Eukaryotic Cells (summary)
In most cells the nucleus is the largest organelle. It contains the DNA from the entire cell as well as the nucleolus within it. It is a membrane bound structure. The nucleus maintains the integrity of the cell as well as controlling all activities of the cell
The nucleolus is a small, non-membrane bound sub organelle found within the nucleus it contains RNA, an important part of the production of proteins and nucleic acids with the ribosomes.
The cytoplasm fills the cell, it is made up of 80% water as well as nutrients. All of the cells organelles are suspended within the cytoplasm. Cytoplasm aids in the dissolving of nutrients and the removal of waste.
Mitochondria convert oxygen and nutrients into Adenosine Triphosphate (ATP) through a process of aerobic respiration. Mitochondria are separate from the animal cell, they reproduce on their own and store their own, separate DNA. ATP provides the energy for all actions to take place.
Plasma membrane surrounded the cell, keeping everything contained within its borders. The membrane has selective permeability, it can decide what enters or leaves the cell.
Rough Endoplasmic Reticulum
The Rough endoplasmic reticulum (rough ER) is covered in ribosomes, their role is to synthesis and package proteins. They are attached around the nucleus. When mRNA moves from the nucleus to a ribosomes, this is behind the process of making the protein. The amino acid chains are pushed into internal space. When complete, they are collected into vesicles and pinched off.
Smooth Endoplasmic Reticulum
Smooth Endoplasmic Reticulum (smooth ER) contains no ribosomes on its surface and therefore smooth. It is a storage organelle containing lipids and steroids.
Ribosomes are the main organelle in protein synthesis. Ribosomes found free in the cytoplasm are going to produce proteins for use within the cell. Their key job is to covert amino acids into polypeptides
Golgi Apparatus is made up of layers of membranes called Golgi bodies. Within the Golgi Apparatus it further process proteins, instructing them where to go as well as converting proteins to hormones are bonding proteins with carbohydrates to form different molecules.
The lysosomes are filled with enzymes with the task of breaking down cellular waste. The enzymes found within are produced by the rough Endoplasmic Reticulum. When enzymes are in the Golgi Apparatus a vesicle filled with these enzymes is produced, known as the lysosomes. They float in the cytoplasm until needed, able to restore useful material back into the cytoplasm for further use.
Lysosomes are produced by a vesicle on the Golgi apparatus which contains protease and lipase. They also contain materials that hydrolyse the cell wall of certain bacteria called lysozymes and enzymes.
As many as 50 enzymes can be found in each lysosome, each lysosome being up to 1µm in diameter. Lysosomes isolate these enzymes from the rest of the cell before releasing them, into either th e outside or into a phagocyte vesicle within the cell
Lysosome functions include:
- Hydrolyse materials ingested by phagocytic cells (e.g. white blood cells and bacteria)
- Release enzymes to the outside of the cell (exocytosis ) in order to destroy materials around the cell
- Digest worn out organelles so that the useful chemicals they are made of can be reused within the cell
- The complete breakdown of cells after they have died (autolysis)
- They are especially abundant in secretory cells such as epithelial cells and in phagocytic cells.
The centriole is used for the division of cells both in mitosis and meiosis They are made up of microtubules arranged into a group when. When the cell divides, threads to the centriole called mitotic spindles.
Found in all plant cells, a cell wall contains microfibrils of the polysaccharide Cellulose, embedded into a matrix. Cellulose microfibrils have considerable strength and so contributes greatly to the strength of the cell wall.
Cell walls have the following features:
- They include a number of polysaccharides including cellulose
- The boundary mark between adjacent cell walls is called the middle lamella. This thin layer also “cements” adjacent cells together.
The function of the cellulose cell wall are:
- To provide mechanical strength in order to prevent the cells bursting under the pressure created by the osmotic entry of water.
- To give mechanical strength to the plant
- To allow water to pass along it and so contributes to the movement of water through the plant
The cell wall of algae are made up of cellulose or glycoproteins of a mixture of both.
The cell wall of fungi does not contain cellulose but comprises a mixture of nitrogen containing polysaccharides call chitin, a polysaccharide call glycan and glycoproteins.