Eukaryotic Organelles

By: Kyle Hancock

The Nucleus: The Control Center

The nucleus is a compact sphere that is the most prominent organelle of Eukaryota cells. It is separated from the cell cytoplasm by an external boundary called a nuclear envelope. The envelope has a unique architecture. It is composed of two parallel membranes separated by a narrow space, and it is perforated with small, regularly spaced openings, or pores formed at sites where the two membranes unite.

A Passageway in the Cell

The endoplasmic reticulum (ER) is microscopic series of tunnels used in transport and storage. Two kinds of endoplasmic reticulum are the rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum (SER).

A Packaging Machine

The Golgi apparatus, also called the Golgi complex or Golgi body, is the site in the cell in which proteins are modified and then sent to their final destinations. It is a discrete organelle consisting of a stack of several flattened, disc-shaped sacs, or cisternae.

Nature's Assembly Line

As the keeper of the Eukaryota genetic code, the nucleus ultimately governs and regulates all cell activities. Endoplasmic reticulum, which is continuously connected with the nuclear envelope, as well as the smooth endoplasmic reticulum and the Golgi apparatus. After being transported to the Golgi apparatus, the protein products are chemically modified and packaged into vesicles that can be used by the cell in a variety of ways.

Energy Generators of the Cell

The bulk of which constant supply of energy is generated in most eukaryotes is by mitochondria. When viewed with light microscopy, mitochondria appear as round or elongated particles scattered throughout the cytoplasm. The folds on the inner membrane, called cristae, may be tubular, like fingers, or folded into shelflike bands. The space around the cristae are filled with a chemically complex fluid called the matrix, which holds ribosomes, DNA, and the pool of enzymes and other compounds involved in the metabolic cycle.

Photosynthesis Machines

Chloroplasts are remarkable organelles found in algae and plant cells that are capable of converting the energy of sunlight into chemical energy through photosynthesis. Inside the chloroplast is a third membrane folded into small, disclike sacs called thylakoids that are stacked upon one another into grana. Surrounding the thylakoids is a substance called the stroma. The role of the photosynthetic pigments is to absorb and transform solar energy into chemical energy.

Protein Synthesizers

In an electron micrograph of a eukaryotic cell, ribosomes are numerous, tiny particles that give a dotted appearance to the cytoplasm. Ribosomes are distributed throughout the cell: some are scattered freely in the cytoplasm and cytoskeleton; others are attached to the rough endoplasmic reticulum. Multiple ribosomes are often found arranged in short chains called polyribosomes. the basic structure of eukaryotic ribosomes is similar to that of bacterial ribosomes.
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A Support Network

The cytoplasm of a eukaryotic cell is crisscrossed by a flexible framework of molecules called the cytoskeleton. Actin filaments are long, thin, protein strands about 7 nanometers in diameter. they are found throughout the cell but are most highly concentrated just inside the cell membrane. Microtubules are long, hollow tubes that maintain the shape of eukaryotic cells when they don't have walls and transport substances from one part of a cell to another. Intermediate filaments are ropelike structures that are 10 nanometers in diameter. Their main role is in structural reinforcement of the cell of the nuclear envelope.