biology notes
The lack of a nucleus and membrane-bound organelles
one way in which prokaryotes differ from the cells of all multicell organisms, called eukaryotes. The DNA of prokaryotes is also organized differently from that of eukaryotes. In prokaryotes, DNA usually exists as a looped molecule. Prokaryotes have neither a nucleus nor organelles.
Prokaryotes and eukaryotes differ at the cellular level.
A glance through a microscope should be enough to help you determine whether an organism is a prokaryote or a eukaryote. As you know, prokaryotes don't have a nucleus or membrane-bound organelles, while eukaryotes do.
Many human diseases are caused by some types of bacteria.
If you've ever had strep throat or tonsillitis, you've had a bacterial infection. Tooth decay and many forms of food poisoning also are caused by bacteria. Disease-causing, or pathogenic, bacteria are actually only a minority of all the bacteria on earth.
The earliest life-forms on earth were prokaryotic cells.
In 1993, a geologist named William Schopf made a discovery of fossilized cylinder-shaped rock formations in the Western Australia. Schopf determined that the rocks were 3.5 billion years old, and that they contained carbon compounds-a sign that those objects were at one time living organisms. Most scientists today consider these rock deposits, called stromatolites, the oldest evidence of life on earth.
Conclusion: All life on earth is either prokaryotic or eukaryotic.
Life on earth is divided into two broad categories based on the types of cells an organism is composed of. Prokaryotes are single-cell organisms that lack a nucleus and membrane-bound organelles such as mitochondria. Eukaryotes can be unicellular or multicellular, and are made of cells that contain a nucleus and membrane-bound organelles.
organelle DNA shares many more traits with bacterial DNA than with the eukaryotic DNA found in the nucleus. Both lines of evidence suggest that those organelles did indeed have a prokaryotic ancestor.
Lynn Margulis theorized that organelles were originally independent prokaryotic cells.
Most scientists suggest that eukaryotes arose from prokaryotes.
Most scientists suggest that eukaryotes arose from prokaryotes. More than 30 years ago, biologist Lynn Margulis championed the idea that organelles originated as independent prokaryotic cells and were engulfed by other prokaryotic cells.
There is a difference with multicellular organisms.
Multicell organisms, however, also contain specialized cells that may function together as tissues and organs. Muscle cells, for example, are specialized for movement, and are arranged together into muscle tissue. Specialized cells, tissues, and organs form some of the levels of biological organization characteristic of multicell life.
Eukaryotes are organisms made of cells with a nucleus and membrane-bound organelles.
One of the most fundamental divisions of life on earth is the division between prokaryotes and eukaryotes. Eukaryotes are organisms that have eukaryotic cells, or cells that contain a nucleus and membrane-bound organelles, such as mitochondria, chloroplasts, Golgi bodies, and lysosomes. The nucleus in eukaryotes contains the genetic material DNA.
Without bacteria, life on the planet would be very different. Many types of bacteria carry out photosynthesis and play important roles in producing atmospheric oxygen.
Others recycle nutrients. Still others are key components of industries like food processing, pharmaceuticals, and genetic engineering. Bacteria live inside the bodies of nearly every organism on earth. In fact, your own digestive tract contains trillions of bacteria that help you digest food.
According to that idea, called the endosymbiotic theory, one prokaryotic cell may have engulfed another, forming a union in which both cells worked cooperatively together.
Over millions of years, that kind of partnership may have evolved, producing the eukaryotic cells we see today. The mitochondria and chloroplasts in today's eukaryotes have their ancestry in prokaryotic cells millions of years ago. Both mitochondria and chloroplasts contain their own DNA, which is separate from the DNA in the cell's nucleus.
Prokaryotes are single-cell organisms.
Prokaryotes are amazingly diverse, but they are all single-cell organisms. Despite having neither a nucleus nor membrane-bound organelles such as mitochondria, prokaryotes still carry out all of the functions of life-growth and development, reproduction, heredity, homeostasis, metabolism, response, and cellular organization
Bacteria are the most abundant organisms on earth.
Prokaryotes are divided into two broad categories of life called domains. One of these domains contains unusual forms of life called archaeans. The other includes all of the bacteria on earth.
Archaeans share several unusual characteristics
Scientists didn't recognize archaeans as an entirely different category of life until about 30 years ago. Before then, scientists classified them as bacteria. Improvements in genetic techniques enabled scientists to discover that archaeans are about as different from bacteria as human beings are.
Modern-Day Stromatolites
Stromatolites form in warm, salty waters, such as those off the coast of Australia and in the Caribbean. Scientists continue to study these modern-day successors to the 3.5-billion-year-old fossils that Schopf discovered.
Some eukaryotes are single-cell organisms.
Yeast is just one example of a single-cell eukaryotic organism. Unlike people, plants, or insects, single-cell eukaryotes do not have specialized cells and tissues. They carry out all of the functions of life inside their single cell. Other single-cell eukaryotes include the amoeba, the paramecium, and a tiny photosynthetic organism called a diatom.
The eukaryotes you see every day are multicellular
each organism is made of trillions of cells. All of those cells share the characteristics of eukaryotic cells: They all contain genetic material inside a nucleus, and they all have membrane-bound organelles.