-
Is Any Form of Life Really Simple?The Origin of Life—Five Questions Worth Asking
-
-
A cell spends a lot of its time making proteins. How does it do so? First, you would see the cell make about 20 different basic building blocks called amino acids. These building blocks are delivered to the ribosomes (5), which may be likened to automated machines that link the amino acids in a precise order to form a specific protein. Just as the operations of a factory might be governed by a central computer program, many of the functions of a cell are governed by a “computer program,” or code, known as DNA (6). From the DNA, the ribosome receives a copy of detailed instructions that tell it which protein to build and how to build it (7).
What happens as the protein is made is nothing short of amazing! Each one folds into a unique three-dimensional shape (8). It is this shape that determines the specialized job that the protein will do.b Picture a production line where engine parts are being assembled. Each part needs to be precisely constructed if the engine is to work. Similarly, if a protein is not precisely constructed and folded to exactly the right shape, it will not be able to do its work properly and may even damage the cell.
The Cell “Factory”—How Proteins Are Made: Like an automated factory, the cell is full of machines that assemble and deliver complex products
How does the protein find its way from where it was made to where it is needed? Each protein the cell makes has a built-in “address tag” that ensures that the protein will be delivered to where it is needed. Although thousands of proteins are built and delivered each minute, each one arrives at the correct destination.
Why do these facts matter? The complex molecules in the simplest living thing cannot reproduce alone. Outside the cell, they break down. Inside the cell, they cannot reproduce without the help of other complex molecules. For example, enzymes are needed to produce a special energy molecule called adenosine triphosphate (ATP), but energy from ATP is needed to produce enzymes. Similarly, DNA (section 3 discusses this molecule) is required to make enzymes, but enzymes are required to make DNA. Also, other proteins can be made only by a cell, but a cell can be made only with proteins.c
-
-
Is Any Form of Life Really Simple?The Origin of Life—Five Questions Worth Asking
-
-
b Enzymes are one example of proteins made by cells. Each enzyme is folded in a special way to accelerate a particular chemical reaction. Hundreds of enzymes cooperate to regulate the cell’s activities.
-