In living organisms, food is broken down and turned into energy through complex biochemical processes over the course of many steps. Before you can understand these pathways, it is important to know the structures within a cell that provide the framework for these reactions—the organelles. The three main organelles involved in breaking down food and producing energy are the mitochondria, lysosomes and peroxisomes.
The mitochondria are responsible for breaking down macromolecules such as carbohydrates and fats into molecules that can be further processed by other chemical reactions in the cell, yielding ATP which is then used as an energy source by cells throughout the body. The lysosomes serve as cellular garbage disposals, digestion macromolecules and unwanted storage materials from other organelles or from outside of the cell. Lastly, peroxisomes are responsible for breaking down fatty acids into smaller molecules known as ketone bodies that can be used for energy production during periods of fasting or exercise. Through their coordinated actions, these three organelles play a vital role in providing cells with their much needed energy source to perform their normal metabolic activities.
Overview of Cell Structures
The cell is the fundamental unit of life and every living organism is composed of one or more cells. Cells are highly organized structures with many components and functions, one of which is breaking down food to produce energy. In this heading, we will take a look at the different structures found in a cell and their role in breaking down food.
Mitochondria
Mitochondria are essential parts of eukaryotic cells and are involved in a wide range of metabolic processes, such as producing energy through the breakdown of food and producing compounds to be used in other cellular pathways. Located within the cytoplasm of the cell, mitochondria are often referred to as “the powerhouse of the cell,” given their vital role in cellular energy production. Mitochondria have an outer membrane and an inner membrane, which form folds called cristae that increase the surface area for reactions. mitochondria also contain DNA and ribosomes, allowing them to produce proteins for energy production.
Metabolism often occurs through two major energy-producing pathways: aerobic respiration and anaerobic respiration. During aerobic respiration, oxygen is consumed along with glucose or fats and molecules such as water and carbon dioxide are released as waste products. Aerobic respiration produces more ATP molecules than anaerobic respiration, so it is often utilized when oxygen is available. During anaerobic respiration, ATP can still be produced without oxygen by using different metabolic pathways. When oxygen is not available or in limited supply, both of these pathways can produce energy in the form of ATP molecules for use within a cell for functions such as protein production or movement across a membrane barrier.
Chloroplasts
Chloroplasts are microscopic organelles found within plant cells that perform the task of photosynthesis. These structures contain pigments that allow them to absorb light, making them green in color and giving plants their green appearance. Chloroplasts contain chlorophyll and carotenoids which are important in converting sunlight into energy. With the help of water and carbon dioxide, light energy is converted into chemical energy, releasing oxygen as a byproduct. This process is known as photosynthesis and produces carbohydrates (sugars and starches) that are stored in the cell for later use by the plant during respiration. The molecules produced during photosynthesis provide energy for other cell processes, including the breaking down of food molecules to produce ATP (adenosine triphosphate), which is an energy source used for various metabolic activities.
Vacuoles
Vacuoles are membranous organelles in a eukaryotic cell that store substances, specifically water and other liquids. They hold and release food, ions and other molecules inside the cell as necessary. Vacuoles play an important role in a cell’s metabolism by storing essential enzymes that help break down food products to produce energy. Vacuoles can also be used to store waste products.
The size and location of vacuoles depend on the type of cell, with plant cells having larger central vacuoles or many small vacuoles throughout the cytoplasm and animal cells typically having one much smaller vacuole near the center of the cell. Depending on the type, vacuoles can have shapes ranging from a spherical shape to an elongated or ovular form. Vacuole membranes have various proteins on their surface that are involved in transport processes for ions and molecules coming in or out of the cell as necessary.
In general, vacuoles maintain cellular homeostasis by regulating solute concentrations within different parts of the cell while also eliminating waste out of it.
Lysosomes
Lysosomes are membrane-enclosed organelles found in both plant and animal cells. They are filled with digestive enzymes that can break down proteins, carbohydrates, and lipids. These enzymes are used to digest food during endocytosis, a process of cellular ingestion in which materials enter the cell through the plasma membrane. Lysosomes also play an important role in autophagy, a self-degradative process that functions to recycle macromolecules and proteins.
In addition to carrying out these digestive processes, lysosomes also contain hydrolytic enzymes which can be used to break down toxins inside a cell before they cause damage by releasing them into the environment through exocytosis. In this way, they play an essential role in protecting cells from contaminates and pathogens.
