Month: April 2021

Some molecules just don’t play nicely with water. Because water is a polar molecule, it tends to stick to itself via hydrogen bonds. Other polar molecules also stick to water molecules and can mix right in, dissolv ing into the water. However, nonpolar molecules have evenly shared covalent bonds and lack the slight negative and positive charges of polar molecules. Because they’re uncharged, nonpolar molecules don’t mix well with water.

Nonpolar molecules are also called hydrophobic molecules because “hydro” means water and “phobic” means to fear.

When nonpolar molecules are placed in a watery environment, the polar mol ecules will all stick to each other and push the nonpolar molecules away. You can think of the scenario as if the polar molecules all belong to a clique that refuses to hang out with the nonpolar molecules. (The name of this clique, by the way, is the hydrophilic molecules.) Because the nonpolar molecules all get pushed together, they become associated with each other.

The interaction between nonpolar molecules is called a hydrophobic interaction.

You can easily demonstrate a hydrophobic interaction to yourself. Just go into your kitchen, put some water in a cup, and then add a little oil. Even if you stir the mixture vigorously to mix the oil into the water, as soon as you stop stirring, all the oil will gather together on top of the water.

The water molecules all stick to each other and push the oil molecules away. Hence the saying, “They get along like oil and water!”

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Viruses attach to cells when viral proteins successfully bind to receptors on the host cell. If the viral protein has the right shape, it will tuck into the cor responding shape on the host cell receptor. You can think of viral attachment as a virus having the right key to fit into the lock on the host cell.

After the virus is attached, it may force itself into the cell by digging a hole through a cell wall slip in by fusing its envelope with the membrane of the host cell, or trick the cell into bringing it inside.

The ability of a virus to infect a host cell depends on a match between pro teins on the surface of the virus and receptors on the surface of the host cell.

The type of cells a particular virus can infect is called the host range of the virus. Because viruses can infect only cells that they can attach to with their proteins, each virus has a very specific range of hosts it can infect. In other words, each virus can infect only the host cells for which it has keys.

Some viruses have a key that works in the lock on many types of cells. These viruses have a broad host range. For example, the rabies virus can infect humans and many other mammals. On the other hand, some viruses have a key that fits into the lock on only a few cells. These viruses have a narrow host range. The HIV virus, which infects only certain cells of the human immune system, is a good example of a virus with a very narrow host range.

The simplest viruses have just two components: a nucleic acid core and protein capsid. The nucleic acid core, which may be DNA or RNA, contains the instructions for taking over cells and making more virions, or viral par ticles. The nucleic acid is surrounded by the capsid, a protective protein coat. Each individual protein that makes up the capsid is called a capsomere.

All viruses have at least a capsid and a nucleic acid core. The core consists of one of four types of nucleic acid:

*Double-stranded DNA

*Single-stranded DNA

*Double-stranded RNA

*Single-stranded RNA

One difference between cells and viruses is that cells contain DNA and RNA. However, a single viral particle contains only DNA or RNA. Also, single stranded DNA and double-stranded RNA are commonly found in viruses, but not in cells.

In addition to the capsid and the core, some viruses have an outer membrane layer called an envelope. It’s no coincidence that the envelope of a virus is similar to the plasma membrane of a cell viruses that have envelopes steal them from their cellular victims as they leave the cell! Viral envelopes aren’t exactly the same as plasma membranes because they’ve been changed to suit the needs of the virus by the addition of viral proteins.

Once modified and adopted, the envelope helps the virus enter and exit from host cells. Viruses may also have proteins that stick out of the envelope or off the sur face of the capsid. These proteins, called spikes, help the virus attach to host cells.

Viruses come in three common shapes:

*Helical viruses have a capsid that forms a twisting helix around the nucleic acid core.

*Polyhedral viruses have a regular geometric shape. The most complex polyhedral viruses are icosahedrons with 20 faces.

*Complex viruses have separate patches of proteins, often forming unique structures or extensions on the virus.

Under the microscope, enveloped viruses appear irregular in shape. However, a helical or polyhedral capsid may be located underneath the envelope.

Food webs
Energy passes from one animate thing to a different within the sort of food. Food webs show however living things go after each other. At very cheap of a food cycle are plants, that build their own food, taking energy from the Sun. At the highest ar predators, that go after alternative animals.

Food chain
Food webs are created from totally different, many various, many alternative food chains that have different levels. In a very organic phenomenon, plants are referred to as producers as a result of they create their own food. Animals that eat plants are referred to as primary customers. Primary customers are ingested by alternative animals referred to as secondary customers, or predators. Once all living things die they become the food of organisms referred to as decomposers.

Food pyramid
As we have a tendency to go up a organic phenomenon, the number of food offered decreases. This is often as a result of living things use most of the energy within the food they eat respiration. A organic phenomenon shows however energy is lost at every level. close to the highest, there ar simply many predators, whereas at very cheap there are more producers.