Cell membrane
A cell membrane, also known as a plasma membrane or plasmalemma, is a crucial structure that surrounds all living cells, serving as a protective barrier and organizational framework. It is primarily composed of a semipermeable lipid bilayer that allows selective passage of substances, enabling essential nutrients to enter while blocking harmful toxins. This membrane plays a vital role in maintaining the cell's shape and integrity, as well as facilitating communication and signaling with the external environment.
The cell membrane is rich in biological molecules, primarily proteins and lipids, which perform a variety of essential functions. Proteins embedded in the membrane can move freely or remain fixed, and they are responsible for processes such as transporting materials, linking cells, and relaying signals. Additionally, the membrane's fluid nature allows for dynamic interactions within the cell and between cells.
In plant cells, the cell membrane is complemented by a rigid outer cell wall, providing extra support. Understanding the structure and function of cell membranes is fundamental to the study of biology, as they are integral to the life processes of both single-celled organisms like bacteria and more complex multicellular organisms, including humans.
Cell membrane
A cell is a small building block of life. Groups of cells make up living organisms such as plants and animals. A cell membrane, also called a plasma membrane, is a layer that surrounds a cell for protection and organization purposes. The cell membrane is the gatekeeper of the cell; it allows needed substances to enter the cell and keeps out harmful substances, including toxins. It also helps keep various parts of the cell contained and maintains the cell's shape.
Cell Overview
Cells compose every living organism. They hold all the biological information necessary for a living thing to stay alive and function. Each cell performs a specific function. Cells are very tiny, only about the diameter of a single strand of human hair. Some are even smaller. They can be seen only with the aid of a microscope. Not all cells look the same. Many have adapted for functional purposes and survival in different environments. For example, plant cells have strong outer layers to provide structural support to trees and plants, and muscle cells have elasticity to allow them to contract and relax.
Organisms may be made of a single cell or many cells. Groups of cells make up every part of a human body, from muscles to organs to organ systems. A prokaryote is a single-celled organism without a nucleus. The nucleus is the central part of a cell that controls it and contains genetic material. A eukaryote may be single-celled or multicellular. A eukaryote differs from a prokaryote because it has a nucleus. Bacteria is an example of a prokaryote, and a skin cell is an example of a eukaryote.
Cells are categorized into animal cells and plant cells, which differ from each other in several ways. First, they do not look the same. Animal cells are irregularly shaped, while plant cells typically have regular shapes. A cell membrane surrounds both types of cells. It acts like a barrier to protect the inside of a cell from the environment outside the cell. In a plant cell, a rigid outer layer known as a cell wall surrounds the cell membrane.
Both plant and animal cells contain a nucleus and a thick liquid known as cytoplasm, which is about 70 percent water. The remaining 30 percent is composed of molecules such as nucleic acids, proteins, carbohydrates, and lipids.
Nucleic acids play a part in a cell's genetic code. Two types exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA and RNA work together to build and maintain a cell. Most DNA is found in the nucleus of a cell, while RNA is located in the cytoplasm.
Proteins are molecules made from amino acids, or small chains of molecules. Proteins have many purposes. Proteins known as enzymes convert other molecules into forms that allow a cell to perform a variety of functions, such as ridding a cell of waste.
Carbohydrates are sugars and starches the cell uses for energy. Lipids are fat molecules in the cell membrane that aid in the storage of energy and relay signals inside and outside cells.
Groups of molecules sometimes form organelles. These structures have an intracellular membrane and perform specific tasks. Mitochondria are one type of organelle. They are responsible for producing energy for a cell.
In plant cells' cytoplasm, a cavity known as a vacuole contains liquid to keep the cell firm, and organelles called chloroplasts aid in photosynthesis, the process by which a plant converts light energy into chemical energy (food).
Function of the Cell Membrane
Cell membranes serve as the protectors of cells. They are semipermeable, which means only certain substances can pass through them. Cell membranes remain in a liquid state at physiological temperatures but become thick like gel at cooler temperatures. They are very thin layers made of phospholipids, or fat-based molecules that help regulate which substances can pass through and how much can move into or out of the cell. Glycerophospholipids and cholesterol are the most abundant phospholipids in a cell membrane.
Cell membranes also are composed of proteins that serve many purposes. Proteins account for almost half of the mass of a cell membrane. Some proteins move freely, while others are nested laterally along the cell membrane, protruding from both sides. The nested proteins cannot move and usually are attached to other proteins or anchors outside the cell. Some proteins determine which substances are safe to pass through the cell membrane. Others link cells together in groups that carry out specific tasks. Some proteins send and receive signals from other cells and the environment.
Other types of membranes exist inside cells. A nuclear membrane, or nuclear envelope, surrounds the nucleus of each cell, and an intracellular membrane encases organelles. These membranes protect these cell parts and work like the main cell membrane, allowing certain substances in and out. These membranes also relay messages to other parts within the cell.
Organelles such as mitochondria in animal cells and chloroplasts in plant cells have two membranes instead of one. The outermost layer has tiny openings that allow molecules to pass into and out of it. The inner membrane contains proteins that help create energy for the cell.
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