Unit 4: Introduction to Cells
Cell theory
In the time when microscope had not been invented, people have no idea of what life is composed of. However, with the invention of microscope in the 16th century, people started to observe that all organisms are made up of small box-like structure, and people named those structures ‘cells’. A theory of “all life is made of cells” is thus put forward and this is known as the Cell theory
Today, cell theory remain as one of the pillars of biology and cell became the basic unit of life. Cell is the basic structural, functional, and biological unit of all known living organisms. It is enclosed by the cell membrane and the space enclosed is known as the cytoplasm. There are also multiple small compartment or structure present in the cytoplasm, known as organelles.
However, cells can be classified into two distinct class, namely prokaryotic (without a true nucleus) and eukaryotic cells (with a true nucleus). Prokaryotes are believed to have existed longer than eukaryotes due to their lower complexity, some 3.5 billion years ago.
For eukaryotic cell, there is a visible nuclear membrane that enclose the genetic material (DNA)
Prokaryotic vs Eukaryotic cells
Cell cycle
Just like any life, all cell goes goes through a “life” that is known as cell cycle. Unlike human, cell does not simply die at the end of the cycle. They divide into two daughter cells, which is known as cell division. When the cell is not in cell division, it is known as the interphase.
For every newly “borned” cell, they go through the interphases until they are ready for cell division again.
The table below shows the different phases that the cell will go through in a cell cycle.
Major cellular processes
Replication
As stated in the above table. Details will be discussed in Course 2.
Growth and metabolism
Involves a lot of biochemical pathway that maintains the normal function of the cell. One of the most important processes is respiration.(discussed in course 2) This process provides the cell with energy to carry out all other active processes by breaking down organic food and releasing energy that is originally stored in it. The process is vastly different between the prokaryotes (Anaerobic respiration) and eukaryotes (mainly aerobic respiration)
Protein synthesis
This process is another extremely essential process. Protein is the building block of the cell and most organelles are composed of proteins. It mainly consist of transcription and translation. However, the process is slightly different between prokaryotes and eukaryotes. It will be discussed in depth in Course 2.
Motility
Unicellular organisms (single-celled organisms like bacteria) can move by using flagella and cilia in order to find food or escape predators.
