Answer:
Transmission electron microscope (MET): allows sample observation in ultra-thin sections. A TEM directs the electron beam towards the object to be increased. A part of the electrons bounce or are absorbed by the object and others pass through it forming an enlarged image of the specimen. To use a TEM, the sample must be cut into thin layers, not larger than a couple thousand thousands of angstroms. A photographic plate or a fluorescent screen is placed behind the object to record the enlarged image. Transmission electron microscopes can increase an object up to a million times.
A scanning electron microscope creates an enlarged image of the surface of an object. It is not necessary to cut the object into layers to observe it with an SEM, but it can be placed in the microscope with very few preparations. The SEM scans the image surface point by point, unlike the TEM, which examines a large part of the sample each time. Its operation is based on traversing the sample with a very concentrated beam of electrons, similar to the scanning of an electron beam on a television screen. The electrons in the beam can disperse from the sample or cause secondary electrons to appear. Lost and secondary electrons are collected and counted by an electronic device located on the sides of the specimen. Each point read from the sample corresponds to a pixel on a television monitor. The higher the number of electrons counted by the device, the greater the brightness of the pixel on the screen. As the electron beam sweeps the sample, the entire image of it is presented on the monitor. Scanning electron microscopes can enlarge objects 200,000 times or more. This type of microscope is very useful because, unlike TEM or optical microscopes, it produces realistic three-dimensional images of the object's surface.
Degeneracy
Degeneracy simply means that most of the amino acids produced during protein synthesis from DNA is coded by more than one codon. A codon is a sequence of 3 <span>nucleotides that codes for a specific amino acid.
Because more than 1 codon can produce the same amino acid, the chances of having the synthesis of proteins affected by mutations (i.e. point mutations) is decreased. For example, if the codon with the nucleotide series GAA, which codes for the amino acid glutamate, becomes the codon GAG, the codon will still produce glutamate because the code is degenerate. </span>
Lipids differ from other large biological molecules in that they are not truly polymers ; Lipids are not all made of the same type of monomer. Their association as a group is related to their behavior rather than their structure.
