We know that humans come in all shapes, sizes, and colors. But why is that? Well, a good clue could be due to our genes, maybe? Or our cellular structures? Is it perhaps our body systems? Well, it's all of it together. In biology, we often talk about how form leads to function. Confused? It's all right; we will clarify biological structures in the following.
Biological structures meaning
¿What is the meaning of biological structures? When we talk about biological structures, we're referencing a key idea in biology: form determines function. This means that the way something is organized, arranged, or structured allows it to play a particular role within living organisms, such as us humans.
The field of structural biology deals with studying all living things at every level of organization.
All living organisms have structural properties, including us humans. The general structure of a living organism, from the least to the most complex, can be understood as: atoms, molecules, organelles, cells, tissues, organs, organ systems, and organisms.
Structures | Description | Examples |
Atoms | The smallest unit of matter, and in biology, we usually study them because they bond to form essential molecules. | Hydrogen (H) and oxygen (O) atoms aggregate to form water (H2O), a necessary molecule for life. |
| Biomolecules | Or organic compounds, contain mainly carbon and can sustain life. Also commonly have hydrogen, oxygen, or nitrogen atoms. | Proteins, carbohydrates, lipids, and nucleic acids. |
Organelles | Specialized structures within a cell. In eukaryotes or multicellular organisms like us humans, they are membrane-bound. | Mitochondria, the cell's powerhouse. |
Cells | The building blocks of life that make up all living organisms and their tissues. They usually have three main parts: cytoplasm (interior liquid that encompasses all cellular structures), nucleus (stores our genetic information or DNA), and the membrane (transports things in and out of the cell). | Muscular, nervous, skin cells |
Tissues | Aggregate of cells that have similar forms and therefore function together as a unit. | Connective tissue such as blood and bone, which support other tissues by structurally supporting them and binding them together. |
Organs | Collections of tissues that are self-contained and perform particular vital functions. | One of the most critical organs in our body is our heart, which pumps and controls blood throughout the body. |
Organ systems | Collection of organs that work together to ensure the functioning of our bodies. | The nervous system which sends signals between the brain and the body allowing for movement, breathing, thinking, etc. |
Organisms | Individual animals, plants, or other life forms. | An example of an organism with many cells would be us: humans. A bacterium is a single-cell organism. |
Table 1: The different levels of biological structures we find in living organisms, their description and examples.
Atoms, are components of biological (and non-biological) structures but are not considered biological structures themselves.
In conclusion, the structure of something, be it living or non-living, refers to the components or parts that compose it and how they are organized. Thus, biological structure deals with living organisms and their biological components at different organizational levels.
General aspects of biological structures
Even if they are so diverse, we can distinguish some general aspects of biological structures. As mentioned earlier, structural biology concerns how living things are organized and why. We went over what biological structures are and the basic structural properties of the human body. This section will mention what makes something a biological structure.
Biological structures are any physical component in a living organism whose shape helps support, sustain, or perform myriad vital functions in our bodies.
Other common characteristics include:
Biological structures self-organize and are dynamic. As they can organize themselves into distinct shapes to perform their functions.
All biological structures in living organisms possess levels of organization that increase in complexity.
For instance, amino acids are the building blocks of proteins, and proteins themselves have structures that bond together to create more complex shapes (more on this later).
For example, cells aggregate into tissues, tissues aggregate into organs, and so on. The aggregation allows for particular functions to be performed by various biological structures such as the digestive system, and an organ system, allowing for the breakdown of food for energy.
Biological structures in food
We can also find biological structures in food. How can this be? Well, remember that biological structures are organized into different levels. This means that the functions performed by our bodies depend on things that happen at the microscopic or molecular level.
Recall that living things need water to function. About 60% of our bodies are made of water, making it an essential molecule. So how do we replenish it? Well, by drinking fresh water.
Similarly, we need to eat to replenish specific macromolecules that perform structural functions in our bodies.
Proteins can be thought of as one of the most crucial molecules whose structural properties determine their functions.
