Cells To Systems Lecture 8- The Molecules Of The Cell Membrane

Front 1

biological membranes are composed mainly of

Back 1

lipids and protein

Front 2

functions of cell membrane

Back 2

1. regulate passage of substances in and out of cell
2. compartmentalize internal components - provides physical barrier so that cellular reaction can occur in appropriate compartments
3. contains membrane proteins serving as receptors that recognize and receive info from chem messengers
4. connect to neighbouring cells by means of attachment between membrane proteins and anchors cells to molecules in extracellular matrix
5. contains enzymes that catalyze chem reactions

Front 3

phospholipids
phsophglycerides

Back 3

have a glycerol backbone, two fatty acid chains, a phosphate group and usually an alcohol
involved in signal transduction

Front 4

sphingolipids

Back 4

derived from sphingosine ( a more complex alcohol)

Front 5

cholesterol

Back 5

major membrane lipid present in roughly equal amounts with phospholipids. large disc like molecule with one end hydrophilic and the rest hydrophobic and embedded in the hydrophobic portion of the plasma membrane
makes the membrane less flexible and even less permeable

Front 6

glycolipids

Back 6

a lipid with a carbohydrate group attached to the lipids hydrophilic head. found exclusivley on the extracellular side of the plasma membrane

Front 7

hydrophilic

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polar
glycerol
phosphate
alochol

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hydrophobic

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non polar
2 fatty acid chains

Front 9

hydrocarbon interior makes them impermeable to

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polar molecules such as aa, sugars, proteins and nucliec acids

Front 10

membrane lipid tail length

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fluidity decreases with length due to increased can der waal interactions

Front 11

degree of unsaturation of fatty acids (number of double bonds) affect on membrane fluidity

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unsaturated lipid tails do not pack together as well so that an increase in the degree of unsaturation leads to an increase membrane fluidity

Front 12

amount of cholesterol present affect on membrane fluidity

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cholesterol reduces the fluidity of the membrane, increase the membrane stability by aligning themselves with the fatty acid of the phospholipids

reduces permeability of the membrane to polar structures and may increase membrane permeability to small water molecules such as glucose by a factor of ten

Front 13

temperature affect on membrane fluidity

Back 13

membrane fluidity increases with temperature

Front 14

integral proteins

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contain transmembrane helices that span the entire lipid bilayer once or several times.
amphipathic
polar and non polar regions align themselves with polar water molecules or with non polar fatty acids in the center of the lipid bilayer membrane

Front 15

peripheral proteins

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only bound to one side of the lipid bilayer
include membrane proteins of the cytoplasmic surface that are non covalently bounded to the polar head of the lipid bilayer or already attached to an integral membrane protein

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function of membrane proteins

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1. act as receptors for external signals
2. involved in selective transport of molecules across the membrane
3. control adhesion and signalling between cells
4. particpiate in electron transport and oxidative phosphorylation

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non polar molecules

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fatty acids, steriod hormones, CO2, O2
pass freely

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small uncharged polar molecules

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H2O
pass freely but slower than non polar molecules

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large polar molecules and ions

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Na+, K+
dont pass freely

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macromolecules

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proteins, polysacchrides, nucelic acids
dont pass

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diffusion

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movement of a substance from one location to another by random motion of its molecules or ions

molecules move from an area of high concentration to an area of low concentration

1. oxygen and nutrients enter the blood
2. molecules leave the blood and enter the ECF
3. exchange of molecules between the cell and ECF is partially by diffusion

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movement of ions is affected by

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electrical charge

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anions move to

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postivley charged areas

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cations move to

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negativley charged areas

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movement of ions of regulated by

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electrochemical gradient
both a concentration gradient and a electrical gradient

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passive diffusion

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may occur though a lipid bilayer between the phsopholipids, or through aqueous channels fromed by integral proteins

Front 27

diffusion is dependent on

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polarity/non polarity of a substance
solute size

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pores

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porin
aquaporin
perforin

Front 29

selectivtiy between different ions

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channels differ with respect to the ions they allow through and to the way they regulate flow of these ions

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NA channels are composed of

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alpha and beta components, with alpha having main functional activity

Front 31

voltage aged channels

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conformational state depends on the difference between ionic charges on two sides of the membrane

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external ligand gated

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actetycholine
binding of the ligand alters the conformation state and opens or closes the gate

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characteristics of transporters

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process much faster than simple diffusion
show substrate specificity
can become saturated if solute concentration is high
exhibit competition between structurally similar substances

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primary active transport

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ATP dependent

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cotransport

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coupling of the transport of two compounds across a membrane. uses transmembrane solute gradients as a source of energy.

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endocytosis

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bind to specific protein receptors in the cell membrane to form intracytoplasmic vesicles.

Front 37

exocytosis

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selective export of macromolecules out of the cell