The Cell Theory, Structure, Function and Types

The discovery of the cell and its cellular component can be attributed to the observations and contributions of 5 major scientist which are;

• Robert Hooke: In 1665, using a high-powered magnifying lens observed dried wine cork tissues and saw small compartment which he called cells. He published his diagrams in his scientific journal called Micrographia.
• Anton Van Leeuwenhoek: In 1674, a Dutch draper who built the first light microscope and used it to observe bacteria cells (pond scum) and blood cells, He observed the cells moving and called it “Animalcules”.
• Mathais Schleiden (Botanist): He was a German botanist. In 1838, he observed plant tissues and saw cells similar to Robert Hooke diagrams.
• Theodore Schwann (Zoologist): He observed animal tissues and saw similar cells as described by Leeuwenhoek.
• Rudolf Virchow (German Physician 1855): He observed cells during division and said that all cells comes from pre-existing cells.

The conclusions of these scientist were remodeled into what is currently known as the “Modern Day Cell Theory”.

MODERN DAY CELL THEORY

The five points of the cell theory are:  

• Cell is the basic fundamental unit of life
•   All living organisms are made up of cells
• There is no life apart from that within a cell
•   All cells come from pre-existing cells
• All cells contain genetic materials which are transferred from parents to off springs

CELL STRUCTURE AND FUNCTION

Cell Wall

It is the rigid external covering found in fungi, bacteria and plant cells. It is made up of complex polysaccharides and proteins and it is responsible for the rigidity cell shape and protection from environmental damage. The cell wall is usually porous (It has holes) and it can freely allow materials move in and out of the cell.

Another name for the cell wall is Plasmodesmata (the name plasmodesmata is used for plant cell wall)

N.B.: Only three organisms have cell wall and they are;

Organism	Type of cell wall
Plant	Cellulose
Bacteria	Peptidoglycan
Fungi	Chitin

Cell Membrane

 This is a lipid bi layer which surrounds all living cell. It is made up of two layers of lipid embedded with proteins. The cell wall can also be called the fluid mosaic model.

The lipids between the membrane are called phospholipids and they are amphipathic molecules (having a head and a tail). The phospholipids have a phosphate head and two fatty acid tail. The phosphate head is polar and hydrophilic (water loving) while the fatty acid tails is non polar and hydrophobic.

The protein within the cell membrane are of three types:

•  Integral/Intrinsic Protein: These are proteins found within the cell membrane.
• Peripheral/Extrinsic Protein: These are proteins found on the surface of the cell membrane.
• Transmembrane Protein: These are proteins found across the length of the cell membrane.

Functions of the cell membrane

• Selective Permeability and movement of materials in and out of the cell
•   It helps to maintain cell integrity
•  It maintains cell action potential
•  It aids in cell to cell signaling
• It prevents the content of the cell from interacting with the external environment

Note:

The cell membrane can also be called plasmalemma (for plant cell), cytoplasmic membrane (for bacteria cell) and neurilemma (for nerve cell)

Special pores in cell membranes that allow water to pass through are called Aqua Porins.

Nucleus

It is the most conspicuous organelle in a eukaryotic cell, it is doubled membrane found at the center in animal cells but at the side in plant cell. It contains genetic DNA and RNA and its major function are regulating all cellular activities and control the transfer of characters from one generation to another (Reproduction)

Mitochondrion

This is a double membrane organelle. It is the site of energy production and oxidative phosphorylation. It is responsible for the core reaction in respiration such as Krebs cycle and electron transport chain.

Ribosome

This is the site for protein synthesis and there are two types of ribosome based on their position;

•  Free Ribosome: These ribosomes are not attached to any surface and they synthesize proteins for use within the cell.
• Bound Ribosome: These ribosomes are attached to the endoplasmic reticulum and they synthesize proteins for use outside the cell.

NOTE:

Suerdberg is a unit of sedimentation co-efficient.

The combination of 60s and 40s makes 80s ribosomes in eukaryotic cells.

 The combination of 30s and 30s makes 70s ribosomes in prokaryotic cells.

(It should be noted that the following above isn’t addition)