Plasma membrane diagram

\( \newcommand\) • • • • • • • • • Cell Wall, Plasma Membrane, and Middle Lamella Figure \(\PageIndex\): The image above shows cells in the epidermis of a red pepper. Two locations are circled and labeled as plasmodesmata. In each of these circles, there is a section of the cell wall that appears to be missing. This is where a section of the plasma membrane traverses through a channel in the middle lamella and cell walls of both cells. Photo by Maria Morrow, The Nucleus Figure \(\PageIndex\): The large, golden, globose structure is an onion cell nucleus, magnification 3000x. Berkshire Community College Bioscience Image Library, CC0, via Wikimedia Commons. Chloroplasts Chloroplasts are plastids that contain green pigments called chlorophylls. Figure \(\PageIndex\): A diagram of chloroplast anatomy. There are two membranes, the outer and inner membrane, that enclose this structure. Within, there are stacks of flat discs. Each stack is called a granum and each individual disc is a thylakoid. The grana float within a jelly-like matrix called the stroma. Artwork by Nikki Harris, Chromoplasts Chromoplasts are plastids that do not contain chlorophyll, but do contain other pigments, such as carotenoids. Carotenoid pigments reflect colors like yellow, orange, and red. Figure \(\PageIndex\): In this image of red pepper epidermal cells, the chromoplasts are larger and easier to distinguish. Each cell is filled with circular, red discs. These are chromoplasts that contain carotenoids....

Learning Objectives • Describe the structure of cell membranes • Identify components of the cell membrane, including phospholipids, cholesterol, proteins, and carbohydrates • Explain why hydrophilic substances cannot pass through the interior of the cell membrane Structure of the Cell Membrane A cell’s plasma membrane defines the boundary of the cell and determines the nature of its contact with the environment. Cells exclude some substances, take in others, and excrete still others, all in controlled quantities. Plasma membranes enclose the borders of cells, but rather than being a static bag, they are dynamic and constantly in flux. The plasma membrane must be sufficiently flexible to allow certain cells, such as red blood cells and white blood cells, to change shape as they pass through narrow capillaries. These are the more obvious functions of a plasma membrane. In addition, the surface of the plasma membrane carries markers that allow cells to recognize one another, which is vital as tissues and organs form during early development, and which later plays a role in the “self” versus “non-self” distinction of the immune response. The plasma membrane also carries receptors, which are attachment sites for specific substances that interact with the cell. Each receptor is structured to bind with a specific substance. For example, surface receptors of the membrane create changes in the interior, such as changes in enzymes of metabolic pathways. These metabolic pathways migh...

The currently widely accepted model is the fluid mosaic model for the basic structure of the plasma membrane. This model was first proposed in the year 1972. According to the fluid mosaic model, the major components of the plasma membrane include phospholipids, proteins, and cholesterols. • A phospholipid is glycerol or lipid, which has two tails of fatty acids, and head of phosphate. A phospholipid forms a bilayer in the plasma membrane with the tail pointing in the inward direction. • Cholesterol is another kind of lipid composed of four fused rings of carbons. It is found alongside the phospholipids in the membrane core. • The proteins present in the membrane may be embedded into the plasma membrane (transmembrane proteins) or may be present on the surface (peripheral proteins). • The group of carbohydrates is present only on the outer surface of the cell membrane or plasma membrane. When attached to the proteins are known as glycoproteins and when attached to the lipids are known as glycolipids. Got a question on this topic? The phospholipids are arranged in the form of the lipid bilayer. They make the basic overall fabric of the cell membrane. The phospholipids are amphipathic in nature (consists of both hydrophobic and hydrophilic portions). The hydrophilic or water-loving part of the phospholipid is its head, which faced towards the exterior direction. It is negatively charged with the phosphate group. Since water is a polar molecule, it forms an electrostatic inter...

