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Biology Basics: Genes & Cells

U.S. Army Veteran. Student of Psychology at Kaplan University with an AA Degree in Applied Science in Complementary Alternative Medicine

Mastering the Basics

I'm new to HubPages and have really enjoyed the journey of authorship so far. It occurred to me recently that certain in-depth, science based articles might be lost on those who vaguely remember the constituent elements of life and the human body. My goal is not to overestimate or underestimate my audience. I see this as an opportunity to develop a strong working foundation that I can reference further along when things get trickier. Sometimes I get so hell-bound on trying to explain the more complicated aspects of life that I lose sight of small, but highly important details.

I am not only trying to help others understand but the process of writing helps me burn the information into my mind as well. There is a certain level of hubris involved speaking openly about science as I have only begun to scratch the surface. If for any other reason, let this be a lesson in humility for us all.

"Success is neither magical nor mysterious. Success is the natural consequence of consistently applying the basic fundamentals"

- Jim Rohn

Figure 1



DNA - Deoxyribonucleic Acid

All living organisms possess DNA molecules. Plants, mammals, insects, fish, reptiles, crustaceans, viruses and bacteria. You can think of it as the microscopic blueprint for all life as we know it. Genes contain billions of years of information from the moment life was possible on this planet. It not only serves as a scaffolding for physical development but is also a large component in how we think and behave.


A molecular basis of inheritance was first conceptualized by Gregor Mendel in the mid-nineteenth century. It wasn't until 1953 that James Watson and Francis Crick discovered the physical structure (double-helix) of DNA with the help of Rosalind Franklin who provided the x-ray imaging as seen in figure 1 1.


In figure 2, you'll notice the familiar ladder-like formation of DNA molecules. The outer-portion of the molecule that holds the rungs together is made up of the combination of sugar (deoxyribose) and phosphate (nucleic acid).

Between the acidic nuclei of the outer structure are the base pairs which make up the rungs. This is how genetic information is stored.

Bases - ATCG

The following bases are always paired together as follows:

Adenine - Thymine

Cytosine - Guanine

The order by which these bases are sequenced in a strand of DNA determines the potential expression of genes and their encoded information. Note that encoded information is never guaranteed to manifest. It might be more helpful to think about this in terms of traits like sex, morphology, eye color, etc.

Fun Fact: The human genome contains 6 Billion base pairs


If we expand the picture a bit wider, packed within the nucleus of cells are woven bundles of genetic material and protein. These bundles are what we call chromosomes. They contain the bulk of our hereditary information. Each cell, with exception of sex cells, contain 23 pairs of chromosomes (totaling 46). In short, chromosomes determine the structure and function of each cell.

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RNA - Ribonucleic Acid

By now you may be wondering how genetic information is able to propagate and behave in a particular way. This is accomplished through replication.

Replication occurs when cells divide and multiply whereby base pairs are split leaving only RNA in the newly made cell. Since each base must be matched with a corresponding partner, the cell is able to use half the information to generate a complete sequence.

Figure 2


Base Pair Review

For each question, choose the best answer. The answer key is below.

  1. Guanine must be paired with...
    • Adenine
    • Cytosine
  2. Thymine must be paired with...
    • Adenine
    • Guanine

Answer Key

  1. Cytosine
  2. Adenine

Human Stem Cell Division


Cells - Smallest Units of Life

Like genes, cells make up the structure of all living things while absorbing nutrients and providing energy. Though cells come in all different shapes, sizes and functions, most share a similar anatomy. Think of it like the similarity between humans and mammals. All mammals have lungs, stomachs, skeletons and nervous systems as a consequence of evolutionary conservation. We will discuss evolution in a later article. First, let's look into the difference between common cells.

Prokaryotic Cells

These are by far the most common and ancient type of cells we know of. They do not contain a nucleus and are most often found in single celled organisms and bacteria. See figure 3.

Eukaryotic Cells

Usually much larger in proportion to prokaryotes, eukaryotic cells contain a nucleus and are found in more complex, multi-cellular organisms. See figure 4.

Fun Fact: In every human body, bacteria outnumber eukaryotic cells 10 to 1. In a 200 pound person, up to 6 pounds of body weight can be accounted for by bacteria alone 2.

Figure 3 - Prokaryotic Cell


Figure 4 - Eukaryotic Cell


Cell Anatomy - Organelles

Cell Membrane/Plasma Membrane

We can think of the plasma membrane as a permeable barrier between the inner contents of the cell and the outside world. Sometimes it can allow things to move in or it can keep hazardous material out. It acts much like our skin does. Embedded within it are numerous receptors that pick up on signals from the environment. This is how the cell is able to perceive, or "see" the world.


Often referred to as the "command center", the nucleus contains hereditary DNA and orchestrates cellular activity such as growth, maturation, division and death. Be sure not to confuse the nucleus with something like a "brain". It's better to think about the nucleus as the cells' reproductive organ.


Surrounding the nucleus is a structure called the nucleolus. This portion of the cell manufactures ribosomes which are molecular mechanisms that produce proteins and amino acids. It plays a vital role in cell division and DNA/RNA transcription.


Found in both plant and animal cells, vacuoles store food, water and nutrients but also act as a repository for waste material to prevent contamination. You can think of it as the cells stomach and liver.


These organelles contain enzymes that break down and digest foreign substances and bacteria that may have breached the membrane. Lysosomes rid the cell of toxic material and recycle damaged cell components.


This is a gelatinous fluid also called cytosol that provides the majority of a cells total mass. It keeps all the organelles suspended in place and protected from one another.


Mitochondria are essential for the manufacturing of cellular energy from food, namely Adenosine Triphosphate or ATP. Anytime we think or act, we can thank mitochondria for doing their job. Furthermore, mitochondria possess their own DNA separate from the nucleus and can reproduce on their own.

Endoplasmic Reticulum (ER)

The ER structure is a long network of membranes that connect with the nucleus. Its job is to package and synthesize various molecules that the nucleus and ribosomes may have coughed up like proteins, lipids, steroids and amino acids.

Golgi Complex

Also described as the Golgi apparatus, the Golgi complex receives lipids and proteins from the ER and condenses them into usable materials.

Cell Review

For each question, choose the best answer. The answer key is below.

  1. We contain more eukaryotic cells in our body than prokaryotic?
    • True
    • False
  2. Which organelle contains DNA?
    • Nucleus
    • Mitochondrion
    • Both Nucleus and Mitochondrion

Answer Key

  1. False
  2. Both Nucleus and Mitochondrion

Thank You

Congratulations, you just completed a speedy review of genes and cells!

Most of the content discussed is simplified and abbreviated for your convenience. If you feel that I have left out any important details or have questions, feel free to engage with me in the comment section.


  1. Pray, L. (2008) Discovery of DNA Structure and Function: Watson and Crick. Retrieved from
  2. NIH (2012) Human Microbiome Project defines normal bacterial makeup of the body. Retrieved from
  3. GHR (2017) What is a cell? Retrieved from

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