How Is a Cell's Membrane Suited to Its Functions?

The purpose of these experiments is to examine the driving force behind the movement of substances across a selective or semiperpeable plasma membrane. Experiment simulations examine substances that move passively through a semipermeable membrane, and those that require active transport. Those that move passively through the membrane will do so in these simulations by facilitated diffusion and filtration. The plasma membrane’s structure is composed in such a way that it can discriminate as to which substances can pass into the cell. This enables nutrients to enter the cell, while keeping unwanted substances out. Active

The phospholipid bilayer that makes up the cell membrane is largely made up of a mixture of lipids and proteins. The lipids give the structure the right level of flexibility, while the proteins help to watch and control the cell’s “chemical climate” and also with molecule movement across the bilayer. This means that the proteins, especially the ones that bridge the whole membrane, can allow passage of say electrolytes and non-lipid substances.

“Active transport, the protein transporter moves molecules against, or up, the concentration gradient” (McCance & Huether, pg. 29).

The cell membrane consists of eight distinctive parts that each have their own unique structure and function. The phospholipid bilayer is an integral part of the cell membrane because it is the external layer of the cell membrane and composes the barriers that isolate the internal cell components and organelles from the extracellular environment. It is composed of a series of phospholipids that have a hydrophobic region and a hydrophilic region. These regions are composed of the hydrophilic heads and the hydrophobic tails of the phospholipids, this organization of the polar heads and nonpolar tails allows the heads of the cell to form hydrogen bonds with water molecules while the tails are able to avoid water. The phospholipid bilayer also has many important functions within the cell, it gives the cell shape, provides protection, and it is selectively permeable which allows it to only let very specific molecules pass through its surface. The phospholipid bilayer is an important structure because it prevents harmful and unwanted molecules from entering the cell and isolates organelles which helps to maintain the internal environmental homeostasis of the cell.

All cells in the human body are surrounded by a plasma membrane made up of lipids and proteins which form a barrier. The proteins and lipids in the membrane occupy different roles. The lipids create a semipermeable barrier and the proteins are part of a cross membrane transport. To pass through the membrane a substance goes through a transport known as diffusion. Diffusion is movement of molecules from a high area of concentration to an area of low concentration. There are two different forms of diffusion. One example of diffusion is known as simple diffusion, an unassisted movement of dissolved substances through a selectively permeable membrane (Marieb pg. 54). The

All cells have a cell membrane. The structure of membranes is formed from a double layer of phospholipids with proteins floating in it. The proteins are embedded on the surface and inside or bridge the double layers of phospholipids. This structure is called a mosaic model. The main function of cell membranes is to provide protection and support for the cell and they also control what enter and exit the cell to maintain internal balance, called homeostasis. There are two types of a membrane protein: integral proteins and peripheral proteins. The integral membrane proteins are

All around and inside cells, substances are continuously being moved back and forth across the cell membrane. At any time, a material can have a higher or lower concentration on one side of the cell membrane opposed to the other. The concentration is the amount of solute in a solvent. In which the concentration gradient means that there is more solute in one part of a solvent than another. A solvent is something that dissolves in a solute to create a solution; for example, when salt (solvent) dissolves in the water (solute) to make salt water (solution). There are several types of transport options for a certain substance, but it depends permeability of the membrane, which determines what moves in and out of the cell. The types of cellular transportation that they used were diffusion, osmosis and filtration. Diffusion is the movement of a material from an area of a higher concentration to a lower concentration, while osmosis is the diffusion of just water. Filtration is a passive transport that moves water and other materials across the cell membrane by a pressure from the cardiovascular system (Michener 2015). These are extremely important to the body, because without these transports our cells and organs could not get the nutrients they need nor get rid of the waste that is toxic.

active transport – journeys against the concentration gradient. Molecules go from low to high levels of concentration. Requires the use of ATP.

Lastly, carrier proteins affect whether a molecule will be able to pass through a biological membrane. Carrier proteins are used if a molecule is too large to pass through channels. If there are many carriers, then not only the process will be quick but it will also allow more molecules to come in.

1c. Explain the difference between an integral protein and a peripheral protein in the cell membrane, and give an example of each type (2).

Cell membrane is a selective boundary composed of a unique phospholipid bi-layer structure consisting of lipids, proteins and carbohydrates. This structure regulates the import and export to maintain homeostasis condition inside the cell. (Knox et al., 2014) The plasma membrane is referred as a fluid mosaic which also has selective permeability. The permeability of the membrane can be varied depending on the external conditions. (Mitchel, 2015)

Cell membranes are surrounded by a phospholipid bilayer that provides a semipermeable barrier for cells, separating the cytosol from the extracellular environment. Phospholipids are ampithatic, meaning that they have a hydrophilic head and hydrophobic tail, which causes the heads to face outwards towards the water and the tails inwards, creating the bilayer [figure 1]. Small hydrophobic molecules such as O2 and CO2 and small uncharged polar molecules such as H2O and ethanol can diffuse through this bilayer, however larger molecules and ions cannot, and thus require proteins, which are polymers of amino acids joined together by strong peptide bonds. These proteins feature throughout the membrane, and account for around 50% of its mass [http://www.ncbi.nlm.nih.gov/books/NBK9898/] . Not only are proteins required for transport of molecules through the membrane, but they also transport signals and are necessary for the cell support; throughout this essay I will focus on the pivotal role they play with regards to the transport of these molecules and signals, and what occurs when these functions are inhibited.

The molecular structure of the plasma membrane is known as the fluid mosaic model; mosaic because of the way in which proteins are scattered around and through the membrane, and fluid because although the phospholipid bilayer forms a firm boundary around the cell, it allows molecules and proteins to travel through it freely.

The cellular membrane is a selectively-permeable phospholipid bilayer that also contains embedded proteins as well as cholesterol which gives the membrane its fluidity. A phospholipid molecule has two ends, a head and tail; the head is hydrophilic, meaning it is attracted to water molecules, while the tail end is hydrophobic and not attracted to water molecules. Selectively-permeable means it will let certain molecules into the cell, while making sure certain particles stay out. The proteins located in the membrane take over as the mechanism to move different molecules in and out of the cell.(“What is a semipermeable membrane?, 2015”)

Cells must move materials throughout membranes and cytoplasm in order to keep on maintaining homeostasis. This movement is regulated through cellular membranes, which are selectively permeable. Membranes have phospholipid bilayers, containing embedded proteins. The phospholipid fatty acids hinder the flow of H2O because of its hydrophobic behavior.