Have you ever wondered what makes up a cell? Cells are the basic units of life, but they are not simple blobs of protoplasm. They are complex and dynamic systems that perform various functions and interact with their environment. Cells are composed of smaller structures called organelles, which are specialized parts of the cell that have specific roles and tasks. Organelles are like the organs of the eukaryotic cell, each with its own function and structure.
The nucleus is the control center of the cell. It contains the genetic material (DNA) that carries the instructions for making proteins and other molecules that the cell needs. The DNA is organized into structures called chromosomes, which are visible under a microscope during cell division. The nucleus is surrounded by a double membrane called the nuclear envelope, which has pores that allow the passage of molecules in and out. The nucleus also contains a small spherical structure called the nucleolus where ribosomes are made.
The cell membrane is the outer layer of the cell that separates it from its surroundings. It is made of a phospholipid bilayer, which has two layers of lipid molecules with hydrophilic (water-loving) heads facing outward and hydrophobic (water-fearing) tails facing inward. The cell membrane is also embedded with various proteins that act as receptors, transporters, enzymes, or anchors for other molecules. The cell membrane is selectively permeable. It regulates what enters and exits the cell and maintains the cell's homeostasis.
The cell wall is an extra layer of protection and support that surrounds the cell membrane of some cells, such as plant cells, fungal cells, and some bacterial cells. The cell wall is made of different materials depending on the type of cell. For example, plant cell walls are mainly composed of cellulose, a polysaccharide that gives plants their rigidity and strength. The cell wall also helps to maintain the shape and size of the cell and prevents it from bursting due to osmotic pressure.
Mitochondria are the powerhouses of the cell. They are responsible for producing energy in the form of ATP, which is used to fuel various cellular processes. Mitochondria have a double membrane: an outer membrane that covers the whole organelle and an inner membrane that have inward folding structures called cristae. The cristae increase the surface area for chemical reactions to take place. Mitochondria also have their own DNA and ribosomes, which suggests that they evolved from ancient bacteria that were engulfed by larger cells.
Chloroplasts are organelles that are found only in plant cells and some algae. They are responsible for photosynthesis, which is the process of converting light energy into chemical energy. Chloroplasts have a double membrane: an outer membrane that covers the whole organelle and an inner membrane that forms flattened sacs called thylakoids. The thylakoids contain chlorophyll, a green pigment that absorbs light and transfers electrons to generate ATP and NADPH. The thylakoids are stacked into structures called grana, which are connected by stroma lamellae. The stroma is the fluid-filled space inside the chloroplast where carbon dioxide is fixed into sugars using ATP and NADPH.
Ribosomes are organelles that are responsible for protein synthesis. They are made of two subunits: a large subunit and a small subunit. Each subunit is composed of ribosomal RNA (rRNA) and proteins. Ribosomes can be found either free in the cytoplasm or attached to the endoplasmic reticulum (ER). Free ribosomes make proteins that stay in the cytoplasm or go to other organelles, while ER-bound ribosomes make proteins that are exported out of the cell or inserted into membranes.
The endoplasmic reticulum (ER) is a network of membranous tubules and sacs that extends throughout the cytoplasm. The ER has two types: smooth and rough. The smooth ER lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage. The rough ER has ribosomes attached to its surface and is involved in protein synthesis and modification. The ER also acts as a transport system for molecules that are destined for other organelles or the cell membrane.
The Golgi body, also known as the Golgi apparatus or the Golgi complex, is an organelle that consists of flattened membranous sacs called cisternae. The Golgi body receives proteins and lipids from the ER and modifies them by adding sugars, phosphates, or other groups. The Golgi body also sorts and packages the modified molecules into vesicles that are either sent to other organelles, such as lysosomes or peroxisomes, or exported out of the cell via exocytosis.
Vacuoles are organelles that are used for storage and maintenance of the cell. Vacuoles can store water, ions, nutrients, waste products, or pigments. They can also help to maintain the cell's pH, osmotic pressure, and turgor pressure. They vary in size and number depending on the type of cell. For example, plant cells have a large central vacuole that occupies most of the cell's volume and provides support and rigidity. Animal cells have smaller vacuoles that are more numerous and scattered throughout the cytoplasm.
Lysosomes are organelles that contain digestive enzymes that break down macromolecules, such as proteins, lipids, nucleic acids, or polysaccharides. They also digest worn-out organelles, foreign particles, or pathogens that enter the cell. Lysosomes have a single membrane that protects the rest of the cell from the acidic and hydrolytic environment inside the lysosome. They fuse with vesicles that carry the materials to be digested and release the products into the cytoplasm.
Peroxisomes are organelles that contain enzymes that catalyze various oxidative reactions, such as breaking down fatty acids or amino acids. Peroxisomes also detoxify harmful substances, such as alcohol or hydrogen peroxide, by converting them into water and oxygen.