Chapter 2- 2.6- Prokaryotic and eukaryotic cells

Prokaryotic- Not present Eukaryotic- Present

Prokaryotic- Circular Eukaryotic- Linear

Prokaryotic- proteins fold and condense DNA Eukaryotic- Associated with proteins called histones

Prokaryotic- Circular DNA called plasmids Eukaryotic- Only present in certain organelles such as chloroplasts and mitochondria

Prokaryotic- Non membrane-bound Eukaryotic- Both membrane-bound and non membrane-bound

Prokaryotic- Peptidoglycan Eukaryotic- Chitin in fungi, cellulose in plants, not present in animals

Prokaryotic- smaller 70S Eukaryotic- larger, 80S

Prokaryotic- Present Eukaryotic- Present, more complex

Prokaryotic- Binary fission Eukaryotic- Asexual or sexual

Prokaryotic- unicellular Eukaryotic- Unicellular and multicellular

Prokaryotic- Present Eukaryotic- Present

Archaea and Bacteria. Which evolved from an ancient common ancestor.

The early cells were adapted to living in extremes of salinity, pH and temperature. These organisms are known as extremophiles and they still exist today. They can be found in hydrothermal cents and salt lakes- similar environments to those believed to have made up the early Earth. They are usually the domain of Archaea and more recently they have been found in more hospitable environments such as soil and the human digestive system.

DNA is not contained within the nucleus. They have few organelles and the organelles are not membrane bound.

They are packaged differently. Prokaryotes generally only have one molecule of DNA, a chromosome, which is supercoiled to make it more compact. The genes on the chromosome are often grouped into operons, meaning a number of genes are switched on or off at the same time.

The ribosomes in prokaryotic cells are smaller than those in eukaryotic cells. Their relative size is determined by the rate at which they settle, or form a sediment, in solution. The larger eukaryotic ribosomes are designated 80S and the smaller prokaryotic ribosomes, 70S. They are both necessary for protein synthesis, although the larger 80S ribosomes are involved in the formation of more complex proteins.

Prokaryotic cells have a cell wall made from peptidoglycan, also known a murein. It is a complex polymer formed from amino acids and sugars.

The flagella of prokaryotes is thinner than the equivalent structure of eukaryotes and does not have the 9+2 arrangement. The energy to rotate the filament that forms the flagellum is supplied from the process of chemiosmosis, not from ATP as in eukaryotic cells. The flagellum is attached to the cell membrane of a bacterium by a basal body and rotated by a molecular motor. The basal body attaches the filament comprising the flagellum to the cell-surface membrane of a bacterium. A molecular motor causes the hook to rotate giving the filament a whip like movement, which propels the cell.

The first eukaryotic cells appeared about 1.5 billion years ago. They are more complex than prokaryotic cells and their DNA is present within the nucleus and exists as multiple chromosomes, which are supercoiled, and each one wraps around a number of proteins called histones, forming a complex for efficient packaging. This complex is called chromatin and chromatin coils and condenses to form chromosomes. Eukaryotic genes are generally switched on and off individually. Eukaryotic cells have membrane-bound organelles including mitochondria and chloroplasts. Organisms from the plant, animal, fungi, and protoctista kingdoms are all composed of eukaryotic cells. Many are multicellular.