Mechanisms of Apoptosis

Apoptosis is programmed cell death. It is the result of activation of enzymes (caspases). The two pathways of apoptosis are the extrinsic pathway and the intrinsic pathway.

Extrinsic (death receptor) pathway

1.       Initiated when a TNF receptor (eg. CD95/Fas) binds to its ligand CD95L.
2.       Triggers multiple receptors to aggregate together at cell surface.
3.       This attracts an adapter protein FADD (Fas-Associated Death Domain).
4.       The protein recruits procaspase 8 to form the death-inducing signalling complex (DISC).
5.       Procaspase 8 is cleaved into active caspase 8.
6.       Caspase 8 activates caspase 3 (an executioner caspase) to initiate cell degradation.
7.       Caspase 8 also cleaves Bid protein to tBid (truncated Bid).
8.       tBid acts as a signal on mitochondria membrane to facilitate release of cytochrome c in the intrinsic pathway.

Intrinsic (mitochondria) pathway

1.       Triggered by stimuli such as deprivation of growth factors/survival signals/ exposure to agents that damage DNA/excessive accumulation of misfolded proteins.
2.       Sensors (BH3 proteins) of the Bcl2 family are activated, which in turn activate pro-apoptotic members called Bax and Bak.
3.       Bax and Bak cause cytochrome c and other mitochondrial proteins to leak out.
4.       These sensors inhibit anti apoptotic molecules Bcl2 and Bcl_XL , enhancing leakage.
5.       Cytochrome c leaks into the cytosol where it binds to APAF-1 (apoptotic protease activating factor 1) forming an apoptosome which in turn activates caspase 9.
6.       Caspase 9 cleaves and activates the executioner caspase (caspase 3) that initiates degradation.
7.       The activation of caspase cascade leads to nuclear fragmentation.

References:
1. Kumar V, Abbas A. K, Aster J.C. Robbins Basic Pathology. 2013. 9th ed. Philadelphia: Elsevier Saunders.
2. http://www.scq.ubc.ca/apoptosis/

  

formation of pollen grains, embryo sac, and process of double fertilisation SPM notes

Formation of pollen grains

1.     Pollen grains are formed in the anther

2.     An anther has 4 pollen sacs

3.     Each pollen sac contains hundreds of cells called pollen mother cells

4.     Each pollen mother cell undergoes meiosis to form 4 haploid microspores

5.     The nucleus of each microspore divides by mitosis to form a tube nucleus and a generative nucleus

6.     The microspores develop into pollen grains

Formation of embryo sac

1.     Ovule develops from ovarian tissue

2.     Ovule has diploid embryo sac mother cell

3.     Embryo sac mother cell undergoes meiosis to form a row of four haploid cells called megaspores

4.     3 of 4 megaspores degenerate, leaving 1 in the ovule

5.     Megaspore continues to grow and enlarges

6.     Nucleus of megaspore undergoes mitosis 3 times to form 8 haploid nuclei

7.     3 of the 8 nuclei migrate to one end to form antipodal cells

8.     2 move to the centre to form polar nuclei

9.     1 of the 3 nuclei nearest to the micropyle develops into an egg cell flanked by 2 synergid cells

10.  The structure formed is called an embryo sac

Process of Double Fertilisation

When the pollen grain lands on the stigma, fertilisation is initiated.

Sucrose solution secreted by the stigma stimulates the pollen grain to germinate and form a pollen tube.

The pollen tube grows down the style towards the ovule.

The generative nucleus divides by mitosis into two male nuclei.

The male nuclei move down the pollen tube led by the tube nucleus.

When the pollen tube reaches the ovary, it penetrates the ovule through the micropyle.

The tube nucleus disintegrates, leaving a clear passage for the male nuclei to enter the embryo sac.

Double fertilisation occurs in the ovule. One male nucleus fuses with the egg cell to form a diploid zygote while the other male nucleus fuses with the two polar nuclei to form triploid nucleus.

After fertilisation, the diploid zygote divides repeatedly by mitosis to form an embryo while the triploid nucleus forms an endosperm which provides nutrients for the growing embryo.

The ovule develops into a seed while the ovary develops into a fruit.

We humans never appreciate what we have

Isn't it obvious? We always want what other people have. We can't see the bright side of what we have. We prefer to look on the dark side of what we have. This is the attitude that we all have, admit it! When we look at rich people, we would wish we are rich. When we look at lucky people who get everything, we would wish we are lucky. When we look at successful people, we would wish we are successful like them. When we look at champions in competitions, we would wish we are the champion. When we look at pretty people, we would wish we are pretty. Isn't that typical human-thinking? We look at those who are better than us, but never look at those who are worse than us! Why don't we look at those who are poorer than us, unluckier, less successful than us, losers in competitions, and less pretty? If you want to feel better, don't compare yourselves with those who are better, but compare yourselves to those who are less. If we keep comparing ourselves with those whose life seems to be perfect, we will never achieve ultimate happiness even at the end of our life! Just take some time to think about yourselves. Who do you normally compare yourselves with? Your smarter friend? Your richer friend? Your luckier friend? Your stronger friend? Your prettier friend? Just ponder about it. We, humans living on this temporary planet, want to be the best. The best among the best. And we compare ourselves with every other human who are better. This makes us forget about the less fortunate but only care about ourselves. It is time to change our mentality. Why don't we start appreciating everything we have?

