Cell Membrane: Definition, Characteristics

Cell

A cell can be described as the functional and structural working unit of life. It has been called a fundamental unit and a building block of an organism. Robert Hooke, an English scientist, coined the term cell in 1665. The functions and compositions of cells can affect the shape and size and dimensions of the cells. Different types of cells can be distinguished based on their presence or absence of certain cell organelles.

Cell membrane

Every cell has a limiting boundary called the cell membrane, plasma membrane, or plasmalemma. It is a living membrane that is located at the outermost of animal cells and within the cell wall of plant cells. It is present in all cells. It separates the inside of the cell from its external environment. Semi-permeable lipid bilayers make up the cell membrane. The cell membrane controls the movement of materials into and out of the cell.

Characteristics

1. All organisms, including plants, contain a cell membrane.
2. The cell membrane is also known by the name plasma membrane.
3. It covers the outside of animal cells but is internal to plant cells’ cell walls.
4. It can be folded in and out and is flexible.
5. Plasma membranes are made up of proteins and lipids.
6. It is a semipermeable membrane, which allows for the transportation of different materials.
7. Hydrophilic and hydrophobic properties are both inherent to the plasma cell membrane.

Some cell membrane functions

1. The cell contents are enclosed by the plasma membrane. It protects the integrity of the inner cell.
2. Supporting and maintaining the cell’s shape.
3. It gives cells their shape, like the red blood cells’ characteristic shape and bone cells.
4. This helps regulate cell growth by balancing endocytosis with exocytosis.
5. Cell membranes play an important role in cell communication and signaling.
6. It allows only certain substances to enter the cell by acting as a selectively permeable barrier.

Endoplasmic Reticulum (ER)

The endoplasmic reticulum is a membrane-bound single structure. The plasma membrane is the same structure as that of the membrane. The endoplasmic reticulum is responsible for the storage and transportation of products. It works in collaboration with golgi and ribosomes.

Structure of the Endoplasmic Reticulum

This is a network made up of membranes with thicknesses around 5 nm. They can be found throughout the cytoplasm, and they are in direct contact with both the cell membrane and the nuclear membrane. There are two types of them:

Rough Endoplasmic Reticulum (RER)

This is where the ribosomes attach, which causes a rough surface appearance. It is also known as the rough endoplasmic retina.

Smooth Endoplasmic Reticulum (SER)

The ER does not have ribosomal attachment. Therefore, it is known as the smooth endoplasmic reticulum.

Function

• The function of the endoplasmic retina is to provide an inner framework, compartment and reaction surfaces.

• It also transports enzymes and other materials through the cell. The rough endoplasmic retina is home to ribosomes responsible for protein synthesis.

• The site of steroid synthesis and storage of carbohydrates is the smooth endoplasmic reticulum.