While at the grocery store, you’ve likely noticed foods with labels saying they contain antioxidants, but what does that mean? In short, antioxidants are substances that may prevent or delay some types of cell damage. Many foods, including fruits and vegetables, naturally produce antioxidants like vitamins C and E, beta-carotene, and selenium. Our bodies also naturally produce antioxidant molecules such as alpha-lipoic acid, glutathione, and coenzyme Q10.
Antioxidants are united by their ability to donate electrons, which helps them protect the body against reactive oxygen species (ROS). ROS form naturally during exercise, when your body converts food into energy, or during exposure to certain environmental factors such as cigarette smoke, air pollution, and sunlight. These molecules can “steal” electrons from other molecules, and though they aren’t always harmful, consistently high amounts of ROS in your body can cause a condition known as oxidative stress that can damage cells. That cell damage may also lead to chronic diseases, especially if ROS steal electrons from DNA or other important molecules and alter their functions.
Some might think that protein is only important for weightlifters. In truth, all life relies on the activity of protein molecules. A single human cell contains thousands of different proteins with diverse roles, including:
Providing structure. Proteins such as actin make up the three-dimensional cytoskeleton that gives cells structure and determines their shapes.
Aiding chemical reactions. Many proteins are biological catalysts called enzymes that speed up the rate of chemical reactions by reducing the amount of energy needed for the reactions to proceed. For example, lactase is an enzyme that breaks down lactose, a sugar found in dairy products. Those with lactose intolerance don’t produce enough lactase to digest dairy.
Supporting communication. Some proteins act as chemical messengers between cells. For example, cytokines are the protein messengers of the immune system and can increase or decrease the intensity of an immune response.
Just as electricity powers almost every modern gadget, the tiny moleculeadenosine triphosphate (ATP) is the major source of energy for organisms’ biochemical reactions. ATP stores energy in the chemical bonds that hold its three phosphate groups together—the triphosphate part of its name. In the human body, ATP powers processes such as cell signaling, muscle contraction, nerve firing, and DNA and RNA synthesis. Because our cells are constantly using and producing ATP, each of us turns over roughly our body weight in the molecule every day!
Our bodies can produce ATP in several ways, but the most common is cellular respiration—a multistep process in which glucose molecules from our diet and oxygen react to form water and carbon dioxide. The breakdown of a single molecule of glucose in this way releases energy, which the body captures and stores in around 32 ATP molecules. Along with oxygen, mitochondria are crucial for producing ATP through cellular respiration, which is why they’re sometimes called the powerhouses of cells.
Have you ever wondered why your cells don’t spill into each other or what keeps your skin separate from your blood? The answer to both is lipids—a diverse group of organic compounds that don’t dissolve in water. They’re one of the four major building blocks of our bodies, along with proteins, carbohydrates, and nucleic acids. Types of lipids include:
Fats, necessary for our bodies’ long-term energy storage and insulation. Some essential vitamins are fat soluble, meaning they must be associated with fat molecules to be effectively absorbed.
RNA, though less well known than its cousin DNA, is equally integral to our bodies. RNA molecules are long, usually single-stranded chains of nucleotides. (DNA molecules are also made up of nucleotides but are typically double-stranded.) There are three major types of RNA, which are all involved in protein synthesis:
Messenger RNA (mRNA) is complementary to one of the DNA strands of a gene and carries genetic information for protein synthesis to the ribosome—the molecular complex in which proteins are made.
Transfer RNA (tRNA) works with mRNA to make sure the right amino acids are inserted into the forming protein.
Ribosomal RNA (rRNA), together with proteins, makes up ribosomes and functions to recognize the mRNA and tRNA that are presented to the ribosomal complex.
Nerve cells, also known as neurons, carry information through our bodies using electrical impulses and chemical messengers called neurotransmitters. A nerve cell’s size and shape depend on its role and location, but nearly all nerve cells have three main parts:
Dendrites that extend like branches and receive signals
A cell body containing the nucleus that holds the genetic material of the cell and controls its actions
Like skin that covers and protects our bodies, membranes surround and protect cells and organelles. Membranes are semi-fluid barriers composed mainly of lipids and proteins. They provide structure; control the import and export of molecules such as ions, nutrients, and toxins; and support cellular communication.
The lipids that compose membranes are primarily phospholipids. (Cholesterol is another lipid often present in membranes that helps regulate their stiffness.) Phospholipids have hydrophilic (water-loving) “heads” and hydrophobic (water-fearing) “tails.” Within the human body, a water-loving environment, they line up so that their tails face one another and their heads point outward. In membranes, this alignment makes a bilayer barrier that is two lipid molecules deep.
Formation of a biofilm often involves a process called quorum sensing. In this process, microbes detect when they reach a certain population density and change their behavior in ways that help them function as a community.
Apoptosis is the process by which cells in the body die in a controlled and predictable way because they have DNA damage or are no longer needed. The term comes from a Greek word meaning “falling off,” as in leaves falling from a tree.
When a cell undergoes apoptosis, it shrinks and pulls away from its neighbors. As the cytoskeleton that gives it shape and structure collapses, the envelope around the cell’s nucleus breaks down, and its DNA breaks into pieces. Its surface changes, signaling its death to other cells and leading a healthy cell to engulf the dying one and recycle its components.
The cytoskeleton is a collection of fibers that gives shape and support to cells, like the skeleton does for our bodies. It also allows movement within the cell and, in some cases, by the entire cell. Three different types of fibers make up the cytoskeleton: actin filaments, intermediate filaments, and microtubules.
Actin filaments contract or lengthen to give cells the flexibility to move and change shape. Along with the protein myosin, they’re responsible for muscle contraction, including voluntary movement and involuntary muscle contractions, such as our heartbeats. Actin filaments are the thinnest and most brittle of the cytoskeletal fibers, but they’re also the most versatile in terms of shape.