Cellular Division and Differentiation Basics
This standard explains how cellular division and differentiation work together to develop and maintain multicellular organisms.
Standard Breakdown
This complex standard ties together several fundamental biological ideas. Specific gene regulatory mechanisms and mitotic processes will be avoided because they are outside the assessment boundary for this standard.
Cellular Division and Differentiation
Cellular Division
The process through which a single-celled zygote develops into an adult organism with trillions of cells is known as cellular division. The process of cellular division begins with the duplication of DNA, followed by mitosis.
A single cell produces two “daughter cells” with identical DNA molecules during ordinary mitosis. Humans would be little more than a gloopy clump of cells if this process continued without cellular differentiation.
Cellular Division and Differentiation
Epigenetic Mechanisms
The term “epi” means “above.” As a result, epigenetics refers to all of the systems that act to express DNA, converting all of that stored DNA information into working proteins and other cellular components. In essence, these processes are influenced by both the exterior and interior environments of the body.
Cells begin to differentiate after the first few cellular divisions of the first zygote. The resulting organism’s development is controlled by a complicated network of hormones, extracellular circumstances, and a number of additional signals (depending on species). These factors work together to express different patterns of genes in different cells, causing them to differentiate into different cell types that perform diverse activities.
As you can see in the figure above, generic totipotent cells have the ability to divide into any cell type. As the cells split, they are transported to different areas of the new embryo, each with somewhat variable hormone, oxygen, and other material concentrations. These seemingly insignificant changes have an effect on epigenetic systems, causing the genes that are really expressed in each cell to change.
After numerous divisions, totipotent cells divide into far more specific pluripotent cells. The ectoderm (outside), mesoderm (middle), and endoderm (interior) of these pluripotent cells begin to divide into three primary cell lines (inside). These three layers then develop into particular tissues and cell types, each of which is exposed to different environments and expresses different genes at varying rates.
A wide range of external circumstances can alter genetic expression patterns within an organism. Everything from sunlight to the food you eat can influence cellular processes and change the precise expression of genes. Scientists have discovered that nicotine is such a strong medicine because it adds to an infinite positive feedback loop.
Nicotine boosts the expression of a select group of genes linked to dopamine receptors. Dopamine is the brain’s “motivation” chemical. When you do something good, your brain releases dopamine, which encourages you to repeat the behaviour in the future. This is a critical pathway and one of the most common ways we learn.
Nicotine makes you feel good at first when you smoke, chew, or vape because it rewards your brain cells with increased dopamine. This stimulates more dopamine receptors, resulting in a bigger dopamine release the next time. As a result, it takes more nicotine to elicit a response, and you begin to use nicotine more frequently. When your brain stores these reward pathways, it tells you to hunt for more nicotine when your receptors are empty.
What Not to Do
The following Assessment Boundary is also included in this NGSS standard:
Specific gene regulatory mechanisms or rote memorization of mitotic steps are not included in the evaluation.
Here’s a more detailed explanation of what that means:
Rote Memorization
Students do not need to understand the precise receptors involved in the smoking (nicotine) process, nor the intricate epigenetic mechanisms that affect gene expression. It’s enough to know that having nicotine in your bloodstream alters the frequency with which particular genes are expressed, making other dopamine-releasing events appear less pleasurable and necessitating more nicotine to activate the reaction. The general process of how particular chemicals and events can influence how often (or if) specific genes are expressed should be the focus of any mechanisms described. Finally, epigenetics is the study of how everyone’s slightly different DNA interacts with a variety of internal and external surroundings to form and maintain multicellular creatures.
