Organelles in animal cells and bacteria cells
- Bacteria Cells
Nucleoid: It is the region within a prokaryotic cell that most or all of the genetic material (primary DNA) is found. This is because the DNA could be present in more than one place within the cytoplasm due to having no nucleus with a membrane. The DNA is found in a circular shape as oppose to eukaryotic cells (which have a more string-like DNA).
Ribosomes: Although the shapes and sizes of prokaryotic ribosomes slightly differ from the eukaryotic ones; they have the same function within the cell, which is building protein by translating the code that is provided by the DNA with the help of tRNA and mRNA. They are composed of around the half of the amount of ribosomal RNA that construct eukaryotic ribosomes.
Cell Wall: The prokaryotic cell wall surrounds the cell membrane and protects it from external factors such as the change in water pressure. The bacterial cell wall is composed of a substance made of sugars and amino acids, named ‘peptidoglycan’. The layer of peptidoglycan in the cell wall differs from gram-positive bacteria (thick- multi layered) to gram-negative bacteria (thin- single layered).
Capsule: Not all bacteria cells possess a capsule. It is an additional layer and surrounds the cell wall. Its functions are; shielding and protecting the cell when engulfed by another organism, aiding in the maintenance of the moisture of the cell, and helping the cell to bind to surfaces and nutrients.
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Mesosome: These structures are formed by the infolding’s of the plasma membrane in prokaryotic cells which perform aerobic cellular respiration and they are distinctive structures from eukaryotic cells. The enzymes linked with respiration are placed within these folding’s and they perform cellular respiration.
Flagella: These are whip-like structures that aid the bacteria in cellular motion by detecting chemical signals and moving towards or retrieving from them, depending on its positive or negative nature. This process is called ‘run and tumble’; ‘run’ occurs as the cell detects a positive signal which may be received by a nutrient; ‘tumble’ occurs when the cell detects a negative signal which may be received from harmful substances.
- Yeast, Plant and Animal Cells
Nucleus: This circular structure surrounded by an outer membrane carries the genetic information which is the DNA within the cell. It has the same function and role in yeast, plant and animal cells. It directs the operations carried out in the cell.
Golgi apparatus: These flattened sac-like structures receive protein from the rough endoplasmic reticulum (including other hormones) and carries out some process to modify them; the modification may include the addition of sugar molecules with the help of enzymes that are located in the sacs. The protein is then packaged and transported to the cell membrane for secretion.
Secretory Vesicles: These are membrane-bound organelles which carry material that will be secreted through the cell membrane, and they usually fuse with it. They are derived from the Golgi apparatus.
Rough Endoplasmic Reticulum: This organelle is membrane-bound and it is responsible in the synthesis of protein which is later secreted through the cell membrane or fused with the membrane. Some modification of the protein that is being synthesised may take place in the rough endoplasmic reticulum; it is sent to the Golgi apparatus for further modification.
Smooth Endoplasmic Reticulum: They are generally responsible in the synthesis of lipids, which are very important substances that are part of the cell membrane. Lipids are combined with an element ‘phosphorus’ to produce phospholipids (a component which is the most abundant in cell membrane).
Plasma (Cell) Membrane: This structure controls what enters and exits the cell, it is universal for all cells to have an outer membrane. A number of proteins are scattered within the cell membrane, they work as receptors and they send and receive signals from the surrounding cells. They can also interact with prokaryotic cells in the case of any infection.
Nuclear Membrane: Surrounds the components within the nucleus and only allows certain substances (proteins, ions or molecules…etc.) which are very small to enter the nucleus. When large molecules are necessary to enter or leave the nucleus, they must have appropriate labels that the proteins within the structure of the membrane will recognise and allow the molecules to cross. This way the genetic material is protected from any harm.
Nucleolus: This organelle plays an important role in assembling the sub-units (small and large) which are put together to form ribosomes (site of protein synthesis). Indirectly, it has a role in protein synthesis which is very crucial.
Mitochondria: This is the site where energy needed for the cell is produced. This is done by using the glucose (a type of sugar) which is broken down into smaller particles before entering the mitochondrial site to produce chemical energy. Adenosine Triphosphate (ATP) is created at the end of the process of cellular respiration.
Chloroplasts: These green and small organelles are mainly found in plant cells. Their function is to produce chemical energy for the cell by converting the sun’s energy; the process is called ‘photosynthesis’. Chlorophylls (green pigments attached to chloroplasts) that capture sunlight and use it to transform carbon dioxide into carbon to make sugar (chemical energy).
Centrioles: These barrel-like organelles are found in animal cells rather than plant cells and yeast cells. They aid in the process of cell division, this is their main function. They produce spindle fibres which pull the each of the sister chromatids to the opposite poles of the cell during mitosis.
Cilia: These hair-like structures are placed on the outer membrane of the cell. They generally work to move substances past the cell, for example, the ciliated cells that line the trachea in animal cells, move past mucus which contains dirt and other particles which may be inhaled is moved back out through the wind pipe to be coughed out.