Cell Structures - AP Biology

Prokaryotes do not have membrane-bound organelles, such as mitochondria or an endoplasmic reticulum.

Flagella are hair-like structures that allow the cell to move, and are present in both prokaryotes and eukaryotes. Although prokaryotes don't have multiple chromosomes like eukaryotes, they do still have DNA in the form of a cyclic chromosome. Ribosomes are not bound by a membrane, and are essential to the process of translation, which creates proteins in the cell. Prokaryotes and eukaryotes possess ribosomes in order to form functional proteins.

Prokaryotes, such as bacteria, do not contain membrane-bound organelles such as the nucleus, mitochondria, and chloroplasts that we might find in a eukaryotic cell. Since we know the electron transport chain (ETC) is important in providing cellular energy, prokaryotes must still perform some form of this process. The complexes of the ETC are found in the actual cellular membrane that separates the cell from the environment in prokaryotes, while they are found in the inner mitochondrial membrane in eukaryotes. Eukaryotes are then able to generate a proton gradient between the two mitochondrial membranes within the intermembrane space, while prokaryotes can generate a gradient between the cell membrane and cell wall.

Prokaryotes do not have membrane-bound organelles, so they would not have mitochondria.

Cell walls and plasma membranes are found in both bacteria (prokaryotes) and plants (eukaryotes). Ribosomes are not bound by a membrane, and are mainly composed of rRNA; they are used for protein synthesis in both prokaryotes and eukaryotes.

In general, prokaryotic cells are smaller and less complex than eukaryotic cells. They lack membrane-bound organelles (such as mitochondria) and contain a nucleoid region instead of a membrane-bound nucleus. They do have ribosomes, but those are small (70S) and composed of one 30S and one 50S subunit. Only eukaryotic ribosomes are 80S. Finally, both prokaryotes and eukaryotes are encased in cell membranes.

One difference between prokaryotic and eukaryotic cells is the organization and storage of genetic material. Both use DNA in the double-helix structure. In eukaryotes, this DNA is stored as chromatin or chromosomes within the nucleus, but in prokaryotes it is stored in a circular bundle known as the nucleoid in the cytoplasm.

When comparing prokaryotes to eukaryotes, the main fact to remember is that prokaryotes do not contain membrane-bound organelles. This means they have no mitochondria, Golgi apparatus, or endoplasmic reticulum. They also lack a membrane-bound nucleus, although they do have genetic material located in a nucleoid region. Prokaryotic cells are surrounded by a plasma membrane, and some types of bacteria have cell walls as well.

Prokaryotic cells differ from eukaryotic cells in that they lack any membrane-bound organelles, including a nucleus. Instead, prokaryotic cells simply have an outer plasma membrane, DNA nucleoid structure, and ribosomes.

Rough endoplasmic reticulum, peroxisomes, and mitochondria are all bound by their own plasma membranes, and are only found in eukaryotic cells. Centrioles are a component of the cytoskeleton of eukaryotic cells, but are not found in prokaryotes.

The organism is likely a prokaryotic organism, since it lacks a nuclear membrane and mitochondria. Prokaryotes lack all membrane-bound organelles, including nuclei, mitochondria, endoplasmic reticulum, chloroplasts, and lysosomes.

Both prokaryotes and eukaryotes contain ribosomes. Ribosomes are not membrane-bound, and are primarily composed of rRNA. Prokaryotes require ribosomes in order to synthesize proteins.

Cilia are composed of microtubules. While many prokaryotes have cilia, we cannot draw any conclusions without knowing more about the identity of the organism.

Prokaryotic cells are simple cells that lack membrane-bound nuclei and complex organelles. Endoplasmic reticulum, microtubules, and the Golgi apparatus are unique to eukaryotic cells, and will not be found in prokaryotes. Prokaryotes do, however, contain ribosomes, though smaller than the ribosomes in eukaryotic cells. Prokaryotes and eukaryotes are both capable of the main processes of the central dogma: DNA replication, transcription, and translation. For this to be possible, prokaryotes must contain DNA, transcription proteins, RNA, and ribosomes.

To compare each trait, consider a bacterium as an example of a prokaryote and a plant or animal cell as an example of a eukaryote.

I. Contains membrane-bound organelles—membrane-bound organelles are a defining characteristic of eukaryotes, and are not found in prokaryotes.

