![]() Proteins that use ATP to move substances from a low concentration to a high concentration across the membrane.Specific proteins are also used for facilitated diffusion.Integral proteins that span the membrane and provide a passageway for molecules to move from an area of high concentration to low concentration.Glycoproteins on the surface can also be used for cell identification purposes.Receptors for neurotransmitters at synapses between two nerve cells.Proteins that form tight bonds between adjacent cells in tissues and organs.Many of these enzymes catalyze metabolic reactions or are a part of a metabolic pathway, such as ATP Synthase in aerobic respiration.Integral proteins that catalyze specific chemical reactions.When the hormone binds, it causes the receptor protein to undergo a conformational change, which signals the cell to perform a function.Proteins embedded in the membrane, which bind to specific hormones. ![]() Hormone binding sites (receptor proteins) Lipid chains with double bonds (unsaturated fatty acids) have kinked hydrocarbon tails that are harder to pack together.Shorter fatty acid tails will increase fluidity as they are less viscous and more susceptible to changes in kinetic energy.Phospholipids may vary in the length and relative saturation of the fatty acid tails To increase stability, many cells have cholesterol imbedded between the phospholipids.Even though it is a very stable structure, it is still fluid, as the phospholipids can move along the horizontal plane.This forms a very stable structure that surrounds the cell because of the attractions and bonds that are formed between the heads to the water and to each other, and the hydrophobic interactions between the tails.When placed in water, the phospholipids naturally form a double layer with the heads facing outwards towards the water and the tails facing each other inwards.The fatty acid hydrocarbon tail has no charge and is therefore repelled by water.The phospholipid head contains a negatively charged phosphate group which because of its charge is attracted water because of its polarity.This property is described as Amphipathic.Cell membranes are composed of phospholipids that consist of a hydrophilic (attracted to water) head and a hydrophobic (repelled by water) tail.Two fatty acid tails (may be saturated or unsaturated).A glycerol molecule (replaced by sphingosine in sphingomyelin).Phospholipids typically share a common basic structure that includes: Phospholipids are one of the principal components of cell membranes (in conjunction with membrane proteins)
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