Re: In what part of a animal cell gives it it's shape and size?

Hi Carmen,

         Don't worry if you don't get this bit of cell biology, its the 
most boring bit and I remember I always forgot all about the thing which 
gave the cell its shape.

         So lets get down to buisness! So... in the cytoplasm of a cell 
there is a network of protein fibers called the cytoskeleton. This is made 
up of three major types of protein fibers, which are;
         - the microfilaments
         - the intermediate filaments
         - the microtubules.


As you may have guessed, these three are different from each other due to 
a difference in size. The microfilaments are the smallest, the 
intermediate filaments are of intermediate size and the microtubules are 
the thicker of the group. This network of protien fibers stretch along the 
inside walls of the cell, so it gives it its shape. All three types of 
protein fibers contribute to the shape of the cell however the most 
important type of the three are the intermediate filaments. ( however the 
other two musn't be ignored ). 

         The size of the cell is also determined by the cytoskeleton. As 
the protein fibers lenghten and increase in size, the whole cytoskeleton 
increases in size, therefore the size of the cell increases.

         Now let me feed you with some extra details of the cytosketeton, 
like that you'll get a better picture of what the cytoskeleton is all 
about and also you may understand better how it determins the shape and 
size of the cell. So... organells do not drifrt about the cytoplasm 
haphazardly, most are attached to the cytoskeleton. Even individual 
enzymes, which are often parts of complex metabolic pathways, may be 
fastened in sequence to the cytoskeleton, so that molecules can be passed 
from one enzyme to the next.

         Also, in cells without cellwall, the cytoskeleton, especially 
networks of intermediate filaments, determines the shape of the cell.

         Cell movement. The assembly, dissasembly, and sliding of 
microfilaments and microtubules cause cell movement. Cell movement 
includes both the 'crawling' of white blood cells, the contraction of 
muscle cells, and the migration and shape changes that occuir during the 
development of multicellular organisms.

         Organelle movement. Microtubules and microfilaments move 
organelles from place to place within a cell. For example, microfilaments 
attach to vesicles formed during endocytosis, when large particles are 
engulfed by the plasma membrane and pull the vesicals into the cell. 
Vesicals budded off the endoplasmic reticulum and Golgi Apparatus are 
probably guided by the cytoplasm as well.

         Cell division. Microtubules and microfilaments are essential to 
cell division in eukaryotic cells. First, when eukaryotic nuclei divide, 
microtubules move the chromosomes into the daughter nuclei. Second, in 
animal cells, division of the cytoplasm of a single parent cell into two 
new daughter cells results from the contraction of a ring of 
microfilaments that pinch the 'waist' of the parent cell around the 
middle. 


So.. I hope you got an idea of what gives the shape and size of an animal 
cell. Good luck with your studies

Kristen 
kristen@maltanet.net