Cellular organelles

Organelles common to animal and plant eukaryotic cells

All eukaryotic cells, both plant and animal, have the following parts:

• Nucleus.
• Plasma membrane.
• Cytoplasm.
• Ribosomes.
• Cilia and flagella.
• Endoplasmic reticulum.
• Golgi apparatus.
• Lysosomes.
• Vacuoles.
• Mitochondria.

Nucleus

Eukaryotic cells have genetic material (DNA condensed in the form of chromosomes) surrounded by a double membrane, the cell nucleus, with pores to allow the exchange of substances.

As the nucleus is of special importance in cell division, we will dedicate a section to it when we finish describing the cellular organelles of eukaryotic cells.

Plasma membrane

The  plasma membrane delimits the cell, regulates the passage of substances and receives stimuli from the external environment. It is made up of a double layer of lipids with proteins and carbohydrates.

• The lipids prevent the passage of polar substances.
• The proteins are among the lipids, creating channels through which can pass some substances.
• The carbohydrates are only on the outside of the membrane and are responsible for receiving information from the outside of the cell.

Cytoplasm

The cytoplasm is the space between the plasma membrane and the cell nucleus. It is composed of:

• Cytosol. It is the aqueous medium, with abundant organic molecules.
• Cytoskeleton. Protein fiber network that serves as the internal support of eukaryotic cells. They are involved in fixing the position of organelles and in cell division.

Ribosomes

The ribosomes are small membranous organelles not may be isolated, dispersed in cytosol, or attached to the membrane of the rough endoplasmic reticulum. They are made up of RNA and proteins.

They are responsible for synthesizing proteins from the information provided by the messenger RNA from the nucleus (where the DNA is).

Cilia and flagella

The cilia and flagella are extensions of the membrane formed by microtubule protein.

• The cilia are short and numerous, and may cover all or part of the surface of the cell.
• The flagella are long and few in number.

Its function is to allow cell movement or to produce small currents in the external environment to capture nearby nutrients.

By Kohidai, L. (File:Flagellum-beating.svg) [CC BY 3.0], via Wikimedia Commons

Endoplasmic reticulum

The  endoplasmic reticulum is a membranous organelle formed by a set of tubes and flattened or rounded sacs communicating with each other. It is responsible for synthesizing, transforming, storing and transporting substances. Two types of endoplasmic reticulum are distinguished:

• Rough endoplasmic reticulum. It is so called because of the rough appearance it presents due to the ribosomes attached to its membrane. It is responsible for synthesizing and transporting proteins that act inside a vesicle or are expelled outside the cell.
• Smooth endoplasmic reticulum. Its appearance is smooth, without ribosomes attached to its membrane. Its function is to synthesize and transport lipids.

Golgi apparatus

The Golgi apparatus is another membranous organelle, formed by a set of flattened sacs, without contact between them, surrounded by vesicles. It is formed from vesicles from the endoplasmic reticulum.

In the Golgi apparatus, the substances produced in the endoplasmic reticulum are modified and vesicles are produced with which substances are secreted outside the cell by binding to the plasma membrane. They also originate some organelles, such as lysosomes.

Lysosomes

The lysosomes are organelles formed by membranous vesicles roundish containing enzymes digestive. They come from the Golgi apparatus. They intervene in the degradation of preceding substances from the outside of the cell or from the inside of the cell, destroying damaged parts of the cell.

Vacuoles

The vacuoles are large and rounded vesicles. In animal cells they are small and numerous, but in plant cells they are few but they can occupy a large part of the cell. They store all kinds of substances such as water, reserve substances, waste substances, pigments, etc.

Mitochondria

The mitochondria are organelles some large, oval, with double membrane. The outer membrane is smooth, and the inner membrane has numerous folds called mitochondrial ridges. The interior of the mitochondria is called the mitochondrial matrix, which contains circular DNA, RNA, and ribosomes (like those in bacteria), with which mitochondria can make their own proteins and divide.

In the mitochondria, cellular respiration is carried out, through which most of the energy that the cell needs is obtained. The oxidation of organic matter occurs, releasing energy and carbon dioxide.

Remember that both animal and plant eukaryotic cells have mitochondria.