Cells in a multicellular organism go through a series of changes to eventually produce a new, distinct cell type. These changes involve the cell nucleus, the membrane surrounding the nucleus, and the DNA contained within the nucleus.
The stages of cell division include interphase, when the cell does not divide, and mitosis and meiosis, when the cell divides. Interphase occurs in between these division stages, lasting approximately 8–12 hours in humans.
Observing cells during interphase is difficult due to two main issues: individual chromosomes are hard to see, and it is difficult to distinguish what parts of the cell are nuclear and what parts are cytoplical. This article will discuss these issues in further detail.
Interphase is an important phase of the cell cycle because this is when cells grow and prepare to divide. By understanding how to observe cells during interphase more clearly, we can learn more about how cells grow and prepare to divide.
Very small objects are hard to see
Microscopes are used to view the small structures and components of living things. Most microscopes use light to illuminate the objects, but transmission electron microscopes use electrons instead of light.
The size of the object you want to observe determines the kind of microscope you need. If you want to observe cells that are just a few micrometers in diameter, then you need a transmission electron microscope.
Cells in a very early stage of division are called interphase cells. During this time, the cell does not have its nucleus filled with chromosomes. This makes it easier to observe individual chromosomes with a light microscope because there is no surrounding material.
This article will discuss why it is difficult to observe individual chromosomes with a light microscope during interphase.
Chromosomes are very small objects
A light microscope can only resolve objects down to about 100 nm in width. This is roughly 1000 times larger than a single chromosome.
Because chromosomes are so small, they cannot be observed during interphase when the cell’s DNA is densely coiled. When the cell transitions into mitosis, the chromosomes uncoil and become visible.
Because cells cycle at different rates, it can be difficult to identify which stage of the cell cycle a particular cell is in unless you have some other identifying features. For example, if a cell has already begun to divide into two cells, it is likely already in mitosis.
Cells can also display signs of the different stages of the cell cycle by changing their structure and behavior. For example, cells in G0 phase are quiescent, or not dividing; this can be recognized by its shape and behavior.
There are many chromosomes in the cell
As you learned in the previous chapter, chromosomes are structured bundles of DNA and protein. During interphase, the cell has many chromosomes that can be observed with a light microscope.
The problem is that you can only see one side of each chromosome. Because of this, it is impossible to tell which part of the chromosome is being projected onto the microscope slide.
Because every cell has two sets of chromosomes (one set from your mother and one set from your father), looking at the individual chromosomes in a cell during interphase would require two separate slides. One slide would require a slide with all of the mother’s chromosomes and one with all of the father’s, or vice versa. The other would need both sets mixed together to show both sets of chromosomes together.
Light microscopes cannot see cells as well as electron microscopes
A light microscope uses a special lens to project the cell’s structure into a image. This lens uses light to observe the cell.
Due to the thickness of the lens, some details are lost. The thinner the lens, the more detail it can capture.
Because of this, electron microscopes are used more frequently to observe cells in detail. Electron microscopes use a beam of electrons to project the cell structure into a image. This method captures much more detail than a light microscope does.
Interphase is the phase between the cell cycle phases of mitosis and cytokinesis. During this phase, the cell does not divide nor does it grow in size. Because of this, it is difficult to observe individual chromosomes with a light microscope during interphase.
There is not enough contrast between the object and its background
A major difficulty in observing individual chromosomes is the lack of contrast between the chromosome and the nuclear membrane.
The nuclear membrane is essentially a barrier that separates the inside of the cell nucleus from the cytoplasm. The nuclear membrane is made of a double layer of lipid molecules, or fats.
Chromosomes are made up of proteins called histones, which are wrapped around DNA. When cells are in interphase, or the phase between the cell division stages of mitosis and meiosis, chromosomes appear as long threads without any shape. This makes it difficult to identify which chromosome is which.
To observe interphase chromosomes, researchers must first stain them with a special chemical solution that binds to specific parts of the chromosome. A solution that stains all of the chromosomes in a cell green, for example, allows you to see all of them at once.
The light microscope only sees a very narrow range of wavelengths of light
This is called the optical domain and is typically 400 to 700 nm wide.
chromosomes are too small to be observed with a light microscope during interphase
Because chromosomes are so long and contain so many genes, it is very difficult to observe just one chromosome. The genes on the chromosome would be too small to observe, and they would blend together.
Because the interphase stage occurs before the cell divides into two new cells, it is impossible to observe individual chromosomes in a living cell using a light microscope. Interphase can only be observed in tissue or living organisms that undergo apoptosis (cell death).
Apoptotic cells can be observed with a light microscope because they break down into individual proteins, DNA, and individual chromosomes. Because of this, researchers can use apoptotic cells to examine individual chromosomes during interphase.