The Structure and Function of Plasma membrane and Cell Wall

The Structure and Function of the
PLASMA MEMBRANE & CELL WALL
INTRODUCTION
Cellular Organization
Every human cell has a plasma membrane, a nucleus, and cytoplasm. (Some exceptions to this rule exist. A mature erythrocyte, or red blood cell, eliminates its nucleus once development is complete. Thus, erythrocytes are a nucleate. Cells of skeletal muscle, liver, and other tissues may have up to 50 nuclei and are multinucleate.).
The major components of the cell are:
Cell Membrane (Plasma Membrane), Cytoplasm, Nucleus and Organelles.
The Cell Membrane (Plasma Membrane), which surrounds the cell and keeps it intact, regulates what enters and exits a cell. The plasma membrane is a phospholipid bilayer that is said to be semipermeable because it allows certain molecules but not others to enter the cell. Proteins present in the plasma membrane play important roles in allowing substances to enter the cell.
The Nucleus is a large, centrally located structure that can often be seen with a light microscope. The nucleus contains the chromosomes and is the control center of the cell. It controls the metabolic functioning and structural characteristics of the cell.
The Nucleolus is a region inside the nucleus. The Cytoplasm is the portion of the cell between the nucleus and the plasma membrane. Cytoplasm is a gelatinous, semifluid medium that contains water and various types of molecules suspended or dissolved in the medium. The presence of proteins accounts for the semifluid nature of cytoplasm.
The cytoplasm contains various Organelles (Table 1). Organelles are small, usually membranous structures that are best seen with an electron microscope. Each type of organelle has a specific function. For example, one type of organelle transports substances, and another type produces ATP for the cell. Organelles compartmentalize the cell, keeping the various cellular activities separated from one another. Just as the rooms in your house have particular pieces of furniture that serve a particular purpose, organelles have a structure that suits their function. Cells also have a Cytoskeleton, a network of interconnected filaments and microtubules in the cytoplasm. The name cytoskeleton is convenient in that it allows us to compare the cytoskeleton to our bones and muscles. Bones and muscles give us structure and produce movement. Similarly, the elements of the cytoskeleton maintain cell shape and allow the cell and its contents to move. Some cells move by using cilia and flagella, which are made up of microtubules.