1. Cell structure and Function
1.7. Cellular Functions
Cellular Functions
Dr V Malathi and Mrs Sushumna Rao
The basic functions of the cell include:
- Movement of substances across cell membrane,
- Cell division
- Protein Synthesis
I.Movement of substances across the cell membrane
The cell maintains a difference in the concentration of material between its exterior and interior . This is very important for the cell survival. The plasma membrane of the cell plays an active role in regulating the concentration of substances between the cell interior and exterior .
The plasma membranes are selectively permeable i.e., they allow some substances to pass through, but not others.
The main mechanisms of movement across cell membrane include:
Passive transport : is a naturally occurring phenomenon . The cell does not require energy to accomplish this movement. In this mode of transport substances move from an area of higher concentration to an area of lower concentration. A physical space in which there is a range of concentrations of a single substance is said to have a concentration gradient.
Diffusion : Nonpolar molecules, such as Oxygen, Carbon dioxide and Nitrogen
can move across the membrane from a higher concentration region to a lower concentration region through the process of diffusion. Diffusion does not require energy and hence this is called passive transport.
“Simple Diffusion across Plasma membrane” is licensed under CC BY 3.0
Facilitated diffusion : In this type of movement membrane proteins helps in the transport of materials across plasma membrane . The existing concentration gradient exists allow these materials to diffuse into the cell without expending cellular energy. However, these materials are ions or polar molecules and hence are repelled by the hydrophobic parts of the cell membrane. Facilitated diffusion proteins called transport proteins , shield these materials from the repulsive force of the membrane and helps them to diffuse into the cell. The transport proteins and can be channels or carrier proteins.
Channel proteins : These are transmembrane proteins. These proteins fold forming a channel or pore through the membrane specific for one particular substance. These proteins have hydrophilic domains exposed to the intracellular and extracellular fluids and also have a hydrophilic channel through their core that provides a hydrophilic opening through the membrane layers. Polar compounds can easily pass through the channel avoiding the nonpolar central layer of the plasma membrane that would otherwise slow or prevent their entry into the cell. are channel proteins that allow water to pass through the membrane at a very high rate.
“Facilitated transport” by Mariana Ruiz Villareal (modified ) is licensed under CC BY-NC 4.0
Carrier Proteins : Like channels, carrier proteins are trans membrane proteins, usually specific for particular molecules. These bind a substance and, in the process, trigger a change of its own shape, moving t