Eukaryotic cells refer to the cells that have a complex membrane surrounding its nucleus. Other than the nucleus being surrounded by a membrane, the organelles in a eukaryotic cell are either membrane bounded or non-bounded. Organelles are the vital membrane-bounded structures found inside the cells which make the cells accomplish its functions. These micro-organs have a phospholipids double layer, which helps insulate the smaller units within the cell. Organelles can be seen as small specialized units within the cell, whose roles are complementary to the overall normal functioning of the cell. The organelles exist within a vicious liquid called cytoplasm within the membrane of the eukaryotic cell and it provides a base and favourable conditions for the cellular activities. This article examines the structure of a eukaryotic cell with a view of identifying the organelles and their respective structures and functions. The figure outlined here below shows how such organelles as the endoplasmic reticulum (ER), lysosomes, mitochondria, peroxisomes, and Golgi apparatus are located within cytoskeleton, a network that helps retain the shape of the cell and hold the intracellular components together. Eukaryotic cells’ genome is arranged in several rod-like chromosomes, unlike single rounded chromosomes which are found in prokaryotic cells.
Nucleus
Nucleus is the part of the cells that is surrounded by a nuclear membrane and contains the DNA genome. Since the nucleus carries the DNA of the cell, it implies that it is the region that controls all activities within the cell and carries the information regarding heredity and reproduction. All DNA within eukaryotic cells are well-organized multi-linear chromosomes. This organization is achieved through condensed chromosomes to fit within nucleus by having the DNA wrapped by histones. Safe for a few cases, there is one nucleus in nearly all eukaryotic cells. The few exceptions are protozoans which have two separate and specialized nuclei. One nucleus is larger than the other one and it controls metabolism within the cell, whereas the smaller one is for reproduction. In addition, there are some fungi (heterokaryotic) which temporarily develop two nuclei for the sake of sexual reproduction only.
Delegate your assignment to our experts and they will do the rest.
The nucleus is surrounded by a nuclear envelope, a complex nuclear membrane which is made up of two contiguous lipid layers. Despite being contiguous, each of the two layers has unique proteins and lipids on the outer and inner surfaces. The movement of substances into and from the nucleus is controlled by rosette-like proteins located in the nuclear pores. Inside the nuclear envelope is a network of filaments called nuclear lamina and it is the component that determines the nucleus shape (Lamond & Earnshaw, 1998).
Nucleolus
Nucleolus is a thick section inside the nucleus where biosynthesis of ribosomal ribonucleic acid (rRNA) takes place. It is at this location where the assembly of ribosomes commences prior to transportation to the cytoplasm. The initial assembly entails merging of rRNA with proteins to for pre-ribosomal complexes within the nucleolus.
Endoplasmic Reticulum
This is a plasma membrane located within the cells which is folded within itself to create a lumen. The lumen is an internal space created by endoplasm and is continuous from the space just outside the nuclear. Therefore, from this description, endoplasmic reticulum is connected to the nuclear envelope. Endoplasmic reticulum is either rough or smooth. The production of proteins takes place within the rough endoplasmic reticulum whereas lipids are produced at the smooth endoplasmic reticulum. As the name suggests, rough endoplasmic reticulum has ribosomes studs within its surface and its main role is to determine the proteins which should leave the cells and those that should remain. Therefore, it is useful in helping the cells specialize and support the complexity of organisms. On the other hand, smooth endoplasmic reticulum synthesizes steroids and lipids and plays a key role in cell detoxification. The shape is distinguished by a rough endoplasm and does not necessarily extend from the nuclear envelope.
Golgi apparatus
Golgi apparatus is made up of dictyosomes, the membranous disks having one lipid bilayer. The main role of these organelles is managing communications from the smooth and rough endoplasmic reticulum to the cell membrane where the synthesized parts are transferred to. Golgi apparatus makes the transportation of proteins and lipids easy by adding the components of carbohydrates to them, thereby producing glycoproteins, proteoglycans, and glycolipids. Once these parts have been produced, the transport vesicles from the endoplasm reticulum combines with Golgi apparatus to facilitates movements of components to other organelles within the cell.
Ribosomes
Ribosomes organelles bring together proteins and enzymes as per the information available in the DNA code. It is within this organelle where proteins are produced. The structure of ribosomes is made up two sub-units. Whereas the major sun-unit arranges amino acids to form a peptide chain that will be formed into protein, the smaller sub-unit reads mRNA. Their shapes resemble small dots within the cell and are either connected to the rough endoplasmic membrane or exist loosely within the cytoplasm.
Lysosomes
Lysosomes are organelles which help the cell recycle its wastes. They are spherical in shape and contain enzymes which can easily hydrolyse all the substances leaving the membrane, thereby helping the cell recover the raw materials.
The optimal conditions for these disposal enzymes is a pH of 5 which indicate that they are a little more acidic than the inside the cell which has a pH of 7. Since it is slightly acidic, lysosome proteins is the cell’s safety mechanism for holding the enzyme which would denature the important proteins if it leaks.
Peroxisome
These organelles are similar is shape as lysosomes and are responsible for destruction of contents within its spherical shaped part. It breakdown fatty acids and protects the cell from reactive oxygen species
Mitochondria
Mitochondrion is regarded as the cell’s powerhouse. It i sin this organelle where the energy is produced through cellular respiration. The product of this activity is adenosine triphosphate (ATP) which is a unit on which energy currency is contained. Mitochondria have a two lipid bilayer such as the nuclear envelope, which creates a barrier between the cytoplasm and its contents. The two membranes are referred to as outer and inner mitochondrial membranes depending on which side is closer to the cytoplasm. Inside these membranes is a matrix which receives pyruvate after it is generated from initial glucose breakdown in the glycolysis process. In-between the outer and inner membranes of the mitochondrion is an inter-membrane space which is acidic due to accumulation of hydrogen ions (H+) from electron transport chain found in the inner membrane. The energy that is used to make ATP is generated from the protons while moving across the matrix from the acidic space in-between the membranes. One unique feature of mitochondria is self-replication due to its own DNA ( Lodish, et al., 1995).
Membranous Organelles
Nucleus
Ribosomes
Endoplasmic reticulum
Golgi apparatus
Vacuoles
Lysosomes
Mitochondria
Chloroplasts
Non-Membranous Organelles
Proteasome
Cytoplasm
References
Lamond, A. I., & Earnshaw, W. C. (1998). Structure and Function in the Nucleus. Science , 280 (5363), 547-553.
Lodish, H., Baltimore, D., Berk, A., Zipursky, S. L., Matsudaira, P., & Darnell, J. (1995). Molecular Cell Biology (Vol. 3). New York: Scientific American Books.
