The Phospholipids: The Plasma Membrane

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The plasma membrane also known as the cell membrane is found in every cell. The cell membrane is around 7-10nm, making it difficult to view even with a transmission scanning electron microscope (it only shows a double black line), this means that no one knows exactly what the membrane looks like. All membranes have the same basic structure made up from phospholipids (fats). The membrane is made up of a phospholipid bilayer; consisting of a polar phosphate head and two fatty acid tails. The head is made from an alcohol and glycerol group and has a non-polar fatty acid tail made up from two strings of hydrogen and carbon atoms. The head cannot pass through the tails giving the bilayer stability. Despite the stability of the bilayer, the phospholipid …show more content…
Also the proteins can move laterally through the membrane giving it fluidity. The fluid mosaic model is arranged in a phospholipid bilayer, with intrinsic and extrinsic proteins embedded between the phospholipids, for example channel (carrier) proteins allow molecules to pass through the hydrophilic channel of the membrane. Cholesterol molecules are hydrophobic and made up from four rings of carbon and hydrogen atoms. Cholesterol is found in between the phospholipids in the tail to reduce fluidity and permeability, consequently increasing the stability by making it more complete. Decreasing the permeability is helpful as it stops the membrane from breaking down. The membrane can become leaky when it is heated because the molecules have more kinetic energy and collide more often, making the membrane unstable. If the membrane becomes leaky more molecules can pass through the membrane that won 't be controlled by the nucleus. Glycolipids bind to glycoproteins (the extrinsic proteins in the membrane) these are used for cell recognition. The plasma membrane and the cytoskeleton interact closely together, helping to provide shape to the …show more content…
The nucleus has two membranes which are separated by perinuclear space. The plasma membrane of the nucleus is useful for transcription as it keeps the DNA within the nucleolus but also allows the DNA to leave the cell through endocytosis, the DNA leaves the nucleus in the form of mRNA. The membrane controls what goes in out of the cell through the nuclear pores. The mitochondria have a double membrane like the nucleus: it has an outer membrane and an inner folded membrane forming cristae. The inner membrane contains enzymes to help with aerobic respiration, and is folded to increase the surface area therefore increasing the rate of reaction for the production of ATP. The chloroplasts have three membranes: an inner and outer membrane and thylakoids stacked into grana. The inner and outer membrane holds the stroma, which makes up most of the mass of the organelle. The outer membrane is partially permeable to allow small molecules or ions to pass through. Chlorophyll is stored in the thylakoids for photosynthesis.

The lungs are an example of an organ in the human body which requires a thin cell membrane for the exchange of gases used in respiration, the alveoli have extremely thin walls of about 0.5μm thick. They are also found next to the cappillaries which have thin walls aswell this means that the rate of diffusion is increased

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