Biology Essay: Parts of a Cell
Kate Rowe
Biology 4
10-8-09
Biology Essay: Parts of a Cell
Describe the fluid-mosaic model of a plasma membrane. Discuss the role of the membrane in the movement of materials through each of the following processes:
a.) Active Transport
b.) Passive Transport All living cells contain a plasma membrane, which acts a boundary for the cell. The plasma membrane regulates the cell’s chemical composition because it uses selective permeability to allow certain substances to enter or exit the cell more easily than others. The formation of this membrane is believed to be one of the earliest parts of evolution as it was the first method of a cell taking in nutrients and eliminating waste. This idea behind selective permeability is critical to life because this process allows cells to survive and maintain their chemical composition. Today, scientists accept the fluid-mosaic as the structure of the plasma membrane. The fluid mosaic model consists of a mosaic of proteins imbedded into a bilayer of phospholipids. Phospholipids obtain the ability to form membranes because of the fact that it is an amphipathic molecule. This means it contains polar hydrophilic heads and nonpolar hydrophobic tails, which make up the hydrophilic and hydrophobic regions of the membrane. The two types of proteins found in the fluid-mosaic model are integral proteins, which go through the hydrophobic core of the lipid bilayer, and peripheral proteins, which are appendages that are attached to the surface of the membrane. These proteins have many functions for the membrane including transport, enzymatic activity, signal transduction, cell-to-cell recognition, intercellular joining, and attachment to the cytoskeleton and the extra cellular matrix. The fluidity of the membrane, according to this model, is important because it allows for the processes of endocytosis and exocytosis to occur. Membranes are fluid due to the lateral movement of the phospholipids. Cholesterol molecules are found among
Biology 4
10-8-09
Biology Essay: Parts of a Cell
Describe the fluid-mosaic model of a plasma membrane. Discuss the role of the membrane in the movement of materials through each of the following processes:
a.) Active Transport
b.) Passive Transport All living cells contain a plasma membrane, which acts a boundary for the cell. The plasma membrane regulates the cell’s chemical composition because it uses selective permeability to allow certain substances to enter or exit the cell more easily than others. The formation of this membrane is believed to be one of the earliest parts of evolution as it was the first method of a cell taking in nutrients and eliminating waste. This idea behind selective permeability is critical to life because this process allows cells to survive and maintain their chemical composition. Today, scientists accept the fluid-mosaic as the structure of the plasma membrane. The fluid mosaic model consists of a mosaic of proteins imbedded into a bilayer of phospholipids. Phospholipids obtain the ability to form membranes because of the fact that it is an amphipathic molecule. This means it contains polar hydrophilic heads and nonpolar hydrophobic tails, which make up the hydrophilic and hydrophobic regions of the membrane. The two types of proteins found in the fluid-mosaic model are integral proteins, which go through the hydrophobic core of the lipid bilayer, and peripheral proteins, which are appendages that are attached to the surface of the membrane. These proteins have many functions for the membrane including transport, enzymatic activity, signal transduction, cell-to-cell recognition, intercellular joining, and attachment to the cytoskeleton and the extra cellular matrix. The fluidity of the membrane, according to this model, is important because it allows for the processes of endocytosis and exocytosis to occur. Membranes are fluid due to the lateral movement of the phospholipids. Cholesterol molecules are found among