[Heronumber0]

I sometimes wonder about this.  The nucleus contains all the DNA and has genes for maintaining the cell, producing enzymes to keep the cell metabolically 'ticking over'.

However, the cell membrane is SO important...! It controls all of the good things that need to get in the cell like sugars, wraps up in a bubble all the nasty things like bacteria and sends them to get wasted by lysosomes (waste disposal membrane bubbles with enzymes inside) and has receptors for hormones and other chemicals to be selectively allowed into the cell. It also measures just the correct amount of substances entering or leaving the cell.

In my book, the cell membrane is just as important as the nucleus, yet the nucleus gets all the credit. Anyone disagree?

[kdlynn]

i've always considered the membrane like our skin. our skin keeps things in and out as well, but it does not control us the same way our brain does. so, i think the nucleus is the brain.

[Heronumber0]

i've always considered the membrane like our skin. our skin keeps things in and out as well, but it does not control us the same way our brain does. so, i think the nucleus is the brain.

Oh...it is so much more than a passive skin around a cell kdlynn. Membranes are an amazingly dynamic structure which resemble either  computer or a sophisticated, state-of-the-art warehouse depending on your perspective. They have fine tuning of molecules received or expelled that is amazing in its complexity.

[another_someone]

The problem is with your analogy with a brain.  You can certainly say that the cells membrane is as important to the cell as its nucleus - but that is like saying that the human skin is as important to the human as the human brain (humans will not survive long without either or them), but that is not the same as saying that the skin is the brain.  The skin is the skin, and the brain is the brain - although both are important.

[Heronumber0]

I agree that we cannot use the brain analogy for the nucleus. I think what I am trying to say is that the membrane does things which are equal to the nucleus in the control of the cell's interior milieu. For example, preteins in the outer membrane can react to the concentrations of organic compounds or ions outside. The membrane receptors have to respond to temperature in the brain or pressure in the case of the skin.  The nucleus also responds to outside stresses by changing the nature of the proteins that it allows to be manufactured from internal cell membranes (the Rough Endoplasmic Reticulum) these proteins are then transported to parts of the cell by membranous delivery vans (membrane vesicles). Membranes seem to perform more metabolic tasks in the cell than the nucleus.

[Heronumber0]

I have just found a lovely link to show how important mambrane vesicles and microtubules are in exocytosis (export from the cell) of important extracellular materials.
http://www.youtube.com/watch?v=mUUZuirJTkY

[Carol-A]

It's not so much the membrane as the proteins that reside in the membranes.... but of course these are coded for by the DNA in the nucleus (and in the mitochondria and chloroplasts!)

[dkv]

Strange question. Brain is made of cells.
Therefore collection of cells can be identified as brain. The brain of the dnosaurs t-rex was of the size of nut.
When talking about single cell .. I wonder how one can define brain?

[another_someone]

Strange question. Brain is made of cells.
Therefore collection of cells can be identified as brain. The brain of the dnosaurs t-rex was of the size of nut.
When talking about single cell .. I wonder how one can define brain?

The question pertained to the function of the brain rather than its physiology.

Ofcourse it still difficult to draw analogies between the functions of two very different organisms (a full sized animal, or a single cell), but nobody assumed the question was asking if the cell has a multicellular brain within it.

With regard to the brain size of a dinosaur, you are ofcourse talking about the stegosaurus (even there, there has been speculation that the stegosaurus may have had a second brain elsewhere in its body, but that theory is no longer the preferred theory).  Other dinosours had much larger brains.

http://dinodatabase.com/gloss/DNOGLOSD.asp

Not all dinosaurs had minuscule brains. In relation to their body mass, ceratopsians had relatively large brains, as did such theropods as the dromaeosaurids. Dromaeosaurids, in fact, are considered to be the smartest of dinosaurs, and they were probably at least as intelligent as the Emu (a modern, ostrich-like bird).

As for the size of the brain of a T.Rex:

http://www.enchantedlearning.com/subjects/dinosaurs/dinos/trex/Trexintell.shtml

T. rex was a relatively smart dinosaur. Although the ratio of brain size to body mass was very small for T. rex, it was larger than most other dinosaurs. T. rex's brain was larger than the human brain, but the cerebrum (the part of the brain that we use to think) was tiny. T. rex's brain was long and almost cylindrical in shape.

Only very advanced theropods, like the dromaeosaurid dinosaurs (for example, Deinonychus and Velociraptor), were probably smarter than T. rex.

T. rex probably ranked close to the carnosaurs in intelligence.