Key Features of Living Things
Water
Carbon
Splitting and reforming water molecules
Electron transport chains
Cells and Membranes
=> DNA and RNA - reproduction and heredity
DNA and RNA - Reproduction and Heredity
The final critical element of life - Genetic Material - RNA and DNA
DNA: Deoxyribonucleic acid.
The "thread of life", is deoxyribonucleic acid, otherwise known as DNA. It is the spiral
shaped molecule found in the nucleus of cells.
Scientists have known since 1952 that DNA is the basic substance of heredity.
This was hypothesized, and later confirmed by James D. Watson and Francis Crick.
They also know that it acts like a biological computer program over 3 billion bits
long that "spells" out instructions for making the basic building blocks of life.
DNA carries the bodies genetic code, controls the development of an embryo, is capable of
duplicating itself, and is able to repair damage to itself. DNA can be manipulated to change all kinds of things. It stays in the cell nucleus.
RNA: Ribonucleic acid
Single-stranded messenger RNA carries single pages of instructions out of the nucleus
to places they're needed throughout the cell. There is no error detection or repair; it makes flawed copies of itself. It evolves ten times faster
than DNA. Transfer RNA helps translate the mRNA message into chains of amino acids in the
ribosomes.
Every cell is bounded by its own outer membrane and contains a full set of instructions
necessary for its operation and reproduction. Furthermore, every cell uses the same operating system: "DNA makes RNA makes protein."
DNA is a long complex molecule that contains all the cell's instructions. It is transcribed into RNA, another long complex molecule similar to DNA;
and then the RNA transcript is translated into protein. There are hundreds of billions of different proteins used by living things, but all of
them are made from the same twenty amino acids, the "building blocks of life."
Another kind of life, entirely different from ours, is conceivable. But the only kind we have ever seen is the one we are part of here on Earth.
The only life we know for certain is cellular life using life's DNA -->RNA -->protein
operating system.
Viruses and prions lie on the fringe of life. Viruses contain instructions encoded in
DNA or RNA. (Prions don't.)
Both are reproduced. Viruses certainly and prions probably can evolve.
But neither can reproduce itself; a virus or prion needs the machinery of a living cell
to carry out its reproduction.
Without a cell, each is merely an inert, complicated particle which does nothing.
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