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2.1 Cell Structure - Coggle Diagram
2.1 Cell Structure
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Protein Production
Translation of mRNA into a polypeptide chain takes place on ribosomes which are either floating alone in the cytoplasm or attached to the rough ER.
The long polypeptide chain is folded at the rough ER and transported to the Golgi apparatus inside vesicles.
At the Golgi, they are modified and processed by various enzymes. The protein may have a carbohydrate chain stuck onto its surface, or the addition of a sulfate or phosphate group.
It is packaged inside another vesicle which travels to the part of the cell where the protein is needed. If the protein is a carrier protein, the vesicle will deliver the protein to the plasma membrane where it will be incorporated.
Microscopy
The light microscope uses light to magnify objects up to 1,500x their actual size. They have a resolution of approximately 0.2 μm which isn’t large enough to visualise any of the smaller organelles, such as ribosomes and lysosomes. They are more commonly used for visualising whole cells or tissues. An advantage of light microscopy is that it can visualise living cells so we can watch behaviours such as cell division in real time.
Laser scanning confocal microscopes are a special type of light microscope. They use laser beams to scan a specimen, which will be labelled with a fluorescent tag. When the laser beam hits the tag, it gives off light which is focused through a pinhole to a detector. The detector transmits the 3D image to a computer. Confocal microscopes produce clearer images than normal light microscopes and can be used to look at the specimen as different depths.
The transmission electron microscope (TEM) is more powerful than a light microscope and has a high enough resolution (around 0.0002 μm) to visualise individual organelles. A TEM uses electromagnets to focus a beam of electrons at a sample. Electrons have a much shorter wavelength compared to visible light which means higher-resolution, detailed images can be produced. A disadvantage of TEM is that the sample needs to be fixed and placed in a vacuum, which means that live cells cannot be used.
The scanning electron microscope (SEM) has a lower resolution (around 0.002 μm) than the TEM but they can produce 3D images of cells and organelles. They emit a beam of electrons towards a sample, knocking electrons off it which are used to build an image. Like TEMs, SEMs cannot be used with live cells. Both types of electron microscope are pretty big and expensive so you’ll only find them in specialised research facilities and hospitals.
Magnification
Resolution is defined as how well a microscope distinguishes between two points that are close together (i.e. how much detail it can make out).
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Light microscopes have a much lower resolution, so produce less detailed images, compared to electron microscopes.
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Cytoskeleton
The cytoskeleton is a network of protein threads that run through the cytoplasm. In eukaryotes, the protein threads are arranged as microfilaments and microtubules which support the cell’s organelles and keep them in position. When organelles and chromosomes move around the cell (i.e. during cell division), they do so by attaching and moving along the microtubules. The cytoskeleton also helps strengthen the cell and maintain its shape and it is responsible for the movement of cilia and flagella.
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