BIOL 2020 Lecture Notes - Lecture 3: Transmembrane Protein, View Camera, Cytoskeleton
Structure and Function of the Plasma Membrane
o You would not be able to have a cell without a membrane, the whole cell is a
compartment
o Even within the cell - compartmentalization can happen inside away from the
exterior environment
o Scaffold for biochemical activity - an area where proteins can latch onto and they have
a much higher chance of interacting with another protein than they would just floating
around the cytoplasm
o Allows for multi protein structures to build
o Provide a selectively permeable barrier - meaning that it doesn't allow to flow in and
out unrestricted
o Only certain things can go through. Such as lipid soluble molecules
o Transporting solutes - depending on what is embedded inside that barrier
o Things that are soluble in water
o Responding to external signals - on the plasma membrane, we have a lot of receptors
that can respond to the external environment. This is important because the cell needs
to be able to respond to the exterior environment which is always changing
o Intercellular interactions - cells can recognize one another and either interact or not
o Energy transduction - imperative to energy production in cells
o Intracellular interactions
o Membrane composition
o Lipids - biomolecular layer
o Proteins - can form up to 60%-70% of membranes
o Carbohydrates - can be added to either membrane lipids or membranes
o Amphipathic remember means that they have hydrophillic parts and hydrophobic parts
o Hydrophobic chains will face one another automatically
o Polar head groups face the water
o In between fatty acid chains, is cholesterol (green)
o Polar head groups face the water inside and outside the cell
o Fatty acid chains face each other (grey)
o Less cholesterol results in more fluid while more cholesterol results in more of a rigid
structure
o Side chains flex every 10 to the 9th (9 billion times a second)
o Does a lateral shift a million times a second
o Lipids "flip flop" which refers to the movement of the lipids from one side to another
o An enzyme is required to do this movement which are called flippases
o This is refers to phospholipids
o Cholesterol flips a lot and goes from one side to another all the time
o They can move in the plane of the membrane very quickly
o Fatty acids the most often
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Document Summary
This is important because the cell needs to be able to respond to the exterior environment which is always changing. Intercellular interactions - cells can recognize one another and either interact or not: energy transduction - imperative to energy production in cells. Integral membrane proteins - these proteins penetrate through the lipid bilayer and they stick out on the other side. Often, thy will loop through the cytoplasm and go through many times. Channel proteins, g coupled receptor proteins are examples of the multiloop proteins: this type of a protein is asymmetric, the part of the protein that comes out on the cytoplasm side will look and act differently. Each individual protein or phospholipid is not distributed in a homogenous manner. This protein is not restricted at all: protein b - is the exact opposite, it is completely stuck and does not move. On the cytoplasmic side, protein b is anchored to the cytoskeleton.
