Which statement best describes some protein molecules in a cell?
A. They all remain inside the nucleus.
B. They are surrounded by a membrane.
C. They move about randomly within the cytoplasm.
D. They do not require water to disperse.
A. They All Remain Inside the Nucleus.
The nucleus of a cell contains chromosomes that are tightly coiled and folded. This is where protein synthesis takes place, and it is where the cell’s DNA is stored. Inside the nucleus, the DNA strands are arranged into structures called chromatin, which includes nucleosomes (DNA-protein complexes). These bundles are actually held together by hydrogen bonds.
This is where proteins come in. Proteins play many important roles in cells. They form structures that help keep the cell intact, they transport molecules from one part of the cell to another, they signal other cells and tell them what to do, and they facilitate chemical reactions that break down food or make new cells. Some proteins are also responsible for regulating genes.
The critical thing about proteins is that they’re not just found floating around freely in the cytoplasm of a cell; this would interfere with other vital functions of a cell. Instead, all proteins remain inside the nucleus where they’re formed. The way that this happens is through the use of various special mechanisms that control how much protein can enter or exit the nucleus at any given time.
B. They are Surrounded By a Membrane.
Some protein molecules are found inside a cell’s membrane. When used in conjunction with genetic information contained within the DNA of the cell, these proteins are essential for the cell to function properly.
A typical cell membrane has a phospholipid bilayer structure and is made up of two layers of lipids—a fat-soluble compound that is not soluble in water. This membrane prevents harmful compounds from entering the cell, while still allowing necessary compounds to pass through it.
The membrane also controls which substances can enter the cell, while preventing other substances from leaving it.
Because of the structure of their outer shells, protein molecules are unable to freely float in the cytoplasm, which contains all the cell’s other organic and inorganic material, but instead only move about within it.
Although they can’t leave the cytoplasm, these protein molecules are still able to interact with each other and other substances through diffusion, a process by which substances naturally spread into an area where they are needed.
Within the cell, this is most often seen with chemical reactions; for example, a molecule of glucose might diffuse into the cytoplasm after being consumed by a cell.
C. They Move about Randomly within the Cytoplasm.
The movement of molecules within the cytoplasm is a key part of cellular function. Many molecules are bound to structures like microtubules and actin filaments, but there are also plenty of unbound molecules that travel about freely.
Protein can move about in this way, but it can also make directed movements by a process called facilitated diffusion. Facilitated diffusion is essentially the process of protein moving from a region of high concentration to a region of lower concentration without being directly powered by ATP or any other energy source.
The rate at which proteins move along their concentration gradients is determined by the size and shape of the protein, and its tendency to bind with other molecules in the cytoplasm.
It’s important that proteins can move around randomly so they don’t build up in one place while they’re working; if they did, they’d be unable to perform their functions properly.
This means that it’s very likely that the protein you’re studying has already moved away from where you put your dye so that it can do its job elsewhere in the cell. The movement is random, however, so it’s possible that some of these molecules have stayed nearby and thus would still be labeled with dye.
D. They Do Not Require Water to Disperse.
Some proteins, like those found in muscle cells, are naturally hydrophobic. In other words, they don’t require water to disperse. However, as we know from the process of osmosis, living things use water to get rid of harmful substances and materials that aren’t essential for survival.
In order for this to happen naturally, the cell membrane must be permeable to water. While most proteins are not soluble in water, they do interact with it by creating hydrogen bonds that help keep toxins out of the cell and aid in their removal. In this sense, proteins are working with water instead of against it.
Last Words
Protein molecules in the cell act as messengers, receptors and channels. They consist of different amino acid chains and have unique shapes that define their function. The patterns of gene expression in cells are determined by activating or silencing different gene regulatory proteins (MRNA, tRNA) and proteolytic enzymes (trypsin, lipase). The cell cycle is controlled by the cyclin-dependent kinase (CDK) synthesis-dependent family.