Biological Structures

• 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.

• All biological structures work together or aggregate into forms that function together.

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.

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.

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.

Other macromolecules that we can get from foods are lipids and carbohydrates:

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.

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.

• 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.

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.

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.

1. 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.
2. 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.
3. 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.
4. 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.

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.

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.

2. Proteins are biological structures at the molecular level. Featured below are some of the common functions 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.

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.

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.