Lecture 2 The Cell Membrane Function in Transport Introduction 1665 Robert Hooke inspected thin slices of cork and found they consisted of millions of small irregular units This research produced the cell theory o Cells are building blocks of all plants and animals o All cells come from division of preexisting cells o Cells are smallest units that perform all vital physiological functions o Each cell maintains homeostasis at cellular level Cytology the study of cellular structure and function part of cell biology integrates aspects of biology chemistry and physics Two general classes of cells o 1 Sex cells germ reproductive cells are either the sperm of males or oocytes of females o 2 Somatic cells include all other cells in human body The plasma membrane separates the cell from its surrounding environment and performs various 3 1 Plasma Membrane functions Extracellular Fluid Interstitial Fluid A watery medium that surrounds a cell Plasma membrane cell membrane separates cytoplasm inside of cell from extracellular fluid o Cytoplasm region of cell found between the plasma membrane and the nuclear membrane o Cytosol liquid component of the cytoplasm o Organelles Intracellular structures Plasma Membrane outer boundary of a cell also called cell membrane Functions of the Plasma Membrane o 1 Physical isolation physical barrier that separates inside of cell from surrounding extracellular fluid o 2 Regulation of Exchange with Environment plasma membrane controls entry of ions and nutrients eliminations of wastes and release of secretions o 3 Sensitivity to Environment first part of the cell affected by changes in the composition concentration or pH of extracellular fluid Contain receptors that allow cell to recognize respond to specific molecules in environment o 4 Structural Support specialized connections between plasma membrane or between membranes and extracellular materials give tissues stability Characteristics of the Plasma Membrane o Plasma membrane is extremely thin o Composed Of 1 Lipids 2 Proteins 3 Carbohydrates Membrane Lipids form most of the surface area of the plasma membrane but only make up 42 of its weight form two layers Plasma membrane is called the Phospholipid bilayer phospholipid molecules in it Has hydrophilic end phosphate portion and hydrophobic end lipid portion In each half of bilayer lie with hydrophilic heads at membrane surface and hydrophobic tails in inside Also contains cholesterol and small quantities of other lipids Water and solutes cannot cross the lipid portion of the plasma membrane Membrane proteins account for about 55 of weight of plasma membrane Integral Proteins part of membrane structure and cannot be removed with damaging destroying the membrane o Most span the width of the membrane one or more times therefore known as Peripheral proteins bound to inner or outer surface of the membrane and easily transmembrane proteins o Greatly separated from it Different types of Functional Proteins o 1 Anchoring Proteins attach plasma membrane to other structures and stabilize its position Inside cell membrane proteins are bound to the cytoskeleton Outside the cell other membrane proteins may attach cell to extracellular protein fibers or to another cell o 2 Recognition Proteins identifiers cells of immune system recognize other cells as normal or abnormal based on presence or absence of characteristic recognition proteins o 3 Enzymes may be integral or peripheral catalyze reactions in extracellular fluid or in cytosol depending on location of the protein and its active site o 4 Receptor Proteins sensitive to the presence of specific extracellular molecules called ligands in the activity of the cell Extracellular ligand will bind to appropriate receptor causing changes o 5 Carrier Proteins bind solutes and transport them across the plasma membrane May require ATP as energy source o 6 Channels some integral proteins contain a central pore or channel that forms a passageway across the plasma membrane Permits movement of water and small solutes across plasma membrane Many are highly specific and permit passage of only one ion Membrane Carbohydrates account for about 3 of weight of plasma membrane components of complex molecules such as proteoglycans glycoproteins and glycolipids Carbohydrates of these molecules extend beyond outer surface of membrane forming layer known as the glycocalyx which has the functions of Functions of Glycocalyx o 1 Lubrication and Protection glycoproteins and glycolipids form a viscous layer that lubricates and protects plasma membrane o 2 Anchoring and Locomotion help anchor cell in place due to stickiness takes part in locomotion of specialized cells o 3 Specificity in Binding glycoproteins and lipids can function as receptors binding specific extracellular compounds o 4 Recognition body s immune system recognizes its own membrane glycoproteins and lipids as self rather than foreign keeping immune system from attacking own cells while still recognizing invading pathogens 3 2 Cell Organelles Organelles within the cytoplasm perform particular functions Cytoplasm general term for the material located between the plasma membrane and membrane surrounding nucleus Contains more proteins than the extracellular fluid Contains cytosol intracellular fluid contains dissolved nutrients ions soluble and insoluble proteins and waste products Contains organelles structures suspended within cytosol that perform specific functions for the cell The Cytosol Cytosol is different from extracellular fluid o Concentration of potassium ions is much higher in cytosol concentration of sodium ions is lower in cytosol o Cytosol contains higher concentration of suspended proteins many being enzymes that regulate metabolic operations others associated with various organelles Consistency of cytosol determined largely by enzymes and cytoskeletal proteins o Cytosol contains small amounts of carbohydrates small reserves for amino acids and for lipids extracellular fluid is a transport medium only and no reserves are stored there The Organelles and functioning normally Organelles internal structures that perform most of the tasks that keep a cell alive o Non membranous not completely enclosed by membranes and all their components are in direct contact with cytosol Cytoskeleton microvilli centrioles cilia ribosomes proteasomes o Membranous isolated from cytosol by phospholipid membranes just as plasma membrane isolates cytosol from extracellular fluid
View Full Document
Unlocking...