The

Usman Sumo Friend Tambunan Arli Aditya Parikesit

Bioinformatics Group Faculty of Mathematics and Science University of Indonesia Overview

• Cell membrane separates living cell from nonliving surroundings • thin barrier = 8nm thick • Controls traffic in & out of the cell • selectively permeable • allows some substances to cross more easily than others

• hydrophobic vs hydrophilic • Made of , & other macromolecules Phospholipids Phosphate

• tails

• hydrophobic • Phosphate group head Fatty acid • hydrophilic • Arranged as a bilayer bilayer

polar hydrophilic heads

nonpolar hydrophobic tails

polar hydrophilic heads Phospholipid bilayer

polar hydrophilic heads

nonpolar hydrophobic tails

polar hydrophilic heads More than lipids…

• In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the

Glycoprotein Extracellular fluid

Glycolipid

Phospholipids Cholesterol Transmembrane proteins Peripheral Cytoplasm Filaments of cytoskeleton Membrane fat composition varies • Fat composition affects flexibility

• membrane must be fluid & flexible

• about as fluid as thick salad oil

• % unsaturated fatty acids in phospholipids

• keep membrane less viscous

• cold-adapted organisms, like winter wheat

• increase % in autumn

• cholesterol in membrane Membrane Proteins

• Proteins determine membrane’s specific functions • cell membrane & organelle membranes each have unique collections of proteins • Membrane proteins: • peripheral proteins • loosely bound to surface of membrane

• cell surface identity marker (antigens) • integral proteins

• penetrate lipid bilayer, usually across whole membrane • transmembrane protein • transport proteins • channels, permeases (pumps) Proteins domains anchor molecule

• Within membrane Polar areas of protein • nonpolar amino acids • hydrophobic • anchors protein into membrane • On outer surfaces of membrane

• polar amino acids

• hydrophilic

• extend into extracellular fluid & into cytosol Nonpolar areas of protein H+ Retinal Examples chromophore NH2 water channel in

Porin monomer b-pleated sheets

Bacterial Nonpolar outer (hydrophobic) COOH membrane a-helices in the Cytoplasm cell membrane H+ proton pump channel in photosynthetic bacteria function through conformational change = shape change Many Functions of Membrane Proteins

Outside

Plasma membrane

Inside Transporter Enzyme Cell surface activity receptor

Cell surface Cell adhesion Attachment to the identity marker cytoskeleton Membrane carbohydrates

• Play a key role in cell-cell recognition

• ability of a cell to distinguish one cell from another

• antigens

• important in organ & tissue development

• basis for rejection of foreign cells by The Cell Membrane

Active and Passive Transport Cell Membrane

• Phospholipid bilayer: hydrophilic heads and hydrophobic tails • Semi-permeability • Transport proteins (passive transport channels) • Ion pumps ( pumps) • Receptor proteins (neurons, , immune system) • Carbohydrate chains ( identification cards)

•What is passive transport? What are the three types of passive transport? Passive Transport

• Diffusion - process by which molecules tend to move from an area where they are more concentrated to an area where they are less concentrated Passive Transport

• In Passive Transport - Molecules move down the concentration gradient (no energy required) • 1) simple diffusion -molecules are small enough and soluble can pass directly through the lipid bilayer • 2) – need transport proteins (molecules are either to large or can’t pass through the lipid bilayer themselves) • 3) osmosis – molecules can’t pass through lipid bilayer at all, but water can(movement of water) • Depends on molecule size, lipid solubility, and concentration gradient

Passive Diffusion

• http://www.youtube.com/watch?v=JShwXBWGMyY • http://www.youtube.com/watch?v=s0p1ztrbXPY Solutions

• A mixture of solid particles (solute) and liquid (solvent) • Most common solvent is water • Cells are surrounded by solutions • Three types: isotonic, hypotonic, and hypertonic solutions Isotonic Solutions

• Particles are equal inside and outside of the cell • Water molecules are equal inside and outside of the cell Hypotonic Solutions

• There are more particles inside than outside • There is more water outside the cell • Water will move INTO the cell Hypertonic Solutions

• There are more particles outside • There is more water inside • Water will move OUT OF the cell

Active Transport

• Molecules move against the concentration gradient • Requires energy

• 1. Solute Pumps (Na+-K+-ATPase pump)

• 2. Bulk Transport • Na+-K+-ATPase pump • https://mail.xavierhs.org/exchange/UngerJ/Inbox/No%20Subject-748.EML/07_16ActiveTransport_A.swf/C58EA28C-18C0-4a97-9AF2-036E93DDAFB3/07_16ActiveTransport_A.swf?attach=1

Transport Across The Membrane

• Endocytosis (pinocytosis, phagocytosis): phagocytes (macrophages)- molecules are coming into cells

• Exocytosis: release of proteins, hormones, - release of proteins, hormones, neurotransmitters • http://www.youtube.com/watch?v=4gLtk8Yc1Zc&NR=1

Transport summary

simple diffusion

facilitated diffusion

active ATP transport How about large molecules?

• Moving large molecules into & out of cell

• through vesicles & vacuoles

• endocytosis

• phagocytosis = “cellular eating”

• pinocytosis = “cellular drinking”

• exocytosis

exocytosis Endocytosis

fuse with phagocytosis lysosome for digestion

pinocytosis non-specific process

triggered by receptor-mediated molecular endocytosis signal The Special Case of Water

Movement of water across the cell membrane

2007-2008 Osmosis is diffusion of water

• Water is very important to life, so we talk about water separately • Diffusion of water from high concentration of water to low concentration of water

• across a semi-permeable membrane Concentration of water

• Direction of osmosis is determined by comparing total solute concentrations

• Hypertonic - more solute, less water

• Hypotonic - less solute, more water

• Isotonic - equal solute, equal water

water

hypotonic hypertonic

net movement of water Managing water balance

• Cell survival depends on balancing water uptake & loss

freshwater balanced saltwater Managing water balance • Isotonic • animal cell immersed in mild salt solution

• example: blood cells in blood plasma

• problem: none • no net movement of water

• flows across membrane equally, in both directions • volume of cell is stable balanced Managing water balance • Hypotonic • a cell in fresh water • example: Paramecium • problem: gains water, swells & can burst

• water continually enters Paramecium cell

• solution: contractile vacuole ATP • pumps water out of cell • ATP • plant cells • turgid freshwater Water regulation

• Contractile vacuole in Paramecium

ATP Managing water balance

• Hypertonic • a cell in salt water

• example: shellfish

• problem: lose water & die

• solution: take up water or pump out salt • plant cells • plasmolysis = wilt

saltwater 1991 | 2003

• Water moves rapidly into & out of cells

• evidence that there were water channels

Peter Agre Roderick MacKinnon John HopkinsRockefeller Osmosis…

.05 M .03 M

Cell (compared to beaker)  hypertonic or hypotonic Beaker (compared to cell)  hypertonic or hypotonic Which way does the water flow?  in or out of cell References

• http:// bioap.wikispaces.com/file/view/Ch%207%20Cell%20Membrane.ppt • http:// www.xavierhs.org/s/717/images/editor_documents/faculty/tanzmanj/Cell%20Membrane%20Transport.ppt • http:// www.lf3.cuni.cz/opencms/export/sites/www.lf3.cuni.cz/en/applicant/premedical/study-materials/biology/8_Premedical_Cell_communication.ppt