BIO 112 Notes: Eukaryotes

Eukaryotic cells

have a nucleus and other membrane-bound organelles, such as mitochondria and a Golgi apparatus. They are structurally more complex than prokaryotic cells.

What allows eukaryotic cells to change shape?

A well-developed cytoskeleton enables eukaryotic cells to have asymmetrical forms and to change shape.

How did eukaryotic cells arise?

Eukaryotic cells arose through endosymbiotic events that gave rise to the energy-producing organelles within the eukaryotic cells such as mitochondria and chloroplasts.

Endosymbiosis

a symbiotic relationship in which one organism lives inside the body or cell of another organism.

Key evidence supporting endosymbiotic theory:

* Inner membranes of mitochondria and plastids are similar to plasma membranes of living bacteria
* Replication of mitochondria and plastids is similar to cell division in bacteria – Mitochondria and plastids have circular DNA, like bacteria
* Mitochondria and plastids transcribe and translate their own DNA into proteins
* Ribosomes of mitochondria and plastids are more similar to bacterial than eukaryotic ribosomes

choanoflagellates

Morphologically, choanoflagellate cells and the collar cells of sponges, a basal group of animals, are almost indistinguishable.

Have collar cells been identified in animals?

Similar collar cells have been identified in other animals, including cnidarians, flatworms, and echinoderms- but they have never been observed in non-choanoflagellate protists or in plants or fungi.

DNA sequence data indicate that choanoflagellates and animals are sister groups. In addition, genes for signaling and adhesion proteins previously known only from animals have been discovered in choanoflagellates.

Flagella

long protein filaments of uniform length that are responsible for cell motility.

Cilia

short eyelash-like filaments that allow locomotion for protists.

Pseudopodia

a temporary protrusion of the surface of an amoeboid cell for movement and feeding.

Protist nutritional diversity

Protists show a wide range of nutritional diversity. Photoautotrophy, heterotrophy, and mixotrophy have arisen independently in protists many times. Producers, or phototrophs, are organisms that use energy from light (or inorganic chemicals) to convert CO2 to organic compounds.

Are mixotrophs photoautotrophs or heterotrophs?

Mixotrophs can be both photoautotrophs and heterotrophs depending on the circumstance.

Protist reproduction

Protists can either reproduce asexually or sexually. Usually, they reproduce asexually.

Binary fission

where one nucleus divides

multiple fission

where many nuclei divide

budding

where a new organism sprouts off a parent organism.

Syngamy

Some unicellular protists even reproduce sexually and are able to create gametes, or sex cells, that can fuse together to form a new organism in a process known as syngamy.

Conjugation

another type of sexual reproduction that mainly only occurs in ciliates. In this process, nuclei from gametes come together and fuse to create a zygotic nucleus.

What are land plants most similar to?

Charophytes share more traits with land plants than do other algae, according to structural features and DNA analysis.

What is similar about charophytes and land plants?

* Their chloroplasts have a similar structure and pigment composition to those of land plants.
* Both charophytes and land plants show apical growth—growth from the tips of the plant rather than throughout the plant body.

Streptohpyta

land plants and the charophytes are now part of a new monophyletic group called **Streptophyta.**