DNA Fingerprinting

1. Tissue samples are obtained from the criminal scene and DNA is extracted

2. A restriction enzyme is added to the DNA to cut it into fragments

3. DNA fragments are separated according to size during a process called electrophoresis using an agarose gel

4. An alkali is added to separate the double stranded DNA into single strands

5. Each single strand is transferred to a nylon membrane and a radioactive probe is added to it

6. A banding pattern appears

7. An x-ray film is produced and the positions of black bands are compared with the part of DNA treated with radioactive probe

Formation of pollen grains

Pollen grains are formed in the anther. An anther has 4 pollen sacs. Each pollen sac contains hundreds of cells called pollen mother cells. Each pollen mother cell undergoes meiosis to form 4 haploid microspores. The nucleus of each microspore divides by mitosis to form a tube nucleus and a generative nucleus. 

Pembinaan negara bangsa

Itali

-itali terbahagi kpd bebrapa buah wilayah

-wilayah venetia dan lombardy di utara dikuasai austria

-org itali ingin menyatukan wilayah2 mereka di bwh sebuah pemerintahan dan menghalau orang austria dari bumi itali

-Count camillo benso de cavour berusaha menyatukan itali dgn mengamalkan realpolitik

-Count camillo benso de cavour sgt menyanjung penyatuan itali berlandaskan pemerintahan monarki

-beliau mengadakan kerjasama dgn napolean 3 bg menentang austria

-hasil bantuan tentera napolean 3, itali berjaya mengalahkan austria

-count camillo memperoleh sokong majoriti rakyat utk menyatukan itali melalui pungutan suara

-pd 1966 wilayah venetia dipulangkan kpd itali sbg membalas jasa itali membantu prussia menewaskan austria

-pd 1870 perancis mengundurkan tenteranya dan count camillo mengmbil peluang ini utk menyatukan rom dan itali

-penyatuan ini membentuk negara bangsa itali

Jerman

-otto eduard von bismarck mengamalkan realpolitik dan politik darah dan besi

-Menggunakan pelbagai taktik spt tipu helah, pemalsuan dokumen, provokasi, penipuan dan ugutan utk mencetuskan peperangan 

-matlamatnya untuk menyatukan jerman

-mengamalkan sistem kediktatoran yang diterima oleh rakyat utk menyatukan jerman

-menggunakan isu membenci kuasa asing utk memenangi dan membangkitkan semangat rakyat prussia di medan tempur

-melancarkan tiga peperangan menentang musuhnya

-iaitu denmark, austria dan perancis

Madinah

-pembentukan kerajaan islam di madinah merupakan contoh penyatuan melalui prinsip islam

-Nabi muhammad saw menyusun perlembagaan terlebih dahulu sblum mengasaskan kerajaan madinah

-piagam madinah berjaya menyatukan pelbagai kaum iaitu yahudi, kristian dan arab

-menggunakan cara diplomasi, musyawarah, dan permuafakatan

-baginda berjaya membentuk kerajaan islam yg kuat

-kejayaan ini membuktikan wujudnya kerjasama antara pemimpin dgn pemimpin dan antara pemimpin dgn rakyat

who is the first man who walked in space?

First spacewalk was performed by cosmonaut Alexei A. Leonov in April 1965. He was followed by US astronaut Edward H. White II in June of the same year while flying aboard Gemini 4.
Cosmonaut Alexel Leonov from Voshkod 2
* The first space walk was carried out byAlexey Leonov on March 18 1965. * The first space walk by an American was by Edward White on June 3 1965. * The first moon walk was by Neil Armstrong on July 20th 1969
The first man ever to make a space walk was USSR cosmonaut Alexei Leonov.
Leonov's space walk occurred on 18 March 1965, when he spent 10 minutes outside the space craft Voskhod 2, while his fellow astronaut Pavel Belyayev waited inside.
Soviet/Russian. Alexey Arkhipovich Leonov (Russian: Алексе́й Архи́пович Лео́нов; born May 30, 1934 in Listvyanka, Kemerovo Oblast, Soviet Union) is a retired Soviet/Russian cosmonaut and Air Force General who, on March 18, 1965, became the first person to leave the confines of a pressurized spacecraft to perform what is called a "walk in space" or extravehicular activity (EVA).