\( \newcommand\) • • • • • • • • In eukaryotic cells, the plasma membrane surrounds a cytoplasm filled with ribosomes and organelles. Organelles are structures that are themselves encased in membranes. Some organelles (nuclei, mitochondria, chloroplasts) are even surrounded by double membranes. All cellular membranes are composed of two layers of phospholipids embedded with proteins. All are selectively permeable (semi-permeable), allowing only certain substances to cross the membrane. The unique functions of cellular membranes are due to their different phospholipid and protein compositions. Decades of research have revealed these functions (see earlier discussions of mitochondrial and chloroplast function for instance). Here we’ll describe general features of membranes, using the plasma membrane as our example. A. The Phospholipid Bilayer Gorter and Grendel predicted the bilayer membrane structure as early as 1925. They knew that red blood cells (erythrocytes) have no nucleus or other organelles, and thus have only a plasma membrane. They also knew that the major chemical component of these membranes were phospholipids. The space-filling molecular model below shows the basic structure of phospholipids, highlighting their hydrophilic (polar) heads and hydrophobic tails. Molecules with hydrophilic and hydrophobic domains are amphipathic molecules. Gorter and Grendel had measured the surface area of red blood cells. They then did a ‘blood count’ and then disrupted a known n...

Structure of Plasma Membranes The plasma membrane (also known as the cell membrane or cytoplasmic membrane) is a biological membrane that separates the interior of a cell from its outside environment. The primary function of the plasma membrane is to protect the cell from its surroundings. Composed of a phospholipid bilayer with embedded proteins, the plasma membrane is selectively permeable to ions and organic molecules and regulates the movement of substances in and out of cells. Plasma membranes must be very flexible in order to allow certain cells, such as red blood cells and white blood cells, to change shape as they pass through narrow capillaries. The plasma membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell, and in attaching to the extracellular matrix and other cells to help group cells together to form tissues. The membrane also maintains the cell potential. In short, if the cell is represented by a castle, the plasma membrane is the wall that provides structure for the buildings inside the wall, regulates which people leave and enter the castle, and conveys messages to and from neighboring castles. Just as a hole in the wall can be a disaster for the castle, a rupture in the plasma membrane causes the cell to lyse and die. Figure \(\PageIndex\): The plasma membrane: The plasma membrane is composed of phospholipids and proteins that provide a barrier between the external environment and the cell, regulate the transportation of m...

Eukaryotic cells also have organelles, which are membrane-bound structures found within the cell. If you looked at eukaryotic cells under a microscope, you'd see distinct structures of all shapes and sizes. Prokaryotic cells, on the other hand, would look more uniform because they don't have those membrane-bound structures to break up the cell. Each phospholipid molecule is made up of a hydrophilic (or water-loving) phosphate head, plus two hydrophobic (or water-hating) fatty acids. The double membrane forms when two layers of phospholipids line up tail to tail, with the fatty acids forming the inner layer of the membrane and the phosphate groups on the outside. If a cell membrane doesn't sound all that strong and secure, you're right – it's not! So your cells need a cytoskeleton underneath to help maintain the cell's shape. The cytoskeleton is made up of structural proteins that are strong enough to support the cell, and that can even help the cell grow and move. • Microfilaments: The smallest class of filaments in the cytoskeleton, microfilaments are made of a protein called actin. Actin is highly dynamic – actin fibers can easily get shorter or longer, depending what your cell needs. Actin filaments are especially important for cytokinesis (when one cell splits into two at the end of mitosis) and also plays a key role in cell transport and mobility. The plant cell wall is part of what helps plants stand up straight (at least, until they're so deprived of water that they...

What is Plasma Membrane? An outermost envelope-like membrane or a structure, which surrounds the cell and its organelles is called the plasma membrane. It is a double membraned cell organelle, which is also called the phospholipid bilayer and is present both in prokaryotic and eukaryotic cells. In all living cells, the plasma membrane functions as the boundary and is selectively permeable, by allowing the entry and exit of certain selective substances. Along with these, the plasma membrane also acts as a connecting system by providing a connection between the cell and its environment. Explore more: Structure of Plasma Membrane A plasma membrane is mainly composed of carbohydrates, phospholipids, proteins, and conjugated molecules, and it is about 5 to 8 nm in thickness. The plasma membrane is a flexible, lipid bilayer that surrounds and contains the cytoplasm of the cell. Based on their arrangement of molecules and the presence of certain specialized components, it is also described as the fluid mosaic model. The fluid mosaic model was first proposed in the year 1972 by American biologists Garth L. Nicolson and Seymour Jonathan Singer. The fluid mosaic model describes in detail, the plasma membrane structure in the eukaryotic cells, and how well it is arranged along with their components – phospholipids, proteins, carbohydrates and cholesterol. These components give a fluid appearance to the plasma membrane. Explore more: Functions of Plasma Membrane • The plasma membrane ...