François Jacob (17 June 1920 – 19 April 2013) was a French biologist. He shared the 1965 Nobel Prize in Physiology or Medicine with Jacques Monod and André Lwoff.
Jacob and Monod discovered a fundamental control system in cells. Enzyme levels in all cells is regulated by feedback on transcription.
Like his colleague Monod, Jacob was an almost lifelong atheist. He was also of Jewish descent.
In 1961 Jacob and Monod explored the idea that the control of enzyme expression levels in cells is a result of feedback on the transcription of DNA sequences.
For many years it had been known that bacterial and other cells could respond to external conditions by regulating levels of their key metabolic enzymes, and/or the activity of these enzymes.
For instance, if a bacterium finds itself in a broth containing lactose, rather than the simpler sugar glucose, it must adapt itself to:
It was known that cells increase the enzymes for these steps when exposed to lactose.
With work on DNA, it became clear that all proteins were being produced from their genetic code. Jacob and Monod demonstrated that, in the bacterium "E. coli"), there are specific proteins that repress the transcription of the DNA to its product (RNA. This reduces the production of those particular enzymes.
The lac repressor is a DNA-binding protein which inhibits the expression of genes which code for lactase enzymes. The repressor is active in the absence of lactose.
This repressor (the lac repressor) is made in all cells. It binds directly to DNA at the genes it controls, and physically prevents transcription. When lactose becomes available, it is converted into allolactose, which inhibits the lac repressor's DNA binding ability.
In this way, a robust feedback loop is constructed that allows the set of lactose-digesting enzymes to be made only when they are needed.
The regulation of gene activity has developed into a very large sub-discipline of molecular biology. There are many mechanisms and many levels of complexity. Current researchers find regulatory events at every level of the processes that express genetic information. In the relatively simple genome of baker's yeast, ("Saccharomyces cerevisiae"), 405 of its 6,419 protein-encoding genes are directly involved in transcriptional control, compared to 1,938 that are enzymes.
Abbey Dawn
Abbey Dawn is a clothing line designed by musician Avril Lavigne. It was designed only for Kohl's in the US. The name is from Lavigne's childhood. Her father had nicknamed her "Abbey Dawn", and her high school friends would often call her "Abbey".
Abbey Dawn is featured in Lavigne's 2011 single, "What the Hell". There, the latter enters a vintage clothing store.
Eimear
Emer, in modern Irish Éimhear, or, Eimhear or Éimear, is the wife of the hero Cú Chulainn in Irish mythology. She is the daughter of Forgall Monach.
Emer was a very common name for girls around the Midlands of Ireland. The name means that she has the "Six Gifts of Womanhood" – "beauty, a gentle voice, sweet words, wisdom, needlework and chastity".
As a child, She was to one day be married to the warrior Cuchulainn. They loved each other very much. But Cuchulainn was attracted to many women. Emer accepted this. She believed that "everything new is fair." But, when he made love to Fand, wife of the sea god Manannan, Emer had to say something. After seeing how much Fand love him, Emer said she would leave him and let them be together. Fand felt this showed that Emer thought more of others than she did of herself. Fand left Cuchulainn to be with Emer and went back to the sea. When Cuchulainn died, Emer spoke lovingly at his graveside.
Capital Dynamos
Capital Dynamos is the internal hockey team for the Islamabad Capital Territory in Pakistan. It is part of the Pakistan Hockey Federation.
Northern Cavaliers
Northern Cavaliers is a field hockey team for the Gilgit–Baltistan in Pakistan. They are part of the Pakistan Hockey Federation.
Precocial
Precocial in biology is a developmental strategy. It refers to species in which the young are relatively mature and mobile from the moment of birth or hatching. It applies mainly to mammals and birds.
The opposite developmental strategy is called altricial, where the young are born or hatched helpless. These two categories are at ends of a continuum. All degrees exist in birds and mammals. With the tiny eggs of invertebrates, different strategies have evolved. Many use some kind of metamorphosis, in which different stages of growth occupy different environmental niches.
A checklist is used to score a species between precocial and altricial. In each case, 'yes' means precocial:
The contrast between the two extremes is seen most clearly in birds. Precocial species leave the nest shortly after birth or hatching. Megapodes are a family of birds found in Australasia. Their eggs are not incubated by the parents. They are buried in compost, covered with sand and left, though the males test the temperature of the heap and make small adjustments. The eggs, which have a large yolk, hatch with full wing feathers. The hatchlings can run and purse prey, and many species can fly on their first day. These birds are super-precocial.
At the other extreme are the most intelligent birds: the passerines (the dominant group of birds, including crows) and hawks, owls and parrots.
Mammals never feed themselves at first. Mother's milk is part of the 'contract' a mammal inherits. But there is a big difference between some new-born deer and antelopes, which can run within an hour or so of birth, and a baby marsupial which is in the pouch for days or weeks.
Of advanced mammals, human beings have a long period before they are independent. This is partly because their brains have to grow and mature after birth, and partly because humans depend more on learning and less on inherited behaviour compared to other mammals. Mammalian carnivores take a long time to perfect their prey-catching skills, and some herd species like elephants also have to do a lot of learning.
Most accounts of the altricial/precocial differences point out that it is a trade-off. Altricial young require a great investment of parental time and care, and are in constant danger of predation. However, that system permits a long period of supervised learning. Also, their brains grow more after birth, fueled by rich food provided by parents.
Precocial young require more pre-birth preparation for larger eggs, but they are less open to predation and take less parental care after birth. Their brains are ready-to-go, but end up smaller in relation to body size.
Humans are rather a special case, for a baby makes great demands on the parent both before and after birth. With its hair, blue eyes, and large head, a baby looks precocial. But few of the bits are working, and a baby is completely helpless on its own. The key fact is that the cerebral cortex is not yet working properly. Nerve growth is still going on. During the first 18 months the cortex is getting larger and getting into working order. Then, after about 18 months to two years, the infant starts to learn language and from then on there's no stopping them.
There is an interesting reason why the brain is not more advanced at birth. It is that the baby's head (during natural birth) has to get through the female birth canal, which is a space between the bones of the female pelvis. Any larger, and the baby's head would not get through.
There is a cost to the human method. It greatly reduces the average number of offspring that any couple can raise.
Jaclyn Linetsky
Jaclyn Linetsky (January 8, 1986 – September 8, 2003) was a Canadian teenage actress who has voiced many different people. She was best known for voicing Caillou in the animated television show between 2000–2003. She later played as Megan in the television show "15/love". She died in a car crash on September 8, 2003 at the age of 17.
Judith Barsi