The ovum contains a small collection of cells in the early stages of human development.
As cells divide (A–D), they are separated into different regions of the ovum.
Each region of the ovum transmits a unique set of chemical signals to nearby cells.
Thus, the signals detected by one cell differ from those detected by its neighbour cells.
The orderly development of an organism depends on a process called cell determination, in which initially identical cells become committed to different pathways of development.
A fundamental part of cell determination is the ability of cells to detect different chemicals within different regions of the embryo.
Careful studies of these and other cell types have shown that all membranes are composed of proteins and fatty-acid-based mitochondrion, the most rapidly metabolizing organelle of the cell, contains as much as 75 percent protein, while the membrane of the Schwann cell, which forms an insulating sheath around many nerve cells, has as little as 20 percent protein.
A synopsis of the curriculum The module begins by overviewing the diverse mechanisms used by cells to communicate, considering the main modes of cell-cell communication, the major classes of signalling molecules and the receptor types upon which they act.
Outside the cell, in the surrounding water-based environment, are ions, acids, and alkalis that are toxic to the cell, as well as nutrients that the cell must absorb in order to live and grow.
The cell membrane, therefore, has two functions: first, to be a barrier keeping the constituents of the cell in and unwanted substances out and, second, to be a gate allowing transport into the cell of essential nutrients and movement from the cell of waste products. Extrinsic proteins are loosely bound to the hydrophilic (polar) surfaces, which face the watery medium both inside and outside the cell.