Organic compounds are compounds that contain mainly carbon and can sustain life. Organic compounds are also commonly made of hydrogen, oxygen, or nitrogen atoms.
Macromolecules are molecules that consist of a large number of atoms, such as proteins, carbohydrates, etc.
Proteins are organic compounds consisting of small molecules called amino acids. Proteins are also macromolecules usually found in eggs, meats, and dairy.
Amino acids are proteins' building blocks or monomers.
Proteins are essential to life as they perform a variety of functions. They can transport materials, control physiological processes such as growth, speed up chemical reactions, store things, etc.
Unfortunately, nine out of the 20 amino acids that we need for our bodies to function cannot be synthesized from our bodies. This means that we must consume them as food.
These are the macromolecules people try to incorporate into their diets when they eat meat, protein bars, and protein shakes.
The nine amino acids we must get from our diet are called essential amino acids. A deficiency in proteins can lead to anemia, loss of muscle mass, slower metabolism, etc.
Other macromolecules that we can get from foods are lipids and carbohydrates:
Carbohydrates are organic compounds that mainly store energy and can be broken down by the body into sugars such as glucose to give us a significant energy source.
Lipids are organic compounds insoluble in water that function in energy storage and as chemical messengers.
Examples of carbohydrates in food include potatoes, bread, noodles, and other foods famous for being "carbs."
Lipids consist of liquid oils and solid fats. Examples of lipids in food include olives, avocados, peanut butter, etc. Liquid oils such as olive and canola oil are also lipids.
Biological structures examples
After understanding common characteristics of biological structures, the foods they are found in, and what biological structures are, we need to go over more in-depth examples of biological structures. We've gone from explaining all of them in the first section to focusing on molecules. This is because all biological functions can be explained by examining what's happening at the molecular level.
An important thing to remember is biological structures occur at all levels of organization.
Figure 1: Protein shapes illustrated. Daniela Lin, Study Smarter Originals.
Proteins are one of the most important macromolecules whose structure allows them to play an essential role in how our bodies function.
There are generally two shapes of proteins: globular and fibrous (Fig. 1).
Globular proteins are spherical, usually act as enzymes or transport materials, are generally soluble in water, have an irregular amino acid sequence, and are usually more sensitive to heat and pH changes than fibrous ones.
A globular protein is hemoglobin.
Fibrous proteins are narrower and more prolonged, usually are structural in function, are generally not soluble in water, have a regular amino acid sequence, and are usually less sensitive to heat and pH changes than globular ones.
An example of a fibrous protein is keratin.
Globular proteins are more soluble than fibrous ones because the amino acids can bend in a way where the polar groups are on the surface. Globular proteins also have weaker interactions between their amino acid sequences when compared to fibrous proteins making them easier to denature.
When proteins denature or break their bonds, the structure unravels and ceases to function.
Proteins are made of a chain of amino acids. When a few chains of amino acids bind together, they create peptide bonds. Longer chains of amino acids bound together are called polypeptide bonds.
- Primary structure: A protein's primary structure is its amino acid sequences linked into a polypeptide chain. This sequence determines a protein's shape. A change in a protein's amino acid sequence would change a protein's shape.
- Secondary structure: The secondary structure is caused by folding amino acids from the primary structure. The most common structures proteins fold into in the secondary level are alpha (\(\alpha\)) helices and beta (\(\beta\)) pleated sheets, which are held together by hydrogen bonds.
- Tertiary structure: The tertiary structure is a protein's three-dimensional structure. This three-dimensional structure is formed by the interactions between the variable R groups.
- Quaternary structure: Not all proteins have a quaternary structure. But some proteins can form quaternary structures that consist of multiple polypeptide chains. These polypeptide chains can be referred to as subunits.
Figure 2: The four levels of protein structure.
Proteins with incorrect sequences can cause adverse side effects like sickle cell anemia, a disease where an individual's hemoglobin is affected into an S shape. Hemoglobin is a protein found in red blood cells (RBCs) that binds to oxygen to deliver it throughout the body—the S shape results in hemoglobin breakdown, leading to anemia. Anemia can result in fatigue and delayed development.
Amino acids, the building blocks of proteins, consist of an alpha (\(\alpha\)) carbon bonded to an amino group (\(NH_2\)), a carboxyl group (\(COOH\)), hydrogen (\(H\)), and a variable side chain named (\(R\)) which gives it different chemical properties.
Biological structures and functions
Now, we need to address the actual functions of some biological structures. We'll see examples of biological structures and functions at different levels.
Recall the organization levels we discussed: atoms, molecules, organelles, cells, tissues, organs, organ systems, and organisms.
Figure 3: Biological structures and functions. The general structure of an animal cell. A cell structure is tightly related to its function.
1. Atoms: Examples of atoms include hydrogen (H), oxygen (O), and carbon (C).
Carbon is a vital part of life because it creates stable bonds with various elements, allowing it to form many complex molecules such as proteins, carbohydrates, etc. This specific property of carbon atoms will enable it to make macromolecules such as proteins, carbohydrates, lipids, etc.
As mentioned earlier, these molecules are crucial in ensuring our bodies function.
2. Proteins are biological structures at the molecular level. Featured below are some of the common functions of proteins:
| Types of Proteins | Functions | Example |
| Enzymes | Enzymes catalyze and speed up reactions. | Amylase breaks down sugars and starches. |
| Structural | Structural proteins maintain cell shape and structure. | Keratin strengthens hair and nails. |
| Transport | Move materials around the body. | Hemoglobin carries oxygen around the body. |
| Defense | They protect your body by maintaining barriers or eliminating threats. | Antibodies bind to foreign molecules (antigens) to facilitate their removal. |
Table #: the main functions and some examples for differente types of proteins.
3. Organelles: An example of an organelle is the mitochondria. The mitochondria have a double membrane structure; the inner membrane has a lot of folds to increase its surface area, giving it more space to break down molecules for cellular respiration.
4. Cells also have structures that also help them do a specific job.
Compare the cell in Figure 3 with the ones in Figure 4, and note how an animal cell can have different shapes and structures (although composition is pretty similar) that are related to their function.
For instance, nerve cells have long extensions that help them simultaneously send multiple messages across the body.
Figure 4: Biological structures and functions. The shape and specific structure of a cell are related to its functions (a neuron, stem, and muscle cells are different animal cells).
5. Tissues are a bunch of cells that work together, such as nerve tissue. Nerve or neural tissue is made up of multiple nerve cells, helping them send many signals throughout the body.
6. Organs are a collection of tissues.
The brain is an organ composed of neural tissue, and its folds allow an increase in surface area relative to volume leading to faster exchanges for information.
7. Organ systems are a collection of organs. If we continue the same example, we're referring to the nervous system. The various organs and tissues with particular structures together function.
Organisms are a collection of all the biological structures together, which means that inside us, we have structures that function due to their specific shapes.
Biological Structures - Key takeaways
- When we talk about biological structures, we're referencing a key idea in biology: form determines function. This means that the way something is organized, arranged, or structured allows it to play a particular role within living organisms, such as us humans.
- The field of structural biology deals with studying all living materials at every level of organization.
- All living organisms have structural properties, including us humans. The general structure of a living organism, from the least to the most complex, can be understood as: atoms, molecules, organelles, cells, tissues, organs, organ systems, and organisms.
Since we know what structural biology deals with and what biological structures are, we can say that biological structures are any physical component in a living organism whose shape helps support, sustain, or perform myriad vital functions in our bodies.
References
- National Academy of Sciences, Molecular Structure and Function, 1989.
- Sarah Malmquist and Kristina Prescott, Structural Organization of the Human Body.
- National Institute of General Medical Sciences.
- Sophie Dumont and Manu Prakash, Emergent mechanics of biological structures, Molecular Biology of the Cell, 2017.
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