Plasma Membrane PDF
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Uploaded by AwesomePathos8986
Roma Tre University
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Summary
This document provides an overview of the plasma membrane, its structure, function, and a brief history, including the fluid mosaic model, and different types of lipids such as saturated and unsaturated fatty acids, triglycerides while including the roles of proteins and Cholesterol.
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# The Plasma Membrane The plasma membrane surrounds the cell, controls the exchange of substances with the outside, and perceives chemical signals. ## Functions - **Delimits** + **is a barrier of permeability** - **Mediates** the flow of substances - **Receives** signals - **Generates** enviro...
# The Plasma Membrane The plasma membrane surrounds the cell, controls the exchange of substances with the outside, and perceives chemical signals. ## Functions - **Delimits** + **is a barrier of permeability** - **Mediates** the flow of substances - **Receives** signals - **Generates** environments (compartmentalization) ## Structure - **Double phospholipid layer** = **hydrophobic substance** soluble in organic solvents ### Structure of the phospholipid layer - **Hydrophilic head** formed by the phosphate group - **Hydrophobic tail** formed by the fatty acids #### Saturated fatty acid - Each C atom is bonded to 4 other atoms, e.g. stearic acid - Linear structure, single bonds #### Unsaturated fatty acid - Contains a double bond that prevents molecule rotation, e.g. oleic acid with *cis* configuration *Changes the structure noticeably, the *trans* variant deviates slightly.* #### The interaction of fatty acids and glycerol - **Fatty acid** interacts with **glycerol** (trivalent alcohol, 3 OH groups) to form a **triglyceride** (ester bond formation with the loss of H<sub>2</sub>O) #### Triglycerides - **Saturated fatty acid** (animal fats, butter) - **Unsaturated fatty acid** (vegetable fats, oil) Adding hydrogen to unsaturated fats can turn them into saturated fats (e.g., margarine production). ### Other important lipids - **Sphingolipids** from sphingosine (aminoalcohol), e.g., glycolipids - **Cholesterol** 4-ring hydrocarbon steroid ## The Plasma Membrane: A Brief History - **1880:** Overton theorized the existence of a lipidic membrane - **1920:** Langmuir measured the surface area of oil solution - **1930:** Gorte and Grendel theorized the existence of the phospholipid bilayer - **1930:** Danielli and Davson theorized the presence of a protein layer - **1960:** Robertson discovered that all membranes are the same - **1970:** Singer-Nicholson model of the plasma membrane. ## The Fluid Mosaic Model of the Plasma Membrane - The plasma membrane is similar to a **mosaic** of **proteins** dispersed in a **phospholipid bilayer** that acts as a **fluid**. - **Proteins** are embedded in the bilayer and can either be: - **Integral:** embedded in the hydrophobic layer of the lipid film - **Peripheral:** on the polar heads of the phospholipids - **Anchored:** anchored to the membrane via lipids ## Characteristics of the Plasma Membrane - **Discontinuity**: integral proteins disrupt the lipid structure. - **Fluidity:** The cell membrane is fluid and can move laterally. - Unsaturated fatty acids lead to high fluidity. - Saturated fatty acids lead to low fluidity. - Cholesterol can either increase fluidity or decrease fluidity, depending on the concentration. - **Asymmetry**: The lipid molecules are arranged asymmetrically between the inner and outer layers of the plasma membrane. - **Cytoplasmic side**: Phosphatidylinositol (in response to external stimuli) - **Inner side**: Phosphoethanolamine (membrane curvature)
