The answer is C.
A virus is made up of or consists of a nucleic acid in varying quantity which may either be RNA or DNA.
The nucleic acid is surrounded by a protein shell called a capsid. The word capsid comes from the Latin word capsa which means box.The capsid and the nucleic acid within it are together referred to as nucleoprotein.The capsid is made up of small sub units called capsomeres.
In many viruses, the nucleoprotein makes up the whole virus. More complex viruses have one or more further enclosing structures also made mostly of protein. These structures are referred to as envelopes and each envelop is specific to a particular virus.
Answer:
B)attach specifically to host cell receptors
Explanation:
Viral spikes are one of the envelope proteins. These proteins are coded for by viral genes. Viral spikes project from the envelope surface. They are also called peplomers. One of the functions of these spikes is to specifically interact with the receptors present on the surface of the host cell to mediate the attachment of the virus to the host cell surface. Viral spikes and the host cell surface receptors are complementary to allow their specific binding. For example, the spike protein of the SARS-coronavirus bind specifically to the human host cell receptor ACE2.
The correct options are as follows:
1. D.
Natural selection refers to the process by which living organisms that are more adapted to their environments usually survive and produce offspring that are like them. In the case of giraffes, the giraffes with the longest necks were able to survive in their environment and they reproduce offspring that are like them.
2. D
In the scientific world, scientists have open minds and they welcome all new ideas. These new ideas have to be tested to ensure that they are correct and superior to the facts that are already known. When a new hypothesis is put forward by a scientist, many scientists all over the world will test the hypothesis is order t confirm if it correct. If the hypothesis is found to be correct it will be accepted by all scientists.
3. A.
DNA test is a laboratory analysis that can be used to assess the level of relationship between living organisms. Related living organisms usually have some similar genes in their DNA, the level of closeness of these organisms will determine the quantity of similar genes that will be found in their DNA. Unrelated organisms on the other hand will have little or no similar genes in their DNA.
4. C.
The genetic code is the same across species, this fact points to the possibility that all living organisms originated from common ancestors. This support the evolution theory which stated that all living organisms descended from a common ancestor.
5. B.
Antibiotic drugs are usually effective against bacteria and other microbes, but the microbes can evolve and develop resistance to these drugs. Microbes are considered to have evolved when drugs that are used to inactivate them before no longer have any effect on them, thus they can easily survive in the presence of the drugs.
6. B.
If a particular specie of animal is able to avoid predators, it will increase in number more that those that are prey on by predators. The kings snakes were probably able to avoid predators, that is why, they were able to survive, reproduce offspring and increase in population in that particular ecosystem.
The structure of a typical antibody molecule
Antibodies are the secreted form of the B-cell receptor. An antibody is identical to the B-cell receptor of the cell that secretes it except for a small portion of the C-terminus of the heavy-chain constant region. In the case of the B-cell receptor the C-terminus is a hydrophobic membrane-anchoring sequence, and in the case of antibody it is a hydrophilic sequence that allows secretion. Since they are soluble, and secreted in large quantities, antibodies are easily obtainable and easily studied. For this reason, most of what we know about the B-cell receptor comes from the study of antibodies.
Antibody molecules are roughly Y-shaped molecules consisting of three equal-sized portions, loosely connected by a flexible tether. Three schematic representations of antibody structure, which has been determined by X-ray crystallography, are shown in Fig. 3.1. The aim of this part of the chapter is to explain how this structure is formed and how it allows antibody molecules to carry out their dual tasks—binding on the one hand to a wide variety of antigens, and on the other hand to a limited number of effector molecules and cells. As we will see, each of these tasks is carried out by separable parts of the molecule. The two arms of the Y end in regions that vary between different antibody molecules, the V regions. These are involved in antigen binding, whereas the stem of the Y, or the C region, is far less variable and is the part that interacts with effector cells and molecules.