II. Undergoes glycolysis—glycolysis is used by both prokaryotes and eukaryotes as a part of cellular respiration

III. Contains ribosomes—ribosomes are responsible for protein synthesis. All living cells must be capable of synthesizing proteins in order to function.

IV. Has a cell wall—cell walls are not found in animal cells, but are present in plant cells and bacteria.

Glycolysis, ribosomes, and cell walls can be found in both eukaryotic and prokaryotic cells.

Unlike eukaryotes, prokaryotes have no membrane-bound organelles. This means that they lack a nucleus, mitochondria, and other advanced cell structures.

All cells rely on protein components in order to function. Protein synthesis takes place on ribosomes, which can be found in all cell types. In prokaryotes, ribosomes are free floating the cytoplasm; in eukaryotes, ribosomes can be free floating in the cytoplasm, bound to the rough endoplasmic reticulum, in mitochondria, or in chloroplasts.

Eukaryotic DNA is separated from the rest of the cell in the nucleus, which is surrounded by a nuclear membrane. Bacteria and archaea are both prokaryotes, and thus do not have any membrane-bound organelles. Note that all cells have ribosomes, since they are not membrane-bound.

Protists consist of single celled eukaryotes and a few closely related multicellular organisms. Plantae contain multicellular eukaryotic organisms. Archaea and Bacteria are all prokaryotic. Examples of a single-celled eukaryotic protist are species of the genus Plasmodium, which cause malaria.

Nucleoids are found in prokaryotic cells. The nucleoid is the area of a cell that contains the DNA, and unlike the nucleus of eukaryotic cells, the nucleoid lacks a membrane to separate the DNA from the rest of the cell. The nucleolus is a structure within the nucleus of eukaryotic cells, and is the site of ribosome assembly.

Prokaryotes are devoid of a nucleus, so their genetic material is contained in a specific region called the nucleoid. While not all eukaryotes will have flagella and cell walls, plant cells have cell walls and sperm cells have flagella. Mitochondria are found in eukaryotes, not prokaryotes.

The state of genetic material differs between eukaryotic and prokaryotic cells. Eukaryotic cells contain multiple linear chromosomes, called "true" chromosomes, while prokaryotic cells contain circular DNA molecules that are not true chromosomes, since they lack histones. Prokaryotic DNA molecules have only one copy of each gene and little repetitive and non-coding DNA, contributing to the compact nature of the prokaryotic genome.

The key difference between prokaryotic and eukaryotic cells is that eukaryotes contain membrane-bound organelles, while prokaryotic cells do not. Chloroplasts, lysosomes, and nuclei are all membrane-bound organelles that may be present in eukaryotic cells only. Cytoplasm can be found in both prokaryotic and eukaryotic cells. The cytoplasm is not a membrane-bound organelle within the cell, but a fluid compartment that provides support to the cell and is the site of many metabolic reactions. The cytoplasm is largely composed of water.

Examples of eukaryotic cells include plant, fungal, protist and animal cells. Myocytes (muscle cells) and human epithelial (skin) cells are both animal cells and are therefore eukaryotic. Parenchyma cells are plant cells that synthesize organic products, and are therefore eukaryotic. Examples of prokaryotic cells include bacteria. E. coli is a species of bacteria often found in the lower intestines of warm-blooded animals. All bacterial cells are prokaryotic, making an E. coli cell an example of a prokaryotic cell.

Genetic recombination is one method by which the genome can change over time; the exchange of genetic material allows for the new combination of genes. Genetic recombination can be observed in both prokaryotic and eukaryotic cells. In eukaryotic cells, genetic recombination occurs during the crossing over event of meiosis, when homologous chromosomes exchange genetic material. In prokaryotes, genetic recombination occurs through the unilateral transfer of DNA. This includes transduction, transformation, and conjugation. Transduction the process by which DNA is transferred between bacterial cells by a virus. Transformation is the uptake of DNA from a bacteria's environment. Conjugation, or “bacterial sexual genetic recombination”, is the transfer of plasmid DNA between cells by physical contact, through a pilus.

Cells are encased in a semi-permeable phospholipid bilayer called the cell (plasma) membrane. Cell membranes serve to organize and protect the cell. Eukaryotic cells also have internal membranes, which enclose organelles, including the nuclear membrane. Plant, and fungal cells have an additional membrane, called the cell wall, outside of the cell membrane that offers additional support, protection, and rigidity.