Lysosomes are variable in size but average around 0.2 to 0.7 microns across; their membranes form everchanging shapes as new enzymes enter them for digestion or excretion purposes through endocytosis or exocytosis respectively. Lysosomes contain chemical receptors that recognize specific molecules and which determine which lysis function it will perform once those molecules enter it, making it an incredibly versatile organelle that has largely replaced the single cell version of lysis from before the times of multicellular organisms such as humans.
Breakdown of Food by Cell Structures
Our cells are responsible for breaking down food and converting it into energy. This process, known as cellular respiration, is powered by a host of different cell structures. The cell structures that are essential for breaking down food and producing energy include the mitochondria, chloroplasts, and lysosomes. In this article, we will explore how these cell structures are responsible for breaking down food and producing energy.
Mitochondria
Mitochondria are organelles in cells that are involved in energy production. All foods containing carbohydrates or fats are used as a source of energy by the mitochondria. The macronutrients from food, such as carbohydrates, proteins, and fats, will undergo chemical reactions within the cells to generate ATP which is then used for a variety of functions in the body. Mitochondria use glucose, fatty acids and ketone bodies to produce ATP while other metabolic processes supply additional sources of energy such as amino acids and NADH (Nicotinamide adenine dinucleotide).
Carbohydrates are the main source of energy for the body. Foods such as grains, rice and pasta contain starches that can be broken down into glucose molecules which occur naturally within food sources or in processed form. These molecules then enter the mitochondrion where they undergo a series of biochemical reactions to produce acetyl-CoA which is converted into ATP molecules by oxidative phosphorylation.
Fats from food serve as an additional source of energy for mitochondria. Through a complex breakdown process known as beta-oxidation, fatty acids are converted into Acetyl-CoA which can be further broken down into larger components such as pyruvate or NADH. This makes fats an ideal source of long-term stored energy since they generate more than double the amount of ATP per molecule compared to glucose.
Lastly, ketone bodies may be used by mitochondria when there is not enough glucose available in the bloodstream or through diet. Ketones are mobilized from fat stores during periods of fasting or following low carbohydrate diets and enter directly into mitochondrial respiration following delivery to specific transporters located on their outer membrane surface.
Chloroplasts
Chloroplasts are primarily responsible for photosynthesis in plants and some species of algae. They absorb energy from sunlight to convert water and carbon dioxide into oxygen and organic compounds, such as glucose. During cellular respiration, these glucose molecules are further broken down in a process called glycolysis. The end products of this reaction are pyruvate molecules that enter the mitochondria where they are further broken down through the Krebs cycle and oxidative phosphorylation to produce ATP (energy). This ATP can be used to power cellular activities or occur at a higher level throughout the body, powering larger muscle movements and allowing organisms to go about their daily life.
Vacuoles
Vacuoles are found in both plant and animal cells and play an important role in maintaining the chemical balance of a cell. They are also responsible for digesting and storing food which is then broken down to produce energy for the cell. Vacuoles can store salts, sugars, proteins, lipids, calcium ions, toxins and many other substances.
The membrane of a vacuole works just like the membrane of an organelle — it assists in keeping what is inside isolated from the rest of the cell to maintain stability. When a vacuole senses that certain harmful or unnecessary particles are present, it can pull these into itself or expel them from the cell entirely. In this way, vacuoles act as a form of waste disposal system by secreting or storing away undigestible materials or items that pose a risk to its survival.
A vacuole breaks down macromolecules such as proteins and carbohydrates into smaller molecules like amino acids and monosaccharides which are used to convert carbon dioxide into energy for the cell. Proteins from food will first be broken down into simple amino acids such as cysteine, leucine and tryptophan before being transported across the plasma membrane outside of vacuoles via ionic channels or enzymes secreted by them with help from electrochemical gradients formed between their own internal compartments and external environment. Afterward, these molecules then serve as fuel once they enter mitochondria where ATP production occurs.
Lysosomes
Lysosomes contain an array of hydrolytic enzymes used to break down macromolecules such as proteins, lipids, and nucleic acids. These enzymes are stored within their membrane-bound organelles until they are needed as part of the digestive process by the cells. Lysosomes enable the cell to digest its own waste material, including large molecules that have been broken down from food sources. Additionally, they help to break down large molecules taken in by endocytosis and phagocytosis and utilise the energy created in that reaction to create ATP, which provides energy for the cell to carry out its functions.
