnancy, when they are exposed to the scent of another male, which is not the father of the embryo carried by the female.
• Still now the Bruce effect has not been confirmed in other non-rodent species.
• In 1959 Bruce kept pregnant female mice with males which were not the father of the carried embryo, it was seen that the female blocked their pregnancy, in the presence of an unfamiliar male. This effect blocking of the pregnancy by the female influenced by the scent of the male mice was termed as BRUCE effect, after the name of HILDA BRUCE.

Mechanism of the appearance of the Bruce-effect.

• The male mouse urine contains MHC CLASS I peptides that binds to the receptor in the females mouse’s vomeronasal organ (it is an organ filled with mucous present in the nasal septum), it stimulates the vomeronasal system to act as a pump and the system draws in the substances actively. These chemical signals which are specific to each male are learned by the females. This chemosensory cue is coupled by the vasopressin, with an appropriate physiological response,
• It is seen that, if the vasopressin 1b gene is knocked out in females, then the presence of an unfamiliar male does not trigger pregnancy disruption.
• Exposure to the male urinal pheromones will activate a neuroendocrine pathway, which leads to the pregnancy failure. However, if these pheromones are pre-memorized by the female mice, then noradrenalin is secreted, which lowers down the receptivity of the olfactory bulb to these pheromones. Thus the pregnancy disruption is averted.
• The hormone oxytocin is also important in Bruce effect, if the males are treated by the oxytocin-antagonist hormone, then the females are unable to recognize the urinary pheromones of the their mate, and terminates pregnancy when exposed any male, known or unknown.

Neuroendocrine pathway and role of oestrogen:
è The activation of vomeronasal neuron receptors by the male pheromones induces a complex neuroendocrine pathway. This works as follows.
i. The pheromonal information is carried by the nerves to the accessory olfactory lobe, and then to the corticomedial amygdala lobe and then to stria.
ii. These areas stimulate the hypothalamus.]
iii. The hypothalamus then secretes the dopamine,
iv. The dopamine prevents the secretion of prolactin from the anterior pituitary (prolactin is necessary for maintaining the corpus luteum, in the absence of the prolactin the corpus luteum undergoes luteolysis)
v. Now in the absence of the corpus luteum the progesterone is not released. Since the progesterone is necessary for maintaining the pregnancy.
vi. Thus in the absence of the progesterone the pregnancy fails.
è Role of oestrogen: oestradiol is a metabolic product of testosterone, the oestrogen (particularly the E2) is a crucial chemo-signal regulating the Bruce effect.
Small steroid molecules such as E2 are able to enter the bloodstream directly via the nasal ingestion, after ingestion the E2 travels to the uterus, which has high level of suitable receptors,
Normally E2 is essential for the preparation of the blastocyst and the uterus for implantation.
However the excessive E2 prevents implantation.
Factors governing the Bruce effect.
1. Timing of exposure: after mating the females experience twice daily surges of prolactin. The incidence of Bruce-phenomena depends on the timing of the exposure to the male pheromones, if the pheromone exposure coincides with the prolactin surges, then only there takes place the Bruce-effect.


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Innate immunity: elements of innate immune system

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1. Innate immunity is present from birth.
2. It provides the first line of defense against pathogens
3. It is not specific to any one pathogen, but rather acts against all foreign molecules.
4. It also does not rely to previous exposure to the pathogens.
5. Its response is functional since birth and has no memory.
Elements of innate immunity:
1. Physical barriers:
Physical barriers are the first line of defence against microorganisms. It includes:

• Mucous membranes
• The acidic pH of sweat and sebaceous glands; fatty acids and hydrolytic enzymes inhibit the growth of microorganisms.
• The respiratory tract is lined by cilia (hair like projection) of epithelial membranes; the synchronous movement of cilia propels mucus entrapped microorganisms from these tracts.
• Conjunctiva is also specialized, the tears contains lysozyme, lactoferin, IgA and thus provide chemical as well as physical protection

In spite of these barriers, some microorganisms are able to penetrate the physical barriers. Then it is up to the adaptive and innate immune system to recognize and destroy them, without harming the host.

2. Chemical mediator:
a. Complement: it is a heat labile component of blood plasma that augments phagocytosis. This activity was said to complement the antibacterial activity of the antibody/
It also bridges the innate and adaptive immunity. The complement system is composed of over 30 serum proteins. Activation of complement in response to certain micro-organism results a controlled cascade of enzymatic reactions which targets the membranes of pathogenic organisms and lead to their destruction. A variety of specific and non-specific immunologic mechanisms can convert the inactive form of complement proteins to active forms with the ability to damage the membranes of pathogenic organisms, either destroying the pathogens or facilitating their clearance. Reactions between the complement molecules or fragments of complement molecules and cellular receptor triggers the activation of innate or adaptive immune systems.
b. Cytokines: the term cytokine is a generic term for any low molecular weight soluble protein or glycoprotein released by one cell population which acts as intercellular mediator. Interferon is cytokines made by cell in response to viral infection which essentially induce generalized antiviral state in surrounding cells.
c. Pattern recognition molecule: many molecules involved in innate immunity have the ability to recognize a give class on molecule. I.e. recognize pattern. Pattern recognition molecule that recognizes pattern associated molecular pattern (PAMP) may be soluble circular proteins or cell surface receptors. E.g. Manose-binding lectin (MBL) and C - reactive protein (CRP) are soluble pattern recognition molecules that bind to microbial surface and promote their opsonization.
3. Cellular defence: leukocytes are responsible for both specific and nonspecific immunity. Many specialized cell such as neutrophils, macrophages, monocytes, NK cells, participate in innate host defense mechanism. Once the pathogen invades the physical and chemical barriers, the specialized cells play and important role in protection, phagocytosis is fundamental protective. The phagocytosis is enhanced by the opsonization of pathogens. (opsonization: the process by which particulate antigen are rendered more susceptible to phagocytosis is called opsonization)
After ingestion the foreign particle is trapped in the phagosome (phagocytic vacuole), which fused with lysosome forming phagolysosomes. Now the antimicrobial and cytotoxic substances present within lysosome destroys the phagocytized micro-organism. The destruction of phagocytized micro-organism takes place as follows.
i. Oxygen dependent killing: during this process the phagocytes increase their O­₂ consumption (such as hydroxyl radicals, superoxide anions, hydrogen peroxide) which acts as antimicrobials.
ii. Oxygen independent killing: activated macrophages also synthesize lysozyme, defensin and various hydrolytic enzymes, who act without oxygen requirement
4. Inflammatory barriers:

•   Inflammation is an important non-specific dense reaction to cell injury.
•   The signs of inflammation are pain redness (erythema) swelling (edema) and heat.
•   Pain is caused due to increased vascular diameter which leads to increased blood flow, thus causing heat and redness in the area.
•   These blood vessels become permeable to fluid and proteins, leading to local swelling and an accumulation of blood proteins that aid in defence.
•   The inflammatory responses are mediated by a variety of signaling molecules. Activated macrophages produce chemo attractants (known as chemokine).
•   Some chemokine attract neutrophils, (which are the first cells, which are recruited in large numbers to the site of infection).
•   Other chemokine attract the monocytes and dendritic cells. The dendritic cells pick up antigens from the invading pathogens and carry them to nearby lymph nodes, where they present antigens to lymphocytes to marshal the forces of adaptive immune system.
•   Two principal mediators of inflammatory response are histamine (released by a variety of cells in response to injury of tissues), kinines (present in blood plasma in active form)

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Basic structure of antibodies

1. The antibodies reside in the serum.

2. The early experiments of kabat and Tiselius resolved serum proteins into three major non-albumin peaks i.e. α, β, ϒ

3. Antibodies are heterodimers. They have common structure of four peptide chains.

4. The structure consists of two identical light (L) chains and two identical heavy (H) chains.

5. Molecular weight of heavy chain (H) is about 50,000.

6. The molecular weight of the light chain (L) is about 25,000.

7. H and L chains are also called immunoglobulin.

8. Each light chain is bounded to heavy chain by disulphide bonds, and other non-covalent interactions such as salt linkage, hydrogen bond etc….

9. It is sometimes called as the dimers of dimer.

10. Around first 110 (or so) AA of amino-terminal region of light or heavy chain varies greatly among antibodies of different specificity, these segments of highly variable regions are called V-regions. i.e. V_L in light chain and V_H in heavy chain.

11. The V-region has an area called complementary-determining region called as CDRs. It is this CDR (on both light and heavy chain) that constitute the antigen binding site of antigen molecule.

12. The region of relatively constant region beyond the variable region have been dubbed C regions. I.e. C_L in light chain and C_H on heavy chains, the site for attatchment of the carbohydrates are restricted to the constant region.

Heavy chain sequencing revealed five basic varieties of heavy chain

a. The sequencing of revealed that the sequence of the heavy chain are very similar to the light chain.

b. The amino terminal part constitute of 100 to 110 amino acid shows great variation among myeloma heavy chains, so were named as V- chains.

c. The remaining part of chains revealed 5 basic sequence patterns corresponding to 5 diferent heavy chain constant regions (i.e. µ, δ, γ, ε, α)

d. Each of these five different heavy chains are called an isotype.

e. The length of constant region is , approximately 330 AA in δ, ϒ, α. And approximately 440 AA in µ, ε.

f. The class of antibody is determined by the type of heavy chain present.

ANTIBODY CLASS	AA length	TYPE OF HEAVY CHAIN
IgM	440	µ
IgE	440	ε
IgG	330	ϒ
IgA	330	α
IgD	330	δ

g. A single antibody molecule may have any one type of light chain, i.e. either kappa (Κ) or lambda(λ) light chain.

h. A single antibody molecule has identical pairs of heavy and light chain respectively. i.e. H₂L₂

i. The isotypes were further classified as subisotypes (similarly were the antibodies classified).

j. In humans there are following subisotypes.

1. α à α_1, α₂ (IgA₁, IgA₂)

2. ϒàϒ₁, ϒ₂, ϒ₃, ϒ₄ (IgG₁, IgG₂, IgG₃, IgG₄)

3. The δ, ε, µ has no subisotypes.

CLASS	H-CHAIN	SUBCLASS	LIGHT CHAIN
IgM	µ	none	K or λ
IgE	ε	none	K or λ
IgG	ϒ	ϒ1, ϒ2, ϒ3, ϒ4	K or λ
IgA	α	α1, α2	K or λ
IgD	δ	none	K or λ

tips for preparing and scoring for the summative assessment ii, class x examination 2012

1. there is nothing other than the text book of N.C.E.R.T to be consulted, so don't bang your heads on other books, it will be just a loss of time.
2. go through the lessons line by line from the N.C.E.R.T text book, all the questions are directly from the book.
3. try to write as concise as possible, don't put useless information in your answers, since science has nothing to do with useless essays and facts, try to write only what you know, and don't just guess answers, it will surely harm you.
4. if possible try to include diagrams/figures wherever possible, whether it is asked in the question or not.
5. for the objective questions, you should have a good concept of all the practicals included in your syllabus, coz the objective questions are all practical oriented conceptual questions, they cant be just guessed and answered.

summative assessment ii guess paper (science) for class x -2012

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SA₂RT

 (SUMMATIVE ASSESSMENT II REVISION TEST)

SHELFORD TUTORIALS

1.      What is the ultimate source of energy on earth?[1]

2.      What is the scientific name of the yellow spot?[1]

3.      Define reflection?[1]

4.      Define Darwinism?[1]

5.      Yeast reproduces through budding. (true/false).[1]

6.      Which functional group does –CHO represents?[1]

7.      What do you mean by valence electrons of and atom?[1]

8.      What do you mean by a food web?[1]

                                                    

9.      Differentiate between the food web and the food chain?[2]

10.  What is the power of accommodation?[2]

11.  Draw a ray diagram of a concave mirror, when the object is placed at the focus.[2]

12.  Draw structures of 1,2-dichloro,pentane and cyclohexane.[2]

13.  What is Newlands’ law of octaves?[2]

14.  What is the function of the vas-defrens and epididymis.[2]

15.  Name two ways of vegetative propagation.[2]

16.  Differentiate between implantation and fertilization in humans?[3]

17.   show the difference between the recessive and the dominant alleles?[3]

18.  What do you mean by the acquired and the inherited traits, which of the following is transferred to the next generation ? give reason.[3]

19.  Draw a well labeled diagram of the human eye. Or. What are the corrective measures for the hypermetropia and myopia, describe with figures[3].

20.  What are sign conventions for the convex mirror?[3]

21.  A convex mirror used for rear-view on an automobile has a radius of curvature of 3.00 m. If a bus is located at 5.00 m from this mirror, find the position, nature and size of the image.[3]

22.  Discuss speciation in brief with the help of  an example?[3]

23.  A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?[3]

24.  What were the limitations of Döbereiner’s classification?[3]

25.  Why should we conserve forests and wildlife?  Suggest some approaches towards the conservation of forests.[3]

26.  Explain why the sky appears reddish during the time of sunset and sunrise, name the phenomena responsible for this.[3]

27.  Describe the structure and function of the male reproductive system.[5]

28.  How is the equal genetic contribution of male and female parents ensured in the progeny, also elaborate how the sex of new individuals are determined.[5]

29.  (a)  Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?[2_­­^1/2]

(b)  Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?[2^1/2]

30.  An object, 4.0 cm in size, is placed at 25.0 cm in front of a concave mirror of focal length 15.0 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? Find the nature and the size of the image. [5]

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Best of luck