Flagellum.
A flagellum (plural: flagella) is a long, slender projection from the cell body and are intracellular extensions used in creating movement.
Structure:
Eukaryotic flagellum is a bundle of nine fused pairs of micro tubule doublets surrounding two central single microtubules.
Function:
Its function is usually to propel a unicellular or small multicellular organism by beating with a whip-like motion.
Cilium.
A cilium (plural cilia) is an organelle found in eukaryotic cells. They are thin, tail-like projections extending approximately 5–10 micrometers outwards from the cell body.
There are two types of cilia: motile cilia, which constantly beat in a single direction, and non-motile cilia, which typically serve as sensory organelles. Along with flagella, they make up a group of organelles known as undulipodia (9+2 organelle).
Cell nucleus (a cell's information centre).
Structure:
The cell nucleus is spherical in shape and is made up of the following parts:
The Nuclear Envelope is made up of two cellular membranes, the inner and the outer membranes. The space in between the two membranes is called the 'perinuclear space', (usually about 20 - 40 nm wide), and each of the two membranes is composed of a lipid bilayer.
The inner membrane is erected upon the nuclear lamina, (a network of intermediate filaments made of lamin), which acts like a shield for the nucleus.
The outer membrane consists of nuclear pores and has ribosomes on it which are continuous with the endoplasmic reticulum. The Nuclear envelope also acts as a barrier to keep the cells cytoplasm separate from the nucleoplasm.
Nucleoli are made of protein and ribosomal DNA (rDNA) sequences of chromosomes. A main function of the nucleolus is the production and assembly of ribosome components.
Similar to the cells cytoplasm. The nucleoplasm is a highly viscous liquid that surrounds the chromosomes and nucleoli.
Chromatin is the complex of DNA and protein that makes up chromosomes. The two types of chromatin present in the nucleus are Heterochromatin and Euchromatin.
Function:
The main function of the nucleus is to maintain the condition of genes and control the activities of the cell.
Mitochondria: (the power generators).
Structure:
A mitochondrion range from 1 to 10 micrometers (μm) in size and contain membranes composed of phospholipid bilayers and proteins. These membranes, however, have different properties.
There are 5 compartments within the mitochondrion:
- The outer membrane
- The Inter membrane space (the space between the outer and inner membranes)
- The inner membrane
- The cristae space (formed by in foldings of the inner membrane
- The matrix (space within the inner membrane).
Function:
Mitochondria occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells. They play a critical role in generating energy in the cell and are involved in other processes such as cell signalling, cellular differentiation, apoptosis, as well as the control of the cell cycle and cell growth.
Chloroplasts: (the power generators).
Structure:
Chloroplasts are the counter-part of the mitochondria and are often involved in storage. They are flat discs usually 2 to 10 micrometers in diameter and 1 micrometer thick. The chloroplast consists of an inner and an outer phospholipid membrane.
Function:
Chloroplasts absorb sunlight and use it with water and carbon dioxide to produce sugars for food.
Endoplasmic reticulum: (macromolecule managers).
Golgi apparatus (macromolecule managers).
Ribosomes: (the protein production centres in the cell).
Structure:
The ribosome is a large complex, composed of many molecules. Ribosomes consist of two subunits (Figure 1) that fit together (Figure 2) and work as one. Ribosomes are classified as being either "free" or "membrane-bound".
Free ribosomes are "free" to move about anywhere in the cytoplasm (within the cell membrane). Proteins formed from free ribosomes are used within the cell.
- Membrane bound ribosomes:
When certain proteins are synthesized by a ribosome they can become "membrane-bound".
Function:
They produce proteins in the cell and are inserted directly into the endoplasmic reticulum by the ribosome and are then transported to their destinations.
Lysosomes: (recycling centres).
Structure:
Lysosomes are organelles that contain digestive enzymes. They are small round structures that contain chemicals.
Function:
Lysosomes digest excess or worn out organelles, food particles, and engulfed viruses or bacteria. They fuse with vacuoles and dispense their enzymes into the vacuoles, digesting their contents. Other functions include helping repair damage to the plasma membrane by serving as a membrane patch, sealing the wound.
Peroxisomes: (recycling centres).
Peroxisomes participate in the metabolism of fatty acids and other metabolites and also have enzymes that rid the cell of toxic peroxides.
Structure:
They have a single lipid bilayer membrane that separates their contents from the cytosol (the internal fluid of the cell).
Function:
A major function is the breakdown of fatty acid molecules. They also play a role in the production of bile acids and proteins.
Centrosome: (The cytoskeleton organiser).
Structure:
Centrosomes are composed of two centrioles, which separate during cell division and help in the formation of the mitotic spindle. A single centrosome is present in the animal cells.
Function:
The centrosome is the main micro tubule organizing centre of the cell, (a key component of the cytoskeleton). It directs the transport through the ER and the Golgi apparatus. The mother centriole, the one that was inherited from the mother cell, also has a central role in making cilia and flagella.
Centrioles: (Makes up the Centrosomes).
Structure:
An associated pair of centrioles, arranged at right angles to each other, makes the compound structure known as the Centrosome. The walls of each centriole are composed of nine triplets of microtubules.
Function:
Centrioles can be used in forming motility organelles such as the flagella or cilia.
In replication, centrioles help with reproduction.
Cytoskeleton: (A cells scaffold).
Structure:
The eukaryotic cytoskeleton is composed of microfilaments, intermediate filaments and microtubules. There is a great number of proteins associated with them, each controlling a cell's structure by directing, bundling, and aligning filaments.
Function:
The cytoskeleton is a cellular "scaffolding" or "skeleton" contained within the cytoplasm. It organizes and maintain the cell's shape, anchors organelles in place and moves parts of the cell in processes of growth and mobility.
Vacuoles: (Storage).
Structure:
Vacuoles are often described as liquid filled space and are surrounded by a membrane.
Function:
Vacuoles can serve a variety of secretory, excretory, and storage functions.
Bibliography
Lysosomes picture: <http://www.nigms.nih.gov/>
Centrosome picture: <http://scienceblogs.com/transcript/2006/08/new_evidence_for_
endosymbiotic.php>
Cytoskeleton Picture: <http://www.nigms.nih.gov/>
Golgi Picture: <http://www.nigms.nih.gov/>
Vacuole Picture: <http://www.revisionworld.co.uk/alevel?q=category/export/html/330>
All other pictures: <http://en.wikipedia.org/wiki/Cell_%28biology